Regular Series

Vol. 38 (2007), No. 4, pp. 1107 - 1610


From Polonium to Artificial Radioisotopes in the 1930’s

Acta Phys. Pol. B 38, 1107 (2007)

page 1107 •

abstract

The word “radioactive” appeared for the first time in Pierre and Marie Curie’s paper announcing the discovery of Polonium. Starting with the memory of this seminal event and the discovery of Radium, we focus on a few of the tremendous successes achieved in the 30’s, namely the successive discoveries of the neutron and the positive electron, followed by the discoveries of artificial radioactivity and later of fission. Experimentalists were confronted with many problems as their interest shifted from radioactivity to “artificial disintegration” and cosmic rays experiments. The first discovered \(\beta ^+\) radioactive isotopes, \(^{30}\)P and \(^{13}\)N, and the first fission produced nuclei appear as early steps towards the quest for more and more exotic nuclei.


full authors' list

E. Roeckl, I. Mukha, L. Batist, A. Blazhev, J. Döring, H. Grawe, L. Grigorenkof, M. Huyse, Z. Janas, R. Kirchner, M. La Commara, C. Mazzocchi, S.L. Tabor, P. Van Duppen

One-Proton and Two-Proton Radioactivity of the (21\(^+\)) Isomer in \(^{94}\)Ag

Acta Phys. Pol. B 38, 1121 (2007)

page 1121 •

abstract

The properties of the (21\(^+\)) isomer of \(^{94}\)Ag, unprecedented in the entire nuclear chart, are presented with particular emphasis on its hindered one-proton and enhanced two-proton radioactivity. The tasks emerging from these results concerning experimental and theoretical efforts are discussed.


full authors' list

R.A. Broglia, S. Baroni, F. Barranco, P.F. Bortignon, G. Potel, A. Pastore, E. Vigezzi, F. Marini

Induced Pairing Interaction in Nuclei and in Neutron Stars

Acta Phys. Pol. B 38, 1129 (2007)

page 1129 •

abstract

For an electron going from \(X\) to \(Y\), the pole of the propagator for a free particle is \(p^2=m^2\). However, making measurements at \(X\) and \(Y\) one could not tell if the electron had emitted or absorbed any number of photons. Such process, the simplest of which corresponds to emission and subsequent absorption of a photon (self-energy process) causes a shift in the position of the pole. Physically, this means that nothing is really free and that what one measures, the experimental mass, is not the “bare mass” but something else which includes the effect of virtual processes mentioned above. If this is true for electrons moving in vacuum it is even more true in the case of nucleons moving inside a nucleus. Bouncing inelastically off the nuclear surface, a nucleon can set it into vibrations exciting a normal mode of the system which it can reabsorb at a later time. The density of levels at the Fermi energy reflects this interweaving between fermionic and bosonic degrees of freedom and the resulting effective nucleon mass. If the vibration is reabsorbed by a second nucleon it leads to an exchange of bosons and thus to an effective interaction, e.g. in the pairing channel. Within the scenario discussed above, both quantum electrodynamics (QED) and nuclear field theory (NFT), are effective field theories. Now, while the photon is an elementary particle and the exchange of photons can be accurately parametrized in terms of the Coulomb interaction, collective surface vibrations do not exist outside the nucleus and there is no simple neither accurate parametrization of the pairing induced interaction, let alone of the \({}^1S_0\) \(NN\)-potential in terms of quarks and gluons. On the other hand, NFT based on effective interactions and HFB plus QRPA, provide a remarkably detailed picture of the induced pairing interaction, with which, together with e.g. the \(v_{14}\) \(NN\)-potential, one is able to calculate rather accurately the pairing gap of superfluid systems, including compact objects like (the inner crust of) neutron stars. The corresponding results are likely to provide the basis of a DFT of pairing in nuclei.


Neutron and Proton Separation in Dense Neutron Star Matter for Realistic Nuclear Models

Acta Phys. Pol. B 38, 1139 (2007)

page 1139 •

abstract

Vanishing of the nuclear symmetry energy implies proton–neutron separation instability in dense nuclear matter. Negative values of the symmetry energy result in disappearance of protons at high densities. The neutron star matter is unstable with respect to formation of domains with high proton concentration immersed in pure neutron matter. We consider bulk separation of protons and neutrons for a number of realistic nuclear models which occurs at densities close to the density of disappearance of protons from the system. The state with separated protons and neutrons strongly influences astrophysical properties of neutron stars.


Inclusion of Continuum Effects in Mean-Field Theories

Acta Phys. Pol. B 38, 1143 (2007)

page 1143 •

abstract

We present a method including continuum effects into nuclear structure mean-field calculations. We solve the Hartree–Fock–Bogoliubov problem in a basis made of the eigenstates of a Woods–Saxon potential. We show that the properties of stable nuclei remain unaffected, while the characteristic features of weakly-bound nuclei are correctly reproduced. We finally discuss the relevance of continuum effects on various nuclear observables.


The First Steps to EURISOL

Acta Phys. Pol. B 38, 1147 (2007)

page 1147 •

abstract

Following the results and recommendations of the EURISOL RTD conceptual design study performed within FP5, the EURISOL Design Study http://www.eurisol.org aims to carry out detailed engineering-oriented studies and technical prototyping work for the next-generation ISOL Radioactive Ion Beam (RIB) facility in Europe. Such a world-class facility, complementary to the “in-flight” FAIR facility being constructed at GSI, is expected to come into operation in the next decade. It would provide unique world-class research opportunities in nuclear physics, nuclear astrophysics and other applications of radioactive beam science. The Design Study addresses the major technological problems which are expected to arise in the creation of a facility able to provide exotic ions in quantities which are orders of magnitude higher than those currently available anywhere else in the world. A feasibility study into the use of the EURISOL facility for the production of pure electron-neutrinos is an integral part of the design study, the so-called “beta-beam” proposal. Synergies which exist between the proposed infrastructure and other European ISOL developments — MAFF, HIE-ISOLDE, SPES, and SPIRAL2 — will be exploited to mutual advantage. Twenty institutes within Europe take part in the design study as full participants, with an additional 20 in Europe, North America and Asia collaborating in the project. In this Design Study the members of the collaboration provide specific technological expertise on superconducting linear accelerators, high-power targetry, RIB production, ion sources and beam manipulation, radiation safety and nuclear instrumentation.


full authors' list

F. Gramegna, A. Andrighetto, C. Antonucci, M. Barbui, L. Biasetto, G. Bisoffi, S. Carturan, L. Celona, F. Cervellera, S. Cevolani, F. Chines, M. Cinausero, P. Colombo, M. Comunian, G. Cuttone, A. Dainelli, P. Di Bernardo, E. Fagotti, M. Giacchini, M. Lollo, G. Maggioni, M. Manzolaro, G. Meneghetti, G.E. Messina, A. Palmieri, C. Petrovich, A. Pisent, L. Piga, G. Prete, M. Re, V. Rizzi, D. Rizzo, M. Tonezzer, D. Zafiropoulos, P. Zanonato

The SPES Direct Target Project at LNL

Acta Phys. Pol. B 38, 1157 (2007)

page 1157 •

abstract

The SPES Direct Target Project at the Laboratori Nazionali di Legnaro (Italy), devoted to the construction of a Radioactive Ion Beam (RIB) Facility within the framework of the new European RIB panorama, is presented. An innovative configuration for the SPES Project, for the production of neutron-rich exotic nuclei, proposes the use of a primary proton beam (40 MeV, 0.2 mA), directly impinging on a large Multi-Slice Uranium Carbide Direct Target. The goal is to reach a high number of fission products (up to \(10^{13}\) fissions/s), still keeping a quite low power deposition inside the target. The description of the overall facility together with details on the Direct Target configuration is presented. Thermo-mechanical calculations, material preparation and characterisation, effusion–diffusion model predictions for the estimation of the release time and total release fraction for different life times and isotopes will be discussed. Finally, a scaled (1:5) prototype of the Target System built to be tested and compared under existing proton beam facilities, will be described.


full authors' list

P.E. Garrett, A. Andreyev, R.A.E. Austin, G.C. Ball, D. Bandyopadhyay, J.A. Becker, A.J. Boston, R.S. Chakrawarthy, D. Cline, R.J. Cooper, R. Churchman, D. Cross, D. Dashdorj, G.A. Demand, M.R. Dimmock, T.E. Drake, P. Finlay, F. Gagon-Miosan, A.T. Gallant, K.L. Green, A.N. Grint, G.F. Grinyer, G. Hackman, L.J. Harkness, A.B. Hayes, R. Kanungo, W.D. Kulp, K.G. Leach, G. Lee, J.R. Leslie, J.-P. Martin, C. Mattoon, W.J. Mills, A.C. Morton, S. Mythili, L. Nelson, O. Newman, P.J. Nolan, E. Padilla-Rodal, C.J. Pearson, A.A. Phillips, M. Porter-Peden, J.J. Ressler, R. Roy, C. Ruiz, H. Savajols, F. Sarazin, M.A. Schumaker, D.P. Scraggs, H.C. Scraggs, M.D. Strange, C.E. Svensson, J.C. Waddington, J.M. Wan, A. Whitbeck, S.J. Williams, J. Wong, J.L. Wood, C.Y. Wu, E.F. Zganjar

Nuclear Structure Research at TRIUMF

Acta Phys. Pol. B 38, 1169 (2007)

page 1169 •

abstract

The radioactive beam laboratory at TRIUMF is currently the highest power ISOL facility in the world. Taking advantage of the high-intensity beams, major programs in nuclear astrophysics, nuclear structure, and weak interaction studies have begun. The low-energy area, ISAC-I, is capable of delivering beams up to mass 30 at \(\approx 1.7\) MeV/u or 60 keV up to the mass of the primary target, whereas ISAC-II will ultimately provide beams up to mass 150 and \(\approx 6.5\) MeV/u. Major \(\gamma \)-ray spectrometers for nuclear structure research consist of the 8\(\pi \) spectrometer at ISAC-I, and the TIGRESS spectrometer now being constructed for ISAC-II. Results from recent experiments investigating the \(\beta \)-decay of nuclei near \(N=90\) and Coulomb excitation of \(^{20,21}\)Na are presented that highlight the capabilities of the spectrometers.


full authors' list

E.F. Zganjar, T. Achtzehn, D. Albers, C. Andreoiu, A.N. Andreyev, R.A.E. Austin, G.C. Ball, J.A. Behr, G.C. Biosvert, P. Bricault, S. Bishop, R.S. Chakrawarthy, R. Churchman, D. Cross, E. Cunningham, J.M. D'Auria, M. Dombsky, P. Finlay, P.E. Garrett, G.F. Grinyer, G. Hackman, V. Hanemaayer, J.C. Hardy, D.F. Hodgson, B. Hyland, V. Iacob, P. Klages, K.A. Koopmans, W.D. Kulp, J. Lassen, J.P. Lavoie, J.R. Leslie, T. Linder, J.A. Macdonald, H.-B. Mak, D. Melconian, A.C. Morton, W.E. Ormand, C.J. Osborne, C.J. Pearson, M.R. Pearson, A.A. Phillips, A. Piechaczek, J. Ressler, F. Sarazin, G. Savard, M.A. Schumaker, H.C. Scraggs, C.E. Svensson, J.J. Valiente-Dobon, I.S. Towner, J.C. Waddington, P.M. Walker, K. Wendt, J.L. Wood

Superallowed Beta Decay Studies at TRIUMF — Nuclear Structure and Fundamental Symmetries

Acta Phys. Pol. B 38, 1179 (2007)

page 1179 •

abstract

Precision measurement of the \(\beta \)-decay half-life, \(Q\)-value, and branching ratio between nuclear analog states of \(J^{\,\pi } = 0^+\) and \(T=1\) can provide critical and fundamental tests of the Standard Model’s description of electroweak interactions. A program has been initiated at TRIUMF-ISAC to measure the ft values of these superallowed beta transitions. Two \(T_z = 0\), \(A \gt 60\) cases, \(^{74}\)Rb and \(^{62}\)Ga, are presented. These are particularly relevant because they can provide critical tests of the calculated nuclear structure and isospin-symmetry breaking corrections that are predicted to be larger for heavier nuclei, and because they demonstrate the advance in the experimental precision on \(ft\) at TRIUMF-ISAC from 0.26% for \(^{74}\)Rb in 2002 to 0.05% for \(^{62}\)Ga in 2006. The high precision world data on experimental \(ft\) and corrected \(Ft\) values are discussed and shown to be consistent with CVC at the \(10^{-4}\) level, yielding an average \(Ft = 3073.70(74)\) s. This \(Ft\) leads to \(V_{ud} = 0.9737(4)\) for the up-down element of the Standard Model’s CKM matrix. With this value and the Particle Data Group’s 2006 values for \(V_{us}\) and \(V_{ub}\), the unitarity condition for the CKM matrix is met. Additional measurements and calculations are needed, however, to reduce the uncertainties in that evaluation. That objective is the focus of the continuing program on superallowed-beta decay at TRIUMF-ISAC.


Nuclear Reactions Used to Probe the Structure of Nuclei Far from Stability

Acta Phys. Pol. B 38, 1195 (2007)

page 1195 •

abstract

The study of nucleon pairing phenomena and of nucleon pair correlations, particularly in very neutron-rich or neutron-deficient exotic nuclei, is of considerable interest. This paper begins to address the capabilities of fast two-nucleon knockout reactions to make a positive contribution to such studies. Specifically, we address the sensitivity of two-nucleon knockout partial reaction cross-sections (and the associated momentum distributions of the reaction residues), measured by the combination of particle and coincident gamma-ray detection, to the details of (a) nuclear structure models (here the large-basis shell model), (b) the removed nucleons’ wave function configurations, and their ability to investigate nucleon pair-correlations in exotic nuclei. We do this by combining recent theoretical and experimental developments.


full authors' list

K.L. Jones, A.S. Adekola, D.W. Bardayan, J.C. Blackmon, K.Y. Chae, K. Chipps, J.A. Cizewski, D.J. Dean, L. Erikson, R.P. Fitzgerald, A.L. Gaddis, U. Greife, C. Harlin, R. Hatarik, J.A. Howard, M.S. Johnson, R.L. Kozub, J.F. Liang, R.J. Livesay, Z. Ma, B.H. Moazen, P.D. O'Malley, C.D. Nesaraja, S.D. Pain, N.P. Patterson, S.V. Paulauskas, D. Shapira, J.F. Shriner Jr, D.J. Sissom, M.S. Smith, T.P. Swan, J.S. Thomas

Single Neutron Transfer Experiments Close to the \(r\)-Process Path

Acta Phys. Pol. B 38, 1205 (2007)

page 1205 •

abstract

The first measurements using the \((d,\,p)\) transfer reaction to study single-particle states in nuclei on the expected \(r\)-process path have been made at the Holifield Radioactive Ion Beam Facility. The shell closure at \(N=50\) has been crossed using the \(^{82}\)Ge\((d,\,p)\) and \(^{84}\)Se\((d,\,p)\) reactions. The properties of the lowest-lying states have been determined. Furthermore, the \(^{132}\)Sn\((d,\,p)\) reaction has been used for the first time to populate single-particle states in \(^{133}\)Sn.


full authors' list

H. Mach, L.M. Fraile, O. Arndt, A. Blazhev, N. Boelaert, M.J.G. Borge, R. Boutami, H. Bradley, N. Braun, B.A. Brown, P.A. Butler, A. Covello, Z. Dlouhy, C. Fransen, H.O.U. Fynbo, A. Gargano, Ch. Hinke, P. Hoff, A. Joinet, A. Jokinen, J. Jolie, U. Köster, A. Korgul, K.-L. Kratz, T. Kröll, W. Kurcewicz, J. Nyberg, E.-M. Reillo, E. Ruchowska, W. Schwerdtfeger, G.S. Simpson, M. Stanoiu, O. Tengblad, P.G. Thirolf, W.B. Walters

The Single-Particle and Collective Features in the Nuclei Just Above \(^{132}\)Sn

Acta Phys. Pol. B 38, 1213 (2007)

page 1213 •

abstract

The Advanced Time Delayed method has been used to measure the lifetimes of excited states in the exotic nuclei \(^{134}\)Sb, \(^{135}\)Sb and \(^{136}\)Te populated in the beta decay of \(^{134}\)Sn, \(^{135}\)Sn and \(^{136}\)Sn, respectively. High purity Sn beams were extracted at the ISOLDE separator using a novel production technique utilizing the molecular SnS\(^+\) beams to isolate Sn from contaminating other fission products. Among the new results we have identified the 1/2\(^+\) state in \(^{135}\)Sb and its E2 transition to the lower-lying 5/2\(^+\) state was found to be surprisingly collective. This measurement represents also one of the first applications of the LaBr\(_3\) scintillator to ultra fast timing.


full authors' list

M. Górska, A. Banu, P. Bednarczyk, A. Bracco, A. Bürger, F. Camera, E. Caurier, P. Doornenbal, J. Gerl, H. Grawe, M. Honma, H. Hübel, A. Jungclaus, A. Maj, G. Neyens, F. Nowacki, T. Otsuka, M. Pfützner, S. Pietri, Zs. Podolyák, A. Poves, P.H. Regan, P. Reiter, D. Rudolph, H.J. Wollersheim

Nuclear Structure Far off Stability — Rising Campaigns

Acta Phys. Pol. B 38, 1219 (2007)

page 1219 •

abstract

Nuclear structure studies at GSI attracted recently increased interest for the results of present activities as well as for the future project FAIR. A broad range of physics phenomena can be addressed by high-resolution in-beam \(\gamma \)-ray spectroscopy experiments with radioactive beams offered within the Rare Isotopes Spectroscopic INvestigation at GSI (RISING) project. It combined the EUROBALL Ge-Cluster detectors, the MINIBALL Ge detectors, the HECTOR-BaF detectors, and the fragment separator FRS. The secondary beams produced at relativistic energies were used for Coulomb excitation or secondary fragmentation experiments to study projectile like nuclei by measuring de-excitation photons. The first results of the “fast beam campaign” is discussed in comparison to various shell model calculations. The discussion focuses on the \(N=32,34\) sub-shell closure based on neutron rich Cr isotopes. Alternatively, the relativistic radioactive beams, both in their ground and isomeric states, were implanted and their decay could be investigated. The “stopped beam campaign” has started in October 2005 with a series of \(g\)-factor measurements. It continued from February 2006 with the next configuration and the main goal of identification of new isomers and angular momentum population in fragmentation reactions.


full authors' list

A. Bracco, G. Benzoni, N. Blasi, S. Brambilla, F. Camera, F.C.L. Crespi, S. Leoni, B. Million, D. Montanari, M. Pignanelli, O. Wieland, A. Maj, P. Bednarczyk, J. Grębosz, M. Kmiecik, W. Męczyński, J. Styczeń, T. Aumann, A. Banu, T. Beck, F. Becker, L. Caceres, P. Doornenbal, H. Emling, J. Gerl, H. Geissel, M. Gorska, O. Kavatsyuk, M. Kavatsyuk, I. Kojouharov, N. Kurz, R. Lozeva, N. Saito, T. Saito, H. Shaffner, H.J. Wollersheim, J. Jolie, P. Reiter, N. Warr, G. De Angelis, A. Gadea, D. Napoli, S. Lenzi, S. Lunardi, D. Balabanski, G. Lo Bianco, C. Petrache, A. Saltarelli, M. Castoldi, A. Zucchiatti, J. Walker, A. Bürger

Coulomb Excitation of \(^{68}\)Ni at 600 \(A\)MeV

Acta Phys. Pol. B 38, 1229 (2007)

page 1229 •

abstract

The \(\gamma \) decay following the Coulomb excitation of \(^{68}\)Ni at 600 \(A\)MeV has been measured using the RISING array at GSI. The \(^{68}\)Ni beam has been produced from the fragmentation of \(^{86}\)Kr at 900 \(A\)MeV from the UNILAC-SIS on a \(^{9}\)Be target and selected using the Fragment Separator. After the selection of Coulomb excited \(^{68}\)Ni isotopes a peak centered at approximately 10.8 MeV has been observed in all type of RISING \(\gamma \) detectors. Because of the reaction mechanism the measured peak is interpreted to have a dipole nature and to come from the Pygmy Dipole Resonance. The measured data are consistent with the predictions of the Relativistic Mean Field and the Random Phase Approximation approaches.


full authors' list

G. Neyens, L. Atanasova, D.L. Balabanski, F. Becker, P. Bednarczyk, L. Caceres, P. Doornenbal, J. Gerl, M. Górska, J. Grębosz, M. Hass, G. Ilie, N. Kurz, I. Kojouharov, R. Lozeva, A. Maj, M. Pfützner, S. Pietri, Zs. Podolyak, W. Prokopowicz, T.R. Saitoh, H. Schaffner, G. Simpson, N. Vermeulen, E. Werner-Malento, J. Walker, H.J. Wollersheim, D. Bazzacco, G. Benzoni, A. Blazhev, N. Blasi, A. Bracco, C. Brandau, F. Camera, S.K. Chamoli, S. Chmel, F.C.L. Crespi, J.M. Daugas, M. De Rydt, P. Detistov, C. Fahlander, E. Farnea, G. Georgiev, K. Gladnishki, R. Hoischen, M. Ionescu-Bujor, A. Iordachescu, J. Jolie, A. Jungclaus, M. Kmiecik, A. Krasznahorkay, R. Kulessa, S. Lakshmi, G. Lo Bianco, S. Mallion, K. Mazurek, W. Meczynski, D. Montanari, S. Myalsky, O. Perru, D. Rudolph, G. Rusev, A. Saltarelli, R. Schwengner, J. Styczen, K. Turzó, J.J. Valiente-Dobón, O. Wieland, M. Zieblinski

\(g\) Factor Measurements on Relativistic Isomeric Beams Produced by Fragmentation and U-Fission: The \(g\)-Rising Project at GSI

Acta Phys. Pol. B 38, 1237 (2007)

page 1237 •

abstract

Within the RISING (Rare ISotope INvestigations @ GSI) Collaboration at GSI, \(g\) factor measurements have been performed on isomeric states in neutron-rich isotopes approaching \(^{132}\)Sn and in the neutron deficient Pb-region (the \(g\)-RISING campaign). We present the experimental technique and some typical aspects related to such studies on relativistic beams selected with the FRS fragment separator. First results are presented for the (19/2\(^+\)) 4.5 \(\mu \)s isomeric state in \(^{127}\)Sn, which has been produced by means of fission of a relativistic \(^{238}\)U beam on the one hand, and by the fragmentation of a relativistic \(^{136}\)Xe beam on the other hand. Spin-alignment has been observed in both reactions. It was the first time that spin-alignment has been established in a relativistic fission reaction.


full authors' list

M. Ionescu-Bujor, A. Iordachescu, N. Marginean, C.A. Ur, G. Suliman, D. Bucurescu, D.L. Balabanski, F. Brandolini, S. Chmel, K.A. Gladnishki, H. Hübel, R. Marginean, G. Neyens

Quadrupole Moments for Isomeric States with Normal and Intruder Configurations in Neutron-Deficient Pb Nuclei

Acta Phys. Pol. B 38, 1249 (2007)

page 1249 •

abstract

The quadrupole interaction of the 11\(^-\) and 12\(^+\) isomers in \(^{192,194}\)Pb nuclei has been investigated in the electric field gradient of metallic Bi polycrystalline lattice by the method of time-differential observation of the \(\gamma \)-rays perturbed angular distribution. The electric field gradient strength of the host Bi lattice has been calibrated by using as probe the 12\(^+\) isomer in \(^{194}\)Pb. The intrinsic quadrupole moments derived for the \(11^-\) isomers described by the \(\pi (1h_{9/2}1i_{13/2})\) intruder configuration are compared with the predictions of mean-field and interacting boson models.


full authors' list

S. Pietri, P.H. Regan, Zs. Podolyák, D. Rudolph, M. Górska, A. Jungclaus, M. Pfützner, A.B. Garnsworthy, S.J. Steer, L. Cáceres, E. Werner-Malento, R. Hoischen, J. Gerl, I. Kojouharov, H. Schaffner, H.J. Wollersheim, F. Becker, P. Bednarczyk, P. Doornenbal, H. Geissel, J. Grębosz, A. Kelic, N. Kurz, F. Montes, W. Prokopowicz, T. Saito, S. Tashenov, A. Heinz, T. Kurtukian-Nieto, G. Benzoni, M. Hellström, L.-L. Andersson, L. Atanasova, D.L. Balabanski, M.A. Bentley, B. Blank, A. Blazhev, C. Brandau, J.R. Brown, A.M. Bruce, F. Camera, W.N. Catford, I.J. Cullen, Zs. Dombrádi, E. Estevez, C. Fahlander, W. Gelletly, G. Ilie, E.K. Johansson, J. Jolie, G.A. Jones, M. Kmiecik, F.G. Kondev, S. Lalkovski, Z. Liu, A. Maj, S. Myalski, T. Shizuma, A.J. Simons, S. Schwertel, P.M. Walker, O. Wieland

First Results from the Stopped Beam Isomer Rising Campaign at GSI

Acta Phys. Pol. B 38, 1255 (2007)

page 1255 •

abstract

The first results from a series of experiments focused on the study of the internal structure of nuclei at the extremes of \(N\):\(Z\) ratio using isomer spectroscopy are reported. These experiments represent the first of the Stopped Beam section of the Rare Isotopes Investigations at GSI (RISING) project. Exotic nuclei were synthesized using relativistic projectile fragmentation of \(\sim 500 \rightarrow 1000\) MeV/\(u\) beams of \(^{107}\)Ag, \(^{208}\)Pb, \(^{136}\)Xe and \(^{58}\)Ni, or fission of 750 MeV/\(u\) \(^{238}\)U provided by the SIS synchrotron at GSI. A detailed description of the RISING stopped beam set up is given, together with a report of the performance of the associated gamma-ray spectrometer array. Selected results of the first experimental campaign are presented together with a discussion on the use of isomeric spectroscopy to study GeV range nuclear fragmentation. Details on future research plans of this collaboration are also outlined.


full authors' list

A.B. Garnsworthy, P.H. Regan, S. Pietri, D. Rudolph, L. Cáceres, M. Górska, Zs. Podolyák, S.J. Steer, A. Heinz, F. Becker, P. Bednarczyk, P. Doornenbal, H. Geissel, J. Gerl, H. Grawe, J. Grębosz, A. Kelic, I. Kojouharov, N. Kurz, F. Montes, W. Prokopwicz, T. Saito, H. Schaffner, S. Tachenov, E. Werner-Malento, H.J. Wollersheim, G. Benzoni, B. Blank, C. Brandau, A.M. Bruc, F. Camera, W.N. Catford, I.J. Cullen, Zs. Dombrádi, E. Estevez, W. Gelletly, R. Hoischen, G. Ilie, J. Jolie, G.A. Jones, A. Jungclaus, M. Kmiecik, F.G. Kondev, T. Kurtukian-Nieto, S. Lalkovski, Z. Liu, A. Maj, S. Myalski, M. Pfützner, T. Shizuma, A.J. Simons, S. Schwertel, P.M. Walker, O. Wieland

Isomeric States in the Light Tc Isotopes

Acta Phys. Pol. B 38, 1265 (2007)

page 1265 •

abstract

Preliminary results from the first experiment of the Stopped Beam RISING campaign are presented. The relativistic projectile fragmentation of a 750 MeV/\(u\) beam of \(^{107}\)Ag populated isomeric states in very neutron deficient nuclei at the proton dripline around mass 80–90. Nuclei were unambiguously identified using the FRagment Separator (FRS) and its ancillary detectors located at GSI. The ions produced were slowed down from relativistic energies by means of an Al degrader and implanted in the centre of the high-efficiency Stopped RISING array. This allowed the identification of new excited states in the \(N=Z=43\) nucleus, \(^{86}\)Tc, populated following the de-excitation of a microsecond isomer. Preliminary results of this analysis, as well as previously unobserved isomeric states in \(^{87,88}\)Tc, are reported.


full authors' list

L.S. Cáceres, M. Górska, A. Jungclaus, P.H. Regan, A.B. Garnsworthy, S. Pietri, Zs. Podolyák, D. Rudolph, S.J. Steer, H. Grawe, D.L. Balabanski, F. Becker, P. Bednarczyk, G. Benzoni, B. Blank, C. Brandau, A.M. Bruce, F. Camera, W.N. Catford, I.J. Cullen, Zs. Dombradi, P. Doornenbal, E. Estevez, H. Geissel, W. Gelletly, J. Gerl, J. Grębosz, A. Heinz, R. Hoischen, G. Ilie, J. Jolie, G.A. Jones, M. Kmiecik, I. Kojouharov, F.G. Kondev, T. Kurtukian-Nieto, N. Kurz, S. Lalkowski, L. Liu, A. Maj, S. Myalski, F. Montes, M. Pfützner, W. Prokopowicz, T. Saito, H. Schaffner, S. Schwertel, T. Shizuma, A.J. Simons, S. Tashenov, P.M. Walker, E. Werner-Malento, O. Wieland, H.J. Wollersheim

Identification of Excited States in the \(N=Z\) Nucleus \(^{82}\)Nb

Acta Phys. Pol. B 38, 1271 (2007)

page 1271 •

abstract

Information on the first excited states in the \(N=Z=41\) nucleus \(^{82}\)Nb sheds light on the competition of isospin \(T=0\) and \(T=1\) states in the \(A \sim 80\) region. The measurement was performed at the GSI laboratory using fragmentation of a \(^{107}\)Ag primary beam at 750 MeV/u on a 4 g/cm\(^2\) \(^9\)Be target. The fragments were separated and identified unambiguously in the FRagment Separator. Three excited states were observed and the half-life estimate for the isomeric state was extracted. A tentative spin assignment based on the isobaric analogue states systematics in the \(T_z=1\) nucleus \(^{82}\)Zr, and transition probabilities indicate \(T=1\) character of the first two excited states, and \(T=0\) for the isomeric state.


full authors' list

S. Myalski, M. Kmiecik, A. Maj, P.H. Regan, A.B. Garnsworthy, S. Pietri, D. Rudolph, Zs. Podolyák, S.J. Steer, F. Becker, P. Bednarczyk, J. Gerl, M. Górska, H. Grawe, I. Kojouharov, H. Schaffner, H.J. Wollersheim, W. Prokopowicz, J. Grębosz, G. Benzoni, B. Blank, C. Brandau, A.M. Bruce, L. Cáceres, F. Camera, W.N. Catford, I.J. Cullen, Zs. Dombradi, P. Doornenbal, E. Estevez, H. Geissel, W. Gelletly, A. Heinz, R. Hoischen, G. Ilie, G.A. Jones, A. Jungclaus, A. Kelic, F.G. Kondev, T. Kurtukian-Nieto, N. Kurz, S. Lalkovski, Z. Liu, F. Montes, M. Pfützner, T. Saito, T. Shizuma, A.J. Simons, S. Schwertel, S. Tachenov, P.M. Walker, E. Werner-Malento, O. Wieland

Isomeric Ratio for the \(I^\pi =8^+\) Yrast State in \(^{96}\)Pd Produced in the Relativistic Fragmentation of \(^{107}\)Ag

Acta Phys. Pol. B 38, 1277 (2007)

page 1277 •

abstract

We report on the preliminary results from a study of the decay of the \(I^\pi =8^+\) \(T_{\frac {1}{2}}=2 \mu \)s isomer in \(^{96}\)Pd performed as part of the Stopped-Beam RISING campaign within the Rare Isotope Investigation at GSI (RISING). The \(^{96}\)Pd ions were produced following the projectile fragmentation of a 750 MeV per nucleon \(^{107}\)Ag primary beam. The reaction products were separated and identified by the in-flight method using the GSI Fragment Separator. The residues of interest were stopped in a perspex stopper surrounded by an array of 15, seven-element germanium Cluster detectors. One of the goals of the current work is to investigate the population of high-spin states produced projectile fragmentation reactions using isomeric ratio measurements to infer information on the angular momentum population distribution. In this short contribution the method and results of determining the isomeric ratio for the \(I^{\,\pi } = 8^+\) microsecond isomer in \(^{96}\)Pd nucleus are presented.


full authors' list

S.J. Steer, Zs. Podolyák, S. Pietri, P.H. Regan, D. Rudolph, E. Werner-Malento, A.B. Garnsworthy, R. Hoischen, M. Górska, J. Gerl, H.J. Wollersheim, F. Becker, P. Bednarczyk, L. Cáceres, P. Doornenbal, H. Geissel, J. Grębosz, A. Kelic, N. Kurz, F. Montes, W. Prokopowicz, T. Saito, H. Schaffner, S. Tachenov, A. Heinz, M. Pfützner, T. Kurtukian-Nieto, G. Benzoni, A. Jungclaus, D.L. Balabanski, C. Brandau, A.M. Bruce, W.N. Catford, I.J. Cullen, Zs. Dombradi, E. Estevez, W. Gelletly, G. Ilie, J. Jolie, G.A. Jones, M. Kmiecik, F.G. Kondev, S. Lalkovski, Z. Liu, A. Maj, S. Myalski, T. Shizuma, S. Schwertel, P.M. Walker, O. Wieland

Identification of Isomeric States ‘South’ of \(^{208}\)Pb via Projectile Fragmentation

Acta Phys. Pol. B 38, 1283 (2007)

page 1283 •

abstract

Relativistic fragmentation of \(^{208}\)Pb has been used to produce excited states in neutron-rich nuclei with \(N\approx 126\). Spectroscopic information for a range of nuclei has been obtained through observing delayed \(\gamma \)-ray emissions from isomeric states. Preliminary results for \(^{203,204}\)Pt nuclei are presented. For the first time, excited states have been observed in \(^{203}\)Pt and \(^{204}\)Pt. The yrast structure of \(^{204}\)Pt up to spin-parity, \(I^{\,\pi }=(10^+)\) has been tentatively inferred from the internal decay of two isomeric states.


Simulation of the Electromagnetic Background Radiation for the Rising Experimental Set-Up

Acta Phys. Pol. B 38, 1287 (2007)

page 1287 •

abstract

High level of electromagnetic radiation is produced in the interaction of relativistic ions with matter. A model to simulate it within GEANT4 has been developed in order to evaluate these sources of background and their influence on the experimental spectra. New classes have been added to the standard GEANT4 program libraries, describing the radiative electron capture, primary bremsstrahlung and secondary bremsstrahlung processes. Simulations of experiments within the RISING stopped beam campaign and comparison with the experimental results are presented.


full authors' list

P. Bednarczyk, E. Berdermann, J. Gerl, M. Górska, I. Kojouharov, M. Pomorski, M. Rębisz, B. Voss, L. Acosta, R. Berjillos, I. Martel, M.A.G. Alvarez, J.M. Espino, J.L. Flores, I. Mukha, R. Wolski

Application of Diamond Detectors in Tracking of Heavy Ion Slowed Down Radioactive Beams

Acta Phys. Pol. B 38, 1293 (2007)

page 1293 •

abstract

Results of irradiation of thin Chemical Vapor Deposition (CVD) diamond detectors with low energy: \(p,\,\alpha \) and \(^7\)Li beams are presented. Energy resolution: \(\Delta E / E \lt 1\%\) of a single crystal detector was achieved. A coincident measurement with two diamond detectors showed time resolution of 100 ps and efficiency above 70%. Despite a high beam flux reaching \(10^9\) particles/s cm\(^2\) the tested detectors showed low dead-time and satisfactory radiation hardness. Perspectives of applying thin CVD diamond detectors in monitoring of a slowed down radioactive beam (RIB) are discussed.


In-Beam Test of the AGATA Prototype Triple Cluster

Acta Phys. Pol. B 38, 1297 (2007)

page 1297 •

abstract

The first in-beam test of the AGATA prototype triple cluster detector was carried out in the late summer 2005 at the Tandem laboratory of IKP Köln, Germany. A (\(d,\,p\)) reaction in inverse kinematics was performed, using a \(^{48}\)Ti beam at an energy of 100 MeV, impinging on a deuterated titanium target. The preliminary results from the analysis of the experimental data, compared with the predictions of Monte Carlo simulations, give an estimation of the position sensitivity of these detectors of 6 mm FWHM for a 1382 keV \(\gamma \)-ray.


A Pulse Shape Analysis Algorithm for Segmented HPGe Detectors

Acta Phys. Pol. B 38, 1303 (2007)

page 1303 •

abstract

A simple Pulse Shape Analysis method for the determination of the number of interactions and their radial localization inside one HPGe segmented detector segment is presented. The algorithm processes only the net charge signal using a fast comparison procedure with a basis of reference signals. The efficiency of the algorithm calculated for 600 keV \(\gamma \)-rays ranges between 65 to 95% depending on the complexity of the analyzed event. The algorithm has been applied to real signals acquired during an in-beam test of the MARS 25-fold segmented HPGe detector.


full authors' list

A. Gadea, E. Sahin, J.J. Valiente-Dobón, A. Dewald, E. Farnea, G. De Angelis, M. Axiotis, D.R. Napoli, R. Orlandi, F. Della Vedova, E. Fioretto, L. Corradi, A.M. Stefanini, A. Latina, N. Marginean, S. Szilner, O. Möller, B. Melon, D. Bazzacco, S. Beghini, S.M. Lenzi, S. Lunardi, G. Montagnoli, R. Menegazzo, F. Scarlassara, C. Ur, N.A. Kondratiev, E.M. Kozulin, G. Benzoni, A. Bracco, S. Brambilla, F. Camera, S. Leoni, B. Million, M. Pignanelli, G. Pollarolo, M. Trotta, P.G. Bizzeti, A.M. Bizzeti-Sona, D. Curien, G. Duchene, T. Faul, R. Chapman, X. Liang, F. Azaiez, S.J. Freeman, B.J. Varley, V. Pucknell

Recent Results on Neutron-Rich Nuclei Spectroscopy with the CLARA–PRISMA Setup

Acta Phys. Pol. B 38, 1311 (2007)

page 1311 •

abstract

The CLARA–PRISMA setup consisting of the array of Euroball Clover detectors CLARA, coupled to the LNL large acceptance magnetic spectrometer PRISMA, has been successfully working since spring 2004. Recently, new developments such as the ancillary device DANTE and the use of the differential plunger technique has improved the capabilities of the setup. Results of experiments studying the structure of neutron-rich nuclei together with the preliminary results on the commissioning of the ancillary detector array DANTE and of the plunger technique will be presented.


full authors' list

G. Simpson, J. Genevey, J.A. Pinston, W. Urban, A. Złomaniec, R. Orlandi, A. Scherillo, I. Tsekhanovich, A.G. Smith, A. Thallon, B.J. Varley, J. Jolie, N. Warr

Nuclear Structure Studies of Microsecond Isomers Near \(A=100\)

Acta Phys. Pol. B 38, 1321 (2007)

page 1321 •

abstract

A large variety of shapes may be observed in Sr and Zr nuclei of the \(A~\)= 100 region when the number of neutrons increases from \(N~\)= 58 to \(N\) = 64. The lighter isotopes are rather spherical. It is also well established that three shapes co-exist in the transitional odd-\(A\), \(~N\) = 59, Sr and Zr nuclei. For \(N~\)\(\gt \) 59, strongly deformed axially symmetric bands are observed. Recently, a new isomer of half-life 1.4(2) \(\mu \)s was observed in \(^{95}\)Kr, the odd–odd \(^{96}\)Rb has been reinvestigated and a new high-spin isomer observed in the even–even \(^{98}\)Zr. These nuclei were studied by means of prompt \(\gamma \)-ray spectroscopy of the spontaneous fission of \(^{248}\)Cm using the EUROGAM 2 Ge array and/or measurements of \(\mu \)s isomers produced by fission of \(^{239,241}\)Pu with thermal neutrons at the ILL (Grenoble). To allow spectroscopic studies of isomeric states with lifetimes around 100 ns, across a broad range of medium-heavy neutron-rich nuclei, an experiment was performed at a neutron guide of the ILL using thermal-neutron-induced fission. Fission fragments were identified using a small spectrometer consisting of a section to measure time-of-flight and an ionization chamber. Isomeric \(\gamma \) rays emitted from complementary fragments were detected in an array of Ge detectors.


Physics of the \(N=Z\) and \(N=Z+1\) Nuclei in the \(A = 80\)–\(100\) Region

Acta Phys. Pol. B 38, 1331 (2007)

page 1331 •

abstract

A review of the experimental work performed at the GASP array with the purpose of the identification and first spectroscopic measurements of the heaviest even–even \(N=Z\) and odd-\(A\) \(N=Z+1\) nuclei (mass larger than 80) is made. Systematic experiments in this mass region led to the first study of seven such nuclei: \(^{88}\)Ru, \(^{81}\)Zr, \(^{85}\)Mo, \(^{89}\)Ru, \(^{91}\)Rh, \(^{93}\)Pd, and \(^{95}\)Ag, and extensive data on many other nuclei in their neighborhood. The systematic evolution of the level structures in both even–even and odd-\(A\) nuclei, between \(N \approx Z \approx 40\) and \(N \approx Z \approx 47\) is briefly presented. The possibility that effects of the neutron–proton pairing have been observed, as well as the type of collectivity observed in this region are discussed.


Structure of the \(N \sim Z\ 1f_{7/2}\) Shell Nuclei

Acta Phys. Pol. B 38, 1343 (2007)

page 1343 •

abstract

Detailed experimental investigation with large \(\gamma \)-ray arrays have recently extended the knowledge of many nuclei filling the \(1f_{7/2}\)-shell nuclei. It was shown that these nuclei are characterized by a large variety of phenomena that originate in their particular location in a mass region between light and heavy nuclei having still a low number of valence particles to allow for full shell model description but already large enough to develop collective behavior with all its consequences. The evolution of their structure with spin and excitation energy is marked by the interplay between the single particle and collective degrees of freedom. Nuclei with \(N \sim Z\) are of special interest as they provide valuable information on the proton–neutron interaction and the interplay between the \(T=0\) and \(T=1\) pairing modes. Isospin symmetry studies in \(T_z = \pm 1/2\) mirror nuclei and \(T_z=0\), \(\pm 1\) isospin multiplets were facilitated by the experimental identification of states in many of the nuclei filling the \(1f_{7/2}\)-shell allowing for a systematic study on the origin of the charge symmetry breaking effects. The comparison with accurate large scale shell model calculations leads towards a quantitative understanding of the various contributions to these effects. To illustrate some of the properties that make so appealing these nuclei I discuss in the present paper the \(N=Z\) nucleus \(^{52}\)Fe and the \(A=54\) \(T=1\) multiplet.


full authors' list

A. Bürger, F. Azaiez, M. Stanoiu, Zs. Dombrádi, A. Algora, A. Al-Khatib, B. Bastin, G. Benzoni, R. Borcea, Ch. Bourgeois, P. Bringel, E. Clément, J.-C. Dalouzy, Z. Dlouhý, A. Drouart, C. Engelhardt, S. Franchoo, Zs. Fülöp, A. Görgen, S. Grévy, H. Hübel, F. Ibrahim, W. Korten, J. Mrázek, A. Navin, F. Rotaru, P. Roussel-Chomaz, M.-G. Saint-Laurent, G. Sletten, D. Sohler, O. Sorlin, Ch. Theisen, C. Timis, D. Verney, S. Williams

Spectroscopy Around \(^{36}\)Ca

Acta Phys. Pol. B 38, 1353 (2007)

page 1353 •

abstract

An experiment was performed to study excited states in neutron-deficient nuclei around Ca. After a first fragmentation of the primary beam, the one-neutron knockout reaction was used to produce \(^{36}\)Ca ions from the \(^{37}\)Ca secondary beam and in-beam \(\gamma \) rays were measured. The energy of the first excited \(2^+\) state in \(^{36}\)Ca and the cross section for the 1-neutron knock-out reaction from \(^{37}\)Ca at \(\approx 45\, A\) MeV were obtained. The \(2^+\) energy in \(^{36}\)Ca is compared to the mirror nucleus \(^{36}\)S to deduce information on the isospin dependence of the nuclear force near the proton drip line. Furthermore, for two other \(T_z=-2\) nuclei, \(^{28}\)S and \(^{32}\)Ar, the deexcitation of the first \(2^+\) states has been observed.


full authors' list

A.F. Lisetskiy, E. Caurier, K. Langanke, G. Martínez-Pinedo, P. von Neumann-Cosel, F. Nowacki, A. Richter

\(sd\)–\(pf\) Shell Model Studies of M1 Strength in Ar Isotopes

Acta Phys. Pol. B 38, 1359 (2007)

page 1359 •

abstract

The M1 strength distributions in the \(^{36,38}\)Ar isotopes calculated in configurational space of two major \(N=2\) and \(N=3\) harmonic oscillator shells are discussed. It is shown that considerable breaking of \(^{40}\)Ca core is required to reproduce total M1 sum rule and fragmentation of the M1 strength for \(^{38}\) Ar.


Shell Model Approach to Proton–Neutron Alignment in \(N \sim Z\) Ge–As Nuclei

Acta Phys. Pol. B 38, 1363 (2007)

page 1363 •

abstract

Large-scale shell model calculations were carried out for \(N \sim Z\) Ga–As nuclei with isospin invariant pairing plus \(QQ\) interaction. A particle alignment mechanism was investigated by focusing on the role of the \(g_{9/2}\) orbital. The proton–neutron pairing with isospin zero and angular momentum 9 was found to play an important role in these \(N \sim Z\) nuclei.


Shells Evolution and Core Excitations in Semi-Magic Nuclei

Acta Phys. Pol. B 38, 1369 (2007)

page 1369 •

abstract

Recent advances in Large Shell Model calculations allow now to treat extended valence spaces and more complete descriptions of (semi-)magic nuclei can be achieved with inclusion of core excitations. The interplay between shell evolution and core excitations in semi-magic nuclei will be illustrated for tin isotopic chains in the framework of Large Shell Model calculations. \(pn\) and \(nn\) monopole relative influence will be traced back on Effective Single Particle Energies and \(B(E2)\)’s.


Shell Model Proton Neutron Hole Interaction from the Properties of \(^{208}\)Bi

Acta Phys. Pol. B 38, 1375 (2007)

page 1375 •

abstract

A very reliable and complete set of data on the one proton one neutron hole levels in \(^{208}\)Bi is available. Spectroscopic factors for proton transfer to \(^{207}\)Pb and neutron pick up from \(^{209}\)Bi have been measured. Recently \(\gamma \) and conversion electron spectroscopy with the \(^{208}\)Pb(\({p,\,n})^{208}\)Bi reaction has clarified some questionable points of the level scheme and provided \(\gamma \)-branching ratios. The matrix elements of the shell model residual interaction are calculated by a least square fit from these data. The nondiagonal elements are very sensitive to the \(\gamma \)-branching; therefore for the first time an extensive set could be determined. A comparison of this “measured” interaction with a realistic interaction calculated from the interaction between free nucleons shows remarkably good agreement.


full authors' list

N.J. Thompson, P.H. Regan, A.B. Garnsworthy, A.D. Ayangeakaa, H.C. Ai, L. Amon, R.B. Cakirli, R.F. Casten, C.R. Fitzpatrick, S.J. Freeman, G. Gürdal, A. Heinz, G.A. Jones, E.A. McCutchan, J. Qian, V. Werner, S.J. Williams, R. Winkler

Spectroscopy of \(^{91}\)Zr\(_{51}\) at Medium to High Spins

Acta Phys. Pol. B 38, 1381 (2007)

page 1381 •

abstract

Identification of near-yrast states in the \(\beta \)-stable nucleus \(^{91}\)Zr\(_{51}\) has been carried out using the fusion evaporation reaction, \(^{82}\)Se(\(^{13}\)C,4n)\(^{91}\)Zr at an incident beam energy of 50 MeV. States above the reported \(\tau =6\,\mu \)s, \(I^{\,\pi }={21}/{2}^+\) isomeric level at \(E_x=3167\) keV have been identified for the first time in this work, a tentative decay scheme of near-yrast states to excitation energies in excess of 10 MeV has been constructed. These states are of relevance to shell model structures formed via limited valence-space configurations in this semi-magic \(N=51\) nucleus.


full authors' list

S.F. Ashley, A. Linnemann, J. Jolie, P.H. Regan, K. Andgren, A. Dewald, E.A. McCutchan, B. Melon, O. Möller, N.V. Zamfir, L. Amon, N. Boelaert, R.B. Cakirli, R.F. Casten, R.M. Clark, C. Fransen, W. Gelletly, G. Gürdal, M. Heidemann, K.L. Keyes, M.N-. Erduran, D.A. Meyer, A. Papenberg, C. Plettner, G. Rainovski, R.V. Ribas, N.J. Thomas, J. Vinson, D.D. Warner, V. Werner, E. Williams, K.O. Zell

Lifetime Determination of Excited States in \(^{106}\)Cd

Acta Phys. Pol. B 38, 1385 (2007)

page 1385 •

abstract

Two separate experiments using the Differential Decay Curve Method have been performed to extract mean lifetimes of excited states in \(^{106}\)Cd. The medium-spin states of interest were populated by the \(^{98}{\rm Mo}(^{12}{\rm C},4{\rm n})\) \(^{106}{\rm Cd}\) reaction performed at the Wright Nuclear Structure Lab., Yale University. From this experiment, two isomeric state mean lifetimes have been deduced. The low-lying states were populated by the \(^{96}{\rm Mo}(^{13}{\rm C},3{\rm n})^{106}{\rm Cd}\) reaction performed at the Institut für Kernphysik, Universität zu Köln. The mean lifetime of the \(I^{\,\pi } = 2_1^+\) state was deduced, tentatively, as 16.4(9) ps. This value differs from the previously accepted literature value from Coulomb excitation of 10.43(9) ps.


Nuclear Tetrahedral Symmetry and Collective Rotation

Acta Phys. Pol. B 38, 1389 (2007)

page 1389 •

abstract

There is an increasing number of theoretical predictions suggesting that many nuclear states should be characterised by spatial tetrahedral and/or octahedral symmetries. One of the most crucial points in this domain of research is how to demonstrate the existence of this new exotic quantum mechanism through experiment. We discuss in some detail how the rotational properties of tetrahedral nuclei can be used to pin down the presence of the tetrahedral symmetry in sub-atomic universe.


Exact and Nearly Exact Pairing Treatment for Large Scale Calculations

Acta Phys. Pol. B 38, 1405 (2007)

page 1405 •

abstract

In this article we present an analysis of the practical applicability of the earlier introduced PSY-MB method in solving the nuclear pairing Hamiltonian. In particular, we illustrate the convergence properties of the ground-state correlation energy, as well as the first excitation energy, in the case of the so-called picket-fence model where 32 particles are distributed over 64 equispaced, doubly-degenerated levels. In order to illustrate the ability of the method, we compare the correlation energies of the ground-state to the exact solutions obtained with the Richardson formalism, as well as the BCS approach, in function of the increasing monopole pairing strength parameter.


Simple Picture of the Nuclear System Diverging from the Strong Chiral Symmetry Breaking Limit

Acta Phys. Pol. B 38, 1411 (2007)

page 1411 •

abstract

It is emphasised that the chiral symmetry operator, \(R_yT\), commutes not only with the Hamiltonian but also with the electromagnetic transition operators \(M(\sigma \lambda )\) for \(\sigma \lambda =\) M1, E2, etc. This fact is used to illustrate possible differences in electromagnetic properties between the two chiral partner bands. On the basis of the \(^{132}\)La lifetime data an example is shown where differences in the transition probabilities observed in the partner and in the yrast band can be described in the chiral picture.


full authors' list

E.A. Lawrie, P. Vymers, Ch. Vieu, J.J. Lawrie, C. Schück, R.A. Bark, R. Lindsay, S.M. Maliage, S.M. Mullins, S.H.T. Murray, T.M. Ramashidzha, J.F. Sharpey-Schafer

Pair of Bands in the Oblate Doubly-Odd \(^{198}\)Tl Nucleus

Acta Phys. Pol. B 38, 1417 (2007)

page 1417 •

abstract

The excited states in \(^{198}\)Tl populated in the \(^{197}\)Au(\(\alpha \),3n) reaction at a beam energy of 40 MeV were studied using two complementary experiments aimed at \(\gamma \)-ray spectroscopy at iThemba LABS, and at electron-\(\gamma \) spectroscopy at Orsay, respectively. The level scheme of \(^{198}\)Tl was extended and a weak side band feeding into the yrast \(\pi h_{9/2}\otimes i_{13/2}\) band was observed. The properties of these two bands are similar to these of the pairs of bands in the \(A=130\) mass region initially interpreted as chiral doublets.


full authors' list

B. Herskind, G.B. Hagemann, Th. Døssing, C. Rønn Hansen, N. Schunck, G. Sletten, S. Ødegård, H. Hübel, P. Bringel, A. Bürger, A. Neusser, A.K. Singh, A. Al-Khatib, S.B. Patel, B.M. Nyakó, A. Algora, Z. Dombrádi, J. Gál, G. Kalinka, D. Sohler, J. Molnár, J. Timár, L. Zolnai, K. Juhász, A. Bracco, S. Leoni, F. Camera, G. Benzoni, P. Mason, A. Paleni, B. Million, O. Wieland, P. Bednarczyk, F. Azaiez, Th. Byrski, D. Curien, O. Dakov, G. Duchene, F. Khalfallah, B. Gall, L. Piqeras, J. Robin, J. Dudek, N. Rowley, N. Redon, F. Hannachi, J.N. Scheurer, J.N. Wilson, A. Lopez-Martens, A. Korichi, K. Hauschild, J. Roccaz, S. Siem, P. Fallon, I.Y. Lee, A. Görgen, A. Maj, M. Kmiecik, M. Brekiesz, J. Styczen, K. Zuber, J.C. Lisle, B. Cederwall, K. Lagergren, A.O. Evans, G. Rainovski, G. De Angelis, G. La Rana, R. Moro, R.M. Lieder, E.O. Lieder, W. Gast, H. Jäger, A.A. Pasternak, C.M. Petrache, D. Petrache

Light Charged Particles as Gateway to Hyperdeformation

Acta Phys. Pol. B 38, 1421 (2007)

page 1421 •

abstract

The Euroball-IV \(\gamma \)-detector array, equipped with the ancillary charged particle detector array DIAMANT was used to study the residues of the fusion reaction \(^{64}\)Ni + \(^{64}\)Ni \(\Rightarrow \) \(^{128}\)Ba at \(E_{\rm beam}\) = 255 and 261 MeV, in an attempt to reach the highest angular momentum and verify the existence of predicted hyperdeformed rotational bands. No discrete hyperdeformed bands were identified, but nevertheless a breakthrough was obtained through a systematic search for rotational ridge structures with very large moments of inertia \(J{(2)} \ge \) 100 \(\hbar ^2\) MeV\(^{(-1)}\), in agreement with theoretical predictions for hyperdeformed shapes. Evidence for hyperdeformation was obtained by charged particle + \(\gamma \)-ray gating, selecting triple correlated ridge structures in the continuum of each of the nuclei, \(^{118}\)Te, \(^{124}\)Xe and \(^{124,125}\)Cs. In 7 additional nuclei, rotational ridges were also identified with \(J{(2)} =\) 71–\(77\!\,\hbar ^2\) MeV\(^{(-1)}\!,\) which most probably correspond to superdeformed shape. The angular distributions of the emitted charged particles show an excess in forward direction over expectations from pure compound evaporation, which may indicate that in-complete fusion plays an important role in the population of very elongated shapes.


full authors' list

A. Al-Khatib, H. Hübel, P. Bringel, C. Engelhardt, A. Neußer-Neffgen, G.B. Hagemann, C.R. Hansen, B. Herskind, G. Sletten, A. Bracco, F. Camera, G. Benzoni, P. Fallon, R.M. Clark, M.P. Carpenter, R.V.F. Janssens, T.L. Khoo, P. Chowdhury, H. Amro

High-Spin Spectroscopy of \(^{124,125,126}\)Xe

Acta Phys. Pol. B 38, 1431 (2007)

page 1431 •

abstract

High-spin states in \(^{124,125,126}\)Xe have been populated in the reaction \(^{82}\)Se (\(^{48}\)Ca, \(xn\))\(^{130-x}\)Xe and \(\gamma \)-ray coincidences were measured with the GAMMASPHERE spectrometer. Twelve new bands extending into the spin 50–60 \(\hbar \) region are identified in \(^{125}\)Xe and \(^{126}\)Xe and previously known rotational bands at low spins are confirmed and extended. Earlier known structures in \(^{124}\)Xe are confirmed and a new band is observed. Irregular structures are identified at the top of the yrast and a side band in this nucleus. Configuration assignments for the different structures are suggested.


full authors' list

M. Kmiecik, A. Maj, M. Brekiesz, K. Mazurek, P. Bednarczyk, J. Grębosz, W. Męczyński, J. Styczeń, M. Ziębliński, K. Zuber, P. Papka, C. Beck, D. Curien, F. Haas, V. Rauch, M. Rousseau, J. Dudek, N. Schunck, A. Bracco, F. Camera, G. Benzoni, O. Wieland, B. Herskind, E. Farnea, G. De Angelis

Strong Deformation Effects in Hot Rotating \(^{46}\)Ti

Acta Phys. Pol. B 38, 1437 (2007)

page 1437 •

abstract

Exotic-deformation effects in \(^{46}\)Ti nucleus were investigated by analy- sing the high-energy \(\gamma \)-ray and the \(\alpha \)-particle energy spectra. One of the experiments was performed using the charged-particle multi-detector array ICARE together with a large volume (4 in\(\times \)4 in) BGO detector. The study focused on simultaneous measurement of light charged particles and \(\gamma \)-rays in coincidence with the evaporation residues. The experimental data show a signature of very large deformations of the compound nucleus in the Jacobi transition region at the highest spins. These results are compared to data from previous experiments performed with the HECTOR array coupled to the EUROBALL array, where it was found that the GDR strength function is highly fragmented, strongly indicating a presence of nuclei with very large deformation.


full authors' list

O. Wieland, A. Bracco, F. Camera, G. Benzoni, N. Blasi, F.C.L. Crespi, S. Leoni, B. Million, S. Barlini, V.L. Kravchuk, F. Gramegna, A. Lanchais, A. Maj, M. Kmiecik, G. Casini, M. Chiari, A. Nannini, M. Bruno, E. Geraci

Damping Mechanism of the Giant Dipole Resonance in Hot Nuclei with \(A=130\)

Acta Phys. Pol. B 38, 1447 (2007)

page 1447 •

abstract

The \(\gamma \) decay of the Giant Dipole Resonance (GDR) in \(^{132}\)Ce nuclei has been measured using the reactions \(^{64}\)Ni (\(E_{\rm lab}= 300, 400, 500\) MeV) + \(^{68}\)Zn and \(^{16}\)O (\(E_{\rm lab}= 130,250\) MeV) + \(^{116}\)Sn. The analysis of the data shows clearly that the GDR width increases steadily with temperature at least up to 4 MeV of the temperature. The data can be well interpreted within the thermal shape fluctuation model.


Effective GDR Width of \(^{132}\)Ce at High Spins and Temperatures from the LSD Model

Acta Phys. Pol. B 38, 1455 (2007)

page 1455 •

abstract

The Lublin–Strasbourg Drop (LSD) model, which reproduces quite satisfactorily the nuclear fission barriers, has been used as a basis for the thermal shape fluctuation method in order to compute effective GDR shapes of hot nuclei in particular at the regime of Jacobi shape transitions. In particular, the effective GDR width of \(^{132}\)Ce evolution as a function of angular momentum and temperature was calculated and compared to the existing experimental results. The need of including the effect of compound nucleus lifetime for temperatures higher than 2 MeV is discussed.


full authors' list

I. Mazumdar, H.C. Jain, R. Palit, D.A. Gothe, P.K. Joshi, M. Aggarwal

Search for Rare Shape Transition in Hot Rotating \(^{188}\)Os Nucleus

Acta Phys. Pol. B 38, 1463 (2007)

page 1463 •

abstract

We report on exclusive measurements of angular momentum gated high energy gamma rays from hot rotating \(^{188}\)Os nucleus at two different beam energies. The spectra were measured at four different angles w.r.t. the beam direction for both beam energies. Statistical model fits to the spectra and the analysis of the anisotropy pattern for the high energy data (\(E_{\rm beam}=84\) MeV, corresponding to an effective compound nuclear temperature \(T_{\rm eff} \sim 1.8\) MeV) seem to indicate a non-collective oblate shape for the compound nucleus. The shape at the lower beam energy (65 MeV) could not be determined unambiguously. The data for the higher beam energy is in qualitative agreement with our finite temperature potential energy surface (FTPES) calculations. We have observed significant enhancement in the high energy tail of the spectrum in the region of the IVGQR even after a very meticulous subtraction of the cosmic ray background. Further analysis is on to explain the excess counts in this region.


full authors' list

E. Wójcik, M. Kicińska-Habior, O. Kijewska, M. Kowalczyk, M. Kisieliński, J. Choiński

Giant Dipole Radiation and Isospin Mixing in Hot Nuclei with \(A=32\)–\(60\)

Acta Phys. Pol. B 38, 1469 (2007)

page 1469 •

abstract

High-energy \(\gamma \)-ray spectra from statistical decay of the Giant Dipole Resonance in \(^{60}\)Zn and \(^{61}\)Zn nuclei were measured and analysed. The GDR parameters and the isospin mixing probability for \(^{60}\)Zn at around 50 MeV excitation energy were deduced from both experiments. This result and the previous results obtained for \(^{32}\)S, \(^{36}\)Ar, \(^{44}\)Ti nuclei allowed to establish the dependence of the isospin mixing on the atomic number \(Z\).


full authors' list

B. Martin, D. Pierroutsakou, G. Inglima, A. Boiano, A. De Rosa, M. La Commara, M. Romoli, M. Sandoli, C. Agodi, R. Alba, R. Coniglione, A. Del Zoppo, C. Maiolino, P. Piattelli, D. Santonocito, P. Sapienza, G. Cardella, E. De Filippo, A. Pagano, S. Pirrone, T. Glodariu, M. Mazzocco, C. Signorini

Prompt Dipole \(\gamma \)-Ray Emission in Fusion Heavy-Ion Collisions: Incident Energy Dependence

Acta Phys. Pol. B 38, 1473 (2007)

page 1473 •

abstract

The evolution with beam energy of the prompt dipole radiation, related with entrance channel charge asymmetry effects, was studied in the fusion reactions: \(^{36}\)Ar\(+^{96}\)Zr and \(^{40}\)Ar\(+^{92}\)Zr at \(E_{\rm lab}=16\) and 15.1 MeV/\(u\), respectively. Both reactions populate, through entrance channels having different charge asymmetries, the same compound nucleus at the same average excitation energy and with identical spin distribution. By studying the \(\gamma \)-ray energy spectra of the considered reactions, and by comparing the present result with previous ones obtained at lower energies, we deduce that the prompt dipole \(\gamma \)-ray emission presents a maximum value at 9 MeV/\(u\) and decreases toward lower and higher energies. Moreover, the centroid and the width of the preequilibrium dipole component were found to remain constant, within the errors, by increasing the beam energy.


full authors' list

M. Hunyadi, A.M. van den Berg, N. Blasi, M. Csatlós, L. Csige, B. Davids, M. Fujiwara, U. Garg, J. Gulyás, M.N. Harakeh, M.A. de Huu, A. Krasznahorkay, D. Sohler, H.J. Wörtche

Recent Results from the Decay Studies of High-Energy Isoscalar Giant Resonances

Acta Phys. Pol. B 38, 1479 (2007)

page 1479 •

abstract

The direct and statistical neutron decay of the isoscalar giant dipole resonance and a continuum region at higher excitation energy has been studied in \(^{90}\)Zr, \(^{116}\)Sn and \(^{208}\)Pb using the (\(\alpha ,\alpha 'n\)) reaction at a bombarding energy of 200 MeV. The spectra of fast decay neutrons populating valence neutron-hole states were analyzed, and estimates for the branching ratios were determined to compare to recent theoretical predictions. The observation of the direct nucleon decay channels helped to separate giant resonance strengths and suppress the underlying background and continuum, which lead to an indication for the existence of the first overtone mode of the isoscalar giant quadrupole resonance.


full authors' list

M. Guttormsen, R. Chankova, A.C. Larsen, J. Rekstad, S. Siem, N.U.H. Syed, U. Agvaanluvsan, A. Schiller, A. Voinov

The Role of Broken Cooper Pairs in Warm Nuclei

Acta Phys. Pol. B 38, 1489 (2007)

page 1489 •

abstract

In order to understand warm nuclei and describe the underlying microscopic structure, entropy is measured for several even–even and odd-mass nuclei. Mid-shell nuclei show significant odd–even entropy differences interpreted as the single-particle entropy introduced by the valence nucleon. A method to extract critical temperatures for the pair breaking process is demonstrated.


full authors' list

A.C. Larsen, M. Guttormsen, R. Chankova, F. Ingebretsen, T. Lönnroth, S. Messelt, S.W. Ødegård, J. Rekstad, S. Siem, N.U.H. Syed, A. Schiller, A. Voinov

Radiative Strength Functions of Warm Nuclei in the 1\(f_{7/2}\) Shell

Acta Phys. Pol. B 38, 1495 (2007)

page 1495 •

abstract

The level densities of \(^{50,51}\)V and \(^{44,45}\)Sc have been extracted using the (\(^3\)He,\(\alpha \gamma \)) and (\(^3\)He,\(^3\)He\(' \gamma \)) reactions, respectively. Also the radiative strength functions of \(^{50,51}\)V will be presented. The high \(\gamma \)-energy part of the measured strength functions fits well with the tail of the giant electric dipole resonance. A significant enhancement over the predicted strength in the region of \(E_{\gamma } \leq 3\) MeV is observed. This feature is, at present, without any theoretical explanation.


full authors' list

S. Siem, M. Guttormsen, R. Chankova, A.C. Larsen, J. Rekstad, A. Schiller, N.U.H. Syed

Level Densities and \(\gamma \) Strength Functions in \(^{146,147}\)Sm Nuclei

Acta Phys. Pol. B 38, 1499 (2007)

page 1499 •

abstract

The level density and radiative strength functions (RSF) for \(^{146,147}\)Sm have been extracted and are here compared with the previously published results on \(^{148,149}\)Sm. As one approaches the closed \(N=82\) neutron shell we see that the structures in the level density become more pronounced due to shell effects. Thermodynamic properties, like the temperature, have been derived within the micro-canonical framework. The pygmy resonance seen in the deformed rare earth nuclei was not seen in \(^{146,147}\)Sm, as expected since the scissors-mode resonance is deformation dependent and these isotopes are close to spherical.


full authors' list

L. Csige, M. Csatlós, T. Faestermann, Z. Gácsi, J. Gulyás, D. Habs, R. Hertenberger, M. Hunyadi, A. Krasznahorkay, R. Lutter, H.J. Maier, P.G. Thirolf, H.-F. Wirth

New Excited States and Fission Resonances in the Actinide Region

Acta Phys. Pol. B 38, 1503 (2007)

page 1503 •

abstract

The fission probability has been measured in the \(^{231}\)Pa\((d,\,pf){}^{232}\)Pa and \(^{231}\)Pa(\(^3\)He\(,\,df\))\(^{232}\)U reactions as a function of the excitation energy. In the fission probability of \(^{232}\)Pa new resonance groups were found and were interpreted as hyperdeformed rotational bands with a preliminary rotational parameter of \(\hbar ^2\)/\(\theta =2.0^{+1.5}_{-1.0}\) keV. However, in the case of \(^{232}\)U the fine structure of transmission resonances was not observed.


full authors' list

I. Skwira-Chalot, K. Siwek-Wilczyńska, J. Wilczyński, F. Amorini, A. Anzalone, L. Auditore, V. Baran, J. Błocki, J. Brzychczyk, G. Cardella, S. Cavallaro, M.B. Chatterjee, M. Colonna, E. De Filippo, M. Di Toro, W. Gawlikowicz, A. Grzeszczuk, P. Guazzoni, S. Kowalski, E. La Guidara, G. Lanzanò, G. Lanzalone, C. Maiolino, Z. Majka, N.G. Nicolis, A. Pagano, M. Papa, E. Piasecki, S. Pirrone, R. Płaneta, G. Politi, F. Porto, F. Rizzo, P. Russotto, K. Schmidt, A. Sochocka, Ł. Świderski, A. Trifirò, M. Trimarchi, J.P. Wieleczko, L. Zetta, W. Zipper

Dynamics of “Binary” \(^{197}\)Au+\(^{197}\)Au Collisions as a Test of Energy Dissipation Mechanism

Acta Phys. Pol. B 38, 1509 (2007)

page 1509 •

abstract

\(^{197}\)Au+\(^{197}\)Au collisions at 15 MeV/nucleon were studied using the multidetector array CHIMERA and heavy ion beams from the superconducting cyclotron of LNS Catania. The experiment was aimed at studying the mechanism of energy dissipation in collisions of very heavy systems. In the present contribution we report on a part of our study concentrated on a subject of basically binary damped collisions, in which only two main fragments are formed prior to secondary deexcitation processes. Such “binary” events were selected by using complete information from the exclusive-type data (including all \(Z\ge 3\) fragments) obtained with the CHIMERA multidetector. Results are compared with predictions of a classical dynamical model of Błocki et al. , in which both scenarios of energy dissipation, one-body or two-body dissipation mechanisms, are assumed.


Spectroscopy of Very Heavy Elements

Acta Phys. Pol. B 38, 1515 (2007)

page 1515 •

abstract

Recent results from spectroscopic studies of \(^{254}\)No and \(^{253}\)No, carried out at JYFL by using the JUROGAM-RITU-GREAT spectrometer system in in-beam and focal-plane tagging experiments, are presented and discussed.


Spectroscopy of Proton-Odd Transfermium Nuclei

Acta Phys. Pol. B 38, 1525 (2007)

page 1525 •

abstract

Spectroscopy of the proton-odd transfermium isotopes \(^{247}\)Es, \(^{251}\)Md and \(^{255}\)Lr has been performed using decay and in-beam techniques. Single particle states have been studied at GANIL and the University of Jyväskylä using spectroscopy after \(\alpha \) decay of \(^{255}\)Lr. Prompt gamma-ray spectroscopy of \(^{251}\)Md and \(^{255}\)Lr was performed at Jyväskylä using the Jurogam array coupled to the RITU separator. These experimental results are compared to new Hartree–Fock–Bogoliubov calculations. Future prospects for the study of the heaviest elements at GANIL with the existing facility and the future SPIRAL2 and LINAG beams are presented.


full authors' list

C.W. Beausang, S.R. Lesher, J.T. Burke, L.A. Bernstein, L. Phair, H. Ai, G. Gurdal, L. Ahle, D.S. Brenner, M. Carpenter, R.M. Clark, B. Crider, J. Escher, P. Fallon, J.P. Greene, D.J. Hartley, A.A. Hecht, R.V.F. Janssens, T. Lauritsen, I.Y. Lee, C.J. Lister, A.O. Macchiavelli, M.A. McMahan, C. Plettner, J. Rohrer, D. Seweryniak, E. Williams, S. Zhu

New Results on Fission Cross Sections in Actinide Nuclei Using the Surrogate Ratio Method and on Conversion Coefficients in Triaxial Strongly Deformed Bands in \(^{167}\)Lu from ICE Ball and Gammasphere

Acta Phys. Pol. B 38, 1535 (2007)

page 1535 •

abstract

The surrogate ratio technique is described. New results for neutron induced fission cross sections on actinide nuclei, obtained using this technique are presented. The results benchmark the surrogate ratio technique and indicate that the method is accurate to within 5% over a wide energy range. New results for internal conversion coefficients in triaxial strongly deformed bands in \(^{167}\)Lu are also presented.


In-Beam Spectroscopy in the Actinide Region Using an Evaporation Residue Detector

Acta Phys. Pol. B 38, 1547 (2007)

page 1547 •

abstract

The evaporation-residue counter HERCULES, an auxiliary detector for GAMMASPHERE to perform spectroscopy in the presence of a large fission background, is described. Results from a typical experiment using the \(^{26} {\rm Mg} + {}^{198}{\rm Pt} \rightarrow {}^{224}{\rm Th}^{\ast }\) reaction at 128 MeV are discussed. The discussion focuses on the new \(^{220}\)Th level scheme. The simplex feature (alternating-parity levels) persists up to the highest spins observed. However, \(^{220}\)Th exhibits a more vibrational-like behavior than the heavier Th isotopes. A novel interpretation for \(^{220}\)Th based on a picture of tidal waves on a reflection-asymmetric nuclear surface is briefly reviewed. Finally, the identification of excited states in \(^{219}\)Th is discussed.


full authors' list

S. Antalic, A.N. Andreyev, D. Ackermann, L. Bianco, D. Cullen, I. Darby, S. Franchoo, S. Heinz, F.P. Hessberger, S. Hofmann, M. Huyse, B. Kindler, I. Kojouharov, A.-P. Leppänen, S.R. Lesher, B. Lommel, R. Mann, G. Münzenberg, K. Nishio, R.D. Page, J. Pakarinen, J.J. Ressler, S. Saro, B. Streicher, B. Sulignano, J. Thomson, P. Van Duppen, M. Venhart, D. Wiseman, R. Wyss

The New Isotopes in Po–Rn Region

Acta Phys. Pol. B 38, 1557 (2007)

page 1557 •

abstract

This contribution reviews the results of the recent experiments at the velocity filter SHIP in GSI Darmstadt obtained in the region of neutron deficient isotopes from lead to radon. The data for new very neutron-deficient isotopes \(^{187}\)Po, \(^{193,194}\)Rn and their decay properties are presented. The isotopes were produced and identified in the complete fusion reactions \(^{46}\)Ti+\(^{144}\) Sm\(\rightarrow ^{187}\)Po+3n and \(^{52}\)Cr+\(^{144}\)Sm\(\rightarrow ^{194,193}\) Rn+2,3n.


full authors' list

B. Štreicher, S. Antalic, Š. Šáro, M. Venhart, F.P. Hessberger, S. Hofmann, D. Ackermann, B. Kindler, I. Kojouharov, B. Lommel, R. Mann, B. Sulignano, P. Kuusiniemi

Alpha-Gamma Decay Studies of \(^{261}\)Sg

Acta Phys. Pol. B 38, 1561 (2007)

page 1561 •

abstract

The isotope \(^{261}\)Sg was produced in nuclear reaction \(^{208}\)Pb(\(^{54}\)Cr\(,\,n\))\(^{261}\)Sg at velocity filter SHIP in GSI Darmstadt. Its decay products \(^{257}\)Rf and \(^{253}\)No were studied by means of \(\alpha \), \(\alpha \)–\(\gamma \) and/or \(\alpha \)–X-ray spectroscopy. Improved spectroscopic data for these isotopes is presented as well as new information concerning \(J^{\,\pi }\) values of Nilsson single neutron orbitals in heaviest members of \(N = 151\), 153 and 155 isotonic chains.


Effect of Shell Structure on Saddle Point Masses

Acta Phys. Pol. B 38, 1565 (2007)

page 1565 •

abstract

For nuclei in the range of atomic numbers from \(Z=71\) to \(Z=120\) we present a survey of experimental and theoretical deviations of ground state and fission saddle point masses from their respective macroscopic approximations. The mass deviations (related to shell effects) are an order of magnitude smaller for saddles than for ground states. This can be understood on the basis of the “topographic theorem”.


Search for Less Important Deformations in the Shapes of Heaviest Nuclei

Acta Phys. Pol. B 38, 1577 (2007)

page 1577 •

abstract

Potential energy of the superheavy nucleus \(^{262}\)Sg is analysed in a 5-dimensional deformation space. The space includes two components of the quadrupole deformation and three components of the hexadecapole deformation. The scope of the study is to find the component which has only a small influence on the energy. The analysis indicates that the best candidate for it is one (\(\gamma _4\)) of two non-axial hexadecapole deformations.


Non-Axial Hexadecapole Deformations of Heaviest Nuclei

Acta Phys. Pol. B 38, 1583 (2007)

page 1583 •

abstract

Potential energy of a heavy nucleus (\(^{250}\)Cf) is analysed in a 5-dimensional deformation space. This is the most general space including quadrupole and hexadecapole deformations, when the reflexion symmetry of a nucleus with respect to all three planes of the intrinsic coordinate system is assumed. Main attention is given to the influence of non-axial hexadecapole shapes on the height of the fission barrier of the analysed nucleus. It is found that this influence is small (about 0.1 MeV) for the considered nucleus, in contrast to the influence of non-axial quadrupole deformation, which is large (about 1.8 MeV).


Bimodal Fission in the Skyrme–Hartree–Fock Approach

Acta Phys. Pol. B 38, 1589 (2007)

page 1589 •

abstract

Spontaneous-fission properties of \(^{256}\)Fm, \(^{258}\)Fm, and \(^{260}\)Fm isotopes are studied within the Skyrme–Hartree–Fock+BCS framework. In the particle–hole channel we take the Skyrme SkM\(^*\) effective force, while in the particle–particle channel we employ the seniority pairing interaction. Three static fission paths for all investigated heavy fermium isotopes are found. The analysis of these fission modes allows to describe observed asymmetric fission of \(^{256}\)Fm, as well as bimodal fission of \(^{258}\)Fm and symmetric fission in \(^{260}\)Fm.


Isotopic Dependance of Neutron Emission from Dinuclear System

Acta Phys. Pol. B 38, 1595 (2007)

page 1595 •

abstract

Using the statistical approach, we study the isotopic dependence of the de-excitation of dinuclear systems formed in the entrance channel of heavy ion reactions. The probabilities of neutron emission from the dinuclear systems \(^{62-73}\)Ni+\(^{208}\)Pb are estimated and a possible experiment for the observation of this emission is discussed.


Phase Transitions in the Configuration Mixed Interacting Boson Model: U(5)–O(6) Mixing

Acta Phys. Pol. B 38, 1599 (2007)

page 1599 •

abstract

The phase diagram for the configuration mixed Interacting Boson Model is investigated for the special case of U(5)–O(6) mixing using the methods provided by Catastrophe Theory. It will be shown that this phase diagram exhibits properties not present when only a single configuration is considered.


E(5) and X(5) Dynamical Symmetries from a Microscopic Perspective

Acta Phys. Pol. B 38, 1605 (2007)

page 1605 •

abstract

Microscopic mean field approach based on ATDHFB theory has been applied to describe low energy collective properties of \(^{104}\)Ru, \(^{102}\)Pd and \(^{154}\)Gd nuclei, which recently have been regarded as good examples of phenomenological E(5) or X(5) symmetries.


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