### Regular Series

#### Vol. 36 (2005), No. 4, pp. 975 - 1408

Search for the Nuclear Hyper-Deformation: Motivations and New Strategies

Acta Phys. Pol. B 36, 975 (2005)

page 975 •

abstract

We present arguments suggesting, in contrast to commonly accepted way of thinking, that the mechanisms of the super- and of the hyper-deformation in nuclei, and thus the physics motivations behind, are different. Consequently the research strategies of the nuclear hyper-deformation as opposed to super-deformation should be adapted appropriately, and certainly changed with respect to what seems to be the present day attitude. New results of the corresponding calculations are illustrated and strategies better adapted to the present day instrumental sensitivity are formulated.

Spectroscopy of Strongly Deformed Nuclei — from Super to Hyperdeformation

Acta Phys. Pol. B 36, 1003 (2005)

page 1003 •

abstract

It is possible that some nuclei may attain even greater quadrupole deformations than those observed in superdeformed nuclei and the search for such hyperdeformed shapes has been a goal of nuclear structure for many years. In this talk I will discuss recent developments in the experimental study of superdeformed nuclei and in particular the search for the more exotic hyperdeformed nuclei. I will begin by briefly reviewing the basic concepts connected with nuclei at extreme deformations and introduce the use of intruder occupancy as a method to classify the nuclear shape (normal, super, or hyperdeformed) before turning to our recent attempts to extend these studies from super to hyperdeformations; the focus will be on our work in the cadmium and tin region. Finally, I will say a few words on future prospects.

Search for Hyperdeformation

Acta Phys. Pol. B 36, 1015 (2005)

page 1015 •

abstract

Experiments performed in recent years using the Euroball and Gammasphere spectrometer arrays to search for hyperdeformed shapes in Hf, Nd, Xe and Ba nuclei are discussed. In $^{126}$Xe and $^{126}$B ridge structures in quasi-continuum $\gamma$-ray correlation spectra with a small energy separation are observed, probably resulting from rotational bands with large moments of inertia. These ridges are only found when the highest-multiplicity cascades are selected in the data from experiments with the highest bombarding energies. A statistical analysis shows that the ridges are formed by ten or more bands and that the intensity of the individual bands is below $10^{-6}$ of the reaction-channel intensity. Selected examples of results for normal-deformed and superdeformed states are also presented.

full authors' list

A. Al-Khatib, A.K. Singh, H. Hübel, P. Bringel, A. Bürger, A. Neußer, G. Schönwaßer, G.B. Hagemann, C.R. Hansen, B. Herskind, G. Sletten, A. Algora, Zs. Dombrádi, J. Gál, G. Kalinka, J. Molnár, B.M. Nyakó, D. Sohler, J. Timár, L. Zolnai, M. Kmiecik, A. Maj, J. Styczeń, K. Zuber, K. Hauschild, A. Korichi, A. Lopez-Martens, J. Roccaz, S. Siem, F. Hannachi, J.N. Scheurer, P. Bednarczyk, Th. Byrski, D. Curien, O. Dorvaux, G. Duchène, B. Gall, F. Khalfallah, I. Piqueras, J. Robin, K. Juhász, S.B. Patel, A.O. Evans, G. Rainovski, A. Airoldi, G. Benzoni, A. Bracco, F. Camera, B. Million, P. Mason, A. Paleni, R. Sacchi, O. Wieland, C.M. Petrache, D. Petrache, G. La Rana, R. Moro, G. De Angelis, P. Fallon, I.-Y. Lee, J.C. Lisle, B. Cederwall, K. Lagergren, R.M. Lieder, E. Podsvirova, W. Gast, H. Jäger, N. Redon, A. Görgen

High-Spin States in $^{124}$Ba

Acta Phys. Pol. B 36, 1029 (2005)

page 1029 •

abstract

High-spin states in $^{124}$Ba were populated using the $^{64}$Ni($^{64}$Ni,4n)$^{124}$Ba reaction at beam energies of 255 and 261 MeV. Gamma-ray coincidences were measured using the EUROBALL detector array.The charged-particle detector array DIAMANT provided channel selection. The previously known rotational bands are extended to higher spins. Five new bands are observed, one of them extends up to the spin 40$\hbar$ region.

full authors' list

B.M. Nyakó, F. Papp, J. Gál, J. Molnár, J. Timár, A. Algora, Zs. Dombrádi, G. Kalinka, L. Zolnai, K. Juhász, A.K. Singh, H. Hübel, A. Al-Khatib, P. Bringel, A. Bürger, A. Neußer, G. Schönwaßer, B. Herskind, G.B. Hagemann, C.R. Hansen, G. Sletten, J.N. Scheurer, F. Hannachi, M. Kmiecik, A. Maj, J. Styczeń, K. Zuber, K. Hauschild, A. Korichi, A. Lopez-Martens, J. Roccaz, S. Siem, P. Bednarczyk, Th. Byrski, D. Curien, O. Dorvaux, G. Duchène, B. Gall, F. Khalfallah, I. Piqueras, J. Robin, S.B. Patel, A.O. Evans, G. Rainovski, A. Airoldi, G. Benzoni, A. Bracco, F. Camera, B. Million, P. Mason, A. Paleni, R. Sacchi, O. Wieland, G. La Rana, R. Moro, C.M. Petrache, D. Petrache, G. De Angelis, P. Fallon, I.-Y. Lee, J.C. Lisle, B. Cederwall, K. Lagergren, R.M. Lieder, E. Podsvirova, W. Gast, H. Jäger, N. Redon, A. Görgen

Search for Hyperdeformation in Light Xe Nuclei

Acta Phys. Pol. B 36, 1033 (2005)

page 1033 •

abstract

The ultimate search for hyperdeformation (HD) at high spins with the EUROBALL spectrometer was performed for $^{126}$Ba as a hyper long (HLHD) experiment. The DIAMANT ancillary detector was used to tag $\gamma$-rays in coincidence with the emitted light charged particles. Using $\gamma$-energy correlation methods, the particle–$xn$-$\gamma$ data have been analysed to search for hyperdeformed structures in the corresponding residual nuclei. Data in coincidence with one $\alpha$ particle indicate the presence of normal deformed collective bands up to very high spins and the possible occurrence of HD-like ridge structures in $^{122}$Xe.

Fold Distribution Analysis as a Tool for the Study of Reaction Mechanisms and Entry State Population Distributions at Highest Spins

Acta Phys. Pol. B 36, 1039 (2005)

page 1039 •

abstract

Fold distributions for the $^{114}$Cd ($^{36}$S, $\alpha ypxn$) ($E=182$ MeV), $^{100}$Mo ($^{48}$Ti, $\alpha ypxn$) ($E=215$ MeV) and $^{97}$Mo ($^{51}$V, $\alpha ypxn$) ($E=238$ MeV) reactions have been investigated. Evidence for the existence of an incomplete fusion reaction mechanism for the $\alpha xn$ channels has been obtained. The sensitivity of the fold distributions to nuclear deformations at highest spins has been demonstrated.

Triaxiality and Wobbling

Acta Phys. Pol. B 36, 1043 (2005)

page 1043 •

abstract

The wobbling mode of the collective angular momentum expressed as a phonon excitation with a phonon quantum number, $n_w$, and wobbling frequency, $\hbar \omega _w$, is unique to the rotational motion of a triaxial nucleus. The presence of quasiparticle alignment introduces characteristic trends in the electromagnetic decay properties for transitions between bands with different wobbling quantum number. Evidence for the wobbling mode, and thereby triaxiality, has been obtained in several even-$N$ Lu isotopes, $^{163}$Lu being the best studied case with the strongest population of the wobbling excitations. As an important support for the wobbling interpretation, recent lifetime measurements in $^{163}$Lu have shown that the quadrupole moments of the bands with $n_w = 0$ and $n_w = 1$ are very similar. Triaxial strongly deformed shapes are expected also for neighbouring Hf nuclei, but efforts to identify wobbling in the Hf isotopes where many bands are established, resembling those found in the Lu isotopes, has so far failed. To date the even-$N$ Lu isotopes, $^{161,163,165,167}$Lu, are the only nuclei in which wobbling excitations are identified.

High-$K$ Structures Under Extreme Conditions

Acta Phys. Pol. B 36, 1055 (2005)

page 1055 •

abstract

High-$K$ isomer decay rates are compared and interpreted, with an emphasis on the spin degree of freedom. It is argued that high-$K$ values do not in themselves lead to $K$ mixing. Rather, evidence is presented that the most important consideration is the isomer energy relative to a rotor whose moment of inertia is approximately 85 % of the rigid-body value. The high-spin limit to the occurrence of high-$K$ isomers is then discussed in connection with predictions of competing oblate rotation-aligned structures. Finally, some observations are made regarding the use of $K$ isomers as a tool to access exotic nuclei, including superheavy elements, and exotic nuclear structures.

full authors' list

J. Srebrny, E. Grodner, T. Morek, I. Zalewska, Ch. Droste, J. Mierzejewski, A.A. Pasternak, J. Kownacki, J. Perkowski

Search for Chirality in $^{128}$Cs and $^{132}$La

Acta Phys. Pol. B 36, 1063 (2005)

page 1063 •

abstract

The E2 and M1 intraband transition probabilities have been determined in $^{132}$La and $^{128}$Cs using the Doppler Shift Attenuation method. The $B$(E2) and $B$(M1) values suggest that $^{128}$Cs is a better candidate for the presence of chiral bands than $^{132}$La.

Collective Rotation of Nuclei with Tetrahedral Symmetry

Acta Phys. Pol. B 36, 1071 (2005)

page 1071 •

abstract

Collective rotation of tetrahedral nuclei is analyzed within a three-dimensional cranking model. The favored orientation of the rotational frequency vector with respect to the turning nucleus as function of angular momentum is obtained from the total energy calculations. A new quantum number, resulting from the particular symmetry of the cranking Hamiltonian of the nuclei with tetrahedral nuclei is discussed. Some consequences for the structure of the rotational bands are presented.

full authors' list

J. Enders, M. Babilon, T. Hartmann, A. Heine, P. von Neumann-Cosel, V.Yu. Ponomarev, N. Ryezayeva, S. Volz, A. Zilges, T. Guhr

Electric Dipole Strength Below the Giant Dipole Resonance

Acta Phys. Pol. B 36, 1077 (2005)

page 1077 •

abstract

Recent experimental findings and theoretical approaches to the electric dipole (E1) strength distribution below the particle emission threshold at shell closures are revisited. Results from photon scattering experiments are discussed and compared to predictions within the quasiparticle–phonon nuclear model. An analysis of the fine structure of the E1 strength is presented. Recent studies of the E1 response of light exotic nuclei are also discussed.

full authors' list

S. Siem, M. Guttormsen, E. Algin, U. Agvaanluvsan, T. Belgya, R. Chankova, G. Mitchell, L.A. Bernstein, J. Rekstad, A. Schiller, A.C. Sunde, N. Syed, A. Voinov

Soft Resonances in Hot Nuclei

Acta Phys. Pol. B 36, 1089 (2005)

page 1089 •

abstract

The pygmy resonance at 3.3(1) MeV in $^{172}$Yb has now been established with a strength of $B({\rm M1})= 6.5(15)\mu _N^2$ and M1 multipolarity. In addition, a strong unexpected enhancement of the radiative strength function has been found at low $\gamma$-ray energy in medium light Fe nuclei and also in the heavier Mo nuclei.

Spin–Isospin Giant Resonances: Review and Future Perspectives

Acta Phys. Pol. B 36, 1095 (2005)

page 1095 •

abstract

Gamow–Teller (spin-flip, isospin-flip) transitions have played an important role in nuclear physics. Basic understanding of the processes requires reliable knowledge of the GT strength distribution at large excitation energy range as well as in nuclei far from the stability line. Spin-flip and isospin-flip transitions with higher multipolarities are also important. There is a predictable correlation between the cross section of the spin dipole resonance and the neutron-skin thickness of nuclei, which quantity is important for constraining the symmetry energy of the nuclear interaction. These investigations can be extended to unstable nuclei using $(p,n)$ reactions with radioactive nuclear beams in inverse kinematics. Relativistic heavy-ion beams and especially rare-isotope beams open up a new avenue for studying spin–isospin giant resonances. Kinematically complete experiments can be performed in inverse kinematics and a large part of the physical background can be reduced in this way. After a review of the present status of the spin-flip and isospin-flip giant resonances I am going to discuss the future perspectives for studying such interesting giant resonances.

Giant Monopole Resonance in Cd and Sn Isotopes

Acta Phys. Pol. B 36, 1107 (2005)

page 1107 •

abstract

The giant resonance region from 10 MeV $\lt E_{x}\lt 55$ MeV in $^{110}$Cd, $^{116}$Cd, $^{112}$Sn and $^{124}$Sn has been studied with inelastic scattering of 240 MeV $\alpha$ particles at small angles including 0$^{\mathrm o}$. Essentially, all of the E0 strength in these nuclei was located. The isotopic dependence of the giant monopole resonance energies was found to be consistent with relativistic and nonrelativistic calculations for interactions with $K_{nm} \sim$ 220–240 MeV.

full authors' list

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

Overtones of Isoscalar Giant Resonances Studied in Direct Particle Decay Measurements

Acta Phys. Pol. B 36, 1115 (2005)

page 1115 •

abstract

The isoscalar giant dipole resonance (ISGDR), which is the lowest-energy overtone mode of the isoscalar giant resonances, has been studied in some medium-heavy and heavy nuclei in coincidence measurements. The observation of the direct nucleon decay channels significantly helped to enhance giant resonance strengths with respect to the underlying background and continuum, which gave an indication for the existence of a new mode with $L=2$ character, assumingly the overtone of the ISGQR.

full authors' list

S. Leoni, G. Benzoni, A. Bracco, N. Blasi, F. Camera, C. Grassi, B. Million, A. Paleni, M. Pignanelli, E. Vigezzi, O. Wieland, M. Matsuo, T. Døssing, B. Herskind, G.B. Hagemann, J. Wilson, A. Maj, M. Kmiecik, G. Lo Bianco, C.M. Petrache, M. Castoldi, A. Zucchiati, G. De Angelis, D. Napoli, P. Bednarczyk, D. Curien

Warm Rotating Nuclei: Damping Mechanisms and the Order-to-Chaos Transition

Acta Phys. Pol. B 36, 1121 (2005)

page 1121 •

abstract

The $\gamma$-decay in the quasi-continuum is used as a probe of nuclear structure properties in thermally excited nuclei. The experimental analysis is performed on high-statistics EUROBALL data on $^{163}$Er, and the results are compared to band mixing calculations for this nucleus. Two topics are investigated. First, a direct experimental measurement of the rotational and compound damping width (${\mit \Gamma }_{\rm rot}$ and ${\mit \Gamma }_{\mu }$) is given. From a line-shape analysis of $\gamma$–$\gamma$ coincidence spectra values of 200 and 20 keV are obtained for ${\mit \Gamma }_{\rm rot}$ and ${\mit \Gamma }_{\mu }$, respectively, in the spin region $I\approx 30$–$40 \hbar$, in good agreement with theory. Secondly, the validity of the selection rules associated with the $K$-quantum number are investigated as a function of the internal energy $U$ above yrast. $K$-selection rules are found to be obeyed in the decay along discrete unresolved rotational bands up to $U \approx 1.2$ MeV, while in the interval $U \approx 1.2$–2.5 MeV, where the order-to-chaos transition is expected to take place, selection rules are found to be only partially valid.

Isospin Mixing at High Temperatures

Acta Phys. Pol. B 36, 1133 (2005)

page 1133 •

abstract

The isospin mixing in nuclei in the nuclear temperature range from the ground state to the excitation of the compound nucleus to the effective temperature of about 3 MeV is discussed. Theoretical predictions and experimental information from various types of measurements are reviewed. New results for isospin mixing probability measured for $^{32}$S and $^{36}$Ar at excitation energy around 50 MeV are presented. Possible dependence of the isospin mixing probability on the mass number $A$ in highly excited nuclei is discussed.

full authors' list

F. Camera, M. Kmiecik, O. Wieland, G. Benzoni, A. Bracco, S. Brambilla, F. Crespi, P. Mason, A. Moroni, B. Million, S. Leoni, A. Maj, J. Styczeń, M. Brekiesz, W. Męczyński, M. Ziębliński, F. Gramegna, S. Barlini, V.L. Kravchuk, A.L. Lanchais, P.F. Mastinu, M. Bruno, M. D'Agostino, E. Geraci, A. Ordine, G. Casini, M. Chiari

GDR in Hot Nuclei: New Measurements

Acta Phys. Pol. B 36, 1145 (2005)

page 1145 •

abstract

The measured properties of the Giant Dipole Resonance in hot rotating nuclei are successfully described with the model of thermal fluctuations, even though there are still some open problems especially at very low ($T \lt 1.2$ MeV), very high ($T \gt 2.5$ MeV) temperatures and missing data in some mass regions. Recent experimental works have addressed more specific problems regarding the nuclear shape and its behaviour in very particular and delimited phase space regions. In this paper will be discussed new exclusive measurements of the GDR $\gamma$ decay in heavy $^{216}$Rn nuclei (where the shape of nuclei surviving fission have been probed) and some preliminary data on the $^{132}$Ce nuclei at very high excitation energy.

full authors' list

F. Gramegna, S. Barlini, V.L. Kravchuk, A.L. Lanchais, O. Wieland, A. Bracco, A. Moroni, G. Casini, G. Benzoni, N. Blasi, S. Brambilla, M. Brekiesz, M. Bruno, F. Camera, M. Chiari, F. Crespi, E. Geraci, B. Guiot, M. Kmiecik, S. Leoni, A. Maj, P.F. Mastinu, B. Million, A. Nannini, A. Ordine, G. Vannini

Light Charged Particle Emission and the Giant Dipole Resonance in Ce Nucleus

Acta Phys. Pol. B 36, 1155 (2005)

page 1155 •

abstract

The $^{132}$Ce compound nucleus was formed in fusion reactions $^{64}$Ni + $^{68}$Zn and $^{16}$O + $^{116}$Sn at different excitation energies. High energy $\gamma$-rays have been measured in coincidence with Evaporation Residues (ER) in these reactions. At the same time Light Charged Particles (LCP) were measured with the same gate on ER for all the reactions in order to verify and compare the amount of pre-equilibrium emission using mass-symmetric and mass-asymmetric entrance channels. Results on $\alpha$-particle spectra will be presented together with a moving source fit analysis.

Statistical Description of the Thermal Shape Fluctuations Using Realistic Microscopic and Macroscopic Models

Acta Phys. Pol. B 36, 1161 (2005)

page 1161 •

abstract

We calculate the probability distribution describing the thermal fluctuations of the nuclear shape, using Lublin–Strasbourg Drop (LSD) model for the macroscopic nuclear energies and deformed Woods-Saxon model for the single-nucleonic level densities. Examples of applications are presented in the form of the GDR spectra of hot $^{46}$Ti and $^{216}$Rn nuclei.

full authors' list

M. Kmiecik, A. Maj, J. Styczeń, P. Bednarczyk, M. Brekiesz, J. Grębosz, M. Lach, W. Męczyński, M. Ziębliński, K. Zuber, A. Bracco, F. Camera, G. Benzoni, B. Million, S. Leoni, O. Wieland, B. Herskind, D. Curien, N. Dubray, J. Dudek, N. Schunck, K. Mazurek

GDR Feeding of the Highly-Deformed Band in $^{42}$Ca

Acta Phys. Pol. B 36, 1169 (2005)

page 1169 •

abstract

The $\gamma$-ray spectra from the decay of the GDR in the compound nucleus reaction $^{18}$O+$^{28}$Si at bombarding energy of 105 MeV have been measured in an experiment using the EUROBALL IV and HECTOR arrays. The obtained experimental GDR strength function is highly fragmented, with a low energy ($\approx 10$ MeV) component, indicating a presence of a large deformation and Coriolis effects. In addition, the preferential feeding of the highly-deformed band in $^{42}$Ca by this GDR low energy component is observed.

full authors' list

M. Brekiesz, P. Papka, A. Maj, M. Kmiecik, C. Beck, P. Bednarczyk, J. Grębosz, F. Haas, W. Męczyński, V. Rauch, M. Rousseau, A. Sànchez i Zafra, J. Styczeń, S. Thummerer, M. Ziębliński, K. Zuber

Study of Deformation Effects in the Charged Particle Emission from $^{46}$Ti$^{*}$

Acta Phys. Pol. B 36, 1175 (2005)

page 1175 •

abstract

The $^{46}$Ti$^{*}$ compound nucleus, as populated by the fusion–evaporation reaction $^{27}\!$Al + $^{19}$F at the bombarding energy of 144 MeV, has been investigated by charged particle spectroscopy using the multidetector array ICARE at the VIVITRON tandem facility of the IReS (Strasbourg). The light charged particles have been measured in coincidence with evaporation residues. The CACARIZO code, a Monte Carlo implementation of the statistical model code CASCADE, has been used to calculate the spectral shapes of evaporated $\alpha$-particles which are compared with the experimental spectra. This comparison indicates the possible signature of large deformations of the compound nucleus.

Giant Dipole Resonance and Shape Fluctuations in Rapidly Rotating Hot Nuclei

Acta Phys. Pol. B 36, 1181 (2005)

page 1181 •

abstract

In a macroscopic approach we study giant dipole resonance (GDR) in rapidly rotating hot nuclei. Thermal fluctuations in GDR observables are treated without employing free energy parametrizations. Analysis of their consequences at low temperature and high spin suggest that the parameterizations are not sufficient in this regime. We exemplify that at low temperature the sharp shape transitions due to increasing spin could be well reflected in the GDR observables once we treat the fluctuations properly. Jacobi transition in Zr isotopes leading to hyperdeformation and their survival at higher temperature are discussed.

full authors' list

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

$^{20}$Ne+$^{12}$C Reaction at 5 and 9 MeV/$A$ Studied at the Warsaw Cyclotron

Acta Phys. Pol. B 36, 1185 (2005)

page 1185 •

abstract

Two experiments for $^{20}$Ne+$^{12}$C reaction have been performed at projectile energies 5.2 MeV/$A$ and 9.2 MeV/$A$, respectively, to examine the reaction mechanism as well as to obtain the GDR parameters. Light charged particles were measured at angles in the range of $45^{\mathrm o}$–$135^{\mathrm o}$ by using Si-ball set-up consisting of 12 triple telescopes. The spectra were measured inclusively as well as in coincidence with $\gamma$-quanta. Gamma spectra have been collected at $60^{\mathrm o},\,90^{\mathrm o}$ and $120^{\mathrm o}$ with NaI spectrometer.

Survival Probability in Deexcitation of Heavy Nuclei

Acta Phys. Pol. B 36, 1191 (2005)

page 1191 •

abstract

A method of calculating statistical decay of heavy compound systems characterized by strong competition between fission and evaporation processes is described. The method consistently accounts for shell effects in both evaporation and fission decay modes.

full authors' list

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

Thermal and Electromagnetic Properties of the Light Vanadium Isotopes $^{50, 51}$V

Acta Phys. Pol. B 36, 1197 (2005)

page 1197 •

abstract

The level densities and radiative strength functions (RSFs) in $^{50,51}$V have been experimentally measured using the ($^3$He, $\alpha \gamma$) and ($^3$He,$^3$He’$\gamma$) reactions, respectively. From the level density thermodynamic properties such as entropy and temperature can be extracted. The microcanonical heat capacity shows negative branches. The gross properties of the RSF are described by the giant electric dipole resonance. At $\gamma$ energies below 3 MeV, the RSFs show an unexpected enhancement.

full authors' list

A. Budzanowski, V.A. Karnaukhov, H. Oeschler, S.P. Avdeyev, V.K. Rodionov, V.V. Kirakosyan, A.V. Simonenko, P.A. Rukoyatkin, W. Karcz, I. Skwirczyńska, E.A. Kuzmin, L.V. Chulkov, E. Norbeck, A.S. Botvina

Phase Transitions in Highly Excited Nuclei

Acta Phys. Pol. B 36, 1203 (2005)

page 1203 •

abstract

Phase transition in highly excited nucleus is treated in terms of thermodynamics of microensembles. The emission of intermediate mass fragments from pure thermally excited heavy nucleus $^{197}$Au is an indication of the liquid to fog phase transition. Evidence of the spinodal decomposition of the heavy nuclear system is found and its relation to the multisaddle transition configuration and freeze-out state is presented.

full authors' list

T. Otsuka, T. Suzuki, R. Fujimoto, D. Abe, H. Grawe, Y. Akaishi

Evolution of Shell and Collective Structures in Exotic Nuclei

Acta Phys. Pol. B 36, 1213 (2005)

page 1213 •

abstract

The evolution of shell structure in exotic nuclei due to the tensor interaction is discussed. It will be suggested that the tensor interaction can change the shell structure, for instance, by varying the spin–orbit splitting considerably as a function of $N$ and $Z$.

Nuclear Shell Energy Obtained by Averaging in Particle-Number Space

Acta Phys. Pol. B 36, 1221 (2005)

page 1221 •

abstract

A revised version of the shell-correction method, based on a new way of evaluating the smooth part of the total single-particle energy, is proposed. The folding of the sum of nucleon energies is performed in the particle-number space, not in the energies of individual nucleons, as was done in the old Strutinsky method.

full authors' list

A. Gade, D. Bazin, B.A. Brown, C.M. Campbell, J.A. Church, D.-C. Dinca, J. Enders, T. Glasmacher, P.G. Hansen, M. Honma, T. Mizusaki, W.F. Mueller, H. Olliver, T. Otsuka, L.A. Riley, J.R. Terry, J.A. Tostevin, K.L. Yurkewicz

Nuclear Spectroscopy with Fast Exotic Beams

Acta Phys. Pol. B 36, 1227 (2005)

page 1227 •

abstract

Results on the study of quadrupole collectivity in $^{54,56,58}$Ni and $^{52}$Fe using intermediate-energy Coulomb excitation are summarized and discussed in the context of the $N=Z=28$ doubly-magic shell closure. A complementary experimental approach sensitive to the single-particle structure of exotic nuclei, one-neutron knockout at intermediate beam energies, has been applied to the proton-rich $N=16$ isotones $^{34}$Ar, $^{33}$Cl and $^{32}$S as well as to $^{32}$Ar where the knockout residue $^{31}$Ar is located at the proton drip line. The reduction of single-particle strength compared to USD shell-model calculations is discussed in the framework of correlation effects beyond the effective-interaction theory employed in the shell-model approach.

full authors' list

P. Bednarczyk, A. Banu, T. Beck, F. Becker, M.A. Bentley, G. Benzoni, A. Bracco, A. Bürger, F. Camera, P. Doornenbal, C. Fahlander, H. Geissel, J. Gerl, M. Górska, H. Grawe, J. Grębosz, G. Hammond, M. Hellström, H. Hübel, J. Jolie, M. Kmiecik, I. Kojouharov, N. Kurz, R. Lozeva, A. Maj, S. Mandal, W. Męczyński, B. Million, S. Muralithar, P. Reiter, D. Rudolph, N. Saito, T.R. Saito, H. Schaffner, J. Simpson, J. Styczeń, N. Warr, H. Weick, C. Wheldon, O. Wieland, M. Winkler, H.J. Wollersheim

Status of the RISING Project at Relativistic Energies

Acta Phys. Pol. B 36, 1235 (2005)

page 1235 •

abstract

The RISING project was designed to perform high-resolution $\gamma$-ray spectroscopy with radioactive beams at GSI. Unstable beams were produced by fragmentation of relativistic heavy ion projectiles provided by the SIS synchrotron. The fragment separator FRS was used to select and to focus the exotic fragments at about 100$A$ MeV energy on a secondary target. Various charged particle detectors enabled an event-by-event tracking of the incoming radioactive projectiles and the reaction products, thus allowing for a selection of the nuclei of interest and their velocity vector reconstruction. The $\gamma$-ray detection system consisting of the EUROBALL Cluster Ge detectors and the large volume HECTOR BaF$_{2}$ detectors measured prompt $\gamma$-radiation from nuclei excited in the secondary target. Despite the huge Doppler shift due to the high recoil velocity ($\beta \approx 40$%), RISING achieved a $\gamma$-energy resolution below 2%. The paper reviews the present status of the RISING project.

full authors' list

R. Lozeva, S. Mandal, J. Gerl, M. Górska, J. Grębosz, I. Kojouharov, J. Adamczewski, A. Banu, F. Becker, T. Beck, P. Bednarczyk, A. Blazhev, P. Doornenbal, H. Geissel, M. Hellström, M. Kavatsyuk, O. Kavatsyuk, N. Kurz, M. Mutterer, S. Muralithar, G. Münzenberg, W. Prokopowicz, N. Saito, T. Saitoh, H. Schaffner, K. Sümmerer, H. Weick, M. Winkler, C. Wheldon, H.-J. Wollersheim

Calorimeter Telescope for Identification of Relativistic Heavy Ion Reaction Channels

Acta Phys. Pol. B 36, 1245 (2005)

page 1245 •

abstract

A new $\Delta E$–$E$ CAlorimeter TElescope, CATE, has been developed to identify the reaction products from secondary fragmentation reactions or Coulomb excitation. Radioactive relativistic beams with energies between 90 and 400 MeV/$u$ and instantaneous rates of up to $5\times 10^{4}$ particles/s bombarded the detector system. CATE distinguishes the reaction channels in terms of charge ($Z$) and mass ($A$) and gives position information about the impinging ions, used for impact parameter determination.

full authors' list

A. Bürger, T. Saito, A. Al-Khatib, A. Banu, T. Beck, F. Becker, P. Bednarczyk, G. Benzoni, A. Bracco, P. Bringel, F. Camera, E. Clement, P. Doornenbal, H. Geissel, J. Gerl, M. Górska, A. Görgen, H. Grawe, J. Grębosz, G. Hammond, M. Hellström, H. Hübel, M. Kavatsyuk, O. Kavatsyuk, M. Kmiecik, I. Kojouharov, N. Kurz, R. Lozeva, A. Maj, S. Mandal, W. Męczyński, D. Mehta, B. Million, S. Muralithar, A. Neußer, Zs. Podolyák, T.S. Reddy, P. Reiter, N. Saito, H. Schaffner, A.K. Singh, H. Weick, O. Wieland, C. Wheldon, M. Winkler, H.J. Wollersheim

Relativistic Coulomb Excitation of $^{54,56,58}$Cr

Acta Phys. Pol. B 36, 1249 (2005)

page 1249 •

abstract

The first excited $2^+$ states in $^{54,56,58}$Cr have been populated by relativistic Coulomb excitation using the FRS-RISING setup at GSI. The Cr ions were produced by fragmentation of a $^{86}$Kr beam on a primary Be target and separated by the FRS. The ion beams impinged on a thick secondary Au target at an energy of around 135 $A$MeV. Gamma-rays were observed by the Ge cluster detectors of the RISING setup and stored in coincidence with particle and position signals from a set of tracking detectors. The steps of the analysis and spectra showing the $2^+ \rightarrow 0^+$ transitions are presented.

full authors' list

G. Hammond, M.A. Bentley, F. Becker, J. Grębosz, M.J. Taylor, A. Banu, C.J. Barton, T. Beck, P. Bednarczyk, A. Bracco, A.M. Bruce, L.C. Bullock, A. Bürger, F. Camera, C. Chandler, P. Doornenbal, J. Gerl, H. Geissel, M. Górska, M. Hellström, D. Judson, I. Kojouharov, N. Kurz, R. Lozeva, A. Maj, S. Mandal, B. McGuirk, S. Muralithar, E.S. Paul, Zs. Podolyák, W. Prokopowicz, D. Rudolph, N. Saito, T.R. Saito, H. Schaffner, J. Simpson, D.D. Warner, H. Weick, C. Wheldon, M. Winkler, H.-J. Wollersheim

Spectroscopy of $T={3}/{2}$ Mirror Nuclei via Two-Step Fragmentation Using RISING

Acta Phys. Pol. B 36, 1253 (2005)

page 1253 •

abstract

Two two-step fragmentation reactions were performed using RISING to populate excited states in $A\approx 50$ mirror nuclei near to the proton-drip line, in order to test isospin symmetry. The experiments were designed to observe gamma decays of excited states in the mirror nuclei $^{53}_{28}$Ni$_{25}$ / $^{53}_{25}$Mn$_{28}$, which have a large value of total isospin ($T={3}/$2). In the continuing off-line analysis, gamma transitions have been observed in $^{54}$Ni indicating that two-step fragmentation is a successful technique for spectroscopic investigations of proton-rich nuclear systems in this mass region.

full authors' list

P. Reiter, F. Becker, M.A. Bentley, A. Bracco, G. de Angelis, C. Fahlander, J. Gerl, M. Gorska, H. Grawe, H. Hübel, J. Jolie, A. Maj, P. Mayet, T. Saito, K.-H. Speidel, H.J. Wollersheim

Future RISING Experiments at Relativistic Energies

Acta Phys. Pol. B 36, 1259 (2005)

page 1259 •

abstract

The proposed experiments for the first RISING (Rare ISotope INvestigations at GSI) campaign will exploit secondary unstable beams at relativistic energies in the range from 100 MeV/u to 400 MeV/u. The RISING spectrometer will be employed for relativistic Coulomb excitation and for high-resolution $\gamma$-spectroscopy experiments after secondary nucleon removal reactions and secondary fragmentation. New experimental methods for spectroscopy at relativistic energies will be investigated in order to measure nuclear structure observables beside the directly accessible level energies and quadrupole deformations. The future experiments will focus on: Shell structure of unstable doubly magic nuclei and their vicinity, symmetries along the $N=Z$ line and mixed symmetry states, shapes and shape coexistence, collective modes and E1 strength distribution.

Isomeric Decay Studies with Fragmentation Beams

Acta Phys. Pol. B 36, 1269 (2005)

page 1269 •

abstract

Results from several isomeric decay studies with fragmentation beams are discussed, with special emphasis on heavy ions (above the fission limit). Both nuclear structure and reaction studies have been examined. It has been shown that the structure of the nucleus has to be considered in order to get agreement, within a factor of 2, between the experimental and calculated angular momentum populations.

full authors' list

A. Görgen, E. Clément, E. Bouchez, A. Chatillon, W. Korten, Y. Le Coz, Ch. Theisen, C. Andreoiu, F. Becker, B. Blank, A. Bürger, P. Butler, J.M. Casandjian, W. Catford, T. Czosnyka, P. Davies, S.P. Fox, G. de France, G. Georgiev, J. Gerl, H. Hübel, J. Iwanicki, D.G. Jenkins, F. Johnston-Theasby, P. Joshi, I. Matea, P. Napiorkowski, F. de Oliveira Santos, G. Sletten, C. Timis, R. Wadsworth, M. Zielinska

Shape Coexistence in Light Krypton Isotopes

Acta Phys. Pol. B 36, 1281 (2005)

page 1281 •

abstract

The light Krypton isotopes were studied in a series of Coulomb excitation experiments using radioactive beams at GANIL. The static quadrupole moments found in these experiments give firm experimental evidence for the shape coexistence scenario that is based on theoretical calculations and on the systematics of low-lying excited $0^+$ states.

full authors' list

M. Zielińska, T. Czosnyka, K. Wrzosek, J. Choiński, Y. Hatsukawa, J. Iwanicki, M. Koizumi, H. Kusakari, M. Matsuda, T. Morikawa, P.J. Napiorkowski, A. Osa, M. Oshima, T. Shizuma, J. Srebrny, M. Sugawara, K. Zając

Shape Coexistence in Even–Even Mo Isotopes Studied via Coulomb Excitation

Acta Phys. Pol. B 36, 1289 (2005)

page 1289 •

abstract

The nuclei $^{96}$Mo and $^{100}$Mo have been Coulomb excited using various combinations of beams and targets. The investigation of the electromagnetic structure of these isotopes provides an experimental background for a theoretical description of the shape coexistence observed in the previously studied $^{98}$Mo isotope.

Spectroscopy of Deep Inelastic Reaction Products: Scavenging Pays

Acta Phys. Pol. B 36, 1293 (2005)

page 1293 •

abstract

In the past fifteen years, concentrated efforts with a strong Krakovian flavor have focused on developing thick-target $\gamma \gamma$ coincidence methods for exploring the spectroscopy of neutron-rich heavy ion reaction products that cannot be reached by fusion–evaporation reactions. For a typical system, scores of product nuclei are formed with millibarn cross sections or less, the data analysis tends to be complicated, and isotopic assignments can sometimes be problematic. However, by taking advantage of the analyzing power of modern multidetector arrays, it has been possible to extract important new information about a wide range of poorly studied nuclei on the neutron-rich side of maximum stability. An eclectic sampling of results is presented.

Investigation of Neutron-Rich Nuclei with the Clover Array and the PRISMA Magnetic Spectrometer

Acta Phys. Pol. B 36, 1301 (2005)

page 1301 •

abstract

A new experimental apparatus has been recently installed at the Legnaro National Laboratory (LNL). It combines a large acceptance magnetic spectrometer (PRISMA) with a powerful $\gamma$-detector array (CLARA) and is especially suited for spectroscopy of neutron-rich nuclei produced in deep-inelastic or multi-nucleon transfer reactions. In this talk the results of the first experiments will be presented.

full authors' list

P.H. Regan, C. Wheldon, A.D. Yamamoto, J.J. Valiente-Dobón, D. Cline, C.Y. Wu, A.O. Macchiavelli, F.R. Xu, J.F. Smith, K. Andgren, R.S. Chakrawarthy, M. Cromaz, P. Fallon, S.J. Freeman, A. Gorgen, A. Hayes, H. Hua, S.D. Langdown, I-Y. Lee, C.J. Pearson, Zs. Podolyák, R. Teng

Vibrational and Rotational Sequences in $^{101}$Mo and $^{103,4}$Ru Studied via Multinucleon Transfer Reactions

Acta Phys. Pol. B 36, 1313 (2005)

page 1313 •

abstract

The near-yrast states of $^{101}_{\ 42}$Mo$_{59}$ and $^{103,4}_{\hspace {2mm} 44}$Ru$_{59,60}$ have been studied following their population via heavy-ion multinucleon transfer reactions between a $^{136}$Xe beam and a thin, self-supporting $^{100}$Mo target. The ground state sequence in $^{104}$Ru can be understood as demonstrating a simple evolution from a quasi-vibrational structure at lower spins to statically deformed, quasi-rotational excitation involving the population of a pair of low-${\mit \Omega }$ $h_{{11}/{2}}$ neutron orbitals. The effect of the decoupled $h_{{11}/{2}}$ orbital on this vibration-to-rotational evolution is demonstrated by an extension of the “E-GOS” prescription to include odd-$A$ nuclei. The experimental results are also compared with self-consistent Total Routhian Surface calculations which also highlight the polarising role of the highly aligned neutron $h_{{11}/{2}}$ orbital in these nuclei.

full authors' list

G.A. Jones, Zs. Podolyák, N. Schunck, P.M. Walker, G. De Angelis, Y.H. Zhang, M. Axiotis, D. Bazzacco, P.G. Bizzeti, F. Brandolini, R. Broda, D. Bucurescu, E. Farnea, W. Gelletly, A. Gadea, M. Ionescu-Bujor, A. Iordachescu, Th. Kröll, S.D. Langdown, S. Lunardi, N. Marginean, T. Martinez, N.H. Medina, B. Quintana, P.H. Regan, B. Rubio, C.A. Ur, J.J. Valiente-Dobón, S.J. Williams

Oblate Collectivity in the Yrast Structure of $^{194}$Pt

Acta Phys. Pol. B 36, 1323 (2005)

page 1323 •

abstract

A deep inelastic reaction using a 460 MeV $^{82}$Se beam incident upon a thick $^{192}$Os target was performed at the Legnaro National Laboratory, Italy. The resulting $\gamma$-decays were measured using the GASP array. Results for $^{194}$Pt extend the known level scheme of the yrast structure from spin $I=(12~\hbar$) to (20$~\hbar$). The irregularities in the sequence of the new transition energies and total Routhian surface calculations show a breakdown in collectivity with an yrast oblate shape remaining to high spin.

Experimental Challenges for Studying Needles in a Haystack

Acta Phys. Pol. B 36, 1329 (2005)

page 1329 •

abstract

As a tribute to Rafał Broda and as a celebration of his sixtieth birthday, this short review examines the progress in techniques for in-beam nuclear spectroscopy of weak channels. Illustrative examples will be taken from studies of heavy octupole nuclei and deformed superheavy nuclei, in which various reaction mechanisms have been employed. Future perspectives will also be presented.

full authors' list

J.J. Valiente-Dobón, C.E. Svensson, C.D. O'Leary, I. Ragnarsson, C. Andreoiu, R.A.E. Austin, M.P. Carpenter, D. Dashdorj, P. Finlay, S.J. Freeman, P.E. Garrett, A. Görgen, J. Greene, G.F. Grinyer, B. Hyland, D. Jenkins, F. Johnston-Theasby, P. Joshi, N.S. Kelsall, A.O. Macchiavelli, F. Moore, G. Mukherjee, A.A. Phillips, W. Reviol, D. Sarantites, M.A. Schumaker, D. Seweryniak, M.B. Smith, R. Wadsworth, D. Ward

Lifetimes of High-Spin States in $^{76}$Kr

Acta Phys. Pol. B 36, 1339 (2005)

page 1339 •

abstract

High-spin states in $^{76}_{36}$Kr$_{40}$ have been populated in the $^{40}$Ca($^{40}$Ca,4$p$)$^{76}$Kr fusion–evaporation reaction at a beam energy of 165 MeV, and studied using the Gammasphere and Microball multi-detector arrays. The ground-state band and two signature-split negative-parity bands of $^{76}$Kr have been extended to $\sim$30$\hbar$. Lifetime measurements using the Doppler-shift attenuation method indicate that the transition quadrupole moment of these three bands decrease as they approach their maximum-spin states.

full authors' list

R. Broda, B. Fornal, W. Królas, T. Pawłat, J. Wrzesiński, D. Bazzacco, S. Lunardi, G. de Angelis, A. Gadea, C. Ur, N. Marginean, R.V.F. Janssens, M.P. Carpenter, S.J. Freeman, N. Hammond, T. Lauritsen, C.J. Lister, F. Moore, D. Seweryniak, P.J. Daly, Z.W. Grabowski, B.A. Brown, M. Honma

Yrast States in $N=30$ $^{50}$Ca and $^{51}$Sc Isotones Studied with Deep-Inelastic Heavy Ion Reactions

Acta Phys. Pol. B 36, 1343 (2005)

page 1343 •

abstract

Data from three gamma spectroscopy experiments using deep-inelastic heavy ion reactions provided new information on high-spin states in the neutron-rich $N=30$, $^{50}$Ca and $^{51}$Sc isotones. Shell model calculations restricted to neutron excitations only are shown to reproduce with good accuracy some of the experimental levels. It is demonstrated that proton excitations not accounted in these calculations are abundantly present in the observed yrast structures. High energy of the $4^+$ state in $^{50}$Ca underlines the validity of the $N=32$ shell closure.

Shape Coexistence in the Lead Isotopes Using Algebraic Models: Description of Spectroscopic and Ground-State Related Properties

Acta Phys. Pol. B 36, 1351 (2005)

page 1351 •

abstract

A three-configuration mixing calculation is presented in the context of the Interacting Boson Model (IBM1), with the aim to describe recently observed collective bands built on low-lying $0^+$ states in the neutron-deficient lead isotopes. Possible effects on the nuclear binding energy are addressed, caused by mixing of these low-lying $0^+$ intruder states into the ground state, and a new method is described in order to provide a consistent description of both ground-state and excited-state properties.

Acta Phys. Pol. B 36, 1355 (2005)

page 1355 •

abstract

Large scale calculations in a five-dimensional space of deformation parameters allow us to investigate the influence of quadrupole and hexadecapole non-axialities on the spontaneous fission life time estimates of nuclei. The macroscopic–microscopic method gives the total energy surfaces using the newest Lublin–Strasbourg Drop (LSD) macroscopic energy. The microscopic part is based on the single particle energy spectra of the Woods–Saxon single particle potential with the universal set of parameters in five-dimensional space of deformation parameters for each of about 200 even–even isotopes. Our aim is to obtain the total energy surfaces in the multidimensional space of deformation parameters paying special attention to non-axial quadrupole and hexadecapole parameters $\alpha _{2,2}, \alpha _{4,2}, \alpha _{4,4}$ and to compare them with the total energy surfaces obtained in the axially symmetric space $\alpha _{2,0}, \alpha _{4,0}, \alpha _{6,0}, \alpha _{8,0}, \alpha _{10,0}$ for the region of Cf–Ds and heavier nuclei.

Mechanism of a Decrease of the Fission-Barrier Height of a Heavy Nucleus by Non-Axial Shapes

Acta Phys. Pol. B 36, 1359 (2005)

page 1359 •

abstract

Mechanism of reduction of (static) fission-barrier height $B^{\rm st}_{\rm f}$ by non-axial deformations is studied for the nucleus $^{250}$Cf. Two-dimensional (quadrupole) deformation space is used. It is found that the reduction is the effect of a rather strong change of shell structure with a change of deformation of the nucleus.

Description of $\alpha$-Spectroscopic Data of Odd-$A$ Superheavy Nuclei

Acta Phys. Pol. B 36, 1363 (2005)

page 1363 •

abstract

$\alpha$-decay chain of $^{271}$Ds is studied theoretically within a macroscopic–microscopic approach. It is found that experimental $\alpha$-transition energies are well reproduced by calculations. Rather small single-particle effects are obtained in these energies.

Masses and Half-Lives of Superheavy Elements

Acta Phys. Pol. B 36, 1369 (2005)

page 1369 •

abstract

Spontaneous fission and $\alpha$-decay half-lives of superheavy elements are determined in the macroscopic-microscopic model where the macroscopic part is the Lublin–Strasbourg Drop and the pairing correction is based on the state-dependent two-body interaction of the $\delta$ type. The coupling strengths of the pairing force are fitted to experimentally known masses of heavy nuclei with $Z\ge 98$.

Dependence of Fusion Barrier Heights on the Difference of Proton and Neutron Radii

Acta Phys. Pol. B 36, 1373 (2005)

page 1373 •

abstract

Using the Skyrme effective nucleon–nucleon interaction together with the semiclassical Extended Thomas–Fermi approach (ETF) we investigate the relative change of the fusion barrier heights for the reaction $^{16}$O$\,+^{208}$Pb as function of the nuclear proton or neutron radii of the colliding nuclei.

Temperature Dependence of the Nuclear Shell Energies

Acta Phys. Pol. B 36, 1377 (2005)

page 1377 •

abstract

The $\cal {N}$-averaging Strutinsky shell-correction method is used to obtain the change with temperature of shell effects as well as of the macroscopic part of nuclear energy in a relativistic mean-field approach with the NL3 parameter set for even–even spherical nuclei.

The AGATA Spectrometer

Acta Phys. Pol. B 36, 1383 (2005)

page 1383 •

abstract

The global consensus of opinion is that the next major step in $\gamma$-ray spectroscopy involves abandoning the concept of a physical suppression shield and achieving the ultimate goal of a 4$\pi$ Ge ball through the technique of $\gamma$-ray energy tracking in electrically segmented Ge crystals. The resulting spectrometer will have an unparalleled level of detection power to nuclear electromagnetic radiation. Its sensitivity for selecting the weakest signals from exotic nuclear events will be enhanced by a factor of up to 1000 relative to its predecessors. It will have an unprecedented angular resolution making it ideally suited for high-energy resolution even at recoil velocities of up to 50% of the velocity of light. Therefore, it is ideally suited to be used in conjunction with the new generation of radioactive beam accelerators or existing stable beam facilities. In Europe, a collaboration has been established to construct a 4$\pi$ tracking spectrometer called AGATA (Advanced GAmma Tracking Array). This collaboration has signed a Memorandum of Understanding for the first phase of the project to perform the research and development necessary to finalise the technology for $\gamma$-ray tracking and hence fully specify the full 4$\pi$ spectrometer. The status of this first phase of the AGATA project is described.

Concluding Remarks

Acta Phys. Pol. B 36, 1395 (2005)

page 1395 •

The Current Status of $2p$ Emission Studies

Acta Phys. Pol. B 36, 1399 (2005)

page 1399 •

abstract

A review of recent achievements obtained in the field of the $2p$ emission is given. The results obtained for excited states of $^{17}$Ne and $^{18}$Ne as well as for the ground state of $^{45}$Fe are discussed. Other candidates for $2p$ radioactivity are mentioned. A design of a new type of time projection chamber with optical readout, for studies of $pp$ correlations in the decay of $^{45}$Fe, is briefly presented.

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