### Regular Series

#### Vol. 29 (1998), No. 1 – 2, pp. 11 – 494

Broken Symmetries at the Origin of Matter, at the Origin of Life and at the Origin of Culture

Acta Phys. Pol. B 29, 11 (1998)

page 11 •

abstract

In earliest cosmic history the university started with matter and not with antimatter. Shortly after the beginning the electroweak interaction — prominent in nuclear $\beta$ decay — acted as a lefthander. Much later, in prebiotic evolution, optically left-handed amino acids determined the unique signature of following terrestrial organic life. Again ae- ons later, homo sapiens appears as predominantly right handed and creates cultures with many broken symmetries. Along these pathways of history it was essential that choices were made — left or right, matter or antimatter — but on several instances it seemed less relevant which choices were made. We think that biochirality occurred by global chance; perhaps by local necessity, but without causal links to the PCT theorem. In other cases — e.g. the standardization to right-handed screws — the choice will have been made by causal necessity.

Neutron Stars: Formation and Structure

Acta Phys. Pol. B 29, 25 (1998)

page 25 •

abstract

A short introduction is given to astrophysics of neutron stars and to physics of dense matter in neutron stars. Observed properties of astrophysical objects containing neutron stars are discussed. Current scenarios regarding formation and evolution of neutron stars in those objects are presented. Physical principles governing the internal structure of neutron stars are considered with special emphasis on the possible spin ordering in the neutron star matter.

Neutrinos and Symmetries Studied by Nuclear Double Beta and Rare Decays

Acta Phys. Pol. B 29, 47 (1998)

page 47 •

abstract

Nuclei, which consist of nucleons in good quantum states, are good micro-laboratories for studying fundamental interactions and elementary particles. In particular, nuclear double beta decays and nuclear rare decays are used to study neutrinos ($\nu$) and symmetries in nuclear microlaboratories. Subjects discussed include (i) $\nu$-masses and weak interactions studied by nuclear double beta decays ($\beta \beta$), (ii) neutrino nuclear responses for solar-$\nu$ and $\beta \beta - \nu$, (iii) strange-quark weak processes studied by hyperon weak decays in nuclei, and (iv) nucleon decays studied by nuclear rare deexcitations. All these subjects are associated with neutrinos and symmetries beyond the standard theory.

Symmetry and Symmetry-Violation in Beta Decay; $P, C$ and a Mysterious $T$

Acta Phys. Pol. B 29, 63 (1998)

page 63 •

abstract

Parity experiments with $\beta$ decays were at the basis of the Standard Model for the electroweak interaction and continue to contribute, together with investigations of invariance for time reversal, to basic physics. In specific the essential role of $\beta$-ray polarimetry will be underlined with an extrapolation to a potential NdFe polarimeter for advanced studies of right-handed currents and time-reversal invariance at higher energies.

Test of Physics Beyond the Standard Model in Nuclei

Acta Phys. Pol. B 29, 79 (1998)

page 79 •

abstract

Grand Unifications of the electroweak and the strong interaction prefer that the neutrino is a Majorana particle and therefore essentially identical with its own antiparticle. In such grand unified models the neutrino has also a finite mass and a slight right-handed weak interaction, since the model is left-right symmetric. These models have vector bosons mediating the left- and the right-handed weak interactions. If these models are correct, the neutrinoless double beta-decay is feasible. Although the neutrinoless double beta-decay has not been seen it is possible to extract from the lower limits of the lifetime upper limits for the effective electron-neutrino mass and for the effective mixing angle of the vector bosons mediating right-handed and the left-handed weak interaction. One also can obtain an effective upper limit for the mass ratio of the light and the heavy vector bosons. A condition for obtaining reliable limits for these fundamental quantities from the measured lower limits of the half lives of the $0\nu \beta \beta$ decay are that the nuclear matrix can be calculated correctly. These nuclear structure calculations can be tested by calculating the two neutrino double beta decay $(2\nu \beta \beta )$ for which we have experimental data and not only lower limits as for the $0\nu \beta \beta$ decay. The $2\nu \beta \beta$ decay is dominated by the Gamow Teller (GT) transitions. The intermediate $1^{+}$ states in the odd-odd mass nucleus are usually calculated within the Quasi-Particle Random Phase Approximation (QRPA). The QRPA treats Fermion pairs as bosons. This overestimates the ground state correlations and leads to the collapse of the $2\nu \beta \beta$ decay probability for the physical $J^{\pi } = 1^+, T = 1$ particle-particle interaction. We have extended the QRPA including the Fermi commutation relations. One finds now agreement (in almost all cases) for the $2\nu \beta \beta$ decay probability. This increases also the reliability of the conclusions extracted from the upper limits of the $0\nu \beta \beta$ decay for the neutrino mass, the left-right mixing angle and the lower limit for the mass of the “heavy” vector boson.

A Search for a “New Physics” in Lepton Flavour Violation Processes

Acta Phys. Pol. B 29, 91 (1998)

page 91 •

abstract

Precision measurements and searches for rare processes in flavour physics offer a unique opportunity to test extensions of the Standard Model i.e. so called a “New Physics”. After general presentation of this subject a description of only ongoing experiment on the muon beams — a search for neutrinoless muon — electron conversion on nuclei (SINDRUM II project) is presented and last experimental results are discussed.

full authors' list

S. Kullander, H. Calén, K. Fransson, A. Kupść, B. Morozov, R. Ruber, V. Sopov, J. Stepaniak, V. Tchernychev

Rare $\eta$ Decays and the CP Symmetry

Acta Phys. Pol. B 29, 97 (1998)

page 97 •

abstract

Among the light mesons, the $\eta$ is very well suited for tests of the Standard Model (SM). Besides its negative parity and predominantly SU(3) octet structure, the $\eta$ has the quantum numbers of the vacuum, it is comparatively massive and it is long-lived since first-order strong, electromagnetic and weak decays are suppressed. Since the $\eta$ meson is an eigenstate of both C and CP, these fundamental symmetries can be studied in detail. Searches for C or CP violating decays such as $\eta \rightarrow \gamma \gamma \gamma$, $\eta \rightarrow \pi \pi$, $\eta \rightarrow \pi ^0 e^+e^-$ and for effects beyond the Standard Model in $\eta \rightarrow e^+e^-$ are challenging research topics. New experimental facilities that will come into operation in the next few years will allow detailed investigations of the $\eta$ rare decays. In Uppsala, a wide-angle spectrometer, WASA, is being prepared for investigations of symmetries, searches for exotics and for precise measurements of decays which are sensitive tests of Chiral Perturbation Theory, for example the decays $\eta \rightarrow 3\pi$ and $\eta \rightarrow \pi ^0\gamma \gamma$.

Hypothesis of Tachyonic Neutrinos

Acta Phys. Pol. B 29, 113 (1998)

page 113 •

abstract

Anomalies observed in the electron energy spectrum in tritium decay are expected if electron (anti)neutrino is a tachyon; in particular anhancement of counts near the end point leading to negative values for the electron antineutrino mass squared. Since the tachyonic neutrino field is an eigenstate of the helicity operator, the hypothesis of tachyonic neutrinos offers a natural explanation of the V–A structure of the weak leptonic current. Our “educated guess” for the mass of a hypothetical tachyonic neutrino is $\approx 5$ eV.

Antihydrogen–Testbench for the Symmetry of the Antiworld

Acta Phys. Pol. B 29, 123 (1998)

page 123 •

abstract

Comprising an antiproton and a positron, antihydrogen is the simplest atom of antimatter. The transition frequency of 2.466$\times$10$^{15}$ Hz from the 1S ground state to the 2S metastable state, if measured with the accuracy set by the natural line width of 1.1 Hz, offers the chance to test CPT invariance and the equivalence principle.

full authors' list

G.L. Borchert, H. Gorke, D. Gotta, S. Lenz, T. Siems, D.F. Anagnostopoulos, M. Augsburger, D. Chatellard, J.P. Egger, D. Belmiloud, P. El-Khoury, P. Indelicato, M. Daum, P. Hauser, K. Kirch, L.M. Simons

High Precision Spectroscopy of Pionic and Muonic X-Rays to Extract an Upper Limit for the Muon–Neutrino Mass

Acta Phys. Pol. B 29, 131 (1998)

page 131 •

abstract

A new experiment for a high precision measurement of the pion mass is presented. It combines the cyclotron trap to produce pionic atoms in a small volume, with a doubly focussing crystal spectrometer to measure pionic and muonic X-ray transitions with high accuracy. The muonic X-rays will serve as new high precision standards. The first test experiments demonstrate the feasibility of the project. It yielded a preliminary value for the pion mass of ($139570.71\pm 0.53$) keV$\!/c^2$. In combination with a recent muon momentum result a new value for the muon neutrino was obtained: $M^2_{\nu \mu }=(0.02898\pm 0.03267)$MeV$^2/c^4$. With some improvements which are being prepared, the next measurement can be expected to yield an accuracy of better than 1ppm for the pion mass and hence a limit smaller than 70 keV$\!/c^2$ for the neutrino mass.

full authors' list

M. Fujiwara, T. Hotta, T. Kinashi, K. Takanashi, T. Nakano, Y. Ohashi, S. Daté, H. Ohkuma, N. Kumagai

Physics with Polarized Photons at SPring-8

Acta Phys. Pol. B 29, 141 (1998)

page 141 •

abstract

We discuss physics opportunities at SPring-8 using GeV-photons and MeV-photons obtained by Compton backscattering of laser photons from 8 GeV electrons. We show a principle of Compton backscattering and an overview of applying a high energy photon beam for physics experiments. A new facility at SPring-8 is under construction, aiming at physics experiments using a polarized photon beam in the energy range of $1.5{\sim }3.5$ GeV. The main subject is to study sub-nucleonic degree of freedom through the measurements of various produced mesons. In addition, we present a possibility of nuclear resonance fluorescence (NRF) experiments with high intensity polarized photons at several MeV energies with an intensity of $10^8{\sim }10^9$ per second.

Effects of the Coulomb Interaction in Nuclei: Binding Energies and Isospin Mixing

Acta Phys. Pol. B 29, 157 (1998)

page 157 •

abstract

The effects of Coulomb and other charge-dependent interactions on the structure of nuclei are discussed. First, a method to predict absolute binding energies for proton-rich nuclei that allows a mapping of the proton drip-line up to $A=70$ is presented. Then the effects of isospin-symmetry breaking on tests of the standard model for the weak interaction are examined. The principal areas discussed are (1) superallowed Fermi beta decay, which provides a test of the conserved vector current hypothesis and the unitarity of Cabibbo–Kobayashi–Maskawa matrix; and (2) parity violation in electron scattering, which offers a window into the neutral-current sector of the weak interaction.

Nuclear Resonance Studies with Relativistic and Radioactive Beams

Acta Phys. Pol. B 29, 167 (1998)

page 167 •

abstract

Secondary beams of radioactive ions at high energies are used at GSI to explore the nuclear structure of exotic nuclei. This report concentrates on the investigation of halo nuclei located at the neutron dripline. Relevant reaction mechanisms such as nuclear and electromagnetic break–up are discussed together with the nuclear structure information that can be deduced.

full authors' list

M. Fujiwara, I. Daito, H. Fujimura, H. Akimune, T. Inomata, F. Ihara, K. Ishibashi, A. Tamii, M. Yosoi

Spin–Isospin Giant Resonances by Charge Exchange Reactions

Acta Phys. Pol. B 29, 179 (1998)

page 179 •

abstract

Spin–isospin excitations in nuclei studied via the charge exchange reactions are discussed together with some historical remarks concerning with the findings of the spin–isospin giant resonances. Measurements of the singles ($^3$He,t) spectra at zero degrees and studies of proton decays from the spin–isospin excitations are reported. We report results on the complementary (t,$^3$He) measurements. Special topics treated are the Gamow–Teller excitations, the spin flip dipole resonances, and the feature of the alpha cluster structures in light nuclei, which are observed both in the proton decay and in the (t,$^3$He) measurements.

The Nature of the Nucleon–Nucleon Interaction in the Quark Model

Acta Phys. Pol. B 29, 197 (1998)

page 197 •

abstract

The nucleon–nucleon interaction is studied in the Tuebingen Chiral Quark model. The quark–quark hamiltonian includes, in addition to a quadratic confinement potential and the usual one-gluon exchange, pion and sigma exchanges between quarks generated by chiral symmetry breaking. An expansion up to second order in $v/c$ is used. The requirement of chiral symmetry reduces the number of free parameters in the model. The $\sigma$ meson is exchanged between quarks and not as in earlier versions between nucleons. Within the model the nucleon-nucleon phase shifts and the deuteron properties are studied. The longitudinal and transversal form factors form factors of the deuteron are calculated in this microscopic meson–quark cluster model.

Two-Photon Interference in Micro- and Macro-Systems

Acta Phys. Pol. B 29, 211 (1998)

page 211 •

abstract

Two-photon correlations are discussed within the formalism of Hanbury–Brown and Twiss interferometry and Bose–Einstein correlations. The technique is presented as a universal tool to study the properties of any boson source — light sources such as stars, or photon and meson sources in the early phase of heavy-ion collisions. The method is illustrated using experimental data on photon-pair production in nuclear reactions, available only in the intermediate (several tens of MeV/N) energy domain. The observed interference signal is interpreted in terms of source size and reaction dynamics.

Subthreshold Photons in Heavy-Ion Reactions at Intermediate Energies

Acta Phys. Pol. B 29, 219 (1998)

page 219 •

abstract

In the present talk, I discuss about the properties of the energetic photons produced in heavy-ion reactions. I show that they are sensitive to the maximum density reached in the first stage of the nuclear reaction. Then, the existence of a thermal contribution to the photon differential cross-section is discussed. These photons are sensitive to the properties of the Equation-of-State, to the dynamics of the reaction and represent a new thermometer of heated nuclear matter. I finally describe the future experiments planified at KVI and GANIL.

Nuclear Bremsstrahlung in Proton Induced Reactions at 190 MeV (First Experiments at AGOR)

Acta Phys. Pol. B 29, 235 (1998)

page 235 •

abstract

An overview is given of the first experiments with the new KVI cyclotron AGOR. First experiments have focused on nuclear bremsstrahlung in few– and many–body reactions. A classical introduction to nuclear bremsstrahlung is given. First results on coherent bremsstrahlung are discussed.

Two-Center Structure in Light Exotic Nuclei

Acta Phys. Pol. B 29, 247 (1998)

page 247 •

abstract

The physics of the two-center shell model for the a-a potential and covalent valence neutrons and protons with up to 4 valence nucleons is discussed. The structure of nuclear dimers and their rotational bands is illustrated using published transfer reaction data for Be and Boron isotopes. Based on the state in 12C at an excitation energy of 7.65 MeV which is assumed to be an 3$\alpha$ particle chain and adding the covalent nucleons, chain states (trimers) in the system $^{12}$C*$\,+ x$ neutrons can be constructed.

full authors' list

B. Tamain, M. Assenard, G. Auger, C.O. Bacri, J. Benlliure, E. Bisquer, F. Bocage, B. Borderie, R. Bougault, P. Buchet, J.L. Charvet, A. Chbihi, J. Colin, D. Cussol, R. Dayras, A. Demeyer, D. Dore, D. Durand, P. Eudes, J. Frankland, E. Galichet, E. Genouin-Duhamel, E. Gerlic, M. Germain, D. Gourio, D. Guinet, F. Gulminelli, P. Lautesse, J.L. Laville, C. Lebrun, J.F. Lecolley, A. Lefevre, T. Lefort, R. Legrain, N. Le Neindre, O. Lopez, M. Louvel, J. Lukasik, N. Marie, M. Maskay, V. Métivier, L. Nalpas, A. Nguyen, M. Parlog, J. Pèter, E. Plagnol, A. Rahmani, T. Reposeur, M. F Rivet, E. Rosato, F. Saint-Laurent, S. Salou, M. Squalli, J.C. Steckmeyer, M. Stern, T. Tabacaru, L. Tassan-got, O. Tirel, E. Vient, C. Volan, J.P. Wieleczko

Dynamical and Statistical Aspects in Nucleus–Nucleus Collisions Around the Fermi Energy

Acta Phys. Pol. B 29, 259 (1998)

page 259 •

abstract

This contribution is devoted to two important aspects of intermediate energy nucleus–nucleus collisions: the competition of dynamical and statistical features, and the origin of the multifragmentation process. These two questions are discussed in focusing on Indra data. It turns out that most of collisions are binary and reminiscent of deep inelastic collisions observed at low energy. However, intermediate velocity emission is a clear signature of dynamical emission and establishes a link with the participant–spectator picture which applies at high bombarding energies. Multifragmentation is observed when the dissipated energy is large and it turns out that expansion occurs at least for central collisions, as it is expected if this phenomenum has a dynamical origin.

Meson Production in Dense Nuclear Matter

Acta Phys. Pol. B 29, 273 (1998)

page 273 •

abstract

Pion and Kaon production has been studied in symmetric nucleus–nucleus collisions at beam energies between 0.8 and 1.8 $A$GeV. The anisotropic azimuthal emission of pions in semi-central collisions can be explained by the emission of high-energy pions in an early stage of the collision and a late “freeze-out” of low-energy pions. In nucleus-nucleus collisions at 1 $A$GeV, the $K^+$ multiplicity increases more than linearly both with $A$ (in $A+A$ collisions) and with $A_{\rm part}$ (i.e. the number of participating nucleons in Au+Au collisions). This nonlinear behaviour is due to collective effects such as multiple hadron–hadron encounters. According to transport calculations, the large $K^+$ cross section observed for Au+Au collisions at 1 $A$GeV is a consequence of a soft nuclear equation of state. The large $K^-/K^+$ ratio measured in Ni+Ni collisions at equivalent beam energies (compared to $p+p$ collisions) is a signature for an enhanced in-medium $K^-$ production. In order to reproduce the data, transport models have to consider a reduction of the $K^-$ mass in the dense nuclear medium.

Intrinsic Reflection Asymmetry in Nuclei

Acta Phys. Pol. B 29, 289 (1998)

page 289 •

abstract

The evidence for intrinsic reflection asymmetry in atomic nuclei, with examples from recent experiment work, is reviewed.

Supersymmetry and Exotic Nuclei

Acta Phys. Pol. B 29, 301 (1998)

page 301 •

abstract

The analysis of binding energies of the $sd$ shell nuclei appeared to be a new, interesting application of the supersymmetric model. After fitting the model parameters from masses and excited energy levels of well established nuclei it is possible to describe other exotic nuclei from the edge of a stability line, belonging to the same supermultiplet. We have applied such a procedure to the oxygen isotopes $^{26,28}$O. The method can be treated more generally for the construction of a supersymmetric mass formula for all of the $sd$ shell nuclei. The results are quite satisfactory in comparison with experimental data and also with other theoretical predictions. It provides an additional argument for the approximate supersymmetry of the $sd$ shell nuclei.

A Macroscopic Model of Nuclear Rotation

Acta Phys. Pol. B 29, 313 (1998)

page 313 •

abstract

We have formulated a statistical model of nuclear properties that combines the Thomas-Fermi assumption of two fermions per ${\rm h}^3$ of phase space with an effective interaction between the nucleons. The model has been employed in the calculation of nuclear masses and density distributions. The initial calculations assumed spherical symmetry but a later extension to three dimensions permits the calculation of fission saddle-point shapes and the corresponding fission barriers. It is also possible to include angular momentum and we have constructed an extension of the model which describes approximately ground-state, superdeformed and fission-isomeric rotational bands of even-even nuclei. The model is based on a three-term energy expression corresponding to: a) a rigid rotation of part of the nucleus, b) the energy of initially counter-rotating gyroscopes that the overall rotation gradually aligns in the direction of the total angular momentum, and c) a potential energy resisting such alignment. The model can be used for a macroscopic description of the angular momentum dependence of nuclear fission barriers.

Semiclassical Model of Low-Energy Reactions with Loosely Bound Projectiles

Acta Phys. Pol. B 29, 325 (1998)

page 325 •

abstract

We develop a microscopic classical trajectory approach to low energy reactions induced by projectiles which are loosely bound towards decay in two or three particles. The reactions are assumed to proceed as dissociation of the projectile into its constituent particles, each of which may be absorbed by the target or bypass it. The model is applied to $d-^{93}{\rm Nb}$ collision at $E=15$–25 MeV. The calculated values of $(d,p)$, $(d,n)$, $(d,np)$, and complete fusion cross sections are in reasonable agreement with quantum results and available experimental data. As another application we calculate the integrated cross sections for $(^6{\rm He},n)$, $(^6{\rm He},\alpha )$, $(^6{\rm He},nn)$, $(^6{\rm He},\alpha n)$, $(^6{\rm He},\alpha nn)$, and complete fusion reactions following the $^6{\rm He}+^{232}$Th collision at few MeV above the Coulomb barrier.

Mass Drift in Strongly Damped Reactions as a Tool for Studying Nuclear Dissipation

Acta Phys. Pol. B 29, 333 (1998)

page 333 •

abstract

Experimental results on correlation between the mean normalized mass drift towards symmetry and the reaction time in strongly damped collisions induced by $^{238}$U nuclei, measured by Shen et al. at GSI Darmstadt, have been analysed in terms of a dynamical model based on classical Rayleigh–Lagrange equations of motion assuming alternatively either one-body or two-body dissipation.

Muon Signals of Cosmic Ray Interactions

Acta Phys. Pol. B 29, 339 (1998)

page 339 •

abstract

Muons originate from the decay of hadrons, produced in interactions of the primary cosmic particles with the nuclei of the atmosphere. The observation of the features of the muonic component, arising from the cascading processes induced by the primary particle, a phenomenon called extensive air shower (EAS), provides interesting information about the nature of the primary and its interactions. We illustrate this information potential by: (i) studies of the longitudinal development of EAS by measurements of the relative arrival time distributions of muons the KASCADE experiment, (ii) studies with the Bucharest electromagnetic calorimeter WILLI for energy estimates of TeV muons and for determination of the charge ratio of the atmospheric muon flux.

Singularities of the $S$-Matrix for a Complex Square Well Potential

Acta Phys. Pol. B 29, 349 (1998)

page 349 •

abstract

Trajectories of $S$-matrix poles in complex $k$ plane are presented for a complex square well potential. The conformal character of the connection between the potential and the location of the poles is used to deduce the properties of the trajectories.

Dependence of the Propagation of Ultra-Heavy Cosmic Ray Nuclei on First Ionization Potential

Acta Phys. Pol. B 29, 357 (1998)

page 357 •

abstract

Over 2000 Ultra Heavy ($Z\ge 65$) cosmic ray ions with energies over 3 GeV/n have been recorded in the UHCRE, of which a total of 205 have already been located, measured and positively identified as Ultra Heavy (UH) ions by our group. The histogram of UH elemental abundances in the Earth’s neighbourhood is obtained and the UH cosmic ray source abundances may be determined by means of an appropiate propagation model. This model describes the travel of UH ions from their sources to near the Earth, through the insterstellar medium (ISM). In our case, a dynamical Leaky Box (DLB) model has been used for propagation studies. Due to the nature of the transport equations corresponding to this model, it is necessary to assume given source abundances, perform the transport calculation to near the Earth, and to compare the result with the experimental measurements. A ‘trial and error’ procedure is applied until the source abundances giving the best agreement between the calculated and measured abundances near the Earth are found. Among all variables on which the transport equation depend, this work focuses on the effect of the First Ionization Potencial (FIP) on the propagation process. Although a better agreement between propagated and measured abundances is found when a correction for the effect of FIP is used for lighter cosmic ray nuclei, it has been found that the UHCRE experimental results are better reproduced when no FIP correction is assumed.

full authors' list

J. Gröger, T. Weber, J. de Boer, H. Baltzer, K. Freitag, A. Gollwitzer, G. Graw, C. Günther

Nuclear Structure of $^{228}{\rm Th}$

Acta Phys. Pol. B 29, 365 (1998)

page 365 •

abstract

The level structure of $^{228}$Th was studied using different experimental methods. The complete octupole quadruplet, three excited $K^{\pi }=0^{+}$ bands and two excited $K^{\pi }=2^{+}$ bands were identified.

full authors' list

P.S. Hachaj, J. Brzychczyk, A.J. Cole, P. Désesquelles, W. Gawlikowicz, K. Grotowski, S. Micek, P. Pawłowski, R. Płaneta, Z. Sosin, A.W. Wieloch, D. Benchekroun, E. Bisquer, A. Chabane, A. Demeyer, M. Charvet, B. Cheynis, E. Gerlic, A. Giorni, D. Guinet, D. Heuer, P. Lautesse, L. Lebreton, A. Lléres, M. Stern, L. Vagneron, J.B. Viano

Studying Binary Collisions with the ${}^{40}$Ca$+ {}^{40}$Ca Reaction at $E_{\textrm {lab}}= 35$ MeV/Nucleon

Acta Phys. Pol. B 29, 369 (1998)

page 369 •

abstract

The $^{40}$Ca$+ ^{40}$Ca reaction at 35 MeV/nucleon has predominantly a binary character, in agreement with the deep inelastic scattering scenario. It is well described by the stochastic mass and momentum transfer model, both in the primary reaction stage as well as in the secondary evaporation stage.

Warm Nuclei: The Tansition from Independent Particle Motion to Collisional Dominance

Acta Phys. Pol. B 29, 375 (1998)

page 375 •

abstract

We study large scale collective dynamics of isoscalar type and examine the influence of interactions residual to independent particle motion. It is argued that for excitations which commonly are present in experimental situations such interactions must not be neglected. With respect to dissipation, our results are contrasted with those of wall friction.

full authors' list

M. Jaskóła, P. Guazzoni, L. Zetta, J.N. Gu, A. Vitturi, G. Graw, R. Hertenberger, B. Valnion, F. Nuoffer, G. Staudt

A Study of the $^{90}$Zr(p,t) $^{88}$Zr Reaction

Acta Phys. Pol. B 29, 385 (1998)

page 385 •

abstract

The $^{90}$Zr(p,t)$^{88}$Zr reaction has been studied in a high resolution experiment at an incident energy of 25 MeV. Angular distributions for transitions to the levels of $^{88}$Zr up to an excitation energy of $\sim$ 3.1 MeV have been measured. The data have been analyzed by means of the DWBA theory using double folding triton potential. The energy spectrum of $^{88}$Zr has been studied in the framework of shell model.

A $^5He$+$\alpha$ Cluster Model of $^9$Be

Acta Phys. Pol. B 29, 395 (1998)

page 395 •

abstract

Using a simple $^5$He+$\alpha$ cluster model of $^9$Be we are able to obtain good agreement with the measured values of the ground-state quadrupole moment and $B$ (E2; 3/2$^-$ $\rightarrow$ 5/2$^-$) and $B$ (E2; 3/2$^-$ $\rightarrow$ 7/2$^-$). We use this simple model to fit elastic scattering data in 3-channel coupled-channels calculations and produce predictions for the angular distribution of the breakup of $^9$Be via the 5/2$^-$ resonant state at 2.43 MeV.

The Charged Kaon Production in $^{58}$Ni on $^{58}$Ni Collisions at 1.93 A GeV

Acta Phys. Pol. B 29, 401 (1998)

page 401 •

abstract

The production of charged kaons in the central $^{58}$Ni+$^{58}$Ni reactions at 1.93 $A$ GeV was studied with the FOPI spectrometer. A brief description of the apparatus is provided. The particle identification procedure is described. Two examples of obtained results are discussed.

Various Parametrizations of the Woods–Saxon Potential

Acta Phys. Pol. B 29, 407 (1998)

page 407 •

abstract

The neutron and proton separation energies and mean square charge radii are evaluated within the Woods–Saxon plus BCS model for even–even nuclei with $40 \leq A \leq 256$. The various parametrizations of the Woods–Saxon potential are examined. The improved values of the constants of the central part of Woods-Saxon potential are determined from a least-square adjustment to the existing experimental data.

Observation of ${\mit \Delta }^+\rightarrow p\pi ^0$ Decay in Nuclear Matter

Acta Phys. Pol. B 29, 419 (1998)

page 419 •

abstract

Proton-$\pi ^\circ$ coincidences have been measured at the beam energy of 180A MeV in the reaction Ar+Ca studied by TAPS at SIS/GSI. In the proton-$\pi ^\circ$ invariant mass spectrum we evidence a significant excess of counts above the background obtained by event mixing. We assign this signal to the strength distribution of the ${\mit \Delta }$ baryonic resonance. From the measured yields we deduce a $\pi$/${\mit \Delta }$ ratio of 0.9$\pm$0.3 (preliminary value), pointing that most (if not all) pions produced in subthreshold energy heavy-ion reaction are mediated by the ${\mit \Delta }$-resonance.

full authors' list

A. Metz, A. Gollwitzer, G. Graw, J. Gröger, C. Günther, R. Hertenberger, J. Jolie, B.D. Valnion, N. Warr

High Resolution ($p,d$) and ($\vec {d},t$) Studies of $^{196}$Au and a Test of the IBM Supersymmetry Concept

Acta Phys. Pol. B 29, 425 (1998)

page 425 •

abstract

High resolution spectra of the $^{197}{\rm Au}(p,d)^{196}$Au reaction revealed more than 15 new levels of $^{196}$Au in the energy range between $0$ and 1MeV. From polarized ($\vec {d},t$) angular distributions of differential cross section and asymmetry and from comparison with Distorted Wave Born Approximation (DWBA) calculations transferred angular momenta $l,j$ and spectroscopic factors $S_{lj}$ of the resolved levels have been determined. This leads to restrictions in the spin assignments of states in the odd odd nucleus $^{196}$Au. Comparing with predictions, calculated in the extended supersymmetry version of the Interacting Boson Model (IBM), we observe reproduction of relevant features.

full authors' list

J. Mrázek, M. Honusek, A. Špalek, J. Bielčík, J. Slívová, A.A. Pasternak

Levels of $^{100,101}$Ru Excited in the Reaction $^{100}$Mo($\alpha xn)$

Acta Phys. Pol. B 29, 433 (1998)

page 433 •

abstract

Excited states of $^{100}$Ru and $^{101}$Ru were studied by in-beam gamma-ray spectroscopy methods in reaction $^{100}$Mo($\alpha , xn)$. Angular distributions, excitation functions and coincidences $\gamma$–$\gamma$ were measured. Lifetimes were deduced by DSA method. Particular changes to level schemes were proposed. Alignment was studied and comparison with IBA-1 calculation is discussed.

Optimized Expansion for the Nambu and Jona-Lasinio Model

Acta Phys. Pol. B 29, 439 (1998)

page 439 •

abstract

The optimized expansion is applied to calculate the effective action for the Nambu-Jona-Lasinio model. The method is non-perturbative, the results derived from the effective action calculated to the first order of the optimized expansion corespond to an infinite summation of perturbative Feynman diagrams both in the Schwinger–Dyson equation for propagator and in the two-body Bethe–Salpeter equation. We show that this is equivalent to the mean field (relativistic Hartree plus random phase) approximation. The optimized expansion offers thus a systematic method to improve the relativistic mean field approximation in a consistent way.

full authors' list

M. Popkiewicz, S. Osuch, Z. Szefliński, A. Sztampke, Z. Wilhelmi, M. Wolińska, R. Zagańczyk

Neutron Emission from $^{101}$Rh Produced via $^{12}$C$+^{89}$Y Reaction at 49.5 MeV

Acta Phys. Pol. B 29, 447 (1998)

page 447 •

abstract

The neutron detecor MONA (MOdular Neutron Array) was used to measure neutron spectra originated in the $^{12}$C$+^{89}$Y system. The neutron spectra were measured at six selected angles by TOF method at average laboratory energy of 49.5 MeV. The temperature of the source was determined through off-line analysis and was found to be 1.62 MeV. The level density parameter $a$, was determined within the framework of a Fermi-gas model, to be equal to ${a}=A/9.4$.

Analysis of Pre-scission Neutron Multiplicities in Terms of the Statistical Model with Kramers Dissipative Fission

Acta Phys. Pol. B 29, 451 (1998)

page 451 •

abstract

Pre-scission neutron multiplicities in fusion-fission reactions, reported by Hinde et al., have been analyzed in terms of the statistical model assuming a possible hindrance of the compound-nucleus fission width by the Kramers factor which depends on nuclear dissipation. Contrary to earlier results reported by Hofman, Back and Paul on an analysis of the GDR $\gamma$-decay, the nuclear dissipation deduced in the present analysis does not show a clear dependence on the temperature of the compound nucleus. On average, the deduced values of the nuclear dissipation are consistent with the one-body dissipation estimate.

full authors' list

B. Vereecke, J. Camps, N. Severijns, J. Deutsch, T. Otto, J. Govaerts, B.A. Brown, B. Holstein, R. Kirchner, O. Naviliat-Cuncic, R. Prieels, P.A. Quin, E. Thomas, P. De Moor, P. Schuurmans, A. Van Geert, L. Vanneste

Search for Physics Beyond the Standard Model via a Polarization-Asymmetry Correlation Experiment on $^{107}$In

Acta Phys. Pol. B 29, 457 (1998)

page 457 •

abstract

We report on a new precision measurement of the longitudinal polarization of positrons emitted by polarized $^{107}$In nuclei. If interpreted in the framework of the manifest left-right symmetric model, preliminary results yield a lower limit of 303 GeV/$c^2$ for the mass of a possible, predominantly right-handed W gauge boson.

Neutron and Proton Distribution in Nuclei in Relativistic Mean Field Theory

Acta Phys. Pol. B 29, 463 (1998)

page 463 •

abstract

Differences between neutron and proton distributions were investigated for $\beta$-stable nuclei and for chains of isotopes and isotones up to drip line nuclei. The relativistic mean field theory with the parameter set NL-3 was used in calculations. Dependence of neutron and proton radius and mean density on relative neutron excess $I=(N-Z)/A$ was found. Different deformations of neutron and proton matter were noticed.

Resonance-Like Behaviour in Two-Nucleon Absorption/Emission Mechanism of DCX Reaction

Acta Phys. Pol. B 29, 469 (1998)

page 469 •

abstract

We have studied the effects of pion wave-function distortion on the cross-section of the absorption/emission mechanism of the pionic double charge exchange reaction on $^{56}{Fe}$, $^{76}{Ge}$ and $^{128,130}{Te}$. We are using the pion-nucleus optical potential and the quasiparticle p-n random phase approximation formalisms, considering only the contribution of pion absorption/emission (p-wave mechanism) on the correlated nucleon pair. We confirm the resonant behaviour of the forward cross-section at around $50$ MeV, opposite to the plane wave-function results.

Concluding Remarks

Acta Phys. Pol. B 29, 475 (1998)

page 475 •

abstract

“Ich bin kein ausgeklügelt Buch, ich bin ein Mensch in seinem Widerspruch.” Johann Wolfgang von Goethe

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