摘要:

A systematic study of astrophysical reaction rates of (&agr;, n) and (p, n) reactions on light neutron‐rich nuclei by using low‐energy radioactive nuclear beam is in progress at the tandem facility of Japan Atomic Energy Research Institute. Exclusive measurements of8Li(&agr;, n)11B and16N(&agr;, n)19F reaction cross sections have been performed successfully. Their excitation functions together with the experimental method are presented. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737141

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

An experimental method to determine the (n,&ggr;) cross section of short‐livings‐process branching points using data of the inverse (&ggr;,n) reaction is presented. The method was used to observe the branching point nucleus95Zr because the elemental abundance patterns corresponding to this branching point cannot be reproduced by full stellar models and a possible error source is the neutron capture cross section of95Zr. The analysis of the experiment is still under progress, we will outline the current status in this manuscript. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737142

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The equation of state (EOS) of nuclear matter is discussed within the Brueckner‐Bethe‐Goldstone approach. First the energy per particleE/Ais calculated in the Brueckner‐Hartree‐Fock limit with the Argonnev18potential, using the continuous choice as auxiliary potential. Then, the contribution of three‐body clusters is determined by solving the Bethe‐Faddeev equation, and the equivalence with the same calculations based on the standard choice as auxiliary potential, is demonstrated. In spite of reaching a quite good convergence of the hole‐line expansion, the resulting EOS does not fit the empirical saturation density (&rgr;0= 0.17 fm−3). To this end, three‐body forces (TBF) are introduced. A first class of microscopic TBF comprises effects due toNN¯virtual excitations via &sgr; and &ohgr;‐meson exchanges (the main relativistic correction to Brueckner theory), the 2&pgr;‐exchange, and the virtual excitation of the lowest nucleonic resonanceN*(1440). We compare with a phenomenological TBF, involving two parameters adjusted on the saturation density and energy. Next, using microscopic or phenomenological TBF, the symmetry energy of nuclear matter is computed, allowing to determine the EOS of beta‐stable and charge neutral matter, and the properties of neutron stars, in particular the mass‐radius curve. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737143

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present a brief account of two phenomena taking place in a neutron star crust: the Fermionic Casimir effect and the major density depletion of the cores of the superfluid neutron vortices. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737144

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Universal baryon‐density parameter &OHgr;Binferred from the Big‐Bang nucleosynthesis and cosmic microwave background fluctuations disagrees with each other at the 1&sgr; level. We propose new cosmological models for the Big‐Bang nucleosynthesis to try to recover the concordance of &OHgr;B. Nuclear processes in the Big‐Bang nucleosynthesis are similar to those in the r‐process nucleosynthesis in supernovae. Even in the nucleosynthesis of heavy elements, entropy and density in the neutrino‐driven winds of Type II supernovae are so high that nuclear statistical equilibrium favors production of abundant light nuclei. In such explosive circumstances many radioactive light‐to‐intermediate mass nuclei as well as heavy mass nuclei play the significant roles. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737145

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The compound nucleus76Kr*was populated at the excitation energy of 75 MeV and angular momentum of 39 ℏ in fusion reactions with two complementary, mass‐symmetric (31P+45Sc) and mass asymmetric (12C+64Zn) entrance channels. The neutron evaporation spectra were measured and compared with the predictions of the statistical model calculations. The results for the mass‐asymmetric reaction are found to be consistent with the predictions of the statistical model calculations. However, for the mass‐symmetric reaction (31P+45Sc), the experimental spectra are found to be harder than the theoretical neutron spectra. The dynamical model calculations of Feldmeier show that the formation time for the compound nucleus for the symmetric system is relatively larger as compared to the asymmetric system. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737146

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The unified energy dependence of the induced fission lifetimes obtained by the experimental crystal blocking technique for heavy nuclei with Z = 91 – 94 in the range of initial excitation energy from 5 to 250 MeV was analyzed. It was demonstrated that for the excitation energies of investigated nuclei up to 60 – 70 MeV the fission lifetimes can be described in the framework of the statistical theory of nuclear reactions taking into account the double‐humped structure of the fission barrier and the lifetimes of both classes of excited nuclear states realized in the first and second potential wells. However, for the excitation energies above 70 MeV it is needed to consider the dynamical effects in the fission channel. Analysis of the experimental data in this energy range allows us to extract information on the magnitude of nuclear viscosity. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737147

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Influence of the shell correction damping with increasing of excitation energy on the fission fragment angular anisotropies are considered. Experimental data on the fission fragment angular anisotropies for the compound nucleus produced in the4He +238U reactions is analyzed in the framework of the model of the transitional state in the saddle point and the statistical theory of nuclear reactions. Information about the energy dependence of the shell corrections is obtained from this analysis. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737148

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Non‐uniform structures of nuclear matter are studied in a wide density‐range. Using the density functional theory with a relativistic mean‐field model, we examine non‐uniform structures at sub‐nuclear densities (nuclear “pastas”) and at high densities, where kaon condensate is expected. We try to give a unified view about the change of the matter structure as density increases, carefully taking into account the Coulomb screening effects from the viewpoint of first‐order phase transition. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737149

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A new approach has been investigated to create an ultra‐cold radioactive beam from high‐energy ions. A223Ra alpha‐decay recoil source has been used to produce radioactive ions in superfluid helium. The alpha spectra demonstrate that the recoiling219Rn ions have been extracted out of liquid helium. This first observation of the extraction of heavy positive ions across the superfluid helium surface has been possible thanks to the high sensitivity of radioactive ion detection. An efficiency of 36 &percent; has been obtained for the ion extraction out of liquid helium. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737150

出版商:AIP    

年代:1904

数据来源: AIP