摘要:

Beta decay data of nuclei far from stability are one of the most important nuclear physics inputs for the understanding of the element synthesis in the universe and determination of the age of the universe from cosmochronometers and by the latter have implications for cosmology. Results of new second‐generation microscopic calculations of &bgr;−half‐lives, will be presented. The impact on the above astrophysical questions will be discussed. New results for &bgr;&bgr;‐matrix elements for all potential &bgr;&bgr;‐emitters withA≥70 are given. It results that neutrinoless double beta decay remains the most powerful tool for investigating the electron neutrino mass. Perspectives of a second‐generation &bgr;&bgr;‐experiment using enriched76Ge (Heidelberg‐Moscow cooperation) are briefly presented.

ISSN:0094-243X    

DOI:10.1063/1.41209

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

p‐Process modeling of some rare but stable proton‐rich nuclei requires knowledge of a variety of neutron, charged particle, and photonuclear reaction rates at temperatures of 2 to 3×109°K. Detailed balance is usually invoked to obtain the stellar photonuclear rates, in spite of a number of well‐known constraints. In this work we attempt to calculate directly the stellar rates for (&ggr;,n) and (&ggr;,&agr;) reactions on151Eu. These are compared with stellar rates obtained from detailed balance, using the same input parameters for the stellar (n,&ggr;) and (&agr;,&ggr;) reactions on150Eu and147Pm, respectively. The two methods yielded somewhat different results, which will be discussed along with some sensitivity studies.

ISSN:0094-243X    

DOI:10.1063/1.41210

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have developed a system over the past few years at the Manuel Lujan, Jr. Neutron Scattering Center (LANSCE) for making (n,p) and (n,&agr;) measurements on (mainly) radioactive nuclei. Measurements have included7Be(n,p)7Li,14N(n,p)14C,17O(n,&agr;)14C,22Na(n,p)22Ne,22Na(n,&agr;)19F,35Cl(n,p)35S and36Cl(n,p)36S. The major basic physics motivation for these measurements has been the nuclear astrophysics to be learned. Currently, we are assembling a 4&pgr; detector of barium fluoride (BaF2) for making (n,&ggr;) measurements on radioactive nuclei with relatively short half lives. Once operational, this new detector should allow us to expand our measurements to many more nuclei, and to a broader range of nuclear physics and nuclear astrophysics issues addressed. Results of recent measurements are given and future plans are discussed.

ISSN:0094-243X    

DOI:10.1063/1.41211

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The reaction7Li(n,&ggr;)8Li is a trigger reaction for the nucleosynthesis of intermediate‐mass nuclei in inhomogeneous big‐bang models1. The reaction rate was measured at neutron energy of 30 keV by detecting prompt &ggr;‐ray from the reaction. The obtained value is two times larger than that measured recently and is consistent with the estimated value from the thermal neutron capture cross section by using 1/vlaw.

ISSN:0094-243X    

DOI:10.1063/1.41212

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The cross section of the12C(n,&ggr;)13C reaction was measured at neutron energy of 30 keV by detecting prompt &ggr;‐rays from the reaction. The cross section was obtained as 16.8±2.1 &mgr;b, which favors the nucleosynthesis of intermediate‐mass nuclei in inhomogeneous big‐bang models and in neutrino induced nucleosynthesis.

ISSN:0094-243X    

DOI:10.1063/1.41213

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High resolution neutron capture measurements of56Fe and60Ni were performed with total energy detectors in the energy range 1–200 keV. The data have been used to derive the Maxwellian‐averaged cross sections for thermal energies around kT=30 keV, corresponding to the mean temperature of thes‐process of stellar nucleosynthesis.

ISSN:0094-243X    

DOI:10.1063/1.41214

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We describe a method for the calculation of beta decay rates for somefpshell nuclei which have important bearings on the presupernova evolution of massive stars(M≥10M&THgr;).

ISSN:0094-243X    

DOI:10.1063/1.41215

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Gamma rays from a mixed source of56Co+46Sc were measured in a Ge(Li) detector. The56Co/46Sc intensity ratios I847/I889were determined by careful analysis of line shapes and underlying backgrounds. Based on the known46Sc adopted half‐life value of 83.810(10) d, the fit to the intensity ratios corrected for46Sc decay from 107 runs over an elapsed time of 172 days gave a half‐life of 77.29(3) d. By combining this result with other published data we obtain a half‐life of t1/2=77.27(3) d for56Co.

ISSN:0094-243X    

DOI:10.1063/1.41177

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In the calculations of the isomer production for the175Lu(n,&ggr;)176m,gLu reaction we have found that the inclusion ofE2 transitions from 62 band‐head members of176Lu (a possibles‐process chronometer and/or thermometer) led to anm/total value of 0.82 atEn=30 keV, compared to the 0.62m/total value obtained previously when noE2 transitions from the band heads were considered.

ISSN:0094-243X    

DOI:10.1063/1.41178

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Enriched180mTa samples were irradiated by an intense60Co source of 1.5 PBq and with 4 MeV bremsstrahlung. Using the well known115In(&ggr;,&ggr;’)115mIn cross section as a standard, we obtained a cross section of 0.52 mbarn for the180mTa(&ggr;,&ggr;’)180Ta reaction at 4 MeV, and established an upper limit of 14 nbarn (2&sgr;) at 1.33 MeV. These results mean that180mTa can survive at temperatures lower than ∼5×108K, but that it is quickly destroyed via photoexcitation above 7×108K. Accordingly, ans‐process production of180mTa during stellar helium burning remains a plausible possibility. The respective consequences for the observed abundance of nature’s rarest stable isotope are discussed by means of new cross section information.

ISSN:0094-243X    

DOI:10.1063/1.41179

出版商:AIP    

年代:1991

数据来源: AIP