摘要:

In the present experiment the neutron lifetime has been measured with ultra‐cold neutrons (UCN) confined in a gravitational trap. The measured neutron lifetime is equal to (888.4±2.9)s, &lgr;=−(1.2677±0.0025). This result is in agreement with the results of other experiments: 887.6±3.0)s1and (893.6±5.3)s2. However, parameters &lgr;&tgr;, &lgr;Aextracted from the neutron lifetime experiments and from the &bgr;‐decay asymmetry experiments differ (3.2&sgr;). The reasons of the discrepancy are discussed.

ISSN:0094-243X    

DOI:10.1063/1.41199

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A formalism is developed that incorporates parity violation into the statistical theory of nuclear reactions. It allows the calculation of average square values of observables sensitive to parity breaking starting from well known average parameters (transmission coefficients and level densities) as input. For the case of low‐energy neutron resonance scattering, a systematic study of the expected size of the effect is presented. An enhanced sensitivity of these reactions to parity violation is borne out.

ISSN:0094-243X    

DOI:10.1063/1.41200

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Data taking of the experiment on free neutron oscillation is in progress at ILL reactor in Grenoble. The already achieved oscillation time limit is &tgr;NN¯≥0.7×108s.

ISSN:0094-243X    

DOI:10.1063/1.41201

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.41202

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The polarization left‐right asymmetry and angular fore‐aft asymmetry of &ggr; yields were investigated for the direct transition E&ggr;=9.04 MeV in114Cd near the p‐wave resonanceEp=7 eV. The experiments were performed at the pulsed reactor IBR‐30 using an LMN‐polarizer of neutrons and NaJ (T1)‐detectors.

ISSN:0094-243X    

DOI:10.1063/1.41203

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

TheA‐coefficient, which characterizes the angular correlation between the electron escape and the decaying neutron spin directions, is measured with an intense polarized neutron beam from the new vertical channel of the LNPI reactor. The result isA=−0,1131±0,0014 (A0=−0,1116±0,0014),implying &lgr;=gA/gv=−1,2544±0,0036 for the ratio of the weak coupling constants.

ISSN:0094-243X    

DOI:10.1063/1.41204

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

New measurements and theoretical studies of nuclear properties, together with new astronomical data on the growth of heavy‐element abundances during the early history of the Galaxy, now provide a clearer picture of where in nature the elements heavier than iron are produced by rapid (r‐process) neutron capture reactions. The nuclear data suggest that ther‐process involves a high‐temperature and high‐neutron‐density beta‐flow equilibrium environment.The astronomical data, when compared with simple galactic chemical evolution models, suggests that ther‐process is associated with Type II supernovae and that the neutron source must be manufactured by the star independent of the initial heavy‐element abundance. Low‐mass type II supernovae are proposed as the most important contributors to ther‐process.

ISSN:0094-243X    

DOI:10.1063/1.41298

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Several capture reactions on14C, important in a nonstandard big bang scenario have been studied, the experimental techniques and results are presented here. Network calculations for big bang conditions have been performed and show that the production of heavy elements in the early universe may be possible.

ISSN:0094-243X    

DOI:10.1063/1.41206

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The use of176Lu as a cosmic clock has been in question since the possibility of a thermal coupling between the long‐lived ground state (t1/2=41⋅109yr) and the beta unstable isomer with 3.68 hr half‐life was considered. This coupling requires induced transitions to higher lying states because direct transitions are highly forbidden by selection rules. First experimental evidence for the enhancement of the overall decay rate by that mechanism was provided via photoactivation measurements, but a quantitative discussion became possible only after the level scheme of176Lu had been carefully established in two recent investigations. These studies identified an 1&pgr;=5−state at 838.6 keV to be the most efficient mediating level for the coupling of ground state and isomer. As a consequence, the half‐life of176Lu is drastically reduced above 1.5⋅108K, i.e., at conditions typical for the production of176Lu in thes‐process during the helium burning phase of stellar evolution. Hence, any interpretation of176Lu as a cosmic clock is strongly dependent on the conditions at the stellar site, a problem that cannot be solved reliably enough with present stellar models. Instead, the strong temperature dependence of the176Lu half‐life makes it a sensitive tool for constraining thes‐process temperature to the range between 2.4⋅108to 3.6⋅108K.

ISSN:0094-243X    

DOI:10.1063/1.41207

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Nucleosynthesis of the heavier elements (A≥60) is thought to proceed principally through two processes: slow neutron capture (sprocess) and rapid neutron capture (rprocess). The time scales of the successive neutron captures distinguishes these two processes. In thesprocess the typical time between captures is long enough that beta‐unstable nuclei will almost always have time to decay before the next capture occurs. As a result, thesprocess follows the line of beta stability. In contrast, during therprocess the neutron flux is so high that many neutron captures can occur before the subsequent beta decays occur. This is illustrated in the Figs. 1a,b, where we have highlighted the regions surrounding148Pm and176Lu.

ISSN:0094-243X    

DOI:10.1063/1.41208

出版商:AIP    

年代:1991

数据来源: AIP