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The β-decay half-life of 54Mn is needed to employ this isotope as a cosmic ray chronometer. We have determined the partial half-life of 54Mn for positron emission by counting a highly purified 35-μCi source of 54Mn in GAMMASPHERE to search for the astrophysically interesting β+ decay branch through the observation of coincident positron-annihilatio...
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In this paper, we examined the β--decay half-lives of 94 extremely neutron-rich isotopes with Z = 26 − 57 close to the neutron drip line, which are important for the r-process calculations. The half-lives were calculated using four semi-empirical models and compared to those based on the FRDM+QRPA approach and available measured data. The impact of...
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... Unfortunately, at that time, the uncertainty in 54 Mn half-life ranged over 3 orders of magnitude. Recently, Wuosmaa et al. (1998) and Zaerpoor et al. (1997) (Table 2). ...
Radioactive 36Cl has been resolved from 35Cl and 37Cl for the first time in the cosmic radiation with measurements obtained from the high-resolution High-Energy Telescope (HET) carried on the NASA-ESA Ulysses spacecraft. Within the framework of a homogeneous propagation model wherein all 36Cl is of spallation origin, the average density of the interstellar gas ρ, through which all cosmic-ray nuclei propagate, was determined. Heliospheric modulation was included in the analysis. The abundance ratio 36Cl/Cl=5.2 ± 1.8% at an average energy of 238 MeV u-1 yields ρ=0.28+ 0.12−0.10 atoms cm-3. Although 36Cl has a relatively short half-life (τ½=3.01 × 105 yr) compared with the approximately 20 Myr confinement or escape time Tesc for cosmic rays in the Galaxy derived from 10Be or 26Al analysis, it is shown that the confinement time based on 36Cl analysis is 18+ 10−6 Myr. Radioactive 10Be,26Al, and 36Cl are all produced by nuclear interactions during propagation from Galactic sources to the observer. However,10Be,26Al, and 36Cl are each predominantly products of different primary cosmic-ray nuclei.54Mn is the fourth radioactive isotope measured by the Ulysses HET. Unfortunately, its decay half-life to 54Fe is difficult to determine. Recent measurements yielded τ½=6.3 × 105 yr, leading to ρ=0.40+ 0.23−0.15 atoms cm-3 with a confinement time Tesc=11 Myr.
... In the 144pm experiment, we searched for the [3+ decay to the 697-keV level in 144Nd via 511-511-697 keV coincidences. For details on these experiments, see Zaerpoor et al. [6,7,8]. ...
Sources of 54Mn, 55Ni, and 144Pm were placed at the center of the Gammasphere array and searches were made for the astrophysically interesting β+ decay modes of these isotopes. The results of these searches are presented and the implications for cosmic-ray physics are discussed.
A measurement of the Ni-56 cosmic ray abundance has been discussed as a possible tool to determine the acceleration time scale of relativistic particles in cosmic rays. This conjecture will depend on the halflife of totally ionized Ni-56 which can only decay by higher-order forbidden transitions. We have calculated this halflife within large-scale shell model calculations and find t(1/2) approximate to 4 x 10(4) years, only slightly larger than the currently available experimental lower limit, but too short for Ni-56 to serve as a cosmic ray chronometer.
The 2005 evaluation for A=54 (2006Hu08) has been updated. Detailed experimental nuclear structure data and decay data for all nuclei with mass chain A=54 are presented in this current evaluation. The new data and information are given in following datasets:. 54Ca: 9Be(76Ge, X) and Be(55Sc, p), (56Ti, 2p)54Sc: 54Ca β- decay and 54Sc IT decay54Ti: 54Sc β- decay54Cr: 54Mn ε decay, 56Fe(μ, nupng), and 238U(64Ni, Xγ)54Mn: 51V(20Ne, Xγ), 55Mn(p, pn), and 56Fe(μ, nu2ng)54Fe: 58Ni α decay, 9Be(55Co, Xγ), 54Fe(e, e'), 54Fe(p, p'), and Coulomb Excitation54Co: 54Ni ε decay, 55Cu εp decay, 28Si(32S, αpnγ), 54Fe(p,n), and 54Fe(3He, t)54Ni: 54Ni IT decay, 55Zn εp decay, 9Be(55Ni, Xγ), and 24Mg(32S, Xγ)54Zn: Ni(58Ni, X).
The large multidetector gamma-ray arrays (such as GAMMASPHERE, EUROBALL, and GASP) have played a central role in nuclear-structure studies during the past decade. In this paper I will discuss recent results from experiments on nuclei with very large deformations, including: the measurement of the spins, parities, and excitation energies of superdeformed bands in 152Dy; the observation of extreme deformations in 108Cd and the evidence for hyper-intruder states; the study of superdeformed nuclei around $A \sim 40$ , which provide an opportunity to test our microscopic understanding of collective excitations; and lifetimes of strongly deformed triaxial bands in 163Lu. I will conclude with a brief discussion on the next generation gamma-ray detector array, GRETA.
In order to test the possibility of using 144Pm as a clock to
measure the mean cosmic-ray confinement time in the Galaxy, we counted a
highly purified 1.4 μCi source of this isotope in GAMMASPHERE and
searched for its astrophysically interesting β+ decay
branch through the observation of positron-annihilation γ rays in
coincidence with the characteristic 697-keV γ ray. Analysis of 57
h of source counting and 15 h of background shows no net signal and
results in an upper limit of 3.7 of 511-511-697 keV coincident events.
From this result we establish a 90% confidence level upper limit on the
branch for this decay mode to be 7.4×10-6%. The
implications of this result for the 144Pm cosmic-ray
chronometer problem are discussed.
The nucleus {sup 54}Mn , observed in cosmic rays, decays there dominantly by the {beta}{sup {minus}} branch with an unknown rate. The branching ratio of its {beta}{sup +} decay was determined recently. We use the shell model with only a minimal truncation and calculate both {beta}{sup +} and {beta}{sup {minus}} decay rates. Good agreement for the {beta}{sup +} branch suggests that the calculated partial half-life of the {beta}{sup {minus}} decay, 4.94{times}10{sup 5} yr , should be reliable. However, this half-life is noticeably shorter than the range 1{endash}2{times}10{sup 6} yr indicated by the fit based on the {sup 54}Mn abundance in cosmic rays. We also evaluate other known unique second forbidden {beta} decays from the p and sd shells and show that the shell model can describe them with reasonable accuracy as well. {copyright} {ital 1998} {ital The American Physical Society}
The weak {beta}{sup +} decay of the astrophysically significant radioisotope {sup 54}Mn has been observed. The energies of positrons from a chemically purified {sup 54}Mn source were measured using the APEX spectrometer at Argonne National Laboratory. We deduce a {beta}{sup +} decay branch of (1.20{plus_minus}0.26){times}10{sup {minus}9} , corresponding to a partial half-life of (7.1{plus_minus}1.5){times}10{sup 8} yr . The implications of this value for cosmic-ray confinement times are discussed in light of recent satellite measurements of the cosmic-ray abundance of {sup 54}Mn . {copyright} {ital 1998} {ital The American Physical Society}
A measurement of the 56Ni cosmic ray abundance has been discussed as a
possible tool to determine the acceleration time scale of relativistic
particles in cosmic rays. This conjecture will depend on the halflife of
totally ionized 56Ni which can only decay by higher-order forbidden
transitions. We have calculated this halflife within large-scale shell model
calculations and find t_{1/2} \approx 4 \times 10^4 years, only slightly larger
than the currently available experimental lower limit, but too short for 56Ni
to serve as a cosmic ray chronometer.
For 54Mn there is a discrepancy between the QEC obtained from the endpoint energy of the internal bremsstrahlung (IB) spectrum which accompanies the electron capture decay (QEC=1353±8keV) and that obtained from the accepted mass differences (QEC=1377±1keV). This Q value is needed to deduce the partial-half life of the astrophysically interesting β- decay of 54Mn from the recently measured β+ partial half-life. To resolve this discrepancy, we have remeasured the endpoint energy of the IB spectrum, by recording coincidences between the IB and the 835-keV γ ray, both detected in Compton-suppressed Ge detectors. The QEC we deduce is 1379±8keV, in agreement with the accepted mass differences.
