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J. B. Stoker

Publications and source records attributed to J. B. Stoker.

9 recordsLinked to original sources
arXiv2010

$β$ Decay and Isomeric Properties of Neutron-Rich Ca and Sc Isotopes

The isomeric and $β$-decay properties of neutron-rich $^{53-57}$Sc and $^{53,54}$Ca nuclei near neutron number $N$=32 are reported, and the low-energy level schemes of $^{53,54,56}$Sc and $^{53-57}$Ti are presented. The low-energy level structures of the $_{21}$Sc isotopes are discussed in terms of the coupling of the valence $1f_{7/2}$ proton to states in the corresponding $_{20}$Ca cores. Implications with respect to the robustness of the $N$=32 subshell closure are discussed, as well as the repercussions for a possible $N$=34 subshell closure.

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arXiv2009

Doubly-magic nature of 56Ni: measurement of the ground state nuclear magnetic dipole moment of 55Ni

The nuclear magnetic moment of the ground state of $^{55}$Ni ($I^π=3/2^{-}, T_{1/2}=204$ ms) has been deduced to be $|μ$^{55}Ni)$|=(0.976 \pm 0.026)$ $μ_N$ using the $β$-NMR technique. Results of a shell model calculation in the full \textit{fp} shell model space with the GXPF1 interaction reproduce the experimental value. Together with the known magnetic moment of the mirror partner $^{55}$Co, the isoscalar spin expectation value was extracted as $<\sum σ_z >=0.91 \pm 0.07$. The $<\sum σ_z>$ shows a similar trend as that established in the \textit{sd} shell. The present theoretical interpretations of both $μ(^{55}$Ni) and $<\sum σ_z>$ for the $T=1/2$, A=55 mirror partners support the softness of the $^{56}$Ni core.

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arXiv2009

Low-energy structure of 61Mn populated following $β$ decay of 61Cr

$β$ decay of the $^{61}$Cr$_{37}$ ground state has been studied. A new half-life of 233 +/- 11 ms has been deduced, and seven delayed $γ$ rays have been assigned to the daughter, $^{61}$Mn$_{36}$. The low-energy level structure of $^{61}$Mn$_{36}$ is similar to that of the less neutron-rich $^{57,59}$Mn nuclei. The odd-A $_{25}$Mn isotopes follow the systematic trend in the yrast states of the even-even, Z + 1 $_{26}$Fe isotopes, and not that of the Z - 1 $_{24}$Cr isotopes, where a possible onset of collectivity has been suggested to occur already at N = 36.

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arXiv2009

$β$-Decay Half-Life of the $rp$-Process Waiting Point Nuclide $^{84}$Mo

A half-life of 2.2 $\pm$ 0.2 s has been deduced for the ground-state $β$ decay of $^{84}$Mo, more than 1$σ$ shorter than the previously adopted value. $^{84}$Mo is an even-even N = Z nucleus lying on the proton dripline, created during explosive hydrogen burning in Type I X-ray bursts in the rapid proton capture ($rp$) process. The effect of the measured half-life on $rp$-process reaction flow is explored. Implications on theoretical treatments of nuclear deformation in $^{84}$Mo are also discussed.

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arXiv2008

Quadrupole Moment of 37K

The electric quadrupole coupling constant of the ground state of 37K(3/2+, 1.22 s) in a tetragonal KH2PO4 single crystal was measured to be |eqQ/h| = 2.99 +- 0.07 MHz using the beta-ray detecting nuclear quadrupole resonance technique. The electric quadrupole moment of 37K was determined to be |Q(37K)| = 10.6 +- 0.4 efm2, where the known electric quadrupole coupling constant of stable 39K in the KH2PO4 crystal was used as a reference. The present experimental result is larger than that predicted by shell-model calculations in the sd or the sd and fp model spaces. A possible variation of effective charges was explored to explain the discrepancy.

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arXiv2008

Fast switching NMR system for measurements of ground-state quadrupole moments of short-lived nuclei

A beta-ray detecting nuclear quadrupole resonance system has been developed at NSCL/MSU to measure ground-state electric quadrupole moments of short-lived nuclei produced as fast rare isotope beams. This system enables quick and sequential application of multiple transition frequencies over a wide range. Fast switching between variable capacitors in resonance circuits ensures sufficient power delivery to the coil in the beta-ray detecting nuclear magnetic resonance technique. The fast switching technique enhances detection efficiency of resonance signals and is especially useful when the polarization and/or production rate of the nucleus of interest are small and when the nuclear spin is large.

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arXiv2008

Beta decay of Neutron-Rich 53-56Ca

Beta-decay properties of neutron-rich Ca isotopes have been obtained. Half-life values were determined for the first time for 54Ca [86(7) ms], 55Ca [22(2) ms], and 56Ca [11(2) ms]. The half-life of 230(6) ms deduced for 53Ca is significantly longer than reported previously, where the decay chain 53K -> 53Ca -> 53Sc was considered. A delayed gamma ray with energy 247 keV as identified following beta decay of 54Ca, and is proposed to depopulate the first 1+ level in 54Sc. The beta-decay properties compare favorably with the results of shell model calculations completed in the full pf-space with the GXPF1 interaction. The half-lives of the neutron-rich Ca isotopes are also compared with gross beta-decay theory. The systematic trend of the neutron-rich Ca half-lives is consistent with the presence of a subshell gap at N=32.

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arXiv2006

Nuclear Magnetic Moment of the 57Cu Ground State

The nuclear magnetic moment of the ground state of 57Cu has been measured to be 2.00 +/- 0.05 nuclear magnetons (nm) using the beta-NMR technique. Together with the known magnetic moment of the mirror partner 57Ni, the spin extraction value was extracted as -0.78 +/- 0.13. This is the heaviest isospin T=1/2 mirror pair above the 40Ca region, for which both ground state magnetic moments have been determined. Shell model calculations in full fp shell giving mu(57Cu)~2.4 nm and ~0.5 imply significant shell breaking at 56Ni with the neutron number N=28.

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