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H. L. Crawford

Publications and source records attributed to H. L. Crawford.

48 records · Page 3Linked to original sources
arXiv2014

Nuclear Structure Towards N=40 60Ca: In-beam gamma-ray Spectroscopy of 58,60Ti

Excited states in the neutron-rich N=38,36 nuclei \nuc{60}{Ti} and \nuc{58}{Ti} were populated in nucleon-removal reactions from \nuc{61}{V} projectiles at 90~MeV/nucleon. The γ-ray transitions from such states in these Ti isotopes were detected with the advanced γ-ray tracking array GRETINA and were corrected event-by-event for large Doppler shifts (v/c \sim 0.4) using the γ-ray interaction points deduced from online signal decomposition. The new data indicate that a steep decrease in quadrupole collectivity occurs when moving from neutron-rich N=36,38 Fe and Cr toward the Ti and Ca isotones. In fact, \nuc{58,60}{Ti} provide some of the most neutron-rich benchmarks accessible today for calculations attempting to determine the structure of the potentially doubly-magic nucleus \nuc{60}{Ca}.

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arXiv2012

Beta-delayed proton emission in the 100Sn region

Beta-delayed proton emission from nuclides in the neighborhood of 100Sn was studied at the National Superconducting Cyclotron Laboratory. The nuclei were produced by fragmentation of a 120 MeV/nucleon 112Sn primary beam on a Be target. Beam purification was provided by the A1900 Fragment Separator and the Radio Frequency Fragment Separator. The fragments of interest were identified and their decay was studied with the NSCL Beta Counting System (BCS) in conjunction with the Segmented Germanium Array (SeGA). The nuclei 96Cd, 98Ing, 98Inm and 99In were identified as beta-delayed proton emitters, with branching ratios bp = 5.5(40)%, 5.5+3 -2%, 19(2)% and 0.9(4)%, respectively. The bp for 89Ru, 91,92Rh, 93Pd and 95Ag were deduced for the first time with bp = 3+1.9 -1.7%, 1.3(5)%, 1.9(1)%, 7.5(5)% and 2.5(3)%, respectively. The bp = 22(1)% for 101Sn was deduced with higher precision than previously reported. The impact of the newly measured bp values on the composition of the type-I X-ray burst ashes was studied.

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arXiv2011

High-spin μs isomeric states in 96Ag

The isomeric and β decays of the N = Z +2 nucleus 96Ag were investigated at NSCL. A cascade of γ-ray transitions originating from the de-excitation of a μs isomer was observed for the first time and was found in coincidence with two previously-known transitions with energies of 470 and 667 keV. The isomeric half-life was determined as 1.45(7) μs, more precise than previously reported. The existence of a second, longer-lived μs isomer, associated with a 743-keV transition, is also proposed here. Shell model results within the (p_{3/2}p_{1/2}f_{5/2}g_{9/2}) model space, using the jj44b interaction, reproduced level energies and isomeric decay half-lives reasonably well.

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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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arXiv2010

Observation of isotonic symmetry for enhanced quadrupole collectivity in neutron-rich 62,64,66Fe isotopes at N=40

The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N=40. The results are interpreted by the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N=40 as governed by the number of valence protons with respect to Z~30. The deformation suggested by the experimental data is reproduced by state-of-the-art shell calculations with a new effective interaction developed for the fpgd valence space.

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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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