Search

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., Comment: Accepted to Physics Letters B

The structures of the odd-neutron nuclides {sup 119,121}Te have been investigated following beta decay of {sup 119,121}I. Gamma-ray and conversion-electron singles and coincidence measurements have been performed on mass separated sources using Ge gamma-ray detectors and Si(Li) electron detectors and a mini-orange positron filter. New levels and branching ratios have been determined for both nuclides. {ital E}0 components have been identified on {ital M}1 and {ital M}1/{ital E}2 transitions in {sup 119}Te and interpreted as arising from coupling of particle-hole intruder states with the odd neutron.

The presence of isomeric levels with half-lives in the microsecond range has been identified in $^{125,126,127,128}\mathrm{Cd}$. Neutron-rich Cd isotopes were produced from the fragmentation of a 120 MeV/nucleon $^{136}\mathrm{Xe}$ beam and uniquely identified through their time-of-flight, energy loss, and total kinetic energy. \ensuremath{\gamma} rays from these isomeric levels were measured with an array of Ge detectors that were gated for 15 \ensuremath{\mu}s by a particle implantation trigger from a stack of Si detectors. The \ensuremath{\gamma} rays observed in the decay of $^{126,128}\mathrm{Cd}$ isomers populate low-energy levels previously identified in the \ensuremath{\beta} decay of $^{126,128}\mathrm{Ag}$. The \ensuremath{\gamma} rays found in the decay of $^{125,127}\mathrm{Cd}$ isomers are consistent with expected yrast structures observed in lighter, odd-mass Cd isotopes. The appearance of these isomers at the point where $N/Z$ exceeds 1.6 is interpreted as an indication of the onset of a weakened neutron-neutron interaction that has been proposed for $^{134}\mathrm{Sn}$, whose $N/Z$ also exceeds 1.6.

Intermediate-energy heavy-ion collisions can produce a spin polarization of the projectile-like species. Spin polarization has been observed for both nucleon removal and nucleon pickup processes. Qualitative agreement with measured spin polarization as a function of the momentum of the projectile-like fragment is found in a kinematic model that considers conservation of linear and angular momentum and assumes peripheral interactions between the fast projectile and target. Better quantitative agreement was reached by including more realistic angular distributions and deorientation caused by {gamma}-ray emission and by correcting for the out-of-plane acceptance. The newly introduced corrections were found to apply to both nucleon removal and nucleon pickup processes.

The Radio Frequency Fragment Separator (RFFS) proposed in [1] is now operational at the National Superconducting Cyclotron Laboratory (NSCL). The RFFS is an additional purification system for secondary beams at the NSCL after the existing A1900 fragment separator and will primarily be used to purify beams of rare neutron deficient isotopes. A similar device is already in use at RIKEN [2]. The RFFS uses an rf kicker to angularly separate unwanted particles from the desired ion beam, a pi/2 phase advance cell to rotate the beam in phase space before the beam reaches a collimating aperture for purification, and a final pi phase advance cell to transport the desired beam to the experiment. The final design for the rf kicker and the focusing system is presented and a status report on the building and commissioning effort is given.

The nuclear states in {sup 23}F have been investigated following the {beta} decay of {sup 23}O. The measurement of {sup 23}O was carried out at the National Superconducting Cyclotron Laboratory using fragments from the reaction of a {sup 48}Ca beam in a Be target. The half-life and total neutron emission probability were determined to be 97(8) ms and 7(2)%, respectively, for {sup 23}O {beta} decay. Ten {gamma}-ray decays in {sup 23}F and a single {gamma}-ray in {sup 22}F were observed to establish the {beta} decay scheme for {sup 23}O. Shell model calculations are in reasonable agreement with the measured {beta} branching and B(GT) values for the lowest energy state. The excitation energies of the first 1/2{sup +} and 3/2{sup +} states have been determined to be 2243(8) and 4066(16) keV, respectively, indicating a widening of the 5/2{sup +}-1/2{sup +} state gap in {sup 23}F. The decay scheme of the largest contaminant {sup 26}Ne in the experiment was established.

Intermediate‐energy heavy‐ion collisions can produce a spin polarization of the projectile‐like species. Spin polarization has been observed for both nucleon removal and nucleon pickup processes. Qualitative agreement with measured spin polarization as a function of the momentum of the projectile‐like fragment is found in a kinematical model that considers conservation of linear and angular momentum and assumes peripheral interactions between the fast projectile and target. Improvements to the kinematical model are discussed that aim to achieve quantitative agreement with spin polarization data from both the nucleon removal and pickup processes.

The beta decay of the exotic 30Ne (N=20) is reported. For the first time, the low-energy level structure of the N=19, 30Na (Tz = 4), is obtained from beta-delayed gamma spectroscopy using fragment-beta-gamma-gamma coincidences. The level structure clearly displays "inversion", i.e., intruder states with mainly 2p2h configurations displacing the normal states to higher excitation energies. The good agreement in excitation energies and the weak and electromagnetic decay patterns with Monte Carlo Shell Model calculations with the SDPF-M interaction in the sdpf valence space illustrates the small d3/2 - f7/2 shell gap. The relative position of the "normal dominant" and "intruder dominant" excited states provides valuable information to understand better the N=20 shell gap., Comment: 4 pages, 5 figures

The structure of the $^{56,58,60}\mathrm{Cr}$ nuclei was investigated at Gammasphere using both deep inelastic and fusion-evaporation reactions. As a result of this work, expanded level schemes are now available for these three neutron-rich, even-even isotopes. Experimental signatures were found for both single-particle and collective excitations whose relative importance varies with neutron number. Together with recent structural information on the odd-$A$ $^{55,57,59}\mathrm{Cr}$ neighbors, the present data highlight the changing role of the ${g}_{9/2}$ orbital with neutron number. Comparisons with shell-model calculations using the recently developed GXPF1A interaction and with total Routhian surface calculations are presented.

The shell structure underlying shape changes in neutron-rich nuclei between $N=20$ and $N=28$ has been investigated by a novel application of the transient field technique to measure the first-excited state $g$ factors in $^{38}\mathrm{S}$ and $^{40}\mathrm{S}$ produced as fast radioactive beams. Details of the new methodology are presented. In both $^{38}\mathrm{S}$ and $^{40}\mathrm{S}$ there is a fine balance between the proton and neutron contributions to the magnetic moments. Shell-model calculations that describe the level schemes and quadrupole properties of these nuclei also give a satisfactory explanation of the $g$ factors. In $^{38}\mathrm{S}$ the $g$ factor is extremely sensitive to the occupation of the neutron ${p}_{3/2}$ orbit above the $N=28$ shell gap as occupation of this orbit strongly affects the proton configuration. The $g$ factor of deformed $^{40}\mathrm{S}$ does not resemble that of a conventional collective nucleus because spin contributions are more important than usual.

The one-neutron knockout reaction $^{9}\mathrm{Be}$($^{57}\mathrm{Cr}$,$^{56}\mathrm{Cr}$+\ensuremath{\gamma})X has been measured in inverse kinematics with an intermediate-energy beam. Cross sections to individual states in $^{56}\mathrm{Cr}$ were partially untangled through the detection of the characteristic \ensuremath{\gamma}-ray transitions in coincidence with the reaction residues. The experimental inclusive longitudinal momentum distribution and the yields to individual states are compared to calculations that combine spectroscopic factors from the full $\mathit{fp}$ shell model and nucleon-removal cross sections computed in a few-body eikonal approach.

The two-proton knockout reaction $^{9}\mathrm{Be}$($^{54}\mathrm{Ti}$,$^{52}\mathrm{Ca}+\ensuremath{\gamma}$) has been studied at 72 MeV/nucleon. Besides the strong feeding of the $^{52}\mathrm{Ca}$ ground state, the only other sizeable cross section proceeds to a ${3}^{\ensuremath{-}}$ level at 3.9 MeV. There is no measurable direct yield to the first excited ${2}^{+}$ state at 2.6 MeV. The results illustrate the potential of such direct reactions for exploring cross-shell proton excitations in neutron-rich nuclei and confirms the doubly-magic nature of $^{52}\mathrm{Ca}$.

The low-energy level structure of the exotic Na isotopes $^{27,28,29}\mathrm{Na}$ has been investigated through \ensuremath{\beta}-delayed \ensuremath{\gamma} spectroscopy. Detailed level structure of $^{28,29}\mathrm{Na}$ has been obtained through $\ensuremath{\beta}\ensuremath{\gamma}$ and $\ensuremath{\beta}\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence measurements. The low-lying levels populated in $^{27}\mathrm{Na}$ by \ensuremath{\beta} decay were found to corroborate well with the in-beam data from the literature. Half-lives of the parent nuclides, $^{27,28,29}\mathrm{Ne}$, were measured using \ensuremath{\beta} fragment as well as fragment $\ensuremath{\beta}\ensuremath{\gamma}$ coincidences and compared to previous measurements. The \ensuremath{\beta}-delayed one- and two-neutron emission branching probabilities have been obtained from the \ensuremath{\gamma} activities of the grand daughter nuclei. A comparison of the level schemes and the \ensuremath{\beta}-decay branching ratios is made with shell-model predictions, both with and without intruder configurations, to understand the transition from normal-dominant to intruder-dominant excitations in these neutron-rich nuclei approaching the island of inversion.

A value of 0.28{+-}0.02 s has been deduced for the half-life of the ground state of {sup 60}Mn, in sharp contrast to the previously adopted value of 51{+-}6 s. Access to the low-spin {sup 60}Mn ground state was accomplished via {beta} decay of the 0{sup +} {sup 60}Cr parent nuclide. New low-energy states in {sup 60}Mn have been identified from {beta}-delayed {gamma}-ray spectroscopy. The new, shorter half-life of {sup 60}Mn{sup g} is not suggestive of isospin-forbidden {beta} decay, and new spin and parity assignments of 1{sup +} and 4{sup +} have been adopted for the ground and isomeric {beta}-decaying states, respectively, of {sup 60}Mn.

The shell structure underlying shape changes in neutron-rich nuclei near N=28 has been investigated by a novel application of the transient-field technique to measure the first-excited-state g factors in {sup 38}S and {sup 40}S produced as fast radioactive beams. There is a fine balance between proton and neutron contributions to the magnetic moments in both nuclei. The g factor of deformed {sup 40}S does not resemble that of a conventional collective nucleus because spin contributions are more important than usual.

The odd-odd fp-shell nucleus $^{52}\mathrm{Sc}$ was investigated using in-beam \ensuremath{\gamma}-ray spectroscopy following secondary fragmentation of a $^{55}\mathrm{V}$ and $^{57}\mathrm{Cr}$ cocktail beam. Aside from the known \ensuremath{\gamma}-ray transition at 674(5) keV, a new decay at ${E}_{\ensuremath{\gamma}}=212(3)$ keV was observed. It is attributed to the depopulation of a low-lying excited level. This new state is discussed in the framework of shell-model calculations with the GXPF1, GXPF1A, and KB3G effective interactions. These calculations are found to be fairly robust for the low-lying level scheme of $^{52}\mathrm{Sc}$ irrespective of the choice of the effective interaction. In addition, the frequency of spin values predicted by the shell model is successfully modeled by a spin distribution formulated in a statistical approach with an empirical, energy-independent spin-cutoff parameter.

The nuclear magnetic moment of the ground state of $^{57}\mathrm{Cu}({I}^{\ensuremath{\pi}}=3/{2}^{\ensuremath{-}},{T}_{1/2}=196.3\text{ }\text{ }\mathrm{ms})$ has been measured to be $|\ensuremath{\mu}(^{57}\mathrm{Cu})|=(2.00\ifmmode\pm\else\textpm\fi{}0.05){\ensuremath{\mu}}_{N}$ using the $\ensuremath{\beta}$-NMR technique. Together with the known magnetic moment of the mirror partner $^{57}\mathrm{Ni}$, the spin expectation value was extracted as $⟨\ensuremath{\Sigma}{\ensuremath{\sigma}}_{z}⟩=\ensuremath{-}0.78\ifmmode\pm\else\textpm\fi{}0.13$. This is the heaviest isospin $T=1/2$ mirror pair above the $^{40}\mathrm{Ca}$ region for which both ground state magnetic moments have been determined. The discrepancy between the present results and shell-model calculations in the full $fp$ shell giving $\ensuremath{\mu}(^{57}\mathrm{Cu})\ensuremath{\sim}2.4{\ensuremath{\mu}}_{N}$ and $⟨\ensuremath{\Sigma}{\ensuremath{\sigma}}_{z}⟩\ensuremath{\sim}0.5$ implies significant shell breaking at $^{56}\mathrm{Ni}$ with the neutron number $N=28$.

{beta}-delayed neutron emission branchings (or upper limits) for neutron rich {sup 116-120}Rh, {sup 120-122}Pd, and {sup 124}Ag have been measured. These branching ratios serve as direct inputs to astrophysical rapid neutron capture process models and affect the final abundances calculated in these models. In addition, half-lives for neutron rich {sup 114-115}Tc, {sup 114-118}Ru, {sup 116-121}Rh, and {sup 119-124}Pd near the proposed path of the r-process have also been measured. The results agree with theoretical quasiparticle random-phase approximation calculations within model uncertainties; the only exception is the delayed neutron branching in the decay of {sup 120}Rh, which is found to be much smaller than predicted.

The ground state magnetic moment of $^{35}\mathrm{K}$ has been measured using the technique of nuclear magnetic resonance on \ensuremath{\beta}-emitting nuclei. The short-lived $^{35}\mathrm{K}$ nuclei were produced following the reaction of a $^{36}\mathrm{Ar}$ primary beam of energy 150 MeV/nucleon incident on a Be target. The spin polarization of the $^{35}\mathrm{K}$ nuclei produced at 2\ifmmode^\circ\else\textdegree\fi{} relative to the normal primary beam axis was confirmed. Together with the mirror nucleus $^{35}\mathrm{S}$, the measurement represents the heaviest $T=3/2$ mirror pair for which the spin expectation value has been obtained. A linear behavior of ${g}_{p}$ vs ${g}_{n}$ has been demonstrated for the $T=3/2$ known mirror moments and the slope and intercept are consistent with the previous analysis of $T=1/2$ mirror pairs.

The Department of Energy’s Office of Nuclear Physics, within the Office of Science (SC), has given high priority to consider and analyze design concepts for the target areas for the production of rare isotopes via the ISOL technique at the Rare-Isotope Accelerator (RIA) Facility. Key criteria are the maximum primary beam power of 400 kW, minimizing target change-out time, good radiological protection, flexibility with respect to implementing new target concepts, and the analysis and minimization of hazards associated with the operation of the facility. We will present examples of on-going work on simulations of radiation heating of targets, surrounding components and shielding, component activation, and levels of radiation dose, using the simulation codes MARS, MCNPX, and PHITS. These results are important to make decisions that may have a major impact on the layout, operational efficiency and cost of the facility, hazard analysis, shielding design, civil construction, component design, and material selection overall layout, and remote handling concepts.

The astrophysical r-process is responsible for synthesis of roughly half of the elements heavier than iron. In spite of this significance, there are many uncertainties regarding the site of the r-process and the neutron-rich nuclei involved. Studying these nuclei presents a challenge, as they lie far from the valley of stability. Nuclear properties such as β decay half-lives and βdelayed neutron emission probabilities are critical inputs for r-process models. The neutron rich Ge-Br isotopes are in the region just after the N=50 bottle neck in the “classical” r-process, or may serve as seed material for the high entropy neutrino-wind r-process. Neutron rich nuclei play an important role in both nuclear astrophysics and nuclear structure. 1 Central to the study of nuclear structure are the shape of a nucleus and how that shape changes from spherical to deformed. In some regions there is a smooth change in deformation as nucleons are either added or subtracted, and yet in other regions this transition is very rapid. The Ge-Br isotopes to be measured lie between the N=56 sub-shell closure and the onset of deformation at N=60, just below the Sr-Zr region, for which the most pronounced transition from spherical to deformed ground-state shapes have been observed. Neutron rich Ge-Br isotopes will be studied at the NSCL at Michigan State University. Production will be by fragmentation of a 120 MeV/u 136 Xe beam on a Be target. The A1900 fragment separator will block unwanted species produced in this reaction. The transmitted nuclei will be implanted in a dual-sided silicon detector, which is part of the Beta Counting System detector. Implanted nuclei will be identified by the ∆E-time of flight method. Beta decays will then be detected by a single-sided silicon detector, which is also part of the Beta Counting System. Beta-delayed neutrons will be detected by the NERO neutron counter, which will surround the Beta Counting System. This will provide measurements of the β decay half-lives and β-delayed neutron emission probabilities. Then, SEGA germanium detector array will be used to detect gamma rays from decays of nuclei implanted in the Beta Counting System. The first 2 + and 4 + levels will be measured, determining the deformation of these nuclei.

The low-energy level structure of $^{25}\mathrm{Ne}$ has been investigated following the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{25}\mathrm{F}$. Beta-delayed \ensuremath{\gamma} spectroscopy revealed new \ensuremath{\gamma} transitions in $^{25}\mathrm{Ne}$ at 1234, 1622, and 2090 keV. The new transitions were placed in the level scheme of $^{25}\mathrm{Ne}$ in accordance with the observed $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidences. The total ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay strength has been accounted for. The spins and parities of the first two excited states could be ascertained by comparison with a shell model calculation and the literature. The half-life for $^{25}\mathrm{F}$ decay was also remeasured using fragment-$\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ correlations, revealing a value of 90 \ifmmode\pm\else\textpm\fi{} 9 ms. Comparison with shell model calculations are indicative of a wider $N=16$ gap as compared to the stable nuclei.

The nuclear magnetic moment of the ground state of (57)Cu(Iota(pi) = 3/2(-), T(1/2) = 196.3 ms) has been measured to be /mu((57)Cu)/ = (2.00 +/- 0.05)mu(N) using the beta-NMR technique. Together with the known magnetic moment of the mirror partner (57)Ni, the spin expectation value was extracted asSigmasigma(z)= -0.078 +/- 0.13. This is the heaviest isospin mirror T = 1/2 pair above the (40)Ca region for which both ground state magnetic moments have been determined. The discrepancy between the present results and shell-model calculations in the full f p shell giving mu((57)Cu) approximately 2.4mu(N) andSigmasigma(z)approximately 0.5 implies significant shell breaking at (56)Ni with the neutron number N = 28.

The shell structure underlying shape changes in neutron-rich nuclei near N = 28 has been investigated by a novel application of the transient-field technique to measure the first-excited-state g factors in 38S and 40S produced as fast radioactive beams. There is a fine balance between proton and neutron contributions to the magnetic moments in both nuclei. The g factor of deformed 40S does not resemble that of a conventional collective nucleus because spin contributions are more important than usual.

The {beta}-decay of odd-A, neutron-rich {sup 57}Ti and {sup 59}V are studied. More precise {beta}-decay half-lives of 98{+-}5 and 97{+-}2 ms are deduced for {sup 57}Ti and {sup 59}V, respectively. In addition, {beta}-delayed {gamma}-ray spectroscopy is used to deduce {beta}-decay branching ratios and establish the low-energy-level structures of the daughter nuclides. The new data for levels in {sup 57}V and {sup 59}Cr are compared with the results of shell-model calculations completed in the full pf model space. Both {sup 57}V and {sup 59}Cr show evidence of modest oblate deformation near the ground state.

{gamma} rays from neutron-rich Ti nuclei in the vicinity of N=32 have been studied at Gammasphere using deep-inelastic reactions induced by {sup 48}Ca beams on thick {sup 208}Pb and {sup 238}U targets. The {sup 53}Ti yrast cascade was identified for the first time, and the location in energy of states with spin up to I = 21/2 was determined. The excitations of {sup 53}Ti provide new tests of effective interactions for full-pf-shell calculations. Comparisons between theory and experiment for the highest spin states in {sup 53}Ti favor the recently proposed GXPF1A interaction, which accounts for the appearance of a neutron subshell closure at N=32 in Ti isotopes as well as for the lack of a similar subshell closure at N=34, as predicted by earlier calculations with another interaction.

The low-energy level structure of the exotic Na isotopes (28,29)Na has been investigated through beta-delayed gamma spectroscopy. The N=20 isotones for Z=10-12 are considered to belong to the "island of inversion" where intruder configurations dominate the ground state wave function. However, it is an open question as to where and how the transition from normal to intruder dominated configurations happens in an isotopic chain. The present work, which presents the first detailed spectroscopy of (28,29)Na, clearly demonstrates that such a transition in the Na isotopes occurs between 28Na (N=17) and 29Na (N=18), supporting the smaller N=20 shell gap in neutron-rich sd shell nuclei. The evidence for inverted shell structure is found in beta-decay branching ratios, intruder dominated spectroscopy of low-lying states, and shell model analysis.

The even $^{52\ensuremath{-}56}\mathrm{Ti}$ isotopes have been studied with intermediate-energy Coulomb excitation and absolute $B(E2;{0}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ transition rates have been obtained. These data confirm the presence of a subshell closure at neutron number $N=32$ in neutron-rich nuclei above the doubly magic nucleus $^{48}\mathrm{Ca}$ and provide no direct evidence for the predicted $N=34$ closure. Large-scale shell model calculations with the most recent effective interactions are unable to reproduce the magnitude of the measured strengths in the semimagic Ti nuclei and their strong variation with neutron number.

Nuclei with magic numbers serve as important benchmarks in nuclear theory. In addition, neutron-rich nuclei play an important role in the astrophysical rapid neutron-capture process (r process). 78Ni is the only doubly magic nucleus that is also an important waiting point in the r process, and serves as a major bottleneck in the synthesis of heavier elements. The half-life of 78Ni has been experimentally deduced for the first time at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University, and was found to be 110(+100)(-60) ms. In the same experiment, a first half-life was deduced for 77Ni of 128(+27)(-33) ms, and more precise half-lives were deduced for 75Ni and 76Ni of 344(+20)(-24) ms and 238(+15)(-18) ms, respectively.

The structure and decay of neutron‐rich r‐process nuclides has been studied by a variety of means that take advantage of enhanced selectivity to permit identification of exotic nuclides. New level structures are presented for 134,135Sb along with data for Ag isomers and Cd yrast structures. Some of the properties measured play an important role in calculations of the yields of elements and isotopes produced in r‐process nucleosynthesis that takes place at high temperature in the presence of large densities of neutrons.

An experiment was performed at the National Superconducting Cyclotron Laboratory at Michigan State University to investigate β‐ and isomer decay properties of several isotopes in the vicinity of 78Ni. The identification of an (8+) isomer in 76Ni was confirmed and its deexcitation cascade identified; the β‐decay of 71–73Co was reinvestigated and that of 74Co studied for the first time. First evidence of β‐delayed neutron emission in neutron‐rich cobalt isotopes was also obtained. Preliminary results are reported.

The possible occurrence of sub‐shell gaps at N = 32 and N = 34 in neutron‐rich titanium isotopes is discussed in light of new experimental results from (i) deep‐inelastic reactions measured with Gammasphere at the ATLAS facility at Argonne National Laboratory and from (ii) intermediate‐energy Coulomb excitation performed at the National Superconducting Cyclotron Laboratory at Michigan State University.

Details regarding the $\ensuremath{\beta}$-decay properties of $^{54,55,56}\mathrm{Sc}$ are reported and compared with shell model predictions. The low-energy level structures of even-even $^{54,56}\mathrm{Ti}$ are presented, and the systematic variation of the energy of the first excited ${2}_{1}^{+}$ state is discussed in light of proposed shell closures at $N=32,34$ for the neutron-rich $\mathrm{Ti}$ isotopes.

Gamma rays from neutron-rich nuclei in the vicinity of $Z=20$, $N=28$ have been studied at Gammasphere using deep-inelastic reactions induced by a $330\text{\ensuremath{-}}\mathrm{MeV}$ $^{48}\mathrm{Ca}$ beam on a thick $^{238}\mathrm{U}$ target. The yrast $\ensuremath{\gamma}$-ray cascade of $^{56}\mathrm{Ti}$ was identified for the first time and the location in energy of the ${2}^{+}$, ${4}^{+}$, and ${6}^{+}$ states was determined. The low-spin $^{56}\mathrm{Ti}$ yrast structure does not support the presence of a subshell closure at $N=34$ as suggested on the basis of other data on nuclei in the region as well as shell model calculations with a recently proposed interaction.

The low-energy level structure of the exotic Na isotopes (28,29)Na has been investigated through beta-delayed gamma spectroscopy. The N=20 isotones for Z=10-12 are considered to belong to the "island of inversion" where intruder configurations dominate the ground state wave function. However, it is an open question as to where and how the transition from normal to intruder dominated configurations happens in an isotopic chain. The present work, which presents the first detailed spectroscopy of (28,29)Na, clearly demonstrates that such a transition in the Na isotopes occurs between 28Na (N=17) and 29Na (N=18), supporting the smaller N=20 shell gap in neutron-rich sd shell nuclei. The evidence for inverted shell structure is found in beta-decay branching ratios, intruder dominated spectroscopy of low-lying states, and shell model analysis.

The low-energy levels of $^{120}\mathrm{Pd}_{74}$ were populated by $\ensuremath{\beta}$ decay of $^{120}\mathrm{Rh}_{75}$, which was produced via projectile fragmentation of a $^{136}\mathrm{Xe}_{82}$ beam at $120\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\text{nucleon}$. Delayed $\ensuremath{\beta}$-gated $\ensuremath{\gamma}$ rays with energies of 438 and $618\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ were observed in coincidence with $^{120}\mathrm{Rh}_{75}$ fragments and assigned to the ${2}_{1}^{+}\ensuremath{\rightarrow}{0}^{+}$ and ${4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$ transitions, respectively, in $^{120}\mathrm{Pd}_{74}$. Isomeric $\ensuremath{\gamma}$-ray transitions are also reported for $^{120}\mathrm{Rh}_{75}$ and $^{126}\mathrm{Cd}_{78}$. The low-energy structure of $^{120}\mathrm{Pd}_{74}$ shows remarkable similarity to those of the isotopic $^{108}\mathrm{Pd}_{62}$ and isotonic $^{128}\mathrm{Xe}_{74}$ suggesting that these nuclides share the same $Z=50$ and $N=82$ closed shell structures with neutron-rich $^{120}\mathrm{Pd}_{74}$.

Recent experimental characterization of the subshell closure at $N=32$ in the Ca, Ti, and Cr isotones has stimulated shell-model calculations that indicated the possibility that the $N=34$ isotones of these same elements could exhibit characteristics of a shell closure, namely, a high energy for the first excited ${2}^{+}$ level. To that end, we have studied the decay of $^{56}\mathrm{S}\mathrm{c}$ produced in fragmentation reactions and identified new $\ensuremath{\gamma}$ rays in the daughter $N=34$ isotone $^{56}\mathrm{T}\mathrm{i}$. The first ${2}^{+}$ level is found at an energy of 1127 keV, well below the expected position that would indicate the presence of an $N=34$ shell closure in $^{56}\mathrm{T}\mathrm{i}$.

Recent experimental characterization of the subshell closure at N=32 in the Ca, Ti, and Cr isotones has stimulated shell-model calculations that indicated the possibility that the N=34 isotones of these same elements could exhibit characteristics of a shell closure, namely, a high energy for the first excited 2(+) level. To that end, we have studied the decay of 56Sc produced in fragmentation reactions and identified new gamma rays in the daughter N=34 isotone 56Ti. The first 2(+) level is found at an energy of 1127 keV, well below the expected position that would indicate the presence of an N=34 shell closure in 56Ti.

Spin polarization of 37K nuclei produced via single proton pickup from a 9Be target by a beam of 150 MeV/nucleon 36Ar has been observed. Positive spin polarization with magnitude (8.5+/-0.6)% was deduced near the peak of the 37K momentum distribution. The variation of the spin polarization as a function of outgoing 37K momentum is explained by a classical conservation model, as previously applied to describe the induced spin polarization observed for fragments produced in intermediate-energy heavy-ion reactions, with the condition that the picked-up proton has an average momentum equal to the Fermi momentum and is aligned along the incident beam direction.

$\ensuremath{\beta}$ decay of ${}^{56,57,58}\mathrm{V}$ has been used to populate low-energy levels of ${}^{56,57,58}\mathrm{Cr},$ respectively. The low-energy levels of the even-even Cr isotopes and $\ensuremath{\beta}$-decay half-lives and branching ratios of the parent V isotopes are compared to results of shell-model calculations. The Cr energy level calculations were completed in the full $\mathrm{pf}$-model space, using several different interactions. The systematic variation of ${E(2}_{1}^{+}),$ which is indicative of a subshell closure at $N=32,$ was best reproduced in calculations using a pf-shell-model interaction based on effective two-body matrix elements with some replacement by the G matrix.

We report on the low‐energy structure of the neutron‐rich, even‐even nuclides 54Ti32, 56Cr32, and 58Cr34 studied via β‐delayed γ‐ray spectroscopy. The systematic variation of the excitation energy of first excited 2+ states in the even‐even 24Cr and 22Ti isotopes provides evidence of a subshell closure at N = 32 for neutron‐rich nuclides having Z ⩽ 24. Shell model calculations, which correctly account for the appearance of the N = 32 subshell, also predict a new shell closure at N = 34 for Ti and Ca isotopes.

32 Mg lies within a region of deformed nuclei commonly referred to as the “island of inversion”. The β decay of 33 Al and 33 Mg has been studied to learn about nuclear structure near 32 Mg. Decay curves and precise half-life measurements are presented for both species. Gamma-ray spectra from correlated 33 Al decay events are also presented. The β -decay properties of 33 Al are shown to be well-described by an sd shell model calculation, suggesting that the ground state of 33 Al lies primarily outside the island of inversion.

A new excited state at 2164 keV has been identified in 72Ni with tentative spin and parity of 4+ based on comparison to shell model calculations. This level is suggested to be populated via the ?-decay of an isomeric state in 72Co, and is postulated to be one of the key states that play a role in the disappearance of isomers in Ni. The known low-energy levels in 72Ni are compared with results of shell model calculations using the NR78 interaction to follow the seniority of the observed states. In addition, the half-life of the 8+ isomer in 76Ni has been measured as 630(90) ns and the full cascade of transitions from this isomer has been verified experimentally in this work.

A new data acquisition system including a Field Programmable Gate Array (FPGA) based time-resolved scaler was developed for laser-induced fluorescence and beam bunch coincidence measurements. The FPGA scaler was tested in a collinear laser-spectroscopy experiment on radioactive (37)K at the BEam COoler and LAser spectroscopy (BECOLA) facility at the National Superconducting Cyclotron Laboratory at Michigan State University. A 1.29 μs bunch width from the buncher and a bunch repetition rate of 2.5 Hz led to a background suppression factor of 3.1 × 10(5) in resonant photon detection measurements. The hyperfine structure of (37)K and its isotope shift relative to the stable (39)K were determined using 5 × 10(4) s(-1) (37)K ions injected into the BECOLA beam line. The obtained hyperfine coupling constants A((2)S(1/2)) = 120.3(1.4) MHz, A((2)P(1/2)) = 15.2(1.1) MHz, and A((2)P(3/2)) = 1.4(8) MHz, and the isotope shift δν(39, 37) = -264(3) MHz are consistent with the previously determined values, where available.