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One of the most important global properties of the atomic nucleus is its size. Experimentally determined nuclear charge radii carry unique information on the nuclear force and complex dynamics of protons and neutrons moving inside the nucleus. The intricate behaviour of charge radii along the chain of Ca isotopes, including the unexpectedly large charge radius of neutron-rich 52Ca, poses a daunting challenge for nuclear theory1. Here we present the measurements of the charge radii of proton-rich isotopes 36,37,38Ca, whose properties are impacted by the interplay between nuclear superfluidity and weak binding. Calculations carried out within nuclear density functional theory show that the combination of a novel interaction2 and a state-of-the-art theoretical method can successfully explain the behaviour of charge radii from the lightest to the heaviest Ca isotopes. Through this model, we show how the new data on 36,37,38Ca elucidate the nature of nucleonic pairing in weakly bound proton-rich isotopes. Spectral study on 36,37,38Ca isotopes and calculations based on density functional theory reveal the interplay between charge radii and nucleonic pairing correlations.

A radiofrequency quadrupole (RFQ) ion beam cooler and buncher has been developed to deliver bunched beams with low transverse emittance, energy spread, and time spread to the BECOLA collinear laser spectroscopy system at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The beam cooler and buncher contains new features which enhance performance, especially for high count rate beams, as well as simplifying construction, maintenance, and operation. The transverse emittance, energy spread, and time spread of the bunched beam, as well as buncher efficiency are reported, showcasing the capabilities of the BECOLA facility to perform collinear laser spectroscopy measurements with bunched rare isotope beams at NSCL and at the future Facility for Rare Isotope Beams (FRIB).

Spin polarization in fragmentation reactions has been studied in several nuclei showing mainly that large polarization is produced at the tail of the fragments momentum distribution. Such polarization features are not so well known in pickup reactions, especially in studies of unstable nuclei, such as 35K and 37K. The spin polarization of 35K and 37K produced in single-proton pickup reactions at intermediate energies at the Coupled Cyclotrons at NSCL and the results for the ground-state magnetic moment involving the /3-NMR technique are reported in the present work.

A collinear laser-spectroscopy (CLS) system in the BEam COoler and LAser spectroscopy (BECOLA) facility was constructed at National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The BECOLA facility will be used to advance measurements of nuclear properties of low-energy rare isotope beams generated via in-flight reactions and subsequent beam thermalization in a buffer gas. The CLS studies at BECOLA will complement laser spectroscopy studies of charge radii and nuclear moments mostly obtained so far at Isotope SeOn Line (ISOL) facilities. Commissioning tests of the CLS system have been performed using an offline ion source to produce stable-ion beams. The tests set the ground work for experiments at the future Facility for Rare Isotope Beams (FRIB) as well as experiments at the current Coupled Cyclotron Facility at NSCL.

The dependence of the spin polarization on the incident angle of the primary beam has been measured for {sup 12}B fragments produced in the fragmentation of an {sup 18}O beam on a Nb target at 80 MeV/nucleon. A change in sign of the spin polarization was observed with a change in sign of the incident angle of the projectile. This result is in agreement with the kinematical model presented recently to qualitatively describe the mechanism for the production of spin-polarized fragments following intermediate-energy heavy-ion reactions. The resonance curve for {sup 12}B has also been measured using a technique of multiple adiabatic fast passage with continuous implantation. This technique is briefly compared to the single-pass adiabatic fast passage method employed with beam-on/beam-off data acquisition. {copyright} {ital 1997} {ital The American Physical Society}

A new device has been designed and built at NSCL which provides additional filtering of radioactive beams produced via projectile fragmentation. The Radio Frequency Fragment Separator (RFFS) uses the time micro structure of the beams accelerated by the cyclotrons to deflect particles according to their time-of-flight, in effect producing a phase filtering. The transverse RF (Radio Frequency) electric field of the RFFS has superior filtering performance compared to other electrostatic devices, such as Wien filters. Such filtering is critical for radioactive beams produced on the neutron-deficient side of the valley of stability, where strong contamination occurs at intermediate energies from 50 to 200 MeV/u.

Observed neutron-capture elemental abundances in metal-poor stars, along with ongoing analysis of the extremely metal-poor Eu-enriched sub-class provide new guidance for astrophysical models aimed at finding the r-process sites. The present paper emphasizes the importance of nuclear physics parameters entering in these models, particularly β -decay properties of neutron-rich nuclei. In this context, several r-process motivated β -decay experiments performed at the National Superconducting Cyclotron Laboratory (NSCL) are presented, including a summary of results and impact on model calculations.

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.

New high-spin levels have been identified in the nucleus 120Pd from analysis of the coincidence gamma rays observed in the 238U(α, f γ γ γ ) reaction. Recoiling fragments were detected with the Rochester heavy-ion detector array, CHICO, in coincidence with gamma-rays using Gammasphere. An A=110-130 mass-gated γ − γ − γ cube from this experiment was constructed and analyzed for coincident gamma-rays in several nuclei near A=120. New results for neutron-rich 118Pd and 120Pd have been obtained. The 120Pd level scheme was extended to spin of 10+ by building on the new low-energy gamma rays identified in decay studies of 120Rh. The details of the 118Pd level scheme derived from this work are compared to previous work. The systematics of the yrast levels in even-even Pd and Cd isotopes are presented and the symmetry of energy levels around N = 68 is discussed. A new 10+ level in 124Cd has been observed. The population intensity of even-even neutron-rich Cd isotopes is deduced, indicating that nuclides near 120Cd are preferentially populated following alpha-induced fission of 238U.

β-delayed γ-ray measurements have been part of an experimental program at the NSCL to understand the role of the πf7/2 - νf5/2 proton-neutron monopole interaction in neutron-rich pf-shell nuclei above 48Ca. Central to this study has been an attempt to observe the development of new shell structure at N = 32, 34 through the systematic observation of E(2+1 ) as a function of neutron number. Additionally, the ground state spin and parity of odd-odd and odd-A nuclei were interpreted in an extreme single-particle model to follow the monopole migration of the νf5/2 as protons are removed from the πf7/2state.

The planned rare isotope accelerator facility RIA in the US would become the most powerful radioactive beam facility in the world. RIA's driver accelerator will be a device capable of providing beams from protons to uranium at energies of at least 400 MeV per nucleon, with beam power up to 400 kW. Radioactive beam production relies on both the in-flight separation of fast beam fragments and on the ISOL technique. In both cases the high beam power poses major challenges for target technology and handling and on the design of the beam production areas. This paper will give a brief overview of RIA and discuss aspects of ongoing conceptual design work for the RIA target areas.

The beta-decay properties of neutron-rich nuclides in the vicinity of doubly magic 48 Ca, 78 Ni, and 132 Sn have been measured recently using the beta counting system at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. Some of the technical challenges faced by these experiments, including charge-state ambiguities, prompt gamma radiation flash, and presence of beta-decaying isomeric states, are discussed.

The results of measurements of β-delayed and isomeric γ rays from neutron-rich nuclides produced by projectile fragmentation at the NSCL are summarized.

New half-lives for neutron-rich ruthenium, rhodium and palladium isotopes close to the r-process path along the N=82 closed shell have been measured at the National Superconducting Cyclotron Laboratory at Michigan State University. The studied isotopes are close to the critical A=118-126 mass region in the astrophysical r-process, where incorrect nuclear structure development towards the shell closure may have the most pronounced effect on the abundances of elements produced. Neutron-rich nuclei were produced by fragmentation of a 120-MeV per nucleon 136 Xe beam on Be and were separated by the A1900 fragment separator. The nuclei of interest were implanted into a double-sided Si strip detector at the center of the MSU β counting system. Charge states and fully- stripped isotopes were distinguished by a measurement of the total kinetic energy of each implant. Our measured half-lives will provide first clues on whether our understanding of nuclear structure evolution in this mass region is correct.

Recent results of β-decay studies performed along the expected neutron shell closures at N = 20, 28, 50 and 82 are reviewed and discussed in view of the potentially dynamic nature of neutron single-particle states in nuclei having extreme neutron-to-proton ratios.

The β decay of neutron-rich nuclei in the π 1 f 7/2 and νpf shells has been studied at the NSCL to track the development of new proposed shell closures at N=32 and 34 due to the monopole migration of the ν 1 f 5/2 orbital. From a measurement of absolute γ -ray intensities following the β decay of odd-odd nuclei, the β -decay branching ratios to levels in the even-even daughters can be deduced. The branching ratios, especially to the 0 + daughter ground state, can be used to assign spins and parities to the parent ground states. The interpretation of these assignments for odd-odd nuclei in a single-particle limit can be used to track the migration of the ν 1 f 5/2 single-particle state.

The level structure of 5422Ti32 has been explored for the first time by combining β-decay measurements from fragmentation products with prompt γ-ray spectroscopy following deep inelastic reactions. The latter technique was also instrumental in tracing 52Ti30 to higher spin. The data provide new tests of effective interactions for full pf-shell calculations in neutron-rich nuclei above 48Ca. The data indicate the presence of a significant subshell gap at N=32 and comparisons between theory and experiment suggest an additional shell closure at N=34 in Ca and Ti isotopes.

The existence of a subshell gap at neutron number N =40 is investigated in the odd-mass Ni and Cu isotopes using the Particle-Core Coupling Model (PCM). The calculated properties are in good agreement with the existing experimental data, suggesting that 68 Ni is a good core for the adjacent nuclei. Evaluation of the 2 + 1 excitation energies, two-neutron separation energies, and pairing properties of the Ni isotopes reveals discontinuities at neutron number N =40. These data support the existence of a significant neutron subshell gap at N =40, for Z =28. The systematic behavior of the proton single-particle energies extracted from the particle-core coupling calculations for the odd-mass Cu isotopes is discussed in terms of monopole shifts. The effect is consistent with the existence of a neutron subshell gap at N =40.

A new method has been developed for measuring the magnitude of nuclear spin polarization of a secondary, radioactive beam by making a pulsed magnetic field measurement that does not require advance knowledge of the nuclide's magnetic moment. Using a standard β NMR apparatus, a magnetic double ratio is determined from the counting rates in 0° and 180° β detectors for magnetic field on and off conditions. This ratio provides direct information on the induced spin polarization of a radioactive beam. A demonstration of the method was performed using spin polarized 12B nuclei produced by fragmentation of an 80 MeV/nucleon 18O beam in a Nb target.

The technique of nuclear magnetic resonance on beta-emitting nuclei (β-NMR) has been implemented at the NSCL to measure the ground state g factors of spin-polarized radioactive nuclei produced via projectile fragmentation. Recent developments to extend this technique to very exotic nuclear systems include the implementation of a multiple adiabatic fast passage technique for β-NMR and the use of thick production targets to improve the yield of spin-polarized secondary fragments.

We have measured the parallel momentum distributions of outcoming fragments in the one-neutron breakup of the odd-mass carbon isotopes ${}^{19,17,15}\mathrm{C}$ and ${}^{14}\mathrm{B}$. Owing to their low neutron separation energies, the study of these nuclei is of particular interest regarding the appearance of the halo phenomenon. Discrepancies between experiment and theory observed for ${}^{15}\mathrm{C}$ and ${}^{14}\mathrm{B}$ indicate that their halos are not as prominent as in ${}^{11}$Be or ${}^{11}$Li, and that core excitations start playing a role in the breakup mechanism. In ${}^{17}\mathrm{C}$ the halo appears hindered by a $d$-wave neutron ground state configuration. Finally, the data on ${}^{19}\mathrm{C}$ suggests an $s$-wave neutron around the 2${}^{+}$ excited state in ${}^{18}\mathrm{C}$.

Since the first discovery in 1986 of a rotational band at high angular momentum with deformation parameters near β =0.6, a great deal of research has been devoted to the study of these superdeformed (SD) bands in nuclei leading to the identification of similar bands in numerous nuclei in the mass 130, 150, and 190 regions. While superdeformed shape isomers have been observed at low spin in the actinides via spontaneous fission and in a few cases via γ decay, below mass 200 the low-spin members of the SD bands have not been observed. Theoretical calculations are able to account for the relative stability of the superdeformed bands in the nuclei where they have been observed. These calculations suggest that in the HgPb region the SD shape should be stable at a rotational frequency of 0. Several experiments have been performed to search for the population and decay of the lower spin members of the SD bands in the mass 190 region and some are still in progress. To this date, none has provided conclusive observation of the 0 + bandhead of a superdeformed band. The experimental techniques utilized in several of these are described.

Excited states in the N=30 neutron-rich isotope {sup 49}K have been studied using multinucleon transfer reactions with thin targets and the PRISMA-CLARA spectrometer combined with thick-target {gamma}-coincidence data from Gammasphere. The d{sub 3/2} proton-hole state is located 92 keV above the s{sub 1/2} ground state, and the proton-particle f{sub 7/2} state is suggested at 2104 keV. Three other levels are established as involving the coupling to 2{sup +} of two neutrons above the N=28 shell. The measured or estimated lifetimes served to reinforce the interpretation of the observed level structure, which is found to be in satisfactory agreement with shell-model calculations.

The isomeric and $\beta$-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., Comment: 17 pages, 17 figures, accepted to Phys. Rev. C

A symmetrical four-detector Compton polarimeter was used to measure the linear polarization of gamma-rays emitted from nuclei oriented by the hyperfine interaction at low temperature. Its polarization detection efficiency was determined in the range 0.3–1.4 MeV and compared with some other polarimeters.

The yrast structure of the neutron-rich nucleus $^{97}\mathrm{Zr}$ has been studied using fission of targetlike products in the reaction of a $^{48}\mathrm{Ca}$ beam on a thick $^{238}\mathrm{U}$ target. The level scheme, known from previous studies up to an excitation energy and spin-parity of approximately 4619 keV and $23/{2}^{\ensuremath{-}}$, has been extended by about 3 MeV and a few units of angular momentum. Two states fed in the $\ensuremath{\beta}$ decay of the $27/{2}^{\ensuremath{-}}$ high-spin isomer in $^{97}\mathrm{Y}$ were identified at 5570 and 5606 keV. The located level structure can be discussed in terms of shell-model configurations.

The low-lying yrast states in the {sup 51}Ca and {sup 52}Sc nuclei were investigated to obtain information on the evolution of the p{sub 1/2} and f{sub 5/2} neutron single-particle orbitals in neutron-rich nuclei near proton number Z=20. Level structures associated with neutron excitations into these two orbitals and with proton excitations across the Z=20 shell gap were identified. Shell-model calculations with the recently proposed GXPF1A interaction account reasonably well for the fp-shell states. The energy separation between the {nu}p{sub 1/2} and {nu}f{sub 5/2} orbitals in the Ca isotopes appears to be overestimated by the GXPF1A Hamiltonian.

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.

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 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 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 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 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.

{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 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.

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.

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 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 $^{56}\mathrm{T}\mathrm{i}$.

The neutron-rich argon isotope ${}^{43}\mathrm{Ar}$ has been studied by quasielastic and inelastic proton scattering performed in inverse kinematics. The measured inelastic angular distribution for the second excited state is in good agreement with an $L=2$ transition. Assuming this transition to be $E2,$ yields a ${\ensuremath{\beta}}_{2}$ value for this state of $0.25\ifmmode\pm\else\textpm\fi{}0.03$ when compared with distorted-wave Born approximation calculations. This value is comparable to the one reported for the stable isotope ${}^{40}\mathrm{Ar}.$ Moreover it is similar to those measured by Coulomb excitation for the neighboring even-even isotopes ${}^{42}\mathrm{Ar}$ and ${}^{44}\mathrm{Ar}$ indicating that the structure of the argon isotopes is stable as a function of neutron number.

We have utilized the selective process of β decay to populate low-energy excited states in the neutron-rich 22Ti, 23V, 24Cr, and 25Mn nuclei. The goal was to systematically track the monopole shift of the νf5/2 single-particle level with increased occupancy of the πf7/2 orbital. The β-decay properties of the parent nuclides, along with the low-energy structure of the daughters, are presented and compared with the results of shell model calculations employing the GXPF1 interaction.

The availability of radioactive beams with relatively high intensities and good optical qualities makes possible the study of direct reactions induced by unstable nuclei. The problems of nuclear matter distributions, deformation and the modification of shell structure far from stability can be addressed through inverse kinematics reactions on light targets. The experimental method is presented and two examples in the case of the 38S (p,p′) and 40S (p,p′) reactions measured at the NSCL-MSU are given. Finally, the newly built silicon strip detector system, MUST, dedicated to such studies, is presented.

We have recently studied the structure of the neutron rich sulfur isotope 40S by using elastic and inelastic proton scattering in inverse kinematics. Optical potential and folding model calculations are compared with the elastic and inelastic angular distributions. Using coupled-channel calculations, the β2 value for the 21+ excited state is determined to be 0.35±0.05. The extracted value of Mn/Mp ratio indicates a small isovector contribution to the 21+ state of 40S. The microscopic analysis of the data is compatible with the presence of a neutron skin for this nucleus.

The (d,n) reaction of 7Be to form the ground state of 8B was studied in inverse kinematics using a 25 MeV/nucleon beam of 7Be nuclei from the A1200 fragment separator at the NSCL. The recoiling 8B nuclei were observed in a pair of position sensitive detector telescopes at lab angles between 1° and 5.5° (7° to 38° CMS). A large array of neutron detectors was placed at angles ranging from 158° to 104° (35° to 7° CMS) that measured the energy of coincident neutrons by their time-of-flight. The cross section for the d(7Be,8B)n reaction was determined from both the charged-particle singles and from the neutron coincidence data. In addition to measuring the transfer reaction, the quasi-elastic scattering of 7Be from deuterium was measured. The cross sections of these reactions are compared with DWBA and coupled-channels calculations.