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We present mass excesses (ME) of neutron-rich isotopes of Ar through Fe, obtained via TOF-$B\rho$ mass spectrometry at the National Superconducting Cyclotron Laboratory. Our new results have significantly reduced systematic uncertainties relative to a prior analysis, enabling the first determination of ME for $^{58,59}{\rm Ti}$, $^{62}{\rm V}$, $^{65}{\rm Cr}$, $^{67,68}{\rm Mn}$, and $^{69,70}{\rm Fe}$. Our results show the $N=34$ subshell weaken at Sc and vanish at Ti, along with the absence of an $N=40$ subshell at Mn. This leads to a cooler accreted neutron star crust, highlighting the connection between the structure of nuclei and neutron stars., Comment: Accepted for publication as a Rapid Communication in Physical Review C

Physics letters / B 754, 288 - 293 (2016). doi:10.1016/j.physletb.2016.01.039, Published by North-Holland Publ., Amsterdam

As part of the International Atomic Energy Agency's (IAEA) Physics Section, the Nuclear Science and Instrumentation Laboratory (NSIL) helps Member States (MSs) to establish, operate and maintain various nuclear instrumentation and spectrometry techniques in support of a wide range of applications such as health care, food, agriculture, environment, forensics, cultural heritage, and materials science. NSIL is contributing to capacity building, transfer of knowledge and expertise sharing, including the development of instruments and validation of analytical methodologies. This paper describes NSIL's key activities and provides an overview of the recent developments and achievements, including the commissioning and utilization of an end-station at one of the beam lines in Elettra Sincrotrone Trieste (EST, Italy), the upgrade of an ultralight radiation monitoring system onboarded on a drone, as well as the development of a full field X-ray fluorescence analytical system for forensic applications and characterization of valuable art/archaeological objects.

When a neutron star accretes hydrogen and helium from the outer layers of its companion star, thermonuclear burning enables the α p-process as a break out mechanism from the hot CNO cycle. Model calculations predict ( α , p) reaction rates significantly affect both the light curves and elemental abundances in the burst ashes. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target enables the direct measurement of previously inaccessible ( α ,p) reactions with radioactive beams provided by the rare isotope re-accelerator ReA3 at the National Superconducting Cyclotron Laboratory (NSCL), USA. JENSA is going to be the main target for the Recoil Separator for Capture Reactions (SECAR) at the Facility for Rare Isotope Beams (FRIB). Commissioning of JENSA and first experiments at Oak Ridge National Laboratory (ORNL) showed a highly localized, pure gas target with a density of ∼10 19 atoms per square centimeter. Preliminary results are presented from the first direct cross section measurement of the 34 Ar( α , p) 37 K reaction at NSCL.

Masses of uranium fission fragments have been measured with the FRagment Separator (FRS) combined with the Experimental Storage Ring (ESR) at GSI. A 410-415 MeV/u 238U projectile beam was fast extracted from the synchrotron SIS-18 with an average intensity of 109/spill. The projectiles were focused on a 1g/cm2 beryllium target at the entrance of the FRS to create neutron-rich isotopes via abrasion-fission. The fission fragments were spatially separated with the FRS and injected into the isochronous storage ring ESR for fast mass measurements without applying cooling. The Isochronous Mass Spectrometry (IMS) was performed under two different experimental conditions, with and without B $\rho$ -tagging at the high-resolution dispersive central focal plane of the FRS. The evaluation has been done for the combined data sets from both experiments with a new method of data analysis. The use of a correlation matrix has provided experimental mass values for 23 different neutron-rich isotopes for the first time and 6 masses with improved values. The new masses were obtained for nuclides in the element range from Se to Ce. The applied analysis has given access even to rare isotopes detected with an intensity of a few atoms per week. The novel data analysis and systematic error determination are described and the results are compared with extrapolations of experimental values and theoretical models.

We present the mass excesses of 59-64Cr, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of 64Cr is determined for the first time, with an atomic mass excess of -33.48(44) MeV. We find a significantly different two-neutron separation energy S2n trend for neutron-rich isotopes of chromium, removing the previously observed enhancement in binding at N=38. Additionally, we extend the S2n trend for chromium to N=40, revealing behavior consistent with the previously identified island of inversion in this region. We compare our results to state-of-the-art shell-model calculations performed with a modified Lenzi-Nowacki-Poves-Sieja interaction in the fp shell, including the g9/2 and d5/2 orbits for the neutron valence space. We employ our result for the mass of 64Cr in accreted neutron star crust network calculations and find a reduction in the strength and depth of electron-capture heating from the A=64 isobaric chain, resulting in a cooler than expected accreted neutron star crust. This reduced heating is found to be due to the >1-MeV reduction in binding for 64Cr with respect to values from commonly used global mass models.

The unbound isotopes 10Li, 12Li and 13Li have been observed after nucleon-knockout reactions at relativistic energies with 11Li and 14Be beams impinging on a liquid hydrogen target. The channels , and were analysed in the ALADIN-LAND setup at GSI. The 10Li data confirm earlier findings, while the 12Li and 13Li nuclei were observed for the first time. The relative-energy spectrum shows that the ground state of 12Li can be described as a virtual s-state with a scattering length of -13.7(1.6) fm. A broad energy spectrum was found for the channel. Based on the assumption that the relative-energy spectrum is dominated by a correlated background presumably stemming from initial correlations in the 14Be ground-state, evidence for a 13Li resonance at 1.47(31) MeV above the threshold with a width around 2 MeV has been found.

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.

The level structure of 30 S was studied at the NSCL by using neutron removal reactions with a radioactive 31 S beam. The γ -decay from excited states in 30 S was measured in a Ge-detector array. The results discussed for this work will reduce the uncertainties in the determination of the astrophysical 29 P(p, γ ) 30 S reaction rate under rp -process conditions.

This paper presents the results of experimental investigations of ( p , p n ) , ( p , p α ) and ( p , p 6 He) reactions with relativistic 6 He and 8 He beams impinging on a hydrogen target. Information on the structure of extremely neutron-rich nuclei was obtained by using the unique characteristic of quasi-free scattering processes and inverse kinematics. For the first time, momentum distributions of complex clusters inside 6 He and 8 He were measured. Spectroscopic factors for valence neutrons, α - and 6 He clusters were deduced from the experimental data. They demonstrate that the filling of the p 1 2 shell is the essential feature of the 8 He structure. It is shown that the 8 He cluster structure can be considered as a 6 He core plus two valence neutrons.

Recently, much progress has been made with stored exotic nuclei at relativistic velocities ( v c = 0.7 ) . Fragments of 208Pb and 209Bi projectiles and fission products from 238U ions were produced, separated in flight with the fragment separator FRS, and injected into the storage-cooler ring ESR for precision measurements. 114 new masses of neutron-deficient isotopes in the lead region have been measured with time-resolved Schottky Mass Spectrometry (SMS). A new isospin dependence of the pairing energy was observed due to the improved mass accuracy of typically 1.5×10-7 (30 keV). New masses of short-lived neutron-rich fission fragments have been obtained with Isochronous Mass Spectrometry (IMS). An innovative field of spectroscopy has been opened up with lifetime measurements of stored bare and few-electron fragments after applying both stochastic and electron cooling.

We successfully observed deeply bound pionic 1s states in Sn isotopes ( 115 Sn, 119 Sn, 123 Sn) using the Sn( d , 3 He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were determined to high precision. The present results indicate that the isovector part of the s-wave pion-nucleus interaction is significantly enhanced, giving a clear evidence for partial restoration of chiral symmetry in the nuclear medium.

The relative momentum spread of in-flight separated exotic nuclear beams produced in fragmentation and/or fission reactions is of the order of a few percent. A new technique is presented, which reduces the momentum spread significantly, and first experimental results obtained with relativistic projectile fragments are shown. This technique is the key to experiments with slowed-down and stopped beams, in particular for the efficient stopping of relativistic exotic nuclei in gas-filled stopping cells. It will be employed at the energy-buncher stage of the low-energy branch of the Super-FRS facility. The ion-optical design of the energy buncher is presented and a brief outlook to the experimental program is given.

We observed deeply bound π - is states in 1 1 5 , 1 1 9 , 1 2 3 Sn for the first time in 1 1 6 , 1 2 0 , 1 2 4 Sn(d3,He) reactions at recoil free conditions to determine the 1s binding energies and the widths precisely. A preliminary result is used to deduce the isovector scattering amplitude as b 1 = 0.115 ′ 0.005 m - 1 π . The observed enhancement of b 1 over the free πN value infers 35% reduction of f 2 π at the normal nuclear density. ρ = 0.17 fm - 3 .

The charge-exchange contribution can dominate the energy-loss straggling of partially stripped heavy ions depending on the charge-changing cross sections and the partial stopping powers. We have studied the energy-loss straggling of few-electron uranium ions in different solids in the energy range of (200–1000) MeV/u. Our experimental data are compared with a new model taking into account realistic screening for relativistic scattering of target electrons at close impacts to derive partial stopping powers. Screening of the projectile nucleus by inner-shell electrons reduces the charge-exchange straggling compared to that pertaining to a point-like charge distribution.

A fundamental question in nuclear physics is what combinations of neutrons and protons can make up a nucleus. Many hundreds of exotic neutron-rich isotopes have never been observed; the limit of how many neutrons a given number of protons can bind is unknown for all but the lightest elements, owing to the delicate interplay between single particle and collective quantum effects in the nucleus. This limit, known as the neutron drip line, provides a benchmark for models of the atomic nucleus. Here we report a significant advance in the determination of this limit: the discovery of two new neutron-rich isotopes--40Mg and 42Al--that are predicted to be drip-line nuclei. In the past, several attempts to observe 40Mg were unsuccessful; moreover, the observation of 42Al provides an experimental indication that the neutron drip line may be located further towards heavier isotopes in this mass region than is currently believed. In stable nuclei, attractive pairing forces enhance the stability of isotopes with even numbers of protons and neutrons. In contrast, the present work shows that nuclei at the drip line gain stability from an unpaired proton, which narrows the shell gaps and provides the opportunity to bind many more neutrons.

The coincident detection of particles and gamma rays allows the study of the structure of exotic nuclei via inverse kinematics reactions using radioactive ion beams and thick targets. We report on the status of the project to couple the highresolution charged-particle detector ORRUBA to Gammasphere, a high-efficiency, high-resolution gamma ray detector.

The study of nuclei far from stability elucidates the evolution of nuclear shell structure, and also affects estimates of heavy element nucleosynthesis in supernova explosions. Measurement of transfer reactions in inverse kinematics with radioactive ion beams is a powerful technique for these types of studies. Rare isotope beams often have relatively low intensities, and this places difficult requirements on the detection systems for reaction products. The detectors must provide large solid angle coverage in the laboratory along with good position and energy resolution. The Super ORRUBA detector array has been developed for such measurements and is comprised of 18 double-sided, nonresistive silicon strip detectors. This configuration features low thresholds and improved resolution over detectors employing charge division. As a first implementation of this system, the 80Ge(d,p)81Ge neutron transfer reaction in inverse kinematics was measured at HRIBF at ORNL, to determine the properties of levels in 81Ge.

The astrophysical rapid neutron-capture process (r-process) is believed to have produced approximately half of the nuclear species more massive than Fe. Unfortunately, almost nothing is known about the structure of the majority of the extremely neutron-rich nuclei involved in the reaction flow. At exotic beam facilities such as the Holifield Radioactive Ion Beam Facility (HRIBF), measurements with accelerated beams of fission fragments have provided some of the first spectroscopic information on many r-process nuclei. The new SuperORRUBA (Oak Ridge Rutgers University Barrel Array) detector has been constructed at the HRIBF to study such nuclei, and first results are presented.

The (d, p) reaction was measured with the radioactive ion beams of 126Sn and 128Sn in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory, utilizing the Super ORRUBA silicon detector array. Angular distributions of reaction protons were measured for several states in 127Sn and 129Sn to determine angular momentum transfers and deduce spectroscopic factors. Such information is critical for calculating direct (n,γ) cross sections for the r-process as well as for constraining shell model parameters in the A≈130 region. Combined with previous experiments on 130Sn and 132Sn, these results will provide a complete set of (d, p) reaction data on even tin isotopes between stable 124Sn and doubly-magic 132Sn.

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.

The 14O( , p)17F reaction is an important trigger to the p process in x-ray bursts. Only limited information is available from direct measurements of the reaction cross section, and the time-inverse 17F(p, )14O reaction has been frequently used to constrain the astrophysical reaction rate. These time-inverse measurements must be complemented by inelastic 17F(p, p )17F studies to constrain branches populating the first excited state of 17F. Discrepancies in the literature are examined in relationship to directly measured 17F(p, p )17F data, and it is shown that a resolution is possible. Claims of alternative spin assignments for the 6.15-MeV level are also discussed in relationship to the measured inelastic data.

Galactic 26Al is the first radioactive nucleus to be positively identified by -ray astronomy with detection of the 1.809 MeV ray associated with its decay. This nucleus is destroyed in astrophysical environments in the 26Al(p, )27Si and inelastic 26Al+p scattering reactions where properties of 27Si levels determine reaction rates. To investigate these properties, elastic and inelastic 26Al+p scattering reactions were measured between Ec.m. = 0.5 1.5 MeV at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL). A candidate for a new resonance in the 26Al(p, )27Si reaction was identified. Upper limits were also set on the strengths of postulated resonances and on the cross section of the inelastic reaction, but there is little effect on current reaction rate calculations.

Background: Nuclear structure plays a significant role on the rapid neutron capture process ($r$ process) since shapes evolve with the emergence of shells and subshells. There was some indication in neighboring nuclei that we might find examples of a new $N=56$ subshell, which may give rise to a doubly magic ${}_{34}^{90}$Se${}_{56}$ nucleus.Purpose: $\ensuremath{\beta}$-decay half-lives of nuclei around ${}^{90}$Se have been measured to determine if this nucleus has in fact a doubly magic character.Method: The fragmentation of a ${}^{136}$Xe beam at the National Superconducting Cyclotron Laboratory at Michigan State University was used to create a cocktail of nuclei in the $A=90$ region.Results: We have measured the half-lives of 22 nuclei near the $r$-process path in the $A=90$ region. The half-lives of ${}^{88}\phantom{\rule{-0.16em}{0ex}}$As and ${}^{90}$Se have been measured for the first time. The values were compared with theoretical predictions in the search for nuclear-deformation signatures of a $N=56$ subshell, and its possible role in the emergence of a potential doubly magic ${}^{90}$Se. The impact of such hypothesis on the synthesis of heavy nuclei, particularly in the production of Sr, Y, and Zr elements was investigated with a weak $r$-process network.Conclusions: The new half-lives agree with results obtained from a standard global QRPA model used in $r$-process calculations, indicating that ${}^{90}$Se has a quadrupole shape incompatible with a closed $N=56$ subshell in this region. The impact of the measured ${}^{90}$Se half-life in comparison with a former theoretical predication associated with a spherical half-life on the weak $r$ process is shown to be strong.

Big Bang nucleosynthesis calculations, constrained by the Wilkinson Microwave Anisotropy Probe results, produce {sup 7}Li abundances almost a factor of four larger than those extrapolated from observations. Since primordial {sup 7}Li is believed to be mostly produced by the beta decay of {sup 7}Be, one proposed solution to this discrepancy is a resonant enhancement of the {sup 7}Be(d,p)2{alpha} reaction rate through the 5/2{sup +} 16.7-MeV state in {sup 9}B. The {sup 2}H({sup 7}Be,d){sup 7}Be reaction was used to search for such a resonance; none was observed. An upper limit on the width of the proposed resonance was deduced.

The isomeric and $\ensuremath{\beta}$ decays of the $N=Z+2$ nucleus ${}^{96}\phantom{\rule{-0.16em}{0ex}}$Ag were investigated at the National Superconducting Cyclotron Laboratory. A cascade of $\ensuremath{\gamma}$-ray transitions originating from the deexcitation of a microsecond 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) $\ensuremath{\mu}$s, more precise than previously reported. The existence of a second, longer-lived microsecond isomer, associated with a 743-keV $\ensuremath{\gamma}$ 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.

We report on the first direct measurement of the proton separation energy for the proton-unbound nucleus {sup 69}Br. Bypassing the {sup 68}Se waiting point in the rp process is directly related to the 2p-capture rate through {sup 69}Br, which depends exponentially on the proton separation energy. We find a proton separation energy for {sup 69}Br of S{sub p}({sup 69}Br) = -785{sub -40}{sup +34} keV; this is less bound compared to previous predictions which have relied on uncertain theoretical calculations. The influence of the extracted proton separation energy on the rp process occurring in type I x-ray bursts is examined within the context of a one-zone burst model.

The first direct measurement of the proton separation energy, Sp, for the proton-unbound nucleus 69Br is reported. Of interest is the exponential dependence of the 2p-capture rate on Sp which can bypass the 68Se waiting-point in the astrophysical rp process. An analysis of the observed proton decay spectrum is given in terms of the 69Se mirror nucleus and the influence of Sp is explored within the context of a single-zone X-ray burst model., 6 pages, 6 figures, INPC 2010 conference proceedings

The 14O( ,p)17F reaction is an important trigger reaction leading to the p process in x-ray bursts. The inclusion of reaction channels populating excited 17F levels may significantly increase the calculated 14O( ,p)17F reaction rate. A radioactive 17F beam was used at the Oak Ridge National Laboratory Holifield Radioactive Ion Beam Facility to search for a 18Ne resonance at Ec.m.(17F + p) 3.1MeV that had been previously suggested to decay strongly to the first excited level in 17F. No evidence, however, of inelastic 17F + p scattering was observed at this energy, and an upper limit of 10 mb has been set on the inelastic-scattering cross section.

Experience NSCL; International audience; We report in this study the nuclear properties of proton-rich isotopes located along the rp-process path. The experiments have recently been performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The level properties above the proton separation energy of the nuclei 30S, 36K and 37Ca were measured with precision of < 10 keV. This will allow a reduction in the determination of the astrophysical (p, ) reaction rate under rp-process conditions.

Measurements of $\ensuremath{\beta}$-decay properties of $A\ensuremath{\lesssim}110$ r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory at Michigan State University. $\ensuremath{\beta}$-decay half-lives for $^{105}\mathrm{Y}$, $^{106,107}\mathrm{Zr}$, and $^{111}\mathrm{Mo}$, along with $\ensuremath{\beta}$-delayed neutron emission probabilities of $^{104}\mathrm{Y}$, $^{109,110}\mathrm{Mo}$ and upper limits for $^{105}\mathrm{Y}$, $^{103\ensuremath{-}107}\mathrm{Zr}$, and $^{108,111}\mathrm{Mo}$ have been measured for the first time. Studies on the basis of the quasi-random-phase approximation are used to analyze the ground-state deformation of these nuclei.

A half-life of 2.2 \ifmmode\pm\else\textpm\fi{} 0.2 s has been deduced for the ground-state $\ensuremath{\beta}$ decay of $^{84}\mathrm{Mo}$, more than $1\ensuremath{\sigma}$ shorter than the previously adopted value. $^{84}\mathrm{Mo}$ 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 ($\mathit{rp}$) process. The effect of the measured half-life on $\mathit{rp}$-process reaction flow is explored. Implications on theoretical treatments of nuclear deformation in $^{84}\mathrm{Mo}$ are also discussed.

The {beta}-decay properties of the N=Z nuclei {sup 96}Cd, {sup 98}In, and {sup 100}Sn have been studied. These nuclei were produced at the National Superconducting Cyclotron Laboratory by fragmenting a 120 MeV/nucleon {sup 112}Sn primary beam on a Be target. The resulting radioactive beam was filtered in the A1900 and the newly commissioned Radio Frequency Fragment Separator to achieve a purity level suitable for decay studies. The observed production cross sections of these nuclei are lower than predicted by factors of 10-30. The half-life of {sup 96}Cd, which was the last experimentally unknown waiting point half-life of the astrophysical rp process, is 1.03{sub -0.21}{sup +0.24} s. The implications of the experimental T{sub 1/2} value of {sup 96}Cd on the abundances predicted by rp process calculations and the origin of A=96 isobars such as {sup 96}Ru are explored.

Atomic masses play a crucial role in many nuclear astrophysics calculations. The lack of experimental values for relevant exotic nuclides triggered a rapid development of new mass measurement devices around the world. The Time-of-Flight (TOF) mass measurements offer a complementary technique to the most precise one, Penning trap measurements, the latter being limited by the rate and half-lives of the ions of interest. The NSCL facility provides a well-suited infrastructure for TOF mass measurements of very exotic nuclei. At this facility, we have recently implemented a TOF-Brho technique and performed mass measurements of neutron-rich nuclides in the Fe region, important for r-process calculations and for calculations of processes occurring in the crust of accreting neutron stars., 8 pages, 4 figures, submitted to Journal of Physics G, proceedings of Nuclear Physics in Astrophysics III

The results of measurements of the production of neutron-rich nuclei by the fragmentation of a {sup 48}Ca beam at 142 MeV/nucleon are presented. Evidence was found for the production of a new isotope that is the most neutron-rich silicon nuclide, {sup 44}Si, in a net neutron pickup process. A simple systematic framework was found to describe the production cross sections based on thermal evaporation from excited prefragments that allows extrapolation to other weak reaction products.