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At Argonne we have enhanced the AMS capabilities of the Argonne Tandem Linac Accelerator System (ATLAS) to attempt to minimize crosstalk between samples and to quickly move from one (M/Q) setting to another in order to make measurements on a large number of samples provided by the MANTRA (Measurement of Actinide Neutron Transmutation Rates by Accelerator mass spectrometry) project. Those improvements include the use of a picosecond laser to ablate actinide material into the source, a new 20-sample holder that can switch samples within 1–2 min, and a number of accelerator configuration improvements that allow quick and precise switching between species. In principle, AMS can provide production yields of actinide isotopes produced during the irradiation period at a sensitivity exceeding other mass spectrometry techniques. A total of 27 irradiated samples of a variety of actinides have been provided for measurement. We discuss our experience with these facility improvements and how well we have met our performance goals. In addition, we present preliminary results on a number of the irradiated actinide samples with this approach and compare those results to Multi-Collector ICPMS measurements.

Radiative neutron capture reactions play an important role in nuclear astrophysics. In some cases direct neutron capture reaction studies are not possible and neutron transfer reactions have been suggested as a surrogate approach. We have performed a detailed study of the $^{25}\mathrm{Mg}(d,p)^{26}\mathrm{Mg}$ reaction at a beam energy of 56 MeV as a surrogate reaction to the radiative neutron capture reaction $^{25}\mathrm{Mg}(n,\ensuremath{\gamma})^{26}\mathrm{Mg}$. A large number of neutron bound and unbound states between 10.6 and 12.1 MeV excitation energy in $^{26}\mathrm{Mg}$ were observed. Angular distribution analysis provided information about the orbital momentum transfer populating these levels. The comparison with resonances observed in the $^{25}\mathrm{Mg}(n,\ensuremath{\gamma})^{26}\mathrm{Mg}$ reaction indicate that different levels in $^{26}\mathrm{Mg}$ are being populated through the two reaction mechanisms, causing substantial discrepancies in the reaction-rate prediction. This result demonstrates that neutron transfer reaction studies may not necessarily lead to reliable predictions for neutron capture reaction rates.

Low-lying negative-parity states in $^{11}\mathrm{Be}$ having dominant $p$-wave neutron configurations were studied using the $^{12}\mathrm{B}(d,^{3}\mathrm{He})\phantom{\rule{0.16em}{0ex}}^{11}\mathrm{Be}$ proton-removal reaction in inverse kinematics. The $1/{2}_{1}^{\ensuremath{-}}$ state at 0.32 MeV, the $3/{2}_{1}^{\ensuremath{-}}$ state at 2.56 MeV, and one or both of the states including the $5/{2}_{1}^{\ensuremath{-}}$ level at 3.89 MeV and the $3/{2}_{2}^{\ensuremath{-}}$ level at 3.96 MeV were populated in the present reaction. Spectroscopic factors were determined from the differential cross sections using a distorted wave Born approximation method. The $p$-wave proton removal strengths were well described by the shell model calculations while the Nilsson model calculation underestimates the spectroscopic factors for the higher excited states. Results from both variational Monte Carlo and no-core shell-model calculations were also compared with the experimental observations.

The ^{36}Ar(n,γ)^{37}Ar (t_{1/2}=35 d) and ^{38}Ar(n,γ)^{39}Ar (269 yr) reactions were studied for the first time with a quasi-Maxwellian (kT∼47 keV) neutron flux for Maxwellian average cross section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ^{37}Ar/^{36}Ar and ^{39}Ar/^{38}Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ^{37}Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ^{36}Ar and ^{38}Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron-capture cross sections of ^{36,38}Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak s process. The new production cross sections have implications also for the use of ^{37}Ar and ^{39}Ar as environmental tracers in the atmosphere and hydrosphere.

The single-neutron configurations of several low-lying states in $^{22}\mathrm{F}$ have been determined from neutron-adding cross sections of a ($d,p$) reaction using a $^{21}\mathrm{F}$ radioactive beam in inverse kinematics. Final states in $^{22}\mathrm{F}$ consisting of a proton in the $\ensuremath{\pi}0{d}_{5/2}$ orbital coupled to a neutron in either the $\ensuremath{\nu}0{d}_{5/2}$, $\ensuremath{\nu}1{s}_{1/2}$, or $\ensuremath{\nu}0{d}_{3/2}$ orbitals were observed up to an excitation energy of $\ensuremath{\sim}5$ MeV. Spectroscopic factors and strengths were determined from the angular distribution of the cross sections using a distorted wave Born approximation method. The distribution of the $\ensuremath{\nu}0{d}_{5/2}$ and $\ensuremath{\nu}1{s}_{1/2}$ strength was well described by all USD effective shell model interactions, while only the more recent USDA/USDB interactions showed a marked improvement in describing the observed $\ensuremath{\nu}0{d}_{3/2}$ strength. Diagonal two-body matrix elements of the ${(0{d}_{5/2})}_{J=0--5}^{2}$ effective nucleon-nucleon interaction were extracted from the data and compared with previous determinations of the same matrix elements from particle-particle and hole-hole spectra, as well as the calculated results of the USDA interactions. No significant discrepancies were observed. Inspection of the monopole energies showed that an improved agreement between the different empirical matrix elements is found if a mass dependence is included.

A beam containing a substantial component of both the J^{π}=5^{+}, T_{1/2}=162 ns isomeric state of ^{18}F and its 1^{+}, 109.77-min ground state is utilized to study members of the ground-state rotational band in ^{19}F through the neutron transfer reaction (d,p) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2^{+} band-terminating state. The agreement between shell-model calculations using an interaction constructed within the sd shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei.

The $\ensuremath{\nu}0{h}_{9/2}$ and $\ensuremath{\nu}0{i}_{13/2}$ strength at $^{137}\mathrm{Xe}$, a single neutron outside the $N=82$ shell closure, has been determined using the $^{136}\mathrm{Xe}(\ensuremath{\alpha},^{3}\mathrm{He})^{137}\mathrm{Xe}$ reaction carried out at 100 MeV. We confirm the recent observation of the second $13/{2}^{+}$ state and reassess previous data on the $9/{2}^{\ensuremath{-}}$ states, obtaining spectroscopic factors. These new data provide additional constraints on predictions of the same single-neutron excitations at $^{133}\mathrm{Sn}$.

International audience; We present a status report of recent neutron capture experiments performed with the mA-proton beam (1.92 MeV, 3 kW) of the Soreq Applied Research Accelerator Facility (SARAF) and the Liquid-Lithium Target (LiLiT). Experiments and preliminary results for (n) reactions on 36,38Ar, studied for the first time with 30-keV neutrons, on natKr, natCe and on radioactive targets 147Pm and 171Tm are described.