[en] We have measured the cross sections for the ¹⁹⁷Au(α,γ)²⁰¹Tl and ¹⁹⁷Au(α,2n)¹⁹⁹Tl reactions in the 17.9- to 23.9-MeV energy range, and ¹⁹⁷Au(α,n)²⁰⁰Tl reaction in the 13.4- to 23.9-MeV energy range using an activation technique. Thick-target yields for the ⁶⁴Zn(α,γ)⁶⁸Ge (7- to 14-MeV) and ⁶³Cu(α,γ)⁶⁷Ga (7-MeV) reactions were measured. For all measurements, natural elements were bombarded with He⁺ beams from the 88'' Cyclotron at the Lawrence Berkeley National Laboratory (LBNL). Irradiated samples were counted using a g-spectrometry system at LBNL's Low Background Facility. Measured ¹⁹⁷Au(α,γ)²⁰¹Tl cross-sections were compared with the NON-SMOKER theoretical values. The thick-target yields for the ⁶⁴Zn(α,γ)⁶⁸Ge and ⁶³Cu(α,γ)⁶⁷Ga reactions are also compared with the theoretical yield, calculated numerically using the energy dependent NON-SMOKER cross section data. In both cases, measured values are found to follow a trend of overlapping the predicted value near the alpha nucleus barrier height and fall below with a slowly widening difference between them in the sub barrier energy points

[en] We have measured cross sections for the ⁶³Cu(α,γ)⁶⁷Ga reaction in the 5.9-8.7 MeV energy range using an activation technique. Natural Cu foils were bombarded with alpha beams from the 88'' Cyclotron at Lawrence Berkeley National Laboratory (LBNL). Activated foils were counted using a gamma spectrometry system at LBNL's Low Background Facility. The ⁶³Cu(α,γ)⁶⁷Ga cross-sections were determined and compared with the latest NONSMOKER theoretical values. Experimental cross sections were found to be in agreement with theoretical values

[en] Cross sections for the "4"7Ti(n,p)"4"7Sc and "6"4Zn(n,p)"6"4Cu reactions have been measured for quasi-monoenergetic DD neutrons produced by the UC Berkeley High Flux Neutron Generator (HFNG). The HFNG is a compact neutron generator designed as a “flux-trap” that maximizes the probability that a neutron will interact with a sample loaded into a specific, central location. The study was motivated by interest in the production of "4"7Sc and "6"4Cu as emerging medical isotopes. The cross sections were measured in ratio to the "1"1"3In(n,n′)"1"1"3"mIn and "1"1"5In(n,n′)"1"1"5"mIn inelastic scattering reactions on co-irradiated indium samples. Post-irradiation counting using an HPGe and LEPS detectors allowed for cross section determination to within 5% uncertainty. The "6"4Zn(n,p)"6"4Cu cross section for 2.76_-_0_._0_2"+"0"."0"1MeV neutrons is reported as 49.3 ± 2.6 mb (relative to "1"1"3In) or 46.4 ± 1.7 mb (relative to "1"1"5In), and the "4"7Ti(n,p)"4"7Sc cross section is reported as 26.26 ± 0.82 mb. The measured cross sections are found to be in good agreement with existing measured values but with lower uncertainty (<5%), and also in agreement with theoretical values. This work highlights the utility of compact, flux-trap DD-based neutron sources for nuclear data measurements and potentially the production of radionuclides for medical applications.

[en] The nuclear level densities and γ-ray strength functions of ^138,139,140La were measured using the ¹³⁹La(³He,α), ¹³⁹La(³He,'³He), and 139La(d,p) reactions. The particle-γ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A~140 region is discussed. The ^137,138,139La(n,γ) cross sections were calculated at s- and p-process temperatures using the experimentally measured nuclear level densities and γ-ray strength functions. As a result, good agreement is found between ¹³⁹La(n,γ) calculated cross sections and previous measurements.

[en] We have measured the cross sections for the ¹⁹⁷Au(α,γ)²⁰¹Tl and ¹⁹⁷Au(α,2n)¹⁹⁹Tl reactions in the 17.9- to 23.9-MeV energy range, and ¹⁹⁷Au(α,n)²⁰⁰Tl reaction in the 13.4- to 23.9-MeV energy range using an activation technique. Thick-target yields for the ⁶⁴Zn(α,γ)⁶⁸Ge (7- to 14-MeV) and ⁶³Cu(α,γ)⁶⁷Ga (7-MeV) reactions were measured. For all measurements, natural elements were bombarded with He⁺ beams from the 88 In. Cyclotron at the Lawrence Berkeley National Laboratory (LBNL). Irradiated samples were counted using a γ-spectrometry system at LBNL's Low Background Facility. Measured ¹⁹⁷Au(α,γ)²⁰¹Tl cross sections were compared with the NON-SMOKER theoretical values. The thick-target yields for the ⁶⁴Zn(α,γ)⁶⁸Ge and ⁶³Cu(α,γ)⁶⁷Ga reactions are also compared with the theoretical yield, calculated numerically using the energy dependent NON-SMOKER cross section data. In both cases, measured values are found to follow a trend of overlapping the predicted value near the alpha nucleus barrier height and fall below with a slowly widening difference between them in the sub-barrier energy points

[en] The lifetime of the 2₁⁺ state in ¹⁶C has been measured with the recoil distance method using the ⁹Be(⁹Be,2p) fusion-evaporation reaction at a beam energy of 40 MeV. The mean lifetime was measured to be 11.7(20) ps corresponding to a B(E2; 2₁⁺→0⁺) value of 4.15(73)e² fm⁴ [1.73(30) W.u.], consistent with other even-even closed shell nuclei. Our result does not support an interpretation for ''decoupled'' valence neutrons

[en] An experiment was performed at the 88-inch cyclotron at LBNL to investigate the structure of uranium isotopes and concurrently test the so-called surrogate ratio method. A 28 MeV proton beam was used to bombard ²³⁶U and ²³⁸U targets and the outgoing light ions were detected using the STARS silicon telescope allowing isotopic assignments and the excitation energy of the compound nucleus to be measured. A fission detector was placed at backward angles to give particle-fission coincidences, while the six clover germanium detectors of the LIBERACE array were used for particle-γ coincidences. The (p,d) reaction channels on ²³⁶U and ²³⁸U targets were used as a surrogate to measure the σ(²³⁴U(n,f))/σ(²³⁶U(n,f)) cross section ratio. The results give reasonable agreement with literature values over an equivalent neutron energy range between 0 MeV and 6 MeV. Structure results in ²³⁵U include a new (3/2⁻) level at 1035 keV, that is tentatively assigned as the 3/2⁻[501] Nilsson state. The analogue 3/2⁻[501] state in ²³⁷U may be associated with a previously observed level at 1201 keV, whose spin/parity is restricted to J^π = 3/2⁻ on the basis of newly observed decays to the ground band.

[en] We have indirectly determined the ²³⁷Np(n,f) cross section over an equivalent neutron energy range from 10 to 20 MeV using the surrogate reaction ²³⁸U(³He,tf). A self-supporting ∼761 μg/cm² metallic ²³⁸U foil was bombarded with a 42 MeV ³He²⁺ beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory (LBNL). Outgoing charged particles and fission fragments were identified using the Silicon Telescope Array for Reaction Studies (STARS) consisted of two 140 μm and one 1000 μm Micron S2 type silicon detectors. These results were compared with the ²³⁷Np(n,f) cross section data from the direct measurements, the Evaluated Nuclear Data File (ENDF/B-VII.0), and the Japanese Evaluated Nuclear Data Library (JENDL 3.3) and found to closely follow those datasets

[en] The astrophysical s-process is responsible for the synthesis of many of the nuclei heavier than iron through a series of low-energy (n,γ) reactions and β-decays. For nuclei for which the neutron capture and β-decay rates are comparable, the branching is crucial for tests of s-process models. Direct measurements of (n,γ) cross sections for these nuclei are extremely challenging due to the inherent difficulties associated with radioactive targets and the low intensity of available neutron beams. The surrogate reaction technique can be used to circumvent these difficulties by creating the same compound nucleus through light-ion reactions on a stable target. The cross section can be determined by combining optical model calculations for the formation of the compound nucleus with the measured exit channel probability for γ-ray emission. We have collected data to determine the low-energy (n,γ) cross section for the unstable nucleus ¹⁵³Gd by bombarding a stable ¹⁵⁴Gd target with protons from the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory to create the desired ¹⁵⁴Gd* compound nucleus. The STARS/LiBerACE silicon and clover germanium detector arrays were used to detect γ-rays in coincidence with the scattered protons. Additional cross section measurements using ¹⁵⁶Gd and ¹⁵⁸Gd targets will be compared to direct measurements of the (n,γ) cross sections for ¹⁵⁵Gd and ¹⁵⁷Gd. The current status of the analysis is summarized

[en] A segmented Si telescope and HPGe array is used to study the ¹⁵⁶Gd(p,d-γ)¹⁵⁵Gd direct reaction by d-γ and d-γ-γ coincidence measurements using 25-MeV protons. The present investigation is the first time that this N=91 nucleus and the N=90 region--which is known for a rapid change from vibrational to rotational character, several low-lying 0⁺ states in the even-even nuclei, and large Coriolis (ΔΩ=1) plus ΔN=2 mixing in the even-odd nuclei--have been studied by particle-γ coincidence following a direct reaction with light ions. Gamma-ray energies and branches, excitation energies, angular distributions, and cross sections are measured for states directly populated in the (p,d) reaction. A new low-energy doublet state at 592.46 keV (previously associated with the K=0 x (3/2)^-[521] bandhead) and several new γ-ray transitions (particularly for states with excitation energies >1 MeV) are presented. Most notably, the previous ν (7/2)⁺[404] systematics at and around the N=90 transition region are brought into question and reassigned as ν (5/2)⁺[402]. This reassignment makes the ν (1/2)⁺[400], ν (3/2)⁺[402], and ν (5/2)⁺[402] orbitals, which originate from the 3s_1/2, 2d_3/2, and 2d_5/2 spherical states, respectively, responsible for the three largest cross sections to positive-parity states in the (p,d)¹⁵⁵Gd direct reaction. These three steeply upsloping orbitals undergo ΔN=2 mixing with their N=6 orbital partners, which are oppositely sloped with respect to deformation. The presence of these steeply sloped and crossing orbitals near the Fermi surface could weaken the monopole pairing strength and increase the quadrupole pairing strength of neighboring even-even nuclei, which would bring ν 2p-2h 0⁺ states below 2Δ. Indeed, this could account for a large number of the low-lying 0⁺ states populated in the (p,t)¹⁵⁴Gd direct reaction.