137,138,139^{137,138,139}La(nn, γ\gamma) cross sections constrained with statistical decay properties of 138,139,140^{138,139,140}La nuclei

The nuclear level densities and $\gamma$-ray strength functions of $^{138,139,140}$La were measured using the $^{139}$La($^{3}$He, $\alpha$), $^{139}$La($^{3}$He, $^{3}$He$^\prime$) and $^{139}$La(d, p) reactions. The particle-$\gamma$ 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$\sim$140 region is discussed. The $^{137,138,139}$La($n, \gamma)$ cross sections were calculated at $s$- and $p$-process temperatures using the experimentally measured nuclear level densities and $\gamma$-ray strength functions. Good agreement is found between $^{139}$La($n, \gamma)$ calculated cross sections and previous measurements

Analysis of experimental data on -delayed proton and -particle emission

The spin and parity of the resonance level 2645 keV in 20Na have been studied and discussed for decades among physicists, due to the astrophysical importance of the 19Ne(p,)20Na reaction. The level is situated 450 keV above the threshold for (19Ne+p). In this thesis data from an experiment investigating 20Mg -delayed proton emission, done at CERN-ISOLDE, has been calibrated and analyzed in order to obtain pure proton spectra in search for the resonance level. Simulations of energy deposition in the detectors have also been performed for the setup used and for potential future setups. It was found that the setup used was not sufficiently sensitive to put new limits on the population of the 2645 keV state. Therefore different detectors are discussed, which could allow to lower the amount of detected -background and recoils of 16O, from the decay of 20Na. New findings were -particles from -delayed -emission from 21Mg, identified in the used E E telescope

Summer Student Session 2012 (1/3)

9.15 Tommi Tenkanen: Jet energy offset corrections in CMS 9.30 Malin Klintefjord: Crystal Collimation 9.45 Guillaume Lastecoueres: A CMS DATASETS MONITORING TOO

B(E2) anomalies in the yrast band of 170Os

Background: The neutron-deficient osmium isotopic chain provides a great laboratory for the study of shape evolution, with the transition from the soft triaxial rotor in 168Os to the well-deformed prolate rotor in 180Os, while shape coexistence appears around N = 96 in 172Os. Therefore, the study of the Os isotopic chain should provide a better understanding of shape changes in nuclei and a detailed scrutiny of nuclear structure calculations. In this paper, the lifetimes of the low-lying yrast states of 170Os have been measured for the first time to investigate the shape evolution with neutron number. Purpose: Lifetimes of excited states in the ground-state band of 170Os are measured to investigate the shape evolution with neutron number in osmium isotopes and compare with state-of-the-art calculations. Methods: The states of interest were populated via the fusion-evaporation reaction 142Nd(32S, 4n) at a bombarding energy of 170 MeV at the ALTO facility from IPN (Orsay, France). Lifetimes of the 2+ 1 and 4+ 1 states in 170Os were measured with the recoil-distance Doppler-shift method using the Orsay universal plunger system. Results: Lifetimes of the two first excited states in 170Os were measured for the first time. A very small B(E2; 4+ 1 → 2+ 1 )/B(E2; 2+ 1 → 0+ 1 ) = 0.38(11) was found, which is very uncharacteristic for collective nuclei. These results were compared to state-of-the-art beyond-mean-field calculations. Conclusions: Although theoretical results give satisfactory results for the energy of the first few excited states in 170Os and the B(E2; 2+ 1 → 0+ 1 ) they fail to reproduce the very small B(E2; 4+ 1 → 2+ 1 ), which remains a puzzle

Investigating the gamma decay of Ni 65 from particle-gamma coincidence data

The γ decay of 65 Ni has been studied from particle- γ coincidence data on the 64 Ni ( d , p γ ) 65 Ni reaction. γ -ray spectra at excitation energies below Ex≈ 2 MeV have been studied and compared with previous measurements. Coincidences corresponding to Ex≈ 4.4 – 6.1 MeV have been used to constrain the shape of the nuclear level density and γ -strength function of 65 Ni by means of the Oslo method. The experimental γ -strength function presents an enhancement at γ energies below Eγ ≈ 3 MeV . In addition, a resonance-like structure centered at Eγ ≈ 4.6 MeV is seen together with accumulated strength at Eγ ≈ 2.6 – 3.6 MeV . The obtained results contribute to the systematic study of γ decay in the Ni isotopes, which is of great interest for the understanding of both single-particle and collective nuclear structure phenomena

Statistical γ -decay properties of Ni 64 and deduced (n,γ) cross section of the s -process branch-point nucleus Ni 63

Particle-γ coincidence data have been analyzed to obtain the nuclear level density and the γ -strength function of 64Ni by means of the Oslo method. The level density found in this work is in very good agreement with known energy levels at low excitation energies as well as with data deduced from particle-evaporation measurements at excitation energies above Ex ≈ 5.5 MeV. The experimental γ -strength function presents an enhancement at γ energies below Eγ ≈ 3 MeV and possibly a resonancelike structure centered at Eγ ≈ 9.2 MeV. The obtained nuclear level density and γ -strength function have been used to estimate the (n,γ ) cross section for the s-process branch-point nucleus 63Ni, of particular interest for astrophysical calculations of elemental abundances

Gamma decay from the quasicontinuum of 197,198Au

The average electromagnetic dipole response of levels in the quasicontinuum of 197,198Au has been measured using (3He,3He ) and (d,p) reactions. The extracted γ -ray strength functions have been normalized according to three model assumptions for the nuclear spin distribution. An enhancement in the energy region Eγ = 3.0–6.5 MeV is observed for both isotopes. The E1 component of such excess of strength is studied in detail for 198Au and is interpreted as the pygmy dipole resonance with an energy centroid of 5.9(1) MeV and exhausts about 1% of the total integrated strength. The pygmy dipole resonance is shown to have a significant impact on the calculated 197Au(n,γ ) 198Au cross section

Test of the generalized Brink-Axel hypothesis in 64,65Ni

Previously published particle-γ coincidence data on the 64Ni(p, p′ γ ) 64Ni and 64Ni(d,pγ ) 65Ni reactions were further analyzed to study the statistical properties of γ decay in 64,65Ni. To do so, the γ decay to the quasicontinuum region and discrete low-lying states was investigated at γ -ray energies of 2.0–9.6 and 1.6–6.1 MeV in 64Ni and 65Ni, respectively. In particular, the dependence of the γ -strength function with initial and final excitation energy was studied to test the validity of the generalized Brink-Axel hypothesis. Finally, the role of fluctuations in transition strengths was estimated as a function of γ -ray and excitation energy. The γ -strength function is consistent with the hypothesis of the independence of initial excitation energy, in accordance with the generalized Brink-Axel hypothesis. The results show that the γ decay to low-lying levels displays large fluctuations for low initial excitation energies

Revised spin values of the 991 keV and 1599 keV levels in 140Sm

The previously accepted spin values of the 991 and 1599 keV levels in Sm140 have been revised and established as 2+ and 0(+), respectively. The γ−γ angular correlation method was used to determine the new spin values. The excited low-spin levels in Sm140 were populated in the Eu140→140Sm and Gd140→ Eu140→140Sm decays. The Gd140 and Eu140 nuclei were produced in the Cd112+S32 reaction at a beam energy of 155 MeV. © 2015 American Physical Societ