Level densities, thermodynamics and the γ-ray strength functions in 163,164Dy

The nuclei 163,164 Dy were analyzed at the Oslo Cyclotron laboratory (OCL) by use of the so-called Oslo method. This method enables us to extract both the level density and the γ -ray strength function simultaneously from one and the same experiment. The method relies on the Brink-Axel hypothesis, which states that the primary-γ spectrum is proportional to both the level density and the γ -transmission coefficient. The γ -transmission coefficient is itself proportional to the γ -ray strength function. The level density and the γ -ray strength function provides fundamental information about nuclear structure. The level density is the starting point for extracting thermodynamic properties, whereas the γ -ray strength function characterizes the average electromagnetic properties of excited nuclei. In this thesis results for the experimental level densities, thermodynamic properties and the γ -ray strength functions for 163,164 Dy are extracted. Several interesting features were found when studying the γ -ray strength functions. We observe an enhanced strength at around 5 MeV of excitation energy. Similar characteristics may also be recognized in other rare earth isotopes. The results for the γ -ray strength functions also indicates that the width of the pygmy resonance located in the 3 MeV region is reaction dependent

Pygmy resonance and low-energy enhancement in the γ\gamma-ray strength functions of Pd~isotopes

An unexpected enhancement in the $\gamma$-ray strength function, as compared to the low energy tail of the Giant Dipole Resonance (GDR), has been observed for Sc, Ti, V, Fe and Mo isotopes for $E_\gamma<4$ MeV. This enhancement was not observed in subsequent analyses on Sn isotopes, but a Pygmy Dipole Resonance (PDR) centered at $E_\gamma\approx8$ MeV was however detected. The $\gamma$-ray strength functions measured for Cd isotopes exhibit both features over the range of isotopes, with the low-energy enhancement decreasing- and PDR strength increasing as a function of neutron number. This suggests a transitional region for the onset of low-energy enhancement, and also that the PDR strength depends on the number of neutrons. The $\gamma$-ray strength functions of $^{105-108}$Pd have been measured in order to further explore the proposed transitional region. Experimental data were obtained at the Oslo Cyclotron Laboratory by using the charged particle reactions ($^{3}$He, $^{3}$He$^{\prime}\gamma$) and ($^{3}$He, $\alpha$$\gamma$) on $^{106,108}$Pd target foils. Particle$-\gamma$ coincidence measurements provided information on initial excitation energies and the corresponding $\gamma$-ray spectra, which were used to extract the level densities and $\gamma$-ray strength functions according to the Oslo method. The $\gamma$-ray strength functions indicate a sudden increase in magnitude for $E_{\gamma}>4$ MeV, which is interpreted as a PDR centered at $E_{\gamma}\approx8$ MeV. An enhanced $\gamma$-ray strength at low energies is also observed for $^{105}$Pd, which is the lightest isotope measured in this work. Further, the results correspond and agree very well with the observations from the Cd isotopes, and support the suggested transitional region for the onset of low-energy enhancement with decreasing mass number. The neutron number dependency of the PDR strength is also evident

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

Average properties of nuclear states in the quasi-continuum region

Intense effort to explore the atomic nucleus has persisted through the past century. Despite of the great efforts, there still remains many open questions regarding the properties of the nucleus. In particular, the low energy region of excited nuclei is a poorly known area. In this thesis we have used two complimentary techniques to investigate nuclear structure in the low energy region. Through 3He induced reactions we apply the so-called Oslo method to extract nuclear properties at excitation energies below the neutron separation threshold. Beyond the neutron threshold we have used photo-neutron experiments and studied nuclei with energies up to 13 MeV. The new experimental data reviles special excitation modes of the nucleus, also known as resonances, some of which cannot be explained by existing theoretical models. Furthermore, radiative neutron capture cross sections, relevant for astrophysical calculations, are extracted by use of the reaction code TALYS. Astrophysical reaction rates are also calculated, and we find that resonance features in the low energy region of excited nuclei have a significant impact on the reaction rates

Photoneutron reactions in nuclear astrophysics

Highly-monochromatic γ-ray beams are produced at the NewSUBARU synchrotron radiation facility by the inverse Compton scattering of laser photons from relativistic electrons. The latest s-process study in nuclear astrophysics with the γ-ray beam is presented.SCOPUS: cp.jinfo:eu-repo/semantics/publishe

Photoneutron cross section measurements on Sm isotopes

The Extreme Light Infrastructure - Nuclear Physics, one of the three pillars of the Extreme Light Infrastructure Pan-European initiative, is a new large scale facility dedicated to nuclear physics with extreme electromagnetic fields. ELI-NP will host two 10 PW lasers and a very brilliant Gamma beam system with unprecedented intensity and energy resolution parameters. We propose to perform photon induced nuclear reactions using the very brilliant γ-ray beams provided by the Gamma beam system to examine in detail the photon absorption process and its decay modes. Here the experimental program related to nuclear research on reactions above the neutron separation threshold, which is under preparation at ELI-NP, is presented.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Photoneutron cross sections for samarium isotopes: Toward a unified understanding of (y, n) and (n, y) reactions in the rare earth region

Photoneutron cross sections were measured for the seven stable samarium isotopes Sm-144,Sm-147,Sm-148,Sm-149,Sm-150,Sm-152,Sm-154 near the neutron threshold with quasi-monochromatic laser-Compton scattering gamma rays. Our photoneutron cross sections are found to be low by 20%-37% relative to existing data. The photoneutron data are analyzed with the TALYS reaction code by considering the Skyrme Hartree-Fock-Bogoliubov (HFB) plus quasiparticle random phase approximation (QRPA) model and the axially symmetric deformed Gogny HFB plus QRPA model of the E1 gamma-ray strength. Using the gamma-ray strength function constrained by the present photoneutron data, we made a thorough analysis of the reverse (n,gamma) cross sections including the radioactive nucleus Sm-151 with a half-life of 90 yr. The radiative neutron capture cross section for Sm-153 with the half-life of 1.928 d is deduced with the gamma-ray strength function method

Analisis pengaruh nilai pelanggan, kualitas pelayanan dan kedekatan emosional terhadap loyalitas nasabah : studi kasus pada BANK CIMB NIAGA Universitas Sanata Dharma

The level densities and γ-ray strength functions of 105,106,111,112Cd have been extracted from particle-γ coincidence data using the Oslo method. The level densities are in very good agreement with known levels at low excitation energy. The γ-ray strength functions display no strong enhancement for low γ energies. However, more low-energy strength is apparent for 105,106Cd than for 111,112Cd. For γ energies above ≈4 MeV, there is evidence for some extra strength, similar to what has been previously observed for the Sn isotopes. The origin of this extra strength is unclear; it might be due to E1 and M1 transitions originating from neutron skin oscillations or the spin-flip resonance, respectively. © 2013 American Physical Societ

Photoneutron cross sections for neodymium isotopes: Toward a unified understanding of (γ,n) and (n,γ) reactions in the rare earth region

Photoneutron cross sections were measured for five stable Nd isotopes, Nd-143,Nd-144,Nd-145,Nd-146,Nd-148, near neutron threshold with highly monochromatic laser-Compton scattering gamma rays. The photoneutron data were compared with the calculations performed with the TALYS reaction code with inputs of the Skyrme Hartree-Fock-Bogoliubov (HFB) plus quasi-particle random phase approximation (QRPA) model and the axially symmetric deformed Gogny HFB plus QRPA model of E1 gamma-ray strength. Using the gamma-ray strength function constrained by the present photoneutron data, a thorough analysis of the reverse (n, gamma) cross sections is made. Radiative neutron capture cross sections for an s-process branching-point nucleus in the rare earth region, Nd-147 with the half-life 10.98 d, are deduced with the gamma-ray strength function method. The impact of the newly evaluated Nd-147(n, gamma)Nd-148 cross section on s-process nucleosynthesis is discussed

Verification of detailed balance for γ absorption and emission in Dy isotopes

The photoneutron cross sections of 162,163Dy have been measured for the first time in an energy region from the neutron threshold (Sn) up to ≈13MeV. The (γ,n) reaction was induced with quasimonochromatic laser Compton-scattered γ rays, produced at the NewSUBARU laboratory. The corresponding γ -ray strength functions (γ SF) have been calculated from the photoneutron cross sections. The data are compared to reanalyzed γSFs of 160–164Dy, which are measured below Sn. The excellent agreement with the photoneutron data at Sn confirms the principle of detailed balance. Thus, a complete γ SF is established covering in total the energy regionof1 Eγ 13MeV.Thesemid-shellwell-deformeddysprosiumisotopesallshowscissorsresonances with very similar structures. We find that our data predict the same integrated scissors strength as (γ,γ′) data when integrated over the same energy range, which shows that the scissors mode very likely is consistent with the generalized Brink hypothesis. Finally, using the γSFs as input in the reaction code TALYS, we have deduced radiative neutron-capture cross sections and compared them to direct measurements. We find a very good agreement within the uncertainties, which gives further support to the experimentally determined γ SFs