No abstract

The photo-neutron cross sections of 162,163 Dy have been measured for the first time in an energy region from the neutron threshold (S n ) up to ≈ 13 MeV. The (γ,n) reaction was induced with quasi-monochromatic laser Compton-scattered γ rays, produced at the NewSUBARU laboratory. The corresponding γ-ray strength functions (γSF) have been calculated from the photo-neutron cross sections. The data are compared to reanalyzed γSFs of 160−164 Dy, which are measured below S n . The excellent agreement with the photo-neutron data at S n confirms the principle of detailed balance. Thus, a complete γSF is established covering in total the energy region of 1 MeV ≤ E γ ≤ 13 MeV. These mid-shell well-deformed dysprosium isotopes all show scissors resonances 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 γSFs.

Photodisintegration of 9 Be through the 1/2 + state near neutron threshold and cluster dipole resonance below giant dipole resonance was measured with quasi-monochromatic γ-ray beams produced in the inverse Compton scattering of laser photons. The cross section for the 1/2 + state is revisited, being consistent with the 2001 data. The cross section for the cluster dipole resonance is consistent with the cluster dipole sum-rule which however degenerates for the two-body (n-8 Be) and three-body(n-α-α) configurations.

Photoneutron cross sections were measured for the seven stable samarium isotopes 144,147,148,149,150,152,154 Sm near the neutron threshold with quasi-monochromatic laser-Compton scattering γ 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 γ -ray strength. Using the γ -ray strength function constrained by the present photoneutron data, we made a thorough analysis of the reverse (n,γ ) cross sections including the radioactive nucleus 151 Sm with a half-life of 90 yr. The radiative neutron capture cross section for 153 Sm with the half-life of 1.928 d is deduced with the γ -ray strength function method.

Gamma-Beams at the HIγS facility in the USA and anticipated at the ELI-NP facility, now constructed in Romania, present unique new opportunities to advance research in nuclear astrophysics; not the least of which is resolving open questions in oxygen formation during stellar helium burning via a precise measurement of the 12 C(α, γ) reaction. Time projection chamber (TPC) detectors operating with low pressure gas (as an active target) are ideally suited for such studies. We review the progress of the current research program and plans for the future at the HIγS facility with the optical readout TPC (O-TPC) and the development of an electronic readout TPC for the ELI-NP facility (ELITPC).

No abstract

No abstract

The γ-ray strength functions and level densities of 73,74 Ge have been extracted up to the neutron separation energy S n from particle-γ coincidence data using the Oslo method. Moreover, the γ-ray strength function of 74 Ge above S n has been determined from photo-neutron measurements; hence these two experiments cover the range of E γ ≈ 1-13 MeV for 74 Ge. The obtained data show that both 73,74 Ge display an increase in strength at low γ energies. The experimental γ-ray strength functions are compared with M1 strength functions deduced from average B(M1) values calculated within the shell model for a large number of transitions. The observed low-energy enhancements in 73,74 Ge are adopted in the calculations of the 72,73 Ge(n,γ) cross sections, where there are no direct experimental data. Calculated reaction rates for more neutron-rich germanium isotopes are shown to be strongly dependent on the presence of the low-energy enhancement.