We have performed for the first time the simultaneous measurement of the two-body and threebody photodisintegration cross-sections of 4 He in the energy range from 21.8 to 29.8 MeV using monoenergetic pulsed photons and a 4π time projection chamber containing 4 He gas as an active target in an event-by-event mode. The photon beam was produced via the Compton backscattering of laser photons with high-energy electrons. The 4 He(γ,p) 3 H and 4 He(γ,n) 3 He cross sections were found to increase monotonically with energy up to 29.8 MeV, in contrast to the result of a recent theoretical calculation based on the Lorentz integral transform method which predicted a pronounced peak at around 26−27 MeV. The energy dependence of the obtained 4 He(γ,n) 3 He cross section up to 26.5 MeV is marginally consistent with a Faddeev-type calculation predicting a flat pattern of the excitation function. The cross-section ratio of 4 He(γ,p) 3 H to 4 He(γ,n) 3 He is found to be consistent with the expected value for charge symmetry of the strong interaction within the experimental uncertainty in the measured energy range. The present results for the total and two-body crosssections of the photodisintegration of 4 He are compared to previous experimental data and recent theoretical calculations.

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Spin-flip M1 strengths in 208 Pb have been measured in photon scattering experiments with a quasimonochromatic, linearly polarized photon beam. The data resolve an M1 giant resonance into at least seven, possibly eight, discrete transitions at excitation energies between 7.1 and 7.4 MeV below the neutron separation energy. The M1 strengths are measured with uncertainties considerably smaller than those in a previous study, which leads to a reexamination of the total strength. Experimental results are compared with an estimation of self-consistent random phase approximation using a semirealistic interaction.

New measurements of the photoneutron reaction on 181 Ta have been conducted with the AIST-LCS ͑laser Compton scattering͒ beam in the 7.8ՇE͓MeV͔Շ12 energy range. The major advantage of the present ␥-ray experiment is its intense peaking in the energy window of astrophysical interest, i.e., close to the neutron threshold. Details on photon beams from the laser Compton scattering, neutron counting, and experimental determination of the 181 Ta photoneutron cross section are given. The present experimental data are in good agreement with the IAEA evaluation. Reaction rate calculations in the Hauser-Feshbach statistical model are performed and confronted with the experimental data. The data provide constraints on the low-energy tail of the dipole strength function. It is found that among the three different models for the E1-strength considered, only the microscopic quasiparticle random phase approximation model can reproduce the extra strength observed in the 181 Ta(␥,n) 180 Ta reaction at energies of about 8.5 MeV. Such an experiment helps to improve the determination of the corresponding stellar photodisintegration rate of

Photoneutron cross sections were measured for 94 Mo, 95 Mo, 96 Mo, 97 Mo, 98 Mo, and 100 Mo near the neutron threshold with quasi-monochromatic laser-Compton scattering γ rays. The photoneutron data were analyzed with the Skyrme Hartree-Fock-Bogoliubov (HFB) plus quasiparticle random phase approximation (QRPA) model and the axially symmetric-deformed Gogny HFB plus QRPA model of E1 γ -ray strength. Combining the γ -ray strength function constrained by the present photoneutron data with either the nuclear resonance fluorescence data or the updated Oslo data to supplement the data below the neutron threshold, a thorough analysis of the reverse (n,γ ) cross sections is made whenever measurements are available. The Oslo data and the corresponding uncertainties are updated based on the latest results of the s-wave neutron spacing and the average radiative width determined in particular for 96 Mo. Finally, radiative neutron capture cross sections for two radioactive nuclei, 93 Mo and 99 Mo, are deduced with the γ -ray strength function method.