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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The MajoranaDemonstratorwill search for the neutrinoless double-beta(ββ0ν)decay of the isotopeGe with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate that the neutrino is its own antiparticle, demonstrate that lepton number is not conserved, and provide information on the absolute mass scale of the neutrino. The Demonstratoris being assembled at the 4850-foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be situated in a low-background environment and surrounded by passive and active shielding. Here we describe the science goals of the Demonstratorand the details of its design.

The gamma strength function and level density of 1^{-} states in ^{96}Mo have been extracted from a high-resolution study of the (p[over →], p[over →]^{'}) reaction at 295 MeV and extreme forward angles. By comparison with compound nucleus γ decay experiments, this allows a test of the generalized Brink-Axel hypothesis in the energy region of the pygmy dipole resonance. The Brink-Axel hypothesis is commonly assumed in astrophysical reaction network calculations and states that the gamma strength function in nuclei is independent of the structure of the initial and final state. The present results validate the Brink-Axel hypothesis for ^{96}Mo and provide independent confirmation of the methods used to separate gamma strength function and level density in γ decay experiments.

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.

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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.

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