C. Iwamoto

Striking behavior of photoneutron cross sections for 90Zr near threshold

Photoneutron cross sections for 90Zr near neutron threshold were examined with a photon difference technique using laser Compton scattering γ‐ray beams. The cross section decreasing in the vicinity of neutron threshold exhibited a steep rise within 150 keV above the threshold. We draw attention to a possible relation of this striking behavior to the 3P valence neutron resonance known in neutron capture in the mass region A≈90.

THE γSF method

The γ‐ray strength function (γSF) interconnects radiative neutron capture and photoneutron emission as a common ingredient in the statistical model. Outlined here is an indirect method of determining radiative neutron‐capture cross sections for unstable nuclei based on the γ‐ray strength function. Application examples of the γSF method are demonstrated.

APPLICATION OF THE γSF METHOD TO PALLADIUM

Photoneutron cross sections were measured for 108Pd, 106Pd, and 105Pd with laser‐Compton scattering γ‐ray beams in an application of the γSF method to a radioactive nucleus 107Pd. We present radiative neutron cross sections for 107Pd[6.5×106u2009y] obtained with the γSF method.

Threshold photoneutron cross sections for {sup 208,207,206}Pb isotopes

Photoneutron cross sections for three Pb isotopes (206Pb, 207Pb, 208Pb) near neutron threshold were measured with the laser inverse‐Compton scattering gamma rays at the National Institute of Advanced Industrial Science and Technology. The cross section data are presented.

M1 and E1 transition cross sections in D(y→,n) reactions near reaction threshold

M1 and E1 transition cross sections in the D(y→, n) reaction were separately determined by measuring the analyzing power for emitted neutrons with linearly‐polarized γ rays at four energies between 2.26 MeV and 3.70 MeV near reaction threshold at 2.224 MeV. We compared the experimental result with the JENDL evaluated data.

Extra γ-ray strength for 116,117Sn arising from pygmy dipole resonance

Photoneutron cross sections were measured for 117Sn and 116Sn near neutron thresholds with quasi‐monochromatic laser Compton scattering γ‐rays. The measured cross sections for 117Sn and 116Sn are strongly enhanced from the threshold behavior expected for Lu2009=u20091 neutron emissions after E1 photoexcitation. This suggests the presence of extra γ‐ray strength in the low‐energy tail of the giant dipole resonance. The present cross sections were analyzed together with radiative neutron capture cross sections for 116Sn within the framework of the statistical model calculation. It is shown that the extra γ‐ray strength can be interpreted as pygmy E1 resonance which was previously reported in the nuclear resonance fluorescence experiment for 116Sn and 124Sn.