Takeo Kondo

Photoneutron Cross Sections for Au Revisited: Measurements with Laser Compton Scattering γ-Rays and Data Reduction by a Least-Squares Method

Photoneutron cross section measurements were made for Au in the entire energy range of the (γ,n) channel based on a direct neutron counting with quasi-monochromatic γ-rays produced in inverse Compton scattering of laser photons with relativistic electrons. The data were analyzed by a least-squares method to deduce photoneutron cross sections. The analysis significantly reduced experimental uncertainties compared with those resulting from the photon difference method. The result is compared with the previous data by direct neutron counting with γ-rays produced in positron annihilation in flight and by photoactivation with bremsstrahlung. The present data are in good agreement with the previous data near the neutron threshold, while there remain some discrepancies between the present and the previous data above 10 MeV.

Pygmy dipole resonance and dipole polarizability in 90Zr

Electric dipole (E1) reduced transition probability B(E1) of 90Zr was obtained by the inelastic proton scattering near 0 degrees using a 295 MeV proton beam and multipole decomposition analysis of the angular distribution by the distorted-wave Born approximation with the Hartree-Fock plus random-phase approximation model and inclusion of El Coulomb excitation, and the E1 strength of the pygmy dipole resonance was found in the vicinity of the neutron threshold in the low-energy tail of the giant dipole resonance. Using the data, we plan to determine the precise dipole polarizability αD which is defined as an inversely energy-weighted sum value of the elecrric dipole strength. The dipole polarizability is expected to constrain the symmetry energy term of the neutron matter equation of state. Thus systematical measurement of the dipole polarizability is important.

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.

PHOTONEUTRON CROSS SECTIONS FOR Au

Photoneutron cross sections were measured for Au in the entire energy range of the (γ,n) channel based on a direct neutron‐counting technique with quasimonochromatic γ rays produced in inverse Compton‐scattering of laser photons with relativistic electrons. We present results of the measurement in comparison with the past data.

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[6.5×106 y] obtained with the γSF method.

Determination of photoneutron cross sections for [sup 197]Au by using laser inverse-Compton scattering gamma-rays

We measured photoneutron cross sections for 197Au with quasi‐monochromatic laser inverse‐Compton scattering gamma rays. We present results of the measurement in comparison with the existing data.We measured photoneutron cross sections for 197Au with quasi‐monochromatic laser inverse‐Compton scattering gamma rays. We present results of the measurement in comparison with the existing data.

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 L = 1 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.