Search

Photoneutron reactions on 208Pb in the Giant Dipole Resonance (GDR) energy range have been investigated at the γ-ray beam line of the NewSUBARU synchrotron radiation facility in Japan. Making use of quasi-monochromatic laser Compton scattering (LCS) γ-ray beams and of a novel flat-efficiency neutron detection system along with associated neutron-multiplicity sorting method, total and partial (γ,xn) photoneutron cross sections with x = 1 to 4 have been measured for 208Pb in a broad energy range covering the neutron threshold up to 38 MeV.

The Coordinated Research Project (CRP) with the code F41032 has been launched by the International Atomic Energy Agency (IAEA) in 2016 as a 5-year project with the scientific goal being two-fold: 1) updating the 2000 photonuclear data library and 2) constructing a reference database of photon strength functions. We report the experimental technique and methodology used for the former goal and selected giant-dipole resonance (GDR) data updated in the IAEA-CRP.

The well-known problem of noticeable disagreements between photoneutron cross sections from various experiments was discussed in detail for 209Bi. Data for partial photoneutron reactions cross sections obtained at Livermore (USA) using quasimonoenergetic annihilation photons and the method of neutron multiplicity sorting were analyzed using the objective physical criteria and the experimental-theoretical method for evaluation. Because of significant systematic uncertainties involved in the method for determining the neutron multiplicity, experimental data do not satisfy the criteria of reliability and differ noticeably from the evaluated data. The new experimental data for 209Bi (γ, in) reactions with i = 1–4 were obtained using quasimonochromatic laser Compton-scattering (LCS) γ-ray beams at the NewSUBARU synchrotron radiation facility and the novel technique of direct neutron-multiplicity sorting with a flat-efficiency detector. It was found that new σ(γ, 1n), σ (γ, 2n), and σ (γ, 3n) contradict noticeably to the Livermore data. It was shown that at the same time the new 209Bi photoneutron cross-sections are in good agreement with data evaluated using experimental-theoretical method and assuring the reliability of those.

We discuss the role of photoneutron reaction data in nuclear physics and astrophysics in conjunction with the Coordinated Research Project of the International Atomic Energy Agency with the code F41032 (IAEA-CRP F41032).

New data of total and partial (γ,xn) cross sections with x = 1–3 are proposed to be measured by direct neutron multiplicity sorting using Laser Compton scattering (LCS) gamma ray beams at the ELI-NP to solve long standing discrepancies between existing Lawrence Livermore National Laboratory (USA) and France Centre d'Etudes Nucleaires de Saclay photonuclear data. Pioneering experiments are currently performed at the NewSUBARU facility. We present here preliminary results on 209Bi(g,xn) cross section measurements.

We discuss the γ-ray strength function toward a unified understanding of (γ,n) and (n,γ) reactions and propose a novel technique of direct neutron-multiplicity sorting to resolve the long-standing discrepancy between the Livermore and Scalya data of partial photoneutron cross sections.