Photoneutron cross-section measurements in the Bi209 ( γ,xn ) reaction with a new method of direct neutron-multiplicity sorting

Abstract

Photoneutron cross sections were measured in the 209 Bi(γ , xn) reaction with x = 1-4 at energies from the neutron threshold to 40 MeV using quasimonochromatic laser Compton-scattering γ-ray beams. A novel technique of direct neutron-multiplicity sorting with a flat-efficiency detector was used. Results are compared with the positron in-flight annihilation data of Livermore and Saclay as well as with bremsstrahlung data. The present neutron yields are consistent with the latest photoactivation measurement with bremsstrahlung. The giant dipole resonance component of the total photoneutron cross section is reasonably reproduced by model calculations of the Hartree-Fock Bogoliubov plus quasiparticle random phase approximation based on the Gogny D1M interaction for both E1 and M1 components. In contrast, the quasideuteron component of the total photoneutron cross section requires a factor of ∼3 enhancement of the Levinger parameter. Furthermore, a survival of large (γ,n) cross sections above 20 MeV may indicate the surface effect on the two-component particle-hole state density. The threshold behavior of photoneutron emission is discussed in terms of the average neutron kinetic energy.

Photoneutron Cross-section Measurements for $^{165}$Ho by the Direct Neutron-Multiplicity Sorting at NewSUBARU

“…A new direct neutron multiplicity sorting method which employs a constant neutron detection efficiency system has been developed for IAEA-CRP F41032 on Photonuclear Data and Photon Strength Functions. The first measured test case was 209 Bi nucleus [4] and the measurements continued for 197 Au, 169 Tm, 89 Y, 181 Ta, 165 Ho, 59 Co, 159 Tb, 139 La, 103 Rh.…”

“…The DNM method is based on the constant neutron detection efficiency with no dependence on the energy of the neutrons. The method, with a recently developed detector, was applied for the first time to 209 Bi [4] at the experimental hutch GACKO of the laser-Compton scattering (LCS) γ-ray beam line of the NewSUBARU synchrotron radiation facility [5].…”

E1moments from a coherent set of measured photoneutron cross sections

“…Above the 2n threshold, LCS γ -ray beams were produced with 532 nm photons. The first measurement for 209 Bi [13,14], was limited by the minimum operating frequency 16 kHz of the INAZUMA laser; the INAZUMA laser was operated in the second harmonics (532 nm) at 16.66 kHz to produce LCS γ -ray beams with 60 μs pulse intervals. The laser frequency was downscaled by blocking seven out of eight consecutive laser pulses with a Pockels cell and a polarizer to extend the pulse interval to 480 μs.…”

“…Photoneutron cross sections (γ , xn) with x = 1-4 were recently measured for ten odd-even nuclei at energies ranging between the neutron threshold and 40 MeV using quasimonochromatic laser Compton-scattering (LCS) γ -ray beams [13][14][15]. A new method of direct neutron multiplicity sorting was applied [16], which, in combination with several to tens of MeV LCS γ -ray beams, allows complete mapping of the photoneutron reaction cross sections within the GDR energy range.…”

Photoneutron measurements in the GDR region at ELI-NP

“…Total and partial cross section of (γ,xn) with x=1,...,4 for 209 Bi, 9 Be, 197 Au, 169 Tm, 89 Y, 181 Ta, 165 Ho, 59 Co , 159 Tb, 139 La, 103 Rh were measured. First case for 209 Bi nucleus was already published [34]. Finally, commissioning experiment of ELIGANT-TN array was performed at IFIN-HH using (p,n) monitoring reaction at nat Cu and nat Al (T. Ronsetrom et al).…”