166
H. Utsunomiya et al.
Physics (ELI-NP), “Horia Hulubei” National Institute for Physics and Nuclear
Engineering (IFIN-HH), Skobeltsyn Institute of Nuclear Physics of Lomonosov
Moscow State University (SINP-MSU), and Shanghai Institute of Applied Physics
(SINAP). The new data acquired are classified into two groups, (γ,xn) cross section
data with x = 1–4 for 11 nuclei with 100% natural abundances at γ-ray energies
from 1n threshold up to 40 MeV and (γ, n) cross section data for 21 enriched
isotopes at energies below 2n thresholds. The construction of γSFs was carried out
in collaboration with the Université Libre de Bruxelles (ULB).
2 Key Technical Factors
2.1 Laser Compton-Scattering γ -Ray Beam
Quasi-monochromatic pencil-like γ-ray beams are produced in the head-on collision
of laser photons from relativistic electrons circulating in the NewSUBARU storage
ring. Both INAZUMA (1064 nm) and Talon (532 nm) Q-switch lasers are used
to produce quasi-monochromatic pulsed γ-ray beams that are energy-tunable from
4.5 to 76 MeV in collision with electrons from 0.5 to 1.5 GeV. The electron
beam is energy-calibrated with the accuracy on the order of 10 −5 [2]. The electron
beam energy is precisely reproduced by the automated control of the beam optics
parameters. The γ-ray energy is determined by the calibrated electron beam energy.
The energy profile of the γ-ray beam is determined by reproducing the response
function of a 3.5” x 4.0” LaBr 3 (Ce) detector to the laser Compton-scattering
(LCS) γ-rays with the GEANT4 code which incorporates the kinematics of the
LCS process and interactions between the γ-rays and the LaBr 3 (Ce) detector. The
LCS γ-ray beam is accompanied by a low-energy tail unique to the electron beam
emittance and the collimator size. The energy spread for the standard emittance and
a collimator of 2 mm aperture located at 18.5 m from the most efficient collision
point is typically a few % in the full width at half maximum. The beam size on
target approximately follows the geometrical aperture of the collimator with respect
to the collision point.
The γ-ray flux is accurately determined from the pile-up/multi-photon spectrum
with the Poisson-fitting method [3, 4] based on the fact that the number of photons
involved in a γ-pulse follows the Poisson distribution.
2.2 Direct Neutron-Multiplicity Sorting
The Talon laser is operated at 1 kHz to produce a pulsed γ-ray beam that offers 1 ms
pulse intervals during which one can identify multi-neutron coincidence events with
a moderator-based slow neutron detector. We have developed a neutron detector
H. Utsunomiya et al.
Physics (ELI-NP), “Horia Hulubei” National Institute for Physics and Nuclear
Engineering (IFIN-HH), Skobeltsyn Institute of Nuclear Physics of Lomonosov
Moscow State University (SINP-MSU), and Shanghai Institute of Applied Physics
(SINAP). The new data acquired are classified into two groups, (γ,xn) cross section
data with x = 1–4 for 11 nuclei with 100% natural abundances at γ-ray energies
from 1n threshold up to 40 MeV and (γ, n) cross section data for 21 enriched
isotopes at energies below 2n thresholds. The construction of γSFs was carried out
in collaboration with the Université Libre de Bruxelles (ULB).
2 Key Technical Factors
2.1 Laser Compton-Scattering γ -Ray Beam
Quasi-monochromatic pencil-like γ-ray beams are produced in the head-on collision
of laser photons from relativistic electrons circulating in the NewSUBARU storage
ring. Both INAZUMA (1064 nm) and Talon (532 nm) Q-switch lasers are used
to produce quasi-monochromatic pulsed γ-ray beams that are energy-tunable from
4.5 to 76 MeV in collision with electrons from 0.5 to 1.5 GeV. The electron
beam is energy-calibrated with the accuracy on the order of 10 −5 [2]. The electron
beam energy is precisely reproduced by the automated control of the beam optics
parameters. The γ-ray energy is determined by the calibrated electron beam energy.
The energy profile of the γ-ray beam is determined by reproducing the response
function of a 3.5” x 4.0” LaBr 3 (Ce) detector to the laser Compton-scattering
(LCS) γ-rays with the GEANT4 code which incorporates the kinematics of the
LCS process and interactions between the γ-rays and the LaBr 3 (Ce) detector. The
LCS γ-ray beam is accompanied by a low-energy tail unique to the electron beam
emittance and the collimator size. The energy spread for the standard emittance and
a collimator of 2 mm aperture located at 18.5 m from the most efficient collision
point is typically a few % in the full width at half maximum. The beam size on
target approximately follows the geometrical aperture of the collimator with respect
to the collision point.
The γ-ray flux is accurately determined from the pile-up/multi-photon spectrum
with the Poisson-fitting method [3, 4] based on the fact that the number of photons
involved in a γ-pulse follows the Poisson distribution.
2.2 Direct Neutron-Multiplicity Sorting
The Talon laser is operated at 1 kHz to produce a pulsed γ-ray beam that offers 1 ms
pulse intervals during which one can identify multi-neutron coincidence events with
a moderator-based slow neutron detector. We have developed a neutron detector