Ken Horikawa

Resonant Photonuclear Reactions for Isotope Transmutation

Resonant photonuclear isotope transmutation (RPIT) is shown to be very powerful to produce exclusively radioactive isotopes (RIs) by resonant photonuclear (γ,n) and (γ,2n) reactions via E1 giant resonances. Photons to be used are medium energy [ E (γ) ≈12–25 MeV] photons produced by laser photons backscattered off GeV electrons. The cross sections are as large as σ≈0.2–0.5 b (10 -24 cm 2 ) for all medium-heavy nuclei. A large fraction (∼3%) of photons is effectively used for the photonuclear reactions, while the scattered GeV electrons remain in most storage rings to be re-used. To demonstrate the RPIT feasibility, 99 Mo/ 99 m Tc and 196 Au RIs were produced by RPIT on 100 Mo and 197 Au with laser photons scattered off 1 GeV electrons at the NewSUBARU storage ring. RPIT with medium energy photons around 10 12–15 /s provides specific/desired RIs with the rate of 10 10–13 /s and the RI density around 0.05–50 G Bq/mg for nuclear science, molecular biology and for nuclear medicines.

Absolute calibration of imaging plate for GeV electrons

An imaging plate has been used as a useful detector of energetic electrons in laser electron acceleration and laser fusion studies. The absolute sensitivity of an imaging plate was calibrated at 1 GeV electron energy using the injector Linac of SPring-8. The sensitivity curve obtained up to 100 MeV in a previous study was extended successfully to GeV range.

Iodine Transmutation through Laser Compton Scattering Gamma Rays

Research on laser Compton scattering gamma-ray-based nuclear transmutation has been carried out to identify a method of reducing the hazards of long-lifetime radioactivity of nuclear waste. To study the photonuclear reaction experimentally, a laser Compton scattering gamma-ray facility was built on a storage ring at NewSUBARU and ~17MeV gamma-ray photons were produced. An investigation on the reaction rate of radioactive iodine waste was carried out. Based on the characteristics of laser Compton scattering gamma rays, a cylindrical target was adopted for the irradiation experiment. The radioactivity of the irradiated target was measured and the transmutation reaction rate was deduced. Experimental results were close to simulation findings.

Half-life of {sup 184}Re populated by the ({gamma},n) reaction from laser Compton scattering {gamma} rays at the electron storage ring NewSUBARU

We report a half-life of the ground state of {sup 184}Re populated by the {sup 185}Re({gamma},n){sup 184}Re reaction from laser Compton scattering {gamma} rays generated through relativistic engineering. The {gamma} rays are provided at the electron storage ring NewSUBARU. The previous experiment using deuteron-induced reactions has yielded a recommended half-life of the 3{sup -} ground state of {sup 184}Re of 38.0{+-}0.5 d, including a possible contribution from the 8{sup +} isomer (T{sub 1/2}=169{+-}8 d) of {sup 184}Re since the presence of the isomer was not known at that time. In contrast, the ({gamma},n) reaction has an advantage to selectively populate the ground state because this reaction does not bring large angular momentum. The measured half-life of 35.4{+-}0.7 d is shorter than the previous half-life by about 7%. This difference is crucial for applications using the activation method.

Absolute calibration of imaging plate for electron spectrometer measuring GeV-class electrons

An electron spectrometer (ESM) using imaging plate (IP) is designed and tested to measure relativistic electrons which are generated from laser-plasma interactions. The measurable energy range extends to 1 GeV or even higher. The absolute sensitivity of IP for 1 GeV electrons was calibrated using electrons from Linac in SPring-8. An IP has enough sensitivity for 1-GeV electrons. The electron spectrometer, which is measurable to ~ 1 GeV, has been developed using IP detector.

Experimental Study of Nuclear Astrophysics with Photon Beams

Information on the photonuclear reactions in the energy region below the E1 giant resonances is vital for understanding astrophysical processes relevant to nucleosynthesis. Several topics from recent experimental studies of the photonuclear reactions with a high‐quality monochromatic γ‐ray beam will be presented.

Experiment on Iodine transmutation by laser Compton scattering gamma ray

A laser Compton scattering gamma-ray based nuclear transmutation is proposed to reduce the hazards of long-lived activity nuclear waste. In accordance with this proposal, a laser Compton scattering gamma-ray facility has been built on NewSUABARU storage ring. The facility provides 17.6 MeV gamma-ray photons, which is applicable to the nuclear transmutation research. In order to investigate the reaction rate of Iodine material, the 23Na127I target is adopted for the irradiation experiment. The results show that the experimental data is close to the simulation result.

New probe to Ml strengths in GDR region for supernova neutrino interactions

The Ml strength (or level density of 1+ states) is of importance for estimation of interaction strengths between neutrinos and nuclei for the study of the supernova neutrino- process. We have proposed a method using (γ, n) reactions with linear polarized laser Compton scattering γ-rays to measure Ml strength. In 1957, Agodi predicted theoretically angular distribution of neutrons emitted from states excited via dipole transitions with linearly polarized γ-ray beam at the polar angle of 8=90° can be described by a simple function, a + b cos(θ2), where θ is azimuthal angel. However, this theoretical prediction has not been verified over the wide mass region. We have measured neutron angular distributions with (polarized gamma, n) reactions on Au, NaI, and Cu. We have verified the Agodis prediction for the first time over the wide mass region. This suggests that (polarized gamma, n) reactions may be useful tools to study Ml strength in giant resonance regions.

New probe of M1 and E1 strengths in GDR regions

The M1 strengths (or level density of 1+ states) are of importance for estimation of interaction strengths between neutrinos and nuclei for the study of the supernova neutrino-process. In 1957, Agodi predicted theoretically angular distribution of neutrons emitted from states excited via dipole transitions with linearly polarized gamma-ray beam at the polar angle of θ=90° should be followed by a simple function, a + b cos(2φ), where φ, is azimuthal angel. However, this theoretical prediction has not been verified over the wide mass region except for light nuclei as deuteron. We have measured neutron angular distributions with (polarized gamma, n) reactions on Au, Nal, and Cu. We have verified the Agodis prediction for the first time over the wide mass region. This suggests that (polarized gamma, n) reactions may be useful tools to study M1 strengths in giant resonance regions.

Study of 12C(γ, 2α)4He with NewSUBARU laser Compton scattered gamma‐ray beam

The 16O(γ, 2α)4He reaction cross section was measured in the γ‐ray energy range from 16 MeV up to 39 MeV using an active target method and a quasi‐monochromatic γ‐ray beam provided at the Laboratory of Advanced Science and Technology for Industry (LASTI) of the University of Hyogo. The cross section is found to be rather small in the energy region corresponding to the 2+ and 4+ excited states of the intermediate 8Be nucleus, while it becomes large above the energy corresponding to the 8Be 1− state, being in contrast to the latest result reported by Afanas’ev and Khodyachikh. The present result suggests the cross sections are dominated by the contributions of the 1− states in 12C which are excited with the E1 transition.