S. Amano

Performance measurement of HARPO: A time projection chamber as a gamma-ray telescope and polarimeter

Abstract We analyse the performance of a gas time projection chamber (TPC) as a high-performance gamma-ray telescope and polarimeter in the e + e − pair-creation regime. We use data collected at a gamma-ray beam of known polarisation. The TPC provides two orthogonal projections (x, z) and (y, z) of the tracks induced by each conversion in the gas volume. We use a simple vertex finder in which vertices and pseudo-tracks exiting from them are identified. We study the various contributions to the single-photon angular resolution using Monte Carlo simulations, compare them with the experimental data and find that they are in excellent agreement. The distribution of the azimuthal angle of pair conversions shows a bias due to the non-cylindrical-symmetric structure of the detector. This bias would average out for a long duration exposure on a space mission, but for this pencil-beam characterisation we have ensured its accurate simulation by a double systematics-control scheme, data taking with the detector rotated at several angles with respect to the beam polarisation direction and systematics control with a non-polarised beam. We measure, for the first time, the polarisation asymmetry of a linearly polarised gamma-ray beam in the low energy pair-creation regime. This sub-GeV energy range is critical for cosmic sources as their spectra are power laws which fall quickly as a function of increasing energy. This work could pave the way to extending polarised gamma-ray astronomy beyond the MeV energy regime.

Development of a high repetition rate Nd:YAG slab laser and soft X-ray generation by cryogenic target

Abstract High repetition (320 pps), high average power (100 W) pulse Nd:YAG slab laser has been developed for x-ray driver. A strong X-ray emission around 10.8 nm, which wavelength is attractive for x-ray projection lithography, was generated from cryogenic Xe targets pumped by this laser pulses. CO2 and H2O were also tested for cryogenic targets and we found that the emission intensity from Xe around this wavelength region was at least 10 times higher than that from H2O, CO2.

Studies on cryogenic Xe capillary jet target for laser-produced plasma EUV-light source

In this paper, characterizations of a cryogenic Xe capillary jet target for a laser-produced plasma extreme ultraviolet (EUV) light source are reported. The capillary jet target is a candidate of fast-supplying targets for mitigating debris generation and target consumption in a vacuum chamber without reducing the EUV conversion efficiency. Xe capillary jets (jet velocity ~ 0.4 m/s) were generated in vacuum by using annular nozzles chilled to ~ 170 K at a Xe backing pressure of ~ 0.7 MPa. Forming mechanisms of the capillary jet targets were studied by using numerical calculations. Furthermore, laser-produced plasma EUV generation was performed by irradiating a Nd:YAG laser (1064 nm, ~ 0.5 J, 10 ns, 120 μmφ, ~ 4×1011 W/cm2) on a Xe capillary jet target (outer / inner diameter = 100 / 70 μmφ). The angular distribution of EUV generation was approximately uniform around the Xe capillary jet target, and the peak kinetic energy of the fast-ions was evaluated to be ~ 2 keV.

Experiment on Gamma Ray Generation by Laser Compton Scattering

A gamma ray generation facility was developed through laser Compton scattering on an electron beam storage ring, for the purpose of researching nuclear transmutation. Theoretical analysis on gamma ray yield and energy spectrum was performed, as well as EGS4 simulation code was employed to simulate the interaction of gamma ray and Ge detector. The acquired experimental results are in agreement with theory.

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.

Study of [sup 12]C(γ, 2α)[sup 4]He 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.

Study of {sup 12}C({gamma}, 2{alpha}){sup 4}He 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.