Precise determination of neutron beam polarization at 16 MeV

Abstract

A 16 MeV polarized-n-beam was produced by H-2(polarized-d,polarized-n)He-4 reaction at E(sub d) = 13.15 MeV, and the polarized-n-beam polarization was determined using the polarized-n + He-4 scattering. As for the gas cell for (H-2)2 target, the thickness of Ta window foils for the beam entrance and exit was increased from three to five micrometer so as to increase the (H-2)2 gas pressure from three to five atm. The pressure of the He-3 target gas was also raised from 1.5 to 2.5 atm. The He-4 target was liquid, and worked as a scintillator. Increase of the n-beam energy from 12 MeV to 16 MeV has caused two problems. One problem was a large increase of the n- and gamma-ray-fluxes, and another problem was the absolute determination of the polarized-n-beam polarization. The reasons of the increase of fluxes and the ways to reduce the fluxes have been discussed. Related to the absolute determination of the n-beam polarization, a modified phase shift analysis method was worked out, and the result of modified phase shift analysis curve was shown in a figure.

16MeVの偏極中性子ビームをE(sub d)=13.15MeVの時のH-2(polarized d,polarized n)He-4反応から生成し、偏極n+He-4散乱を用いて偏極中性子ビーム偏極を測定した。(H-2)2ターゲット用の気体セルについては、(H-2)2気体圧力を3気圧から5気圧に増やすために、ビームの入口および出口窓のTa箔の厚さを3マイクロメートルから5マイクロメートルに増やした。He-3ターゲット気体の気圧も1.5から2.5気圧に上げた。He-4ターゲットは液体で、シンチレータの役を果たした。中性子ビームの12Mevから16MeVへの増加は2つの問題を生じた。ひとつは、中性子線束とγ線束の大幅な増大であり、もうひとつは偏極中性子ビーム偏極の絶対測定であった。流束増大の原因と低減法を論じた。中性子ビーム偏極の絶対測定に関しては、変形位相シフト解析法を案出し、変形位相シフト解析曲線の結果を図示した。