• PDF / 510,280 Bytes
• 4 Pages / 612 x 792 pts (letter) Page_size
• 78 Downloads / 153 Views

DOWNLOAD

REPORT

---

evelopment of an in Situ 3He NSF Using SEOP Technique with an Evaluation System for the Pulsed Neutron Source T. Okudairaa, *, T. Okua, K. Sakaia, T. Inob, H. Hayashidac, K. Hiroia, T. Shinoharaa, K. Kakuraic, and K. Aizawaa aJ-PARC

center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan c Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki 319-1106, Japan *e-mail: [email protected] b

Received July 7, 2019; revised August 30, 2019; accepted September 10, 2019

Abstract—A 3He spin filter is a useful device for polarizing a neutron beam. We are developing the 3He spin filters for users of the material and life science facility of the Japan Proton Accelerator Research Complex (J-PARC). An in situ SEOP system with a 3He polarization evaluation system using nuclear magnetic resonance (NMR) method of adiabatic fast passage and electron paramagnetic resonance (EPR) was developed. We conducted an experiment on the neutron beam line BL10 (NOBORU) of J-PARC to confirm the consistency of 3He polarization, estimated using the neutron transmission, NMR and EPR. The polarization of 3He, evaluated using the different methods, was consistent and the evaluation system operated normally for about 6 h. Keywords: neutron instrument, 3He spin filter DOI: 10.1134/S1027451020070356

INTRODUCTION Spin filters utilizing polarized 3He gas are widely used to obtain polarized neutron beams in a wide energy range due to the large spin-dependent crosssection for neutron absorption by 3He nuclei [1]. We employ the Spin Exchange Optical Pumping (SEOP) method [2] to polarize 3He nuclei. 3He gas, N2 gas, and pure Rb or Rb and K are encapsulated in a boronfree glass cell. The 3He nucleus is polarized upon collision with an alkali atom polarized by the laser irradiation. Since the relaxation time of 3He polarization is several hundred hours after the cessation of laser irradiation, a laser system that can polarize 3He while conducting a neutron experiment is sometimes used to obtain stable neutron polarization over a long period of time. This method is called the in situ SEOP method. There are several methods to evaluate the 3He polarization. Since the neutron transmission of a 3He cell depends on the 3He polarization, a relative measurement of the neutron transmission through the an unpolarized and polarized 3He cell will determine the 3He polarization [3]. The electron paramagnetic resonance (EPR) method is also used for polarimetry [4]. The energy level of Rb electrons is shifted due to the

magnetic field created by the 3He polarization. The energy level shift is measured by detecting the de-excitation light emitted by applying an oscillating magnetic field corresponding to the energy level. The nuclear magnetic resonance (NMR) method of adiabatic fast passage (AFP) is used to flip the 3He spin and also to evaluate the 3He polarization by detecting the variation of the magneti