Characterization of glasses for 3 He neutron spin filter cells Y. Sakaguchi a,n , H. Kira a , T. Oku a , T. Shinohara a , J. Suzuki a , K. Sakai a , M. Nakamura a , K. Suzuya a , M. Arai a , M. Takeda a , S. Wakimoto a , D. Yamazaki a , S. Koizumi a , Y. Endoh a , K. Kakurai a , Y. Arimoto b , T. Ino b , H.M. Shimizu b , T. Kamiyama b , K. Ohoyama c , H. Hiraka c , K. Tsutsumi d , K. Yamada e , L.J. Chang a,f a Japan Atomic Energy Agency, Tokai-mura, Ibaraki 319-1195, Japan b High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba 305-0801, Japan c Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan d Graduate School of Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan e WPI-Advanced Institute for Materials Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan f Nuclear Science and Technology Development Center, National Tsing Hua University, Taiwan article info Available online 8 July 2010 Keywords: 3 He polarization Neutron spin filter Glasses abstract Polarized 3 He neutron spin filters are suitable devices for polarizing neutrons at spallation neutron facilities because of the wide coverage in energy range and the large solid-angles. The glass cell plays an important role in the 3 He spin filters. In order to get good quality of glass cells, the investigation on the microscopic structure would be helpful. In this paper, we report on the results of X-ray diffraction for several glasses. We observed a correlation between the position of the first peak and the helium permeation velocity. We also observed a small difference in the diffraction curve among GE180 glasses with different thermal treatment. Desirable structure for 3 He spin filters is discussed. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Recently, a new spallation neutron facility in Japan, named Japan Proton Accelerator Research Complex, Japan, has started. Since it provides intensive pulsed neutrons, one can expect that polarized neutron scattering experiments, which have been suffering from weak scattered intensity, will be more available and the demand for the experiments is becoming higher and higher. Among existing neutron polarizers, polarized 3 He neutron spin filters are encouraged to be used in the spallation neutron facility because they can cover wide energy range including neutrons higher than 100 meV and they have large solid-angles, although the operation is not so easy. Polarized 3 He neutron spin filters use very high spin-dependent neutron capture cross- section of 3 He gas and the 3 He nuclei can be polarized by optical pumping. In order to obtain high 3 He polarization and its long relaxation time, the production of glass cells is very important. There are several requirements for 3 He spin filters. Since we use the cells for neutron scattering experiments, it is not preferable to add boron, which is a strong neutron absorber, in glasses. Magnetic impurity should be as small as possible because it causes 3 He depolarization. Sufficiently low 3 He permeability is required for long term operation at elevated temperature in the spin-exchange optical pumping (SEOP) technique. The interactions of fluid atoms contain- ing walls play a significant role in nuclear-spin relaxation of gasses. Therefore, the 3 He permeability is also responsible for the 3 He depolarization. Considering these requirements, GE180 glass [1], which is one of aluminosilicate glasses, is often used in SEOP. According to Newbury et al., [2] dipole–dipole interactions in bulk 3 He limit the relaxation time of polarized 3 He to (807/P) h (where P is the 3 He pressure in bar, for a cell temperature of 296 K). Dipole– dipole dominated relaxation times have been observed in sealed GE180 SEOP cells, demonstrating that the wall relaxation was minimized with the GE180 cells [3]. Although GE180 is easier to work for a glass blower than other aluminosilicate glasses like Corning 1720, it is not easy to work yet, compared with commonly used glasses like Pyrex glasses. In addition, the largest tubing available is only 15 mm in diameter. This requires producing larger tubes first before completing glass work in cylindrical cell shape. This could be a huge task for a glass blower and limits the size of the cells. Considering the future development, it might be better to search new glasses instead of GE180. For this purpose, there would be a need to have a good measure of evaluating glasses if they are suitable for 3 He neutron spin filters from microscopic structural point of view. In addition, it is said that reblown glass has typically yielded the longest relaxation time [3,4]. This implies that there should be a difference in the microscopic structure of the glasses and the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.06.358 n Corresponding author. Present address: Yoshifumi Sakaguchi Tokai Project Office Comprehensive Research Organization for Science and Society (CROSS) Bldg. Ibaraki Quantum Beam Research Center 162-1, Shirakata Tokai, Ibaraki 319-1106 Japan. Tel: +81-29-219-5300; Fax: +81-29-219-5311. E-mail address: y.sakaguchi@cross.or.jp (Y. Sakaguchi). Nuclear Instruments and Methods in Physics Research A 634 (2011) S122–S125