Trial measurement for para-to-orthohydrogen back conversion under the Fe(OH) catalyst condition at J-PARC cryogenic moderator system

Ariyoshi, Gen  ; Tatsumoto, Hideki*; Teshigawara, Makoto   ; Hasegawa, Takumi*; Shiro, Yuki*; Horikawa, Yuka*

The Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory in the United States of America, which operates at 1.4 MW of high-power proton beam, has recently measured "back conversion production" in which parahydrogen, a nuclear spin isomer, is converted to orthohydrogen in an intense neutron field in a liquid hydrogen circulation system not installing any catalyst, for the first time in the world. The amount of para-to-orthohydrogen back conversion was 0.374 [m/MW/day]. Comparing parahydrogen and orthohydrogen, the total neutron cross section differs more than two orders of magnitude, so the increase in orthohydrogen has a significant impact on the generated neutron performance. Therefore, in the J-PARC hydrogen circulation system, a catalyst is introduced to maintain the parahydrogen state. However, at present, methods have not been developed yet to directly diagnose catalyst performance and/or degradation in-situ. In this study, we devised a new method to easily and intentionally change the amount of orthohydrogen in the J-PARC hydrogen circulation system, and attempted to evaluate catalyst kinetics by intentionally introducing an increase in orthohydrogen equivalent to back conversion into the circulation system. This method has the potential to contribute to the in-situ diagnostic catalyst characterization and to the calculation of neutron performance that depends on the ortho-to-parahydrogen ratio.