Cryogenic hydrogen gas target for a high-intensity monoenergetic neutron source

The triple alpha process is an essential reaction in nucleosynthesis. By that reaction, ¹²C is produced from three alpha particles. In a hot and dense environment, the triple alpha reaction rate can be enhanced by the neutron upscattering process. In such a process, the Hoyle state in ¹²C decays into the bound states by giving its excitation energy to neutrons instead of radiation decay. We are planning to measure a cross section of the inverse reaction to determine the enhancement factor. For the measurement, we have been developing a monoenergetic 10 MeV neutron source by using ¹H(¹³C, n)¹³N reaction at E_¹³C = 72.7 MeV.

In order to obtain a high-intensity monoenergetic neutron beam, we developed a cryogenic hydrogen gas target. The hydrogen gas is cooled to below 77K by a GM refrigerator and the target temperature is monitored by thermocouples. We performed a thermal test of the cryogenic target with heaters to simulate the primary beam energy loss, so that we confirmed the target withstands the beam heat load. We also conducted a performance test with an actual beam at CYRIC in Tohoku University. We measured the monoenergetic neutron intensity and the energy spectrum by the time of flight method. I will report on the development of the gas target and the results of performance tests.