Neutron Monitor

In the deuterium plasma, 2.5 MeV neutrons are generated by d(d, n)He-3 reactions. The neutron emmision rate is the most important parameter to indicate the fusion performance. The neutron monitor measure the absolute neutron emission rate with high temporal resolution.

U235 fission chamber with 5 cm-thick polyetheylene modelator
U238 fission chamber with 5 cm-thick lead gamma-ray shield

¥Time resolution:1 ms
¥Dianamic range:0 ~ 105 counts/s (pulse counting mode)
104 ~109 counts/s (Campbelling mode)
¥Energy range:0.55 eV~ 15 MeV (U235)
> 1 MeV (U238)
¥Position:In front of the horizontal port in P-3, P-7and P-13 sections.
¥Detector:A set of U235 and U238 fission chambers

The relation between the toral neutron emission rate and the detector output was calibrated by scaning the Cf-252 neutron source on the plasma axis inside the vacuum vessl.

(1) T. Nishitani, et al., "Absolute Calibration of the JT-60 Neutron Monitors Using a 252Cf Neutron Source", Rev. Sci. Instrum., Vol. 63 (1992) 5270.