Neutron Monitor


[Objectives]
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.

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

[Specifications]
¥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

[Calibration]
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.

[Reference]
(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.