ELJEN Products List EJ-400 fast neutron detector
This model is obsoleted and replaced to EJ-410
distributed by
This product had discontinued.

The EJ-400 detector is specifficaly designed for detecting fast neutrons while being nearly insensitive to gamma radiation.  It consists of zinc sulfide phosphor embedded in a plastic matrix structured in a series of concentric cylinders of clear plastic to facilitate light collection.  Proton recoil interactions in the strongly hydrogenous polymer materials provide the protons being detected by the phosphor.  Electrons scattered in the detector by gamma interactions interact very weakly with the ZnS:Ag particles providing scintillation pulses easily eliminated from the counting systems by setting an appropriate threshold.
The fast neutron detector is an inert plastic disc 15.9 mm thick (0.625") which can be mounted to a photomultiplier either directly or by means of a suitable light guide.  Optical greases, silicone rubbers or epoxies may be used with EJ-400.  A variety of blue-sensitive phototubes may be used.
Gamma Discrimination
The gamma scintillation pulses are usually smaller thatn those generated by neutrons.  In gamma fields below 1 R/hr pulse height discrimination can easily be used to reject the gamma pulses.  The randomly generated recoil protons will, however, generate a broad scintillation pulse height spectrum.  Hence, in high gamma fields, the simultaneous detection of multiple gammas can generate pulse heights large enough to be in the normal neutron spectrum.  The consequent higher discriminator settings needed will then reduce the neutron detection efficiency.  Additional gamma rejection may be achieved by using time constants of a few microseconds.
Wavelength of
max. emission:
450 nm
decay constant:
0.2 µSec
Max. operating

EJ-400 Neutron Detection Efficiency
G-tech, Corp.    local representative in Japan
365-1, Sayamagahara, Iruma-shi, Saitama 358-0032
Phone# 04-2935-2777 Fax# 04-2935-2778  

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