Neutron Flux Monitor

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Last Updated: Wednesday, 12 February 2014 09:56

Using the standard GEM foils 10x10 cm² a Neutron Monitor for Fusion Reactors has been built.
Some beam tests have been done at FNG (Frascati Neutron Generator) at ENEA Frascati for the measurements of high neutron flux produced by strong nuclear reaction Deuterium-Deuterium e Deuterium-Tritium: Neutron of 2.5 MeV e 14 MeV are produced respectively.

A detector has been built with a cathode made of a suitable thickness of aluminum and polyethylene, and was placed in front of the generator at a few centimeters distance.The impinging neutrons on polyethylene are converted in protons that release its final energy inside the gas producing electrons.
The 128 readout pads 6x12 cm2 organized in a matrix 16x8 allow to create an intensity image of the neutron
source, using scalers with a time gate ranging from few μs up to ten seconds. The efficiency has been measured comparing the rate of GEM monitor with a NE213 scintillator placed at few meters from the target.

neutron flux measurements

 

The active area of this monitor has been divided into two parts with the neutron converter optimized for the two energies 2.4 and 14 MeV: the efficiency
measurements (see the figure aside) shows not only a zone at low gain with no photons contamination but also a good discrimination between the two types of neutrons. 

 
   

Thanks to 128 pads (organized in 16 rows) the chamber is able to measure both the 14 MeV  and 2Mev neutron.
The total counting rate has been compared with the measurement done with a liquid scintillator NE213 detector, placed 10 m far from the neutron source: as shown in the figure on the left : a good linearity up to the maximum flux for FNG (12MHz/cm2) has been obtained.