Neutron Dose Rate Monitoring - NGF

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Revision 1.0, March 30, 2021

Neutron radiation monitoring of the Nuclear Science Laboratory uses a commercially available 3He filled neutron detector, the FHT 762 WENDI-2 manufactured by Thermo Scientific. The detector exploits the

3He + n → 3H + p

reaction with the Q value of Q=0.764 MeV. The thermal neutron cross section for this reaction is 5330 barns, significantly higher than the cross sections of other reactions commonly used for neutron detection. The full neutron dose monitoring system that consists of a 3He gas counter surrounded by a polyethylene moderator, a tungsten powder shell, and a borated silicone absorber is shown in Figure 1.

Fig. 1 The setup for neutron dose monitoring using WENDI-2 detector by Thermo Scientific.

The 3He filled detector of the WENDI-2 system is read out by the FH 40 G-X Dose Rate Measuring Unit shown in Figure 2. The FH 40 G-X can be accessed from an USB port of a control computer via an optical readout port accessible through an adapter cable provided with the unit. The communication follows the RS-232 serial data communication standard and can be programmed by the user as explained in this document.

Fig. 2 The FH 40 G-X Dose Rate Measuring Unit by Thermo Scientific.

The standard configuration setup for neutron monitoring in the Nuclear Science Laboratory is shown in Figure 3. For regular monitoring tasks the FH 40 G-X Dose Rate Measuring Unit is configured manually ahead of the monitoring cycle to operate in a count mode for measurements of the neutron dose in 60 second intervals. Data from WENDI-2/FH 40 G-X is readout, displayed, and logged by the software operated on the c7076-control.chem.sfu.ca computer. The software uses a serial connection via an USB port on /dev/ttyUSB0 to access the dose information available from the FH 40 G-X Dose Rate Measuring Unit. The neutron dose monitoring results can be accessed from this web site via the

Neutron dose rate in the past 5 hours

button in the Safety Monitors menu and is also logged into the InfluxDB data base. The Grafana software operating on the c7076-control.chem.sfu.ca computer provides a way to display and analyze the time series information for the neutron dose stored in the IfluxDB. The

Grafana dashboard for the neutron dose rate

button in the Logs menu is available for access to the tool for visualization and analysis of the neutron dose as a function of time.

Fig. 3 WENDI-2 detector and FH 40 G-X Dose Rate Measuring Unit connected to the c7076-control.chem.sfu.ca computer for the neutron dose monitoring at the staircase between the C7076.4 analytical/physical laboratory and the C7078 neutron vault.

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