Pulsed Neutron Flux Measurement Based on Diamond Detector

A neutron flux measurement system based on CVD diamond detector was established, and system response characteristics of neutron and gamma was analyzed. Pulsed neutron flux measurement was carried out under different working mode at Xi'an Pulsed Reactor (XAPR). The signal of diamond detector was coincidence well with that of Pulsed Power Meter in time response, which can show the variation of neutron flux with time. Finally, a comparative analysis of the signal amplitude of diamond detector and pulse peak power of the XAPR was conducted. Wide bandgap semiconductor detector has strong radiation resistance performance and fast pulse response, and its dark current is usually in the order of pA when working in the current mode, the Full Width of Half Maximum response to the repetition frequency of nanosecond pulse hard X-ray source is about 2.2 ns, diamond detector can also be used for neutron flux measurement. Xi'an pulsed reactor (XAPR) has two kinds of operation mode, steady mode and pulse mode. Both of which can carry out electronic components and subsystem steady neutron radiation effect and the transient radiation effect research in the irradiation experiment apparatus. In order to study the transient radiation effect, it is necessary to obtain the radiation parameters such as the neutron flux over time to evaluate the radiation effects of electronic components and subsystem under the pulse radiation condition. In this paper, the fast neutron flux measurement under different pulse conditions was carried out using the single crystal diamond detector working in the current mode, Fig. 1. Fig. 1. Single crystal diamond detector. Radiation response of diamond detector Neutron spectrum of the displacement damage effect experiment apparatus in the XAPR can be measured by multiple foil activation method, the cumulative flux measurement under different pulse conditions is also using the activation method, with the 58 Ni(n, p), 47 Ti(n, p) threshold activation detector. First of all the average cross section can be obtained according to the neutron energy spectrum and the reaction cross section, therefore the cumulative flux can be calculated using the activation rate of the detector activation rate and the average cross section. Neutron gamma ray ratio of the damage displacement effect experiment apparatus in the XAPR is up to 7.7×10 9 n•cm -2 •rad -1 , Fig. 2. Fig. 2. XAPR and experiment apparatus. The diamond detector response to the neutrons and gamma ray has been simulated by Monte-Carlo method based on the neutron energy spectrum, gamma dose rate which has been measured. In the simulation, we need to know the gamma dose rate of the radiation field, and the gamma energy spectrum which cannot be measured of the radiation field. Here, the Monte Carlo method is used to model the reactor and the radiation experimental apparatus. The gamma-ray energy spectrum and dose rate which can be obtained by measurements of the experimental position have been simulated. They can be both used to simulate the response of diamond detector. The crystal size of the diamond detector used in this paper is Ø5 × 0.4 mm. The response of the diamond detector to the neutron and gamma rays of the radiation field needs to be simulated separately by the Monte Carlo method. The interaction between neutron and diamond detector is mainly composed of scattering and absorption with C nucleus, simulating the energy deposition of a series of charged heavy ions, such as C recoil nucleus, proton, α particle, etc. in diamond detection. The diamond detector used for pulsed neutron flux measurement needs to work in current mode, so the sum of energy deposition of each charged particle in the diamond detector should be recorded in the simulation. Gamma rays deposited energy with C atom of diamond detector by photoelectric effect, Compton effect and electron pair effect, and only recorded the average energy deposition. The ratio of neutron and gamma ray in the irradiation apparatus has been determined by measurement. According to this ratio, the average energy of neutron and gamma in diamond detector can be obtained respectively, the result is shown in Table 1. Table 1. Simulate Results