Experimental Studies On Pulse Photon Fluences At The Calibration Of The γRays Detecting System For Physical Diagnosis In Nuclear Exploding

The Y rays detecting system for physical diagnosis in nuclear exploding must be calibrated in the pulse radiation field according to field spots. So the 12MV pulse X rays accelerator and the fast neutron reactor are selected as radiation sources for calibrating. The method for measurement of photon fluences has been proposed based on the characteristics of the two radiation fields in this paper. There are two steps in this kind of measurement. First the absorbed dose in a small material block is measured. Then the photon fluence is calculated according to these absorbed dose data based on the initial spectrum. The absorbed doses are obtained with a uniform state ion chamber that is formed with LiFTLD cavity and LiF wall and designed by ourselves. The key problem, the dose to fluence conversion factor of the photon with single energy from 0.1 MeV to 12MeV, has been solved by simulating with Monte Carlo code system EGS4 .The photon spectrum data that are used in the calculation for translating the absorbed dose to the photon fluence have been obtained by the experimental method with a 12MV pulse accelerator and the iterative least-squares data analysis technique. The acceptable agreement of the comparison of the experimental results and the Monte Carlo simulation under the same conditions showed that the method for measuring the spectra is correct.The LET factors RLET(RLET = 0.05) of neutron response for LiFTLD in various n + y mixed fields in the fast neutron reactor have been determined experimentally due to the existing LET effects of the response for LiFTLD to neutron absorbed dose . The experimental results show that the LET factor for neutrons from thermal energy to 5MeV energy is about 0.050. So it is workable to measure the photon fluence in the pulse reactor with 7LiFTLD. It fills the white region of the basic dosimetry data with LiFTLD in our country.A uniform state ion chamber with double layers has been developed for distinct measurement in various n + y mixed fields in the fast neutron reactor. Thecavity material is 6LiF+7LiF. The inner wall material is 6LiF and the outer wall material is 7LiF. It clear the interference from thermal neutrons. The Experimental results shows that the ratios of the TL due to the effect of neutrons in 7LiFTLD to the total TL due to the combined effects of the Y -rays and neutrons are between 5.1% to 17.1%. It proves that the accuracy of the obtained photon fluence by this kind of method is acceptable.Overall, pulse photon fluences in the pulse accelerator and the radiation field caused by pulse reactor have been obtained by strict experimental studies and theoretical calculation in this paper. It provides the technological support to calibration of detectors for physical diagnosis in nuclear exploding.