Simulations With GEANT4 For The Self-powered Gamma Detector

A self powered gamma detector(SPGD)is a portable detector that can detect gamma rays without an external power supply.Because of its small volume and large detection dose,SPGD can be used to detect the dose of gamma ray which cannot be reached by other detectors.The detector has a good application prospect.In this paper,the GEANT4 program is used to simulate the detection of self powered gamma detector.It provides an effective method for the research of the self energy gamma ray detector.And it has practical significance and application value.An object consisting of closely arranged materials,including an insulator material,that is irradiated with gamma rays,gives the object a certain electrical charge and produces a higher induced voltage.The thickness of the insulator is chosen so that the absorption of the gamma ray and the hindrance to the secondary electrons are small.And when the atomic number of the insulator is low,the induced electrons are generated in the direction of the radiation of gamma rays,including photoelectrons and Compton electrons.A substance with a high atomic number is used as a collector and placed in an insulator perpendicular to the incident direction of the gamma ray.The substance acts as a barrier to the transport of electrons,causing the charge to accumulate on the collector.And the greater the dose of gamma radiation,the more charge accumulated on the collector.In the experiment,the radiation source is cobalt source.The average energy of the gamma rays emitted by the radiation source is 1.25 MeV.Further,in the range of 0.1-1.25 MeV,the Compton scattering cross section has no change and the Compton scattering effect is dominant when the atomic number Z is less than 13.When gamma rays are irradiated in a self powered gamma ray detector,Compton recoil electrons are generated in the polymer material,and their energy of Compton recoil electrons is continuously distributed from 0 to 0.5 MeV.The direction of the recoil electron transfer with energy greater than 0.1 MeV is consistent with that of the gamma ray.The recoil electrons are produced in the polymer materials,while the positive charges are generated,so the whole state is in a neutral state.If the aluminum(z=13)layer is placed in the polymer material,the situation will change.For the aluminum layer,according to the rule that the Compton scattering cross section is proportional to the atomic number Z of the target material when the gamma ray energy in the range of 0.1-1.25 MeV,recoil electrons are more than recoil electrons produced in polymer materials.The recoil electron multiple scattering near the aluminum layer,and some return to the polymer material.The charge balance is disturbed.Eventually,the aluminum layer is electrified.In this work,based on Geant4,the interaction between gamma rays and collector matter was simulated,and the charge deposition density of collector was acquired.Then the relationship of radiation dose and charge deposition density was analyzed.Besides,the effect of the collector materials,gamma rays incident angle and capacitance ratios(c1/c2)on the charge deposition density were discussed.A good agreement between Geant4 and experiments was achieved.The rationality of the simulation program is verified.It provided an effective method for the research of the self-powered gamma detector.Because of the limitation of experimental conditions to large dose experiment,we had a large dose of simulation.