The Development Of Graphite Cavity Chamber In X-ray Whose Tube Voltage Is Between 250kV And 600kV

The use of nuclear technology gives favor to the development of medical therapy,industry,energy and security.The radiation protection and radiation metrology are taken into account as using the radiation.It is significant to get an accurate results of X-rays measurements,especially in the environment monitor,radiation protection and radiation therapy.So it is necessary to establish primary standards which offer the tracebility of devices in X-ray use.However,the upper limit of X-ray’s tube voltage is 450 kV internationally.Thus there is a energy gap between the X-ray and Cs-137 γ ray.In order to fill this gap and solve the problem of instrument traceability in Xray,it is urgent establish the X-ray air kerma primary standard whose tube voltage is between 250 kV and 600 kV.And the development of standard ionization chamber is an important part during the primary standard establishment.This paper is based on the project of Research of X-ray Air Kerma Primary Standard Whose Tube Voltage is Between 250 kV and 600 kV in National Institute of Metrology.A radiation facility is set up and on which the radiation qualities are established.According to the requirement of the X-ray measurement,six graphite cavity chambers are developed and the properties are tested on the established facility,including saturation property,electric leakage and repeatability.At first,this paper introduces some typical X-ray air kerma primary standards and graphite cavity chambers in several institutes.A series of experiments are made in the self-designed facility and a good radiation uniformity is also got.The inherent filter of the tube is calculated and the radiation qualities under 8 tube voltages are established.The results of half-value layer are calculated by the attenuation method and the effective energy is got through the fitting method.The core of this paper is the development of graphite cavity chamber.The main parameters are determined by investigation,electric field simulation and electron equilibrium calculation.With the confirm of meterials,size,shape and wall thickness,3 types of chambers are designed,including spherical cavity with short collection stern,spherical cavity with long collection stern and spherical-cylindrical one.There are 6 chambers being processed for each type having two.Because of the weak current the cavity chamber gets,it is necessary to build a micro-current measurement system to obtain accurate results.The tests of cavity chambers’ properties are made in the new build system.The establishment of radiation facility provides nice platform and technical support for further measurements experiments.And the development of graphite cavity chambers lay a foundation of the X-ray air kerma primary standard whose tube voltage is between 250 kV and 600 kV establishment and also brings goodness to transfer work.