Development Of γ-Ray Reference Radiation Field And Exposure Standard For Radiation Protection Level

It is the precondition of doing the study of radiation protection that establishing of reference radiation field and exposure standard. The reference field deals with the calibration of dosemeters and dose ratemeters use for radiation protection and calibration of personal dosemeters. It also deal with the determination of the response as a function of photon energy. It is important for giving accurate irradiated quantity which is accepted by missionaries or the pubic.The subject developed gamma-Ray irradiation equipment with multisources, which can hold 7 137Cs sources whose activity are less than 0.37 TBq (10Ci)or 7 60Co sources whose activity are less than 18.5GBq (0.5Ci).Now, the equipment hold a 18.5GBq (0.5Ci) 137Cs source and a74GBq(2Ci) 137Cs source and a 37GBq (1Ci) 60Co source. The equipment is composed of source container and controller. The container stands on the irradiation room. The controller is fixed on the control room, we may select the sources by rotating track, which is to be used. Start irradiating byascending of gas cylinder or stop irradiating by dropping of gas cylinder. Repeatability which sources get at correct point, is less than 0.1%.Dimension of irradiation room is 8m×5m×4m.railway of calibration dolly is paved along the long axis of the room and is finely leveled, which ensures that center axis of beam parallels to the railway. There is a knaggy structure between calibration dolly and the railway, which can prevent the dolly from swaging. Small truck move calmly on the railway by very low center of gravity, brackets of ionization chamber and phantom plantforms can move around on the truck. Laser device which is equipment on the back wall of source container, makes the calibration instruments at the center of irradiation beam.The controller is made up of microcomputer, stepping motor control card, stepping motor driver and stepping motor and so on, which adopted the modularization design. Connection of circuit is easy. The controller runs stabilization and credibility. Main controller is made up of computer, which can process the data and manage the files. Software is programmed in "c" language. It has clearly consecution and friendly interface. The code is easy to maintain and set parameters.Radiation fields have been determined in JC 600CC cylinder ionization chamber and in PTW W3001.3 0.6CC finger-shape ionization chamber. Results of reverse square ratio are less than 3.1% for137Cs(2Ci),less than 3.4% for 60Co(lCi),and less than 3.1% for 137Cs(0.5Ci).Uniformity of radiation fields where is 1m far from the center of source, is less than 1% within the range of 100 mm diameter and less than 5% within the range of 160 mm diameter for 60Co.For 137Cs,less than 1% within the range of 120 mm diameter and less than 5% within the range of 160 mm diameter. Air kerma rate of 60Co and 137Cs gamma-Ray Reference Radiation Field is determined. Uncertainties are evaluated to be 4.6% for 137Cs(0.5Ci),4.6% for 137Cs(2Ci),and 4.2% for60Co(lCi).Result of measurement shows that Y -Ray Reference Radiation which has been established, is up to par and can meet use requirement.