Study On Key Parameters Of Tissue Equivalent Material Absorbed Dose Rate Based On ¹⁴⁷Pm ?-ray Radiation Field

Beta rays are mainly used in radiation protection,industrial applications,medical treatment and scientific research,and relevant workers may be exposed to beta radiation.In order to protect and utilize?-rays better,and improve the traceability chain of measuring instruments related to?-ray dose further,the research carried out the key parameters of the absorbed dose of?-ray tissue equivalent materials under the ¹⁴⁷Pm radiation field.Experimental measurements and Monte Carlo simulation calculations are performed on the correction factors related to the extrapolation chamber cavitylength,including the entrance window correction factor k_wii and the correction factor k_pe for the perturbation of the beta-particle flux density by the side wall of the extrapolation chamber;the uniformity of the radiation field;parameters that relate to extrapolation chamber,such as effective collection area and cavity length correction values.To provide data and method support for the ultimate realization of the recapture of ¹⁴⁷Pm nuclide?-ray tissue equivalent material absorbed dose.The imaging plate was used to measure the uniformity of the radiation field of the ¹⁴⁷Pm source that used in the experiment.The results showed that the dose change within 3%,which was better than the required standard of no more than 10%.It is also determined that the field diameter is 18 cm,when test/calibration distance is 20 cm,and with the flattening filter.By using the capacitance method,the effective collection area of the extrapolation chamber is 4.753 cm² and the cavity length correction value is 1.5 cm.The capacitance method is better than the limit slope method because it does not need to correct the ionization current.The main influencing factors of the entrance window correction factor k_wi of the extrapolation chamber was studied.The entrance window correction factor k_wi of different cavity length under different source-detector distance was measured experimentally.The results show that the k_wii is affected by the source-detector distance and the cavity length.Under the condition that the extrapolation chamber has a cavity length of 3 mm,the k_wi decreases as the source-detector distance increases.Using the Penelope code system simulated and calculated k_wi at a source-detector distance of 20 cm,with flattened filter and the cavity length is 3 mm.The simulation result is 0.1181,which differ from the experiment by 8.4%,which verifies the correctness of the simulation method.Using EGSnrc simulation,the simulation result of the k_pe is 1.00255when the cavity length is 1 mm,which is 0.04%difference from ISO reference value.At the same time,a simple and convenient way of calculating the correction factor is provided.Using this method,to measure the correction factor k_pe through the experiment is 1.00255 when the cavity length is 1.5 mm,which is 0.04%different from the ISO reference value.The above results indicate that the simple calculation method of the correction factor mentioned in the paper is feasible.