Experimental Research On Absolute Measurement Method Of ⁶⁰Co And ⁵⁴Mn Activity Based On Digital Coincidence Device

The coincidence method is based on the 4??counting method and the?-?matching method,and is an absolute measurement method developed by P.J.Campion et al.in the1950s and 1960s.This method was originally used to measure the activity measurement of simple?-?decay nuclides such as ⁶⁰Co.Later,Campion,Bearg et al.developed efficiency extrapolation and efficiency tracing techniques on 4??-?compliance measuring devices.It can be used for the activity measurement of complex?-?decay and pure?decay nuclides,respectively.Internationally,this measurement method is used for the activity measurement benchmarks of countries and the activity measurement standards of other major measurement standards laboratories.The conformity method is one of the methods with the highest measurement accuracy in the field of activity measurement,but the implementation of the method involves many aspects such as complex source and correction.In this paper,by improving the dispersant spraying device,the high detection efficiency of the film source is ensured while simplifying the preparation of the film substrate.Since the 4??-?conforming device needs to prepare the sample into a film source during absolute measurement,the higher the apparent detection efficiency of the film source,the more reliable the extrapolation.The self-absorption of the source and the charge accumulation on the lining film are the main factors affecting the detection efficiency.Therefore,the key requirement of the source is the uniformity of the source and the conductivity of the lining film.In this paper,the original device was improved,and the spraying device with simple operation,high safety and high spraying efficiency was established.Combined with the vacuum coating technology,the film source with high detection efficiency was successfully obtained.The beta detection efficiency for the ⁶⁰Co source reached 93%.This paper improves the proportional counter for measuring??e?and X-rays,which improves the gas pressure resistance and greatly reduces the breakage rate of the film source.Tests on the properties of the flat curve,air tightness,insulation,and high air pressure count stability of the proportional counter indicate that the relevant improvements are applicable to the measurement of positron trapping nuclide.This study also uses the 6700S linear programmable AC power supply to power the measurement device,reducing the impact of electronic noise on the measurement caused by voltage fluctuations.On the basis of the above work,the digital conformity measurement methods of the two kinds of nuclide activities of ⁶⁰Co and ⁵⁴Mn were studied,and the uncertainty evaluation and reliability verification were carried out.The ⁶⁰Co film source was prepared and compared with the calibration equipment of the China Institute of Metrology and the National Defense Science and Technology Industrial Ionizing Radiation Level 1 Station.The measurement results were consistent within the uncertainty range.The ⁵⁴Mn film source was prepared and the absolute measurement was carried out under the pressure of 400 kPa.The measurement result was consistent with the reference value of the solution within the uncertainty range.The expanded uncertainty for measuring ⁶⁰Co and ⁵⁴Mn solutions was 0.5%?k=2?and 1.1%?k=2?,respectively.Through the above work,it laid the foundation for further improving the 4??-?digital coincidence measurement capability.