Study Of The Chance Coincidence Correction Method Of Delayed Coincidence Method About The Measurement Of Radon Isotopes

The measurement of radon and their daughters is an issues of common concern ofmany disciplines,While the measurement of radon isotopes simultaneously is theEmphasis and difficulty.The radon research mainly focus on the measurement of²²²Rn, and less on the study of²²⁰Rn、²¹⁹Rn, so the measurement of radon isotopes isthe needs of the development of radon metrology and radiation protection inChina.At the same time, the measurement of radon isotopes (²²⁰Rn/²¹⁹Rn)simultaneously is an fast and effective method to distinguish radium isotopes(²²⁴Ra/²²³Ra) indirectly,when the measurement of radium isotopes is an importanttechnique and key technology in the studies of oceanography and also is a hot spot incurrent research.The delayed coincidence method is currently recognized as the preferred methodin the measurement of radon isotopes simultaneously.The method is developed firstlyby Giffin in1963, improvement and successfully applied to the measurement ofshort-lived radium isotope²²⁴Ra and²²³Ra by Moore （1996）, and adopted by manyMarine laboratory in the world.The delayed coincidence method based on thedifference of half-life between the short-lived daughter of radon isotopes, and a keyproblem of it is the correction of chance coincidence.Almost all users of use thechance coincidence correction method of Moore currently,however,it is found thatGiffin’s method and Moore’s all have some shortcomings.On the basis of the Moore’sand Giffin’s method,a new chance coincidence correction formula （method1） isdeduced and presented in this article.For the mutual interference between channel isnot considering in Giffin’s chance coincidence correction formula and the lack oftheory evidence in Moore’s,the physical process of the chance coincidence correctionformula is theoretically analyzed and deduced in detail. The experimental verification of the three chance coincidence correctionmethods is done With²²²Rn、²²⁰Rn and²¹⁹Rn standard source,the feasibility ofMoore’s is proved, but also the deficiencies of them is found.The applicability andaccuracy of the method1relative to the Giffin’s and Moore’s is demonstrated throughthe verification and comparison of the²²⁰Rn and²¹⁹Rn mixed radon,and achieve theaim of the measurement of radon isotopes (²²⁰Rn and²¹⁹Rn) in the mixed radon gasfinally.Experiment and comparison show that:1、²²⁰Rn or²¹⁹Rn is measured alone, the three correction methods can accuratelymeasure the²²⁰Rn or²¹⁹Rn activity with a relative error within4.84%under thenormal environment background（about5cpm） when the²²⁰Rn total rate less than70cpm or the²¹⁹Rn total rate less than88cpm.2、The method1of chance coincidence correction and Moore’s method candistinguish²²⁰Rn、²¹⁹Rn simultaneously in mixed radon gas with a relative errorwithin12.3%and the relative error of method1within smaller9.5%under the normalenvironment background（about5cpm） when the total rate less than25cpm.The measurement of²²⁰Rn and²¹⁹Rn simultaneously in mixed radon gas isreached in this research, and the content of delayed coincidence method will be enrichand perfected,it will promotes the application of the delayed coincidence method inthe areas of marine isotope study and radon dosimetry.