Spectrum processing method for measuring low levels of specific activity of 137Cs with a NaI(Tl) detector in the presence of natural radionuclides

Abstract

When measuring low levels of 137 Cs in soil samples using spectrometers with a NaI ( Tl ) detector , identification of the 137 mBa peak ( the 662 keV gamma line of the daughter radionuclide ) is difficult due to the influence of natural radionuclides , the peaks of which fall within the 137 mBa detection region . To i dentify a nd estimate t he a rea u nder t he p eak o f 137 mBa, i t i s n ecessary t o k now t he c ontribution o f t he b ackground c omponent t o t his a rea a nd t he c ontribution o f e ach n atural r adionuclide . W hen u sing s uch a pproach , t he a ccuracy o f e stimating t he 137 mBa p hotopeak a rea d epends o n t he a ccuracy w ith w hich t he l evels o f n atural r adionuclides a re d etermined . The a rticle p roposes a m ethod o f s pectrum d ecomposition b ased o n t he t aking i nto a ccount i ndividual p arameters o f t he s pectrometer a nd a m ore a ccurate d etermination o f s pecific a ctivities o f n atural r adionuclides . The m ethod i nvolves t he m odeling t he s pectral r egions f or e ach n atural r adionuclide i n t he a rea o f 137 mBa p eak a nd s ubtracting t he s imulated r egions a nd t he b ackground s pectrum f rom t he t otal s pectrum u nder t he p eak o f 137 mBa. The u se o f t his a pproach a llows t o m easure w ith a 63×63 N aI ( T l ) d etector t he s pecific a ctivity o f 137 Cs a t a l evel o f 0.7–1 B q / k g w ith a n u ncertainty o f 3 0-50 % i n t he M arinelly g eometry w ith a v olume o f 1 l iter a nd w ith t he m easurement t ime o f 6 h ours .