The Fifth Conference “ Nuclear Science and Its Application”, 14-17 October 2008
DETERMINATION OF239Pu/240PuRATIOIN SEMIPALATINSKTESTING
SITE SOIL BY ICP-MS
S.N. LU K A SH EN K O , A. A. AMIROV, A.ZH.TULEUSHEY, N .M .BERD IN OV A, D.A.ZHELTOV, N.G.KIYATKINA, G .N .CH U M IK O V
Institute o f N uclear Physics, N ational N uclear C entre o f the R epublic o f K azakhstan, Alm aty, the R epublic o f Kazakhstan, silachyov@ inp.kz
Ecological investigations of the Semipalatinsk Testing Site (STS) objects in the territory o f the Republic o f Kazakhstan, specifically _ 239+24opu content of soil, suppose determination of these isotopes mass ratio thus making possible to characterize the source of radiocontamination. This task can be solved by means of inductively coupled plasma mass-spectrometry (ICP-MS) — quadrupole mass-spectrometer ELAN-9000 (Perkin-Elmer) with liquid sample ionization in ICP was used in present study.
To measure 239Pu/240Pu mass ratio in STS soil the following work covering next main components was carried out:
sam pling points
• m aking solutions (3 to 20 pg/1 o f 239+240Pu by alpha-spectrom etry data) from STS soil according to the certified analytical technique [1];
• optim ization o f m ass-spectrom eter operation m ode;
• assessm ent o f m ass-spectrom eter detection lim it w ith the help o f these solutions; • studying the effect o f the potential isobaric interference from polyatom ic ion 238U H + on determ ination o f ^ P u / ^ P u m ass ratio;
• m easuring 239Pu/240Pu m ass ratio in STS soil.
The m easured 239P u/240Pu values in separate samples, collected from D egelen site (adits; S33 and S34 sam pling places, see Fig.) and the so-called “South ray” ( S I 7 sam pling place, see Fig.) o f the atm ospheric fall-out trace, coincided one w ith another and com e up to 20.7±1. T his result witnesses to weapon origin o f plutonium according to the U S A open classification o f P u isotopes [2] . The m easured value differs substantially from global fall-out 239Pu/240P u ratio equals to 5.68 [3] , It was found out experim entally that w ith 239+240Pu content o f soil m ore than 10 Bq/kg, the error o f 239pu/24°pu ratj0 m easurem ent can be less than 1%, w hile analytical signal from 240Pu contributes to the error mostly.
Thus, to determ ine 239Pu/240Pu ratio correctly prelim inary m easurem ent o f uranium co n ten t is necessary to take account o f the isobaric interference (polyatom ic ion 238U H +) w hich m ay result in overestim ation o f the intensity o f analytical signal from 239 m ass if U /239+240P u ratio in a solution is approxim ately m ore than ten.
References
1. A nalytical technique o f artificial radionuclides 239+240Pu, 90S r determ ination in environm ental objects (soil, bottom sedim ents, and vegetation), M V I NeKZ 07.00.00471-2005.
2. A lbright D., B erkhout F., W alker W. Plutonium and H ighly E nriched U ranium . O xford: SIPRI, O xford U niversity Press, 1997.
3. B elyaev N., D om kin V., et al. // Radiochem istry, 2001, v.43, hf°2, p.184-187.
The Fifth Conference “ Nuclear Science and Its Application”, 14-17 October 2008
