Carver, R.D.

Dupzyk, R.J.

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Thia ia a preprint of a paper intended (or publication in a journal or proceeding a. Since chanfea may be made before publication, thia preprint ia made available with the underatandinf that it will not be cited or reproduced without the permiaaion of the author. UCRL - 7UU30 PREPRINT m LAWRENCE UVERMORE LABORATORY UniversityofCaiiforn^/LivermorerCalifomia • MEASUREMENT OF THE MASS SPECTROMETER EFFICIENCY IN TEE ISOTOPIC ANALYSIS OF VERY SMALL PLUTONIUM SAMPLES Ri ley ,? . Carver and R. Jene Dupzyk June 26, 1973 -NOTICE-Thla report \ m prepared at in account of woik sponsored by the Unjttd States Government. Neither the United States nor the United Steles Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability of responsibility for the accuracy, com­pleteness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not Infringe privately owned rights. This paper was prepared for submission t o the Proceedings of the 21st Annual Conference on Mass Spectrometry and Allied Topics. MASTER DISTRIBUTION OF THIS DOCUMENT IS UNUM1TEQ .W*';»a*s«s*3S*i»:ws MEASUREMENT OF THE MASS SPECTROMETER EFFICIENCY IH THE ISOTOPIC ANALYSIS OF VERY SMALL PLUTONIUM SAMPLES* Riley D. Carver and R. Jene Eupzyk Lawrence Livermore Laboratory Livermore, California 9^550 •'•••' Because of increasing interest in the analysis of very small amounts of plutonium (l0~^3g or .016 d/m) in environmental samples, our laboratory has developed the capabil­ity to measure isotopic abundances at these levels. The instrument has a double fila­ment surface ionization source; tandem magnets with 60° sectors of 3h cm radius; and computer-controlled data acquisition, fast magnetic sweep, and on-line data reduction. While the source is not of the Stevens type, it is valve-isolated from the analyzer portion, and with the fast pumping provided, working pressures of 10"? torr can be achieved within 15 minutes. Pressures of 10~ Q torr are attainable within two hours. All plutonium samples are traced with 350 pg of 2 l v 2Pu for isotope dilution normalization. One of the early experiments was progressive dilution of a plutonium chloride solu­tion to determine how small a sample we actually could analyze. The total Pu found in each analysis along with the 2U0/239 isotope ratios measured are summarized in Table I. At about sample #0 the results start to degenerate; we consider this to be the smallest •ample (about .006 d/m, 30fg) which our laboratory can routinely analyze. Because these samples were prepared by direct dilution, there remained some question about possible chemical losses and effects. A plutonium solution was analyzed two times: once- with 2^ 2Pu' tracer added before chemistry, and once with the tracer added after chem­istry. Conventional nitrate anion exchange was used. The results in Table II show that there was high chemical yield with no particular loss in accuracy. Real environmental samples have also been analyzed.^' Mostly these are soil, but others such as plant and animal tissue, water, air filters, etc., have also been run. Table III shows.the results for a series of soil samples sent to us from various parts : of the country. General chemical separation had already been performed, and alpha count-lag had been done. Ve added " 2 P u tracer and did an additional nitrate anion exchange to further purify the sample. Previous work(2) has shown that atmospheric fall-out plutonium has a much -higher mass 2U0 content than does the typical plutonium from produc­tion reactors such a% those at Hanford and Savannah River. The measurement of the 2U0/239 ratio then is a good method for differentiating between the inescapable fall-out of nuclear test debris from the stratosphere and other sources of plutonium such as accidental spiles from plutonium handling facilities. Other work^3) has indicated that chemical processing strongly degrades mass spec-' trometer efficiency. Our efficiency measurements for comparable types,of samples are shown in Table JEV, The efficiencies are the summed counts collected for a given mans, divided by the"number of atoms of that mass present in the original sample (as measured I by isotope dilution), and then multiplied by 100. The chemistry seems to improve the efficiency in most cases. The lower efficiencies were for samples on plates. When a sample is on a plate, it is stripped with HNO3 + HF, and the fluoride may interfere in some unknown manner with chemical yield or ionization efficiency. In summary, samples as small as«.006 d/m 239+240^ (30 f g) c a n ^ isotopically and quantitatively analyzed. The extensive chemical purifications required are a factor, [but do not'cause large losses or insurmountable difficulties. 1; This work was performed under the auspices of the U.S. Atomic Energy Commission. 1. R. J. Dupzyk, et al., Argonne National Laboratory Report 80lU, pp. 32-33, October, 1972. i,2. P. W. Krey and B. T. Krajewski, Health and Safety Laboratory Report 2k9, pp. 167-I9U, April, 1972. 3. F. M. Rourke and J. L. Mewherter, 20th Annual Conference on Mass Spectrometry and Allied Topics, Paper L-2, June U-9, 1972, Dallas, Texas. .A 3«BEBI •» Diluted Plutonium Chloride Tracer » . Gross dpm 239+Ŝ O - 2H0/239 (atomic) by Mass Spectroscopy by Mass Spectroscopy *.*.'.:; ,' 63.9 ± 0 . 1 3 O.063 8 : 19.0 ±0 .05 0.063 • " 7 - - ' • ' • • • ' $.2 +0 .02 O.O63 6 1.9" ± 0 . 0 1 o.osit '.VII •'•'. 0.61 +0.005 o.osu • > : > C ^ 0.20 V + 0 . 0 * ^ 0 . 0 6 5 3 . 0.062 +0.002 0.068 O.O2I+O.OOO9 0.066 1 0 .0068+0.0003 0.071 i^f;- 0.0020 + 0.0002 : 0.082 . - 1 ; • •' 0.00070 + 0.00009 .'.'.:.. o . u o Standard Pa Sample UK-131 (1.5 Pg) Accepted Before Chemistry 2JK>/239 (atomic) 'OUlS .0.215 + 0.0* isotope dilution assay - 0.30 d/m After Chemistry 0.21A- + 0.0* 0.27 d/m Chemical yield 90$ TABIE H I Environmental Plutonium in S o i l m^' Location V * 2IW/&?? ^ i s a m p t e S i z e 2 ^ ^ 0 ^ : ' • . - . T . . , O ; , •:.,. .• • _ ... .. . . - . . • .*h±'••:•••• .•••••.-•'••• • •••^P^-'£••><:&• • " • « " ' - • - . . • • - - . . . • • . • . - . . - . . . . : - , V . . - ,-'r •;, - C a l i f o r n i a - ' " ~.~ 07355 ±0 .001 : • ; . • • . • ' . ' ; • .r.-,Hfah .-..:.'.,::-v,.-.^ ; ';-^,o.trr + 0.005.; : Colorado •r]-^ o.jM9±o.odk C". •';; •••;•'•-.'•' ~r. o .290d/h' ' Wv,: ?.&•:' • ^ v * .V*- Kbraska. •r>:^o.aft9,±o.oo^v-; •^•''':f^:^cioW^;;'v^'-^T^-hi* . Sew York * " 0.1t5 +0.007 •(.'r:\'i :/-..•' ...!l,»..:.i..'...v'.-. .r'V>:.^;.i; • i t * _?V .- £ L " •.V!'. -.Vr.VlA.. "mt.irmfa-k. rfSV.- ^-fei;iA:i.X^'^.v-»-„i^^:;..: .:«^:^ w:v£*': TABUS Iv •y"-.«i-.^.'-'-«.-.'j.v ffi^^^fe^i^^88 Spectrometer Efficiency ^ ^^M^tm&M*. ' •"• ' • • • • . " • " • • . • • i ' ' " ' " • ' • , . •. • • * . ' . . . . • ' • ; • . : . " ' • ' ; • : " • ' • • • • " • . • ' • ' • • : • ' " ' ' ; • , • • ; ' • • • • • " ' • • • • ; • • . • • ' . • • ' . - Without Chemistry . ."-. x;' M M ? ; - "; . ' 0 . 1 2 5 ••*:.'•""; ."*• 1 . 2 x 10"' • -* •"• v. O.Oto • > " • • '•••'239421*0 d~2.r:.j^-•-•'.. . s r ." - t •--- •• - " . Pa ( p g ) * 'jarpe o f Chemistry Counts /pg ^ Efficiency ; • 0.<*0 \- < 1 aMorexclarige . : " " i . l x S66" 0.125 - 1 \ 0 . 2 3 d " f C w ^ > i a l a tr ip + 3 . 5 x 1 0 6 O.H* ^ U i ^ ^ i & ^ ^ a n i o n exchange. "_ ..^.S^- • '. •--. ;, ^ i . ^ ' . 20 ;; • Pt plate atrip + 0.9x10° O.036 6.750 Fe plate strip + 1.6 x 106 0.0«»2 :••;•] 

Measurement of the mass spectrometer efficiency in the isotopic analysis of very small plutonium samples

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