I I
.
Determination of Trace Quantities of Uranium by Neutron Activation Analysis DIRK DECAT, BENJAMIN VAN ZANTEN,l and GEORGE LELIAERT2 Chernisfry Deparfrneni', Centre d'Efude de I'Energie Nuclbire, Mol, Belgium
b Trace quantities of uranium are Besides, in most cases more than one determined in varioiis substances such purification step will be necessary as clover (trifolium sp.), human urine, to obtain a selective isolation of the aluminum (housekeeping quality), and uranium, and if /3-measurement is used high purity aluminum The method i s a decay control must be done to check based on the reaction (n, Y ) U ~ ~the purity. and measurement D f the 74-k.e.v. I n the present work a n extraction line of U239. As the half life of method is described which, within ceris only 23 minutes, a fast chemical tain limits, is quantitative, selective, reasonseparation is necessary-the and fast. The counting procedure is ably selective extraction of uranium simplified by measuring directly the from sulfuric acid medium with tri-ngamma activity of the separated soluoctylamine in kerosine. The detection tion on the 74-k.e.v. line. limit for a separation time of 20 to 30 minutes i s calculated to b e about EXPERIMENTAL 5 X lo-" gram.
I
sulfuric acid escape. After cooling for 2 minutes, 10 to 20 ml. of water are added and the solution is neutralized with 4 N NaOH to a DH 1 to 1.4 fabout O . l N ) , using Lymphin indicator 'paper L 6.50. The solution (approximately 40 ml.) is extracted with 25 ml. of a 2.5 vol. yo tri-n-octylamine solution in petroleum ether by mixing for 1 minute. The phases are allowed to separate for 3 minutes and 20 ml. of the organic layer are pipetted for measurement. hleanrrhile the standard is dissolved in 25 ml. of 0.lX sulfuric acid by breaking the quartz ampoule, and is extracted with 25 ml. of tri-n-octylamine solution. Here also 20 ml. of the Irradiation. Sample and standard organic layer are pipetted and measwere packed in a perspex can. This ured. can was made of a perspex bar of 5Measurement. For t h e measurecm. length with a diameter of 2.5 em. ments the decay of UZ391%-asfollowed T h e two borings a t each end could be and the curves of sample and standard closed with a nylon stopper. T ~ P ere interpolated t o a common measurstandard, containing about 0.5 pg. of ing time. The countings were peruranium and packed in a quartz amformed u i t h a 256-channel analyzer of poule, was brought into one boring, the the Technical hleasurement Corp., sample into the other one. The irradiaNorth Haven, Conn., the detector tion was carried out in the BR-1 reactor being a 3 x 3-inch KaI(T1) well-type using the high flux rabbit. The thermal crystal. neutron flux was about 1 O I 2 neutrons per The total counting efficiency of such a sq. em. per second during an irradiation crystal is nearly 80% for a gamma time of 20 minutes. energy of 74 k.e.v. Procedure. Basically, t h e proceThe preset counting time was 10 dure is identical with t h a t described minutes for each sample. The countfor t h e determination of molybdenum ing data were evaluated by the method (18). of Cove11 (4). Immediately after the irradiation the sample is dissolved with about 5 mg. of RESULTS AND DISCUSSION h4003 as carrier. For samples of clover or dry urine the residue is dissolved in The above mentioned procedure was nitric-perchloric-sulfuric acid mixture. applied to clover leaves, urine, and The samples of aluminum are dissolved aluminum. I n all cases the time needed in concentrated hydrochloric acid with for the chemical separation was 20 the help of some Hg(?;O&. Thereto 25 minutes. after, the solution is heated with concentrated sulfuric acid until fumes of Typical rrsults are summarized in
several methods are described for the determination of trace amounts of uranium, based on a-counting (3, 6, l 7 ) , fluorometry ( I S ) , and activation anal.rrsis. The latter method allows for several possibilities, summarized in Table I. The primary purpose of this invmtigation was to develop a method for trace analysis of uranium which was fast and simple and had a good sensitibity. As seen from Table I, some fast procedures are known ( 8 . 12), but they have the disadvantage that the radiochemical procedures are not quantitative. This means th,tt for each determination a yield correction must be applied with help of the added carrier. l
N THE LITERATURE,
Present address, Chemical Laboratory
of the Vrije Univemiteit, Amsterdam, The Xetherlands. The untimely deal h of Mr. Leliaert occurred during the course of this study.
Table I. Isotope
sepd. (TI * ) 17239 ( 2 3 . 3 rnin.) F3alro( 1 2 . 4
days)
Sepn. mpthod E s t n . followed I,? pptn.
Pptn.
F3a1Sq(% min.)
Pptn.
Np239( 2 . 3 days)
Copptn. ~ i t h Ida Estn.
U2Jn ( 2 3 . 5 min.)
Determination of Trace Amounts of
P, Y R
by Activation Analysis
Time needed for Irradiation
hreasure-
inmt
U
( 4 = n.
see.-') 0 .i-1 hr.
+ = .ix +
B
cIIl.-l
(1012
16-200
= ca. l n l ? 16-4.70 hr. 1013
Y
4
limit (yrarn)(eup )
Reference
10-10
8
10-8
8, 21-14
1 hr.
1013
+
8, Y
Hepn. 0 8-1 Iir.
10'3)
+
Iir.
.-, 1013 SO niin.
=
Detection
+ 1014
0 . 4 hr. -+ 3 )
= (1
x
1 hr. 0 3-7 Iir.
0 . 4 Iir. 10'2
10-8
IO
10
+
10-10
8 , 12
+
10-13
1, 7 , 9
