361
K.M. WONG "an gpl UTONIUM JN SEA WATERS. FTC
m TABLE IV
SE
‘MEME| ANALYSIS OF ORGANISMS
ae
Std. dex,
_
2 Ma; Sample no.
a
a a
2
A
Sere 27
iu - 4)
a
a
0.6
“SM 32-R
0
7
cS
.
‘tae
Shark liver
Shark liver
Shark bone
Shark bone
oe
0.28 +0.07
0.21 +0.06
0.025 +0.012
0.05
0.007
0.02
0.035+0.014
«640
Blue mussels
0.33+0.12
Blue mussels
0.36+0.05
4
Sid. der.
(d.p.nt. per kg wer wr}
ee
a is 57
Ty
eo
“39D y
*The + values are the lo of the counting error.
or
9.3
Organisms
te
TABLE V
PLUTONIUM-239 ACTIVITY IN REAGENT AND SIMULATED SEA-WATER BLANKS
ee
l
»
am:
Sa -tple
39 Py {d.p.m. per sample)
Reagent blanks
0.005 + 0.005
:
Simulated sea-water blank
aay,
4
Std. dev,
6
=f .
— 0.005 +0.010
0.010+0.02
—0.010+0.02
Average
a
0.017+0.015
0.007 + 0.007
0.004 + 0.010
.
iggktration of 6 such blanks (50 1), processed along with regular sea-water samples, was
"we =0.004+0.010 d.p.m. per sample, or about a factor of 2 above the detection limit.
,
The present detector background (5.00-5.20 MeV} for 7°? Pu wasless than one
* count per 24 h. The average detector background activity over an extended period of
© about 10,000 min was 4 counts, or 0.0004+ 0.0002 c.p.m., near the region of the
B. 73°Pu w-spectrum. Similar backgroundactivity was also found nearthe regions of the
7
B. a-peaks of 73®Pu (5.30-5.50 MeV) and ?36Pu (5.60-5.80 MeV). This level of back-
g groundactivity is an exception rather than a general rule for most solid-state detec-
n Tables II-IV.
ountingerrorof 28
it and simulated
-ained from deep
e°3°Puconcen- ¥
,
m:
E.
E
tors. Much higher background has been observed in somesolid-state detectors because
of contamination with 7*!Am used by the manufacturer for their calibration!*. The
Present detectors were purchased from the manufacturerbefore any test with 241Am,
Such detectors are not hard to obtain, but the requirement mustbe explicitly specified
to the manufacturer.
The average counting rate of the samples was about 0.5 c.p.m.; build-up of
detector contamination from recoil atoms was negligible in about 15 months of
; Operation. This is consistent with recoil studies of a-emitters with daughters of long
& half-lives such as the decay products of the plutonium isotopes?®.
iz
In the determination of plutonium-238, a serious decontamination problem
a was encountered. Figure 1 shows a typical a-spectrum of the major peaks of 7°°Pu,
*Pu and 7>°Pu: on this are superimposed the peaks. with the same detector and
Anal. Chim. Acta, 56 (1971) 355-364
JOG 4