CORRECTION OF 241am FOR CONTRIBUTION OF 155 Eu
DOE/ERSP TECH NOTE NO.3.0
DATED: November 1977
AUTHOR: F. Tomnoveec, EG&G
The EG&G IMP detects the presence of 241Am by measuring the 59.553 keV gamma-ray emitted
by this isotope. Quite often in the gamma-ray spectrum measured by the IMP there is a quantity of
155fu, This isotope of europium has three gamma-rays. The energies and branching ratios for the
two gammarays of interest are 60.01 keV, 1.32%; 86.55 keV, 32.2%. From the branching ratios we
compute that for every 100 of the 86.55 keV gamma-rays there are 4.1 of the 60.010 keV
gamma-rays. The resolution of the IMP detector system is approximately 1 keV; therefore, we are
unable to resolve the 60.010 keV gamma-ray of 155Eu from the 59.553 keV gamma-rayline of
41am.
Whenever the 155—y 86.550 keV gamma-ray exceeds 10 pCi/gm we make a correction to the
lam by subtracting 4.1% of the 155Eu 86.550 keV gamma-ray from the 241am. Table
B-3-1 shows the correction for Pearl, the only island to need any corrections at this time.
TABLE B-3-1. 155Ey CORRECTION TO 2414m DATA ON PEARL
Run
118
120
122
123
125
101
102
103
105
169
96
68
76
20
22
34
Stake No.
155Fy(86.550 keV)
(pCi/g)
1-N-1
0-N-1
0-BL-0
0-5-1
-1-BL-0
3-8-2
3-N-1
2-N-1
2-BL-0
2-S-1
3-N-2
4-N-2
6-N-2
4-§-3
5-5-3
5-54
155Fu(60.010 keV)
24lam
(pCi/g)
21.7
13.8
13.3
12.9
12.2
14.1
11.9
14.3
13.0
14.2
11.3
10.5
10.6
12.3
22.9
12.6
(pCi/g)
0.89
0.57
0.55
0.53
0.50
0.58
0.49
0.65
0.53
0.58
0.46
0.43
0.43
0.50
0.94
0.52
35.2
23.2
24.0
22.5
19.7
22.2
20.6
21.0
19.5
23.8
23.8
22.9
21.1
21.0
35.9
22.3
241 Am Corrected
(pCi/g)
34.3
22.6
23.4
22.0
19.2
21.6
20.1
20.4
19.0
23.2
23.3
22.5
20.7
20.5
35.0
21.8
REVISION OF 155&zu CORRECTION FACTOR FOR 24lAm
DOE/ERSP TECH NOTE NO,3.1
DATED: 22 March 1979
AUTHOR: R. Jaffe, EG&G
A slight correction is recommended to the original Technical Note 3 subtraction factor that
accounts for the 60.0 keV gamma from the 155—y which appears in the 59.5 keV gamma peak used
to detect 24l1Am.
The factor of 4.53% of the 155Eu should be used, rather than the 4.1%
originally calculated. The 4.53% factor accounts for the greater penetration of the predominant
86.5 keV gamma used to calculate 155—y, as discussed in EG&G Report RSSD-78-177, "In Situ
Determination of 2414m at Enewetak Atoll," by Tipton, Fritzsche, and Villaire (Aug. 1978).
The formula to correct 241 Am concentration is: 241 Am (corrected) = 241Am - 0.0453 155 Eu
Only where 195£uy is greater than half of the 24l1Am concentration is a correction factor above
about 2% required. This condition was encountered at a few locations on Pearl and corrected values
furnished with Tech Note 3. No changes to those values are necessary.
B-3-1