nucteonics DATA SHEET no. 2 
Nomogram for 
Radioisotope Buildup and Decay 
By J. R. STEHN 
and E. F. CLANCY 
Knolls Atomic 
Power Laboratory* 
Schenectady 
New York 
Calculations of build- 
up or decay of radio- 
isotopes involve’ the 
terms e—9®°*/T36 oor 
(1 — e-°-693/T36) and 
often are inconvenient 
or tedious. This nomo- 
gram speeds such com- 
putations. 
By placing a straight- 
edje on appropriate po- 
sitions on the half-life 
and time of decay or 
irradiation scales, de- 
cay factors or buildup- 
toward-saturation _fac- 
tors for a particular iso- 
tope can be read oat the 
straightedge intersection 
with the scale on the 
right. One precaution: 
be sure to state half- 
life and time of cooling 
or irradiation in the 
same units. 
Example A: For a radio- 
isotope whose half-life 
is 300 days (half-life 
scale) and whose par- 
ent is irradiated for 30 
days (time scale), from 
the buildup-factor scale 
it can be seen that the 
radioisotope achieves 
0.066 (6.6%) of its 
saturation activity in a 
given neutron flux. 
Example B: After the 
radioisotope considered 
in example A has been 
removed from the neu- 
tron flux for a period 
of 190 days (time 
scale), from the decay 
scale it is seen thot its 
radioactivity has de- 
cayed' to @ factor af 
0.64 (64%) of whet 
it was at the time of 
removal. 
* Operated by the 
General Electric Co. 
for the U. S. Atomic 
Energy Commission. 
Half-life, 
Ty 
1,000 10,000 
8,000 
800 6,000 
600 4,000 
3,000 
2,000 
400 
1,000 
Ni ota a 800 
ee 600 
XN ee 
200 SN IS 400 
= ~~. _ 300 
‘XN ~ ~~. 
NY 200 
‘XN 
‘XN 
100 ~S 100 
eo a 80 
Ne ace 
‘40 
60 ay 
30> 
20 
40 
10 
30 2 
6 
20 4 
3 
2 
10 1 
08 
8 0.6 
6 04 
0.3 
0.2 
4 
0. 
. 0.08 
0.06 
2 0.04 
0.03 
0.02 
! 0.01 
Decay factor 
-0.693! 
T 
"ve 
0.80 
0.99 
Buildup 
factor 
Isotope Calculations 
-0.693t 
(1-e 
0.999 
0.99 
0.90 
0.80 
0.70 
0.60 
0.50 
0.40 
0.30 
0.20 
0.10 
0.08 
0.06 
0.04 
0.03 
0.02 
0.01 
™e ) 
199 
