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Rate of Decline of Radioactivity in Food Items
The rate of decline is the rat e of change of activity in a group of organisms and is the consequence of the interaction of physical decay, of biological uptake, and of biological decay.
The activity of the principal food items for the five dates of collection
is
presented ir Table 2 and Figure 2.
aging sample counts from all areas,
The values were obtained by aver-
The individual counts from which the
values for the October 1955 collection were determined can be found in
Appendix B.
Table I.
For the earlier dates the values are taken from UWFL-42,
Table 2 and Figure 2 give the general picture of radioactivity of
the fcod items and are useful to those who wish to calculate the health hazard.
The coefficient of variation (standard deviation + mean) for these
values averages about 60 percent, which indicates considerable variability.
Area and species differences and sampling error accountfor this variability.
Im the sections on fish, invertebrates, plants, etc., the samples are
grouped in smaller divisions, with area and species differences eliminated.
From Table 2 the absolute values of the food items can be obtained, and
e ‘from Figure 2 the rate of decline can be directly calculated.
These data
| are closest to being points on a straight line when plotted on a log-log scale —
| With March 1, 1954 as the date of origin.
For the purpose of making an
approximation of the general rate of decline, the slope of a least-squares
line Getermined from the average values for all items on each collecting
date was calculated and found to be -1.75,i.e., r=t7l- 15 {the decay rate
UNVERSIry + Sonpepg
UNTER
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