SAMPLE HETEROGENEITY
721
Table 1— NUMBER OF SPECIMENS* REQUIRED TO ASSESS
PICOCURIES PER SQUARE METER OF “sy IN THE SOIL
OF ONE FIELD WITH STATED PRECISION+
Confidence level
Depth, in.
0.90
0.95
0.99
0 to 1
1 to 2
2 to 3
3 to 4
4to5
5 to 6
6 to 8
10
9
8
8
9
43
20
14
13
10
11
13
60
28
24
23
18
19
22
105
49
*Size of sample = (ZC/P)?, where Z is the confidence-level
constant, C is the standard deviation/mean, and P is the precision level.
t Precision level used was +10% of the mean.
Table 2— NUMBER OF SPECIMENS* REQUIRED TO DEFINE
ALFALFA PRODUCTIVITY IN ONE FIELD WITH STATED PRECISION+
Alfalfa,
g/m?
Confidence level
0.90
0.95
0.99
July
1962
5
7
11
1963
1964
7
7
10
9
17
16
1963
May
June
2
5
3
7
4
12
19
11
33
19
July
August
October
7
13
8
10
17
*Size of sample = (ZC/P)?, where Z is the confidence-level constant,
C is the standard deviation/mean, and P is the precision level.
{ Precision level used was +10% of the mean.
and less than there was in the soil in which the alfalfa grew. The con-
centration of '°"Cs in each of these materials varied more than the mass
of material or the absolute amount of '"cs in the material. We see
again that the variation in the product of two factors is not predictable.
Partitioning the variances among each of the factors involved in finding
the absolute amount of radioactivity and that introduced in specimen
collection, preparation, chemical analysis, and counting of nuclides can
be very troublesome.
Study of arrays of similar tables showed that there was a high de-
gree of variation within each of the different radionuclide matrixes and