B. L. LARSON AND K. E. EBNER
that fairly representative samples are easy to obtain from different parts of the
United States and the world. It is chiefly for these reasons that the general
public has become more aware of Sr-90 in milk than in other food products.
Procedures for analyzing Sr-90 are generally long and tedious and are subject to considerable variation. The common method used is to ash the sample,
dissolve it in hydrochloric acid and add a carrier of radioactive yttrium, which
is subsequently precipitated as the oxalate and counted in special low-level
counters (23). Since there is some experimental error, the values reported may
not be absolute and some caution must be used in interpreting data. The present
level of Sr-90 in milk which gives only 10-15 disintegrations per quart per
minute (23) illustrates the difficulties in making such low-level counts.
Since April of 1954 in the United States, monthly analyses of Sr-90 in milk
samples from six major milk sheds have been made for periods ranging from
TABLE 2
Sr-90 content of dried milks (19e)
Location
Date
1954—April
May
June
July
August
Sept.
Oct.
Nov.
Dec.
1955-——Jan.
Feb.
March
April
May
June
Perry,
New
York
State
College,
Miss.
Japan
United
Kingdom
eat
tae
eae
BE
es
A
O75
ee
0.31
ere
a
.:
a
1.9
2.6
» 4
1.0
7.3
1.7
B80
LO
2.0
1.8
1.9
ow...
ou.
1.8
2.9
be
63
0
98
O08
2.6
on.
St. Louis,
Mo.
OAT ee
2.5
4,7
4.6
B82
°°.
1.9
2.0
Oct.
Nov.
28
0
cee
2D tee
Dec.
1956—Jan.
Feb.
March
April
May
June
July
August
Sept.
Oct.
Nov.
Dec.
1Wg57—Late (12)
Mandan,
North
Dakota
Portland,
Oregon
(Sunshine units)
eee
DB
eee
PB
eee
eee
V5
ee
Vee
nee
VG
ee
VA
ee
ae
nate
Da
ee
Od
eee
July
August
Sept.
Columbus,
Wia.
1.5
4.4
3.9
41...
BB ene
Be tee
20
(eee
2.0
63
..
2.9
6.7
2.8
49
ae
3.0
AA
ok,
2.7
61).
3.1
BB
00
4.9
48
ou.
Se
4.6
0.8
1.2
3.3
4.4
3.7
9.2
2.6
AJ
69
i4
uu.
2.
6.5
20
5.5
ou.
750
BPO
ae
3.0
10.0
3.0
3.5
3.4
3.4
2.8
3.4
4.2
4.7
4.3
85
oo.
27
4.0
a
11.00,
BB
oa
9.6
5.2
3.0
4.6
17.0
64
0°20.
4.5
8.7
5.0
vee
5.0
66
0...
2300
oe
Be
ets
W077
ou...
2.7
ee
4.72
BDO
BQ
56a
besees
BB
vee
gee
46
0.8
5.5
10.0
7.0
ae
tee
eee
nee
eae