is definitely larger than experimental 
error. The range seems in agreement 
with previous results (8-10). This 
analysis of the nature of the variations 
is of course a very superficial one, and a 
further study of the correlation of 
potassium activity with other param- 
eters of the body is planned. (Devia- 
tions from the norm for natural potas- 
sium content of the body arise in 
certain diseases, as for example, mus- 
cular dystrophy. See the discussion at 
right of jobs for the human counter.) 
The counting efficiency of KCl in a 
sugar phantom was found to be 8.7%, 
compared with 10% for KCl alone. 
This indicates 13% self-absorption for 
the average human. The average 
potassium content of men, 61 cps, 
therefore corresponds to about 200 gm 
of potassium and the women’s average, 
51 cps, indicates 170 gm. These 
numbers are larger than the value of 
150 g given by Shohl (7) and the value 
of 140 g recommended by the Inter- 
national Commission on Radiological 
Protection (11); but in view of the 
large scatter, the difference is of little 
significance. 
x * * 
We are deeply indebted to the Los Alamos 
shop department for their collaboration in the 
design and construction. In particular, 
B. H. Pohlmann and R. I. Howes did an ex- 
cellent job of solving the many mechanical 
problems involved. The whole project would 
have been impossible without the support and 
encouragement of Darol Froman. F. N. 
Hayes prepared the scintillation solution and 
J. H. Larkins assisted in the design. The 
work was done under the auspices of the U.S. 
Atomic Energy Commission. 
BIBLIOGRAPHY 
1, Handbook 52, National Bureau of Standards, 
Washington, D. C., 1953 
2. M. A. Van Dilla, R. L. Schuch, E. C. Ander- 
son, NucueEonics 12, No. 9, 22 (1954) 
3. C. L. Cowan, F. Reines, F. B. Harrison, E. C. 
Anderson, F. N. Hayes, Phys. Rev. 90, 493 
(1953) 
4. B. R. Linden, Nucueonics 11, No. 9, 30 
(1953) 
6. E. C. Anderson, R. L. Schuch, J. D. Perrings, 
LA-1717, (1955) 
6. A. D. Suttle, Jr., W. F. Libby, Anal. Chem. 
27,921 (1955) 
7. A. T. Shohl, ‘' Mineral Metabolism,’’ (Rein- 
hold Publishing Corp., New York, 1939) 
8. I. D. P. Wootton, M. D. Milne, E. J. King, 
Ann. Rev, Biochem, 23, 441 (1954) 
9. R. M. Sievert, Ark. f. Fysik 8, 337 (1951) 
10. I. Reines, et al., Nature 172, 521 (1953) 
11. Brit. J. Radiology, Supplement 6, Recom- 
mendations of the International Commission 
on Radiological Protection (1955) 
12. Private communication, M. A. Van Dilla, 
Department of Radiobiology, University of 
Utah 
13. A. F, Stehney, W. P. Norris, H. F. Lucas, 
W. H. Johnston, Am. J. Roentgenol. 73, 774 
(1955) 
14. L. D. Marinelli, C. E. Miller, P. F. Gustafson, 
R. E. Rowland, Am. J. Roentgenol: 73, 661 
(1955) 
L. D. Marinelli, C. E. Miller, R. E. Rowland, 
J. E. Rose, Radiology 64, 116 (1955) 
m 
a 
Jobs for the Human Counter 
These five major research programs are planned for the Human Counter: 
1. Monitoring of Personnel and Foodstuffs 
The extreme sensitivity of the instrument should make it valuable for the 
study of possible gamma contamination from nuclear reactors, uranium mining 
operations, and bomb fallout. The fact that gamma activity can be detected 
rapidly and easily at levels below the maximum permissible concentrations 
means that contamination can be detected before it reaches dangerous levels, 
in time for remedial measures to be taken. For the monitoring of foodstuffs, 
forages, etc., the sensitivity, as mentioned above, is 5 X 10~!" c in samples up to 
300 lb. in weight. For the monitoring of personnel, uncertainty in the natural 
K* level is the limiting factor. If this uncertainty is 50% (a pessimistic 
estimate), the limit of detection is 5% of the permissible amount for Ra??é in 
equilibrium with its daughters, 3% for I*!, and 0.01% for Na*4 and Mo®%, If 
the K*° can be predicted to 5% (by an isotope dilution measurement with K4? 
or by a correlation such as discussed below), the sensitivity is tenfold greater. 
This sensitivity is attainable with counting times of two minutes per sample. 
2. Studies of Body Potassium Content 
The reasons for the large variation of potassium from person to person are of 
considerable intrinsic interest from the viewpoint of physiological chemistry. 
Correlation of potassium content with body type, total body water, lean body 
weight, or similar parameters weuld provide a useful method of calculating the 
“normal”? potassium value for an individual. An independent method of 
estimating body potassium to 5% accuracy would permit the ten-fold increase 
in sensitivity to other gamma emitters mentioned in the previous section. 
Deviations from the norm for natural potassium content of the body are of 
clinical interest in certain diseases, as for example, muscular dystrophy. 
3. Human Retention of Gamma-Emitting Fission Products 
The sensitivity of the instrument is such as to permit these measurements to 
be made on human volunteers with amounts of material far below the permis- 
sible level. In conjunction with small animal counters similar to the Human 
Counter, a series of fission-product retention measurements is planned using a 
number of different species including mice, rats, dogs, monkeys, and men. 
Such a series should aid in the interpretation of animal retention studies and 
their extrapolation to man. 
4. Counting Beta Emitters by Bremsstrahlung 
Van Dilla, using the ‘‘dog counter” at the University of Utah, has measured 
large amounts of Sr’? in the dog by means of the bremsstrahlung (12). At- 
tempts will be made to extend downward the energy range of radiations that 
can be detected, in the hope of obtaining better efficiency for the brems- 
strahlung. The detection of bremsstrahlung will make possible measure- 
ments of such important fission products as the strontium isotopes. A very 
rough theoretical estimate indicates that it may be possible to reach at least 
the maximum permissible level of Sr®°. 
5. Natural Body Gamma Activities 
Radium studies, such as those being made at the Argonne National Labora- 
tory (13), are of considerable interest because of their bearing on the funda- 
mental problem of the maximum permissible radiation level for man. The 
success of the method in this direction will depend on the establishment of an 
independent method for accurate potassium measurement or on the develop- 
ment of a coincidence technique to distinguish radium and potassium. The 
energy discrimination of the instrument appears to be inadequate to separate 
the two profitably. The limit is 5 X 107° ¢ of (equilibrium) Ra if potassium 
is not independently estimated, or 5 X 107! c if the potassium is known to 5%, 
assuming 2 min of counting time per subject. The Argonne Nal crystal 
counter (14, 15) has a reported sensitivity of 3 X 107! c of Ra (equilibrium ?) 
for 2 hr of counting time and does not suffer from K** interference. 
