MEASUREMENTS OF AMERICIUM AND PLUTONIUM
IN THE ATMOSPHERE*
D, W. Efurd, G. L. Merrill, Jr., J. T. Phelps, and K. D. Rosenlof
McClellan Central Laboratory
McClellan Air Force Base, CA
ABSTRACT
Alpha spectrometry and high sensitivity mass spectrometry have provided complementary data which have proven useful in understanding fluctuations in the
atmosphere, particularly the relationship between plutonium activity levels
and variations in the 2"%pu/239py isotope ratios. A summary of past plutonium
data plus some recent measurements are presented. Previously unpublished
24lam data collected from 1963-1970 are also presented.
These data indicate
that the 2414m/235py atom ratio in the atmosphere has been decreasing since
1967.
Explanations for this anomaly are postulated.
INTRODUCTION
Virtually ail the transuranic activity on the surface of the earth has come
Therefore, for any predictive mode! of plutonium buildup
via the atmosphere.
in the biosphere to be accurate, it is critically important to assess the
element's magnitude, distribution, physical form, and chemical form in both
the stratosphere and troposphere.
The primary sources of activity in the past
were 325 KCi of 239°240p, fallout debris from nuclear testing (Hardy et al.,
1973) and 1.7 KCi of 238pu from the burnup of the SNAP-9A capsule in 1964
(Harley, 1964).
Accidents involving aircraft carrying nuclear weapons resulted
in localized releases 1000 times less (Langham, 1968). The largest accidental
releases from land-based facilities have been 50 times smaller still (Hammond,
1971; Krey, 1976).
4This work was conducted under the auspices of the Air Force Technical
Applications Center.
249