least two pathways from
238
U,via production from
‘-ourity in 2398p device materials.
235
U, or as an unburned
It is also produced as a decay product
.
eg
5
25
2
24
of short-lived transamericium isotopes, 254 NG 250e, Fm, $46c¢,
cf een,
The isotcpic compe-ftian of some plutonium fuels can be found in Keller
(op.cit.), and Poet and Martel] (1972).
are commonly reported together (e.g.
The concentrations of 239 Pu and 240 Pu
2394240
Pu) since alpha spectroscopy
measurements cannot distinguish between their energies.
Plutonium-238 is the
next most commonly reported alpha-emitting plutonium isotope in fallout.
2394240,
The
238
.
Pu:"~"
Pu activity ratio measured in samples which have accumulated the
isotioe from fallout is about 20:1 (Noshkin, 1972).
3.2
Introduction of Radioactivity in Fallout
The composition, structures and origins of radioactive fallout
particles produced in the nuclear testing program at the Pacific proving
ground were investigated by Schell (1959) and Adams, Fairlow and Schell (1960).
The formation of fallout particles were then, and have since been, shown to
be governed by the interactions of the condensing vaporized device and soil
materials in the cooling fireball and by entrainment and/or impaction pro-
cesses with non-vaporized materials swept into the fireball at later times.
Because of their extreme dilution, the individual radioactive
elements are never concentrated sufficiently to condense as
individual metal or oxide particles but only condense on to
the particles which are being formed by the major vaporized
constituents and by the soil materials (Adams et al.,op.cit.).
A sianificant effort has been directed toward describing the fractionation
of radionuclides following nuclear explosions.
Quantitatively, fractiona-
tion of volatile and refractory radioelements was first demonstrated by
Freiling (1962).
Heft (1970) reported:
For land Surface and subsurface detonations, the (particle
size] distribution functions may be expressed as linear
combinations of two or three log-normal distribution
functions.
Each component corresponds to a particle group