- 15 -
Before turning
to the biolcgical data it is appropriate to
discuss first the radiation field around a particle of Pu02
and thereby dezine the
rundamental cuestions that need to be
answered by the collateral data from radiobiological studies.
The unigue
form of
tissue irradiation dispiayed by
insoluble particles of Pu-239 occurs because, when Pu-239
decays,
it emits an alpha particle with an energy of 5.1 MeV.
This particle has a range
some 40-45 u
(0.004 cm)
(produces biological damage)
in human tissue.
of only
In other words,
a Pu-239 particle in tissue will only irradiate a volume of
tissue enclosed in a sphere of 45 u radius.
As one moves in-_
ward from the surface of this sphere, the radiation intensity
increases geometrically.
About half of the alpha particle
energy is dissipated at 20 u
is 1/8 the total volume).
(that is, with a volume that
This means that the average dose
delivered in the first 20 u is 8 times that delivered in the
retaining 20 u.
The first column of Table III describes
the radiation field around such a particle in soft tissue;
e.g., the skin.
Since the lung is a Spongy tissue with a large
air volume, the range of alpha particles is longer in the
lung and consequently the mass of irradiated tissue-is larger.
Professor Donald Geesaman made a detailed analysis of plutonium
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