-~
%
15
-
‘
Before turning to the biological data it is appropriate to
discuss first the radiation field around a particle of Pu02
and thereby define the fundamental questions that need to be
answered by the collateral data from radiobiological studies.
The unique form of tissue irradiation displayed 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) of only
in human tissue.
In other words,
a Pu-239 particle in tissue will only irradiate a volume of
tissue enclosed in a sphere of 45 u radius.
ward crom the surface of this sphere,
increases geometrically.
the radiation intensity
About half of the alpha particle
energy is dissipated at 20 u
‘is 1/8 the total volume).
As one moves in-
(that is, with a volume that
This means that the average dose
@elivered in the-first 20 uis 8 times that delivered in the
remaining 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 plutoniun