since exposures to people depend not only on half-life but also the
©
pathway of_ the radioactivity from the air or water into and out of the
body and the effectiveness of the radiation given off.
Further, there
are many radionuclides formed in the fission process with a very short
half-life (i. e., @ few seconds, minutes or hours).
The half-life is
so short that it is not meaningful to relate half-life to exposure.
The problem with such categorization is illustrated by the following Table
: Of relative radiotoxicity taken in part from International Atomic Energy
Agency (IAFA) documents.
; *
Fe
This radiotoxicity classification is pased.
upon the radiological and biological half-life as well as other factors
related to inhalation.
The classification of radiotoxicity changes wren /
the radionuclides enter man by other routes such as ingestion.
t
Table* |
Radiotoxicity
High ©
Nuclide
Plutonium-239
Strontium-90
Grams per |
Half-life
curle
24,360 years
27.7 years
16.2
6.96 x 10
-3
Type of
radiation
Alpha
beta, plus
. yttrium 90
gamma**
Medium
upper
Medium
lower
Low
Iodine-131
Strontium-89
8.08 days
50.5 days
Phosphorous-32
14.22 days
Tron-59,
45.1 days
Uranium-235
7.1 x-:10Y
Tritiun
¥daughter products
12.26 years
years
8.06 x 1076
beta and gam
3.44 x 107?
|
beta, plus
yttrium 89
3.49 x 107°
beta
1.02 x 10-4
beta
2,03 x 10°?
L.65 x 10°
gamnea*
beta
alpha
t
Derived trom IAFA Tectmical Report Series No. 15, A Basic Toxicity Classi-
fication of Radionuclides, 1963