owe
Serte desumed the average
ie
te 2.200 om! of water and
of sir. Values of T, E,
weeetl to obtain the data in the
fare obtained foam Table IV of
] ‘Doss Handbook (5).
;
posure results from a single
} a radicisotope, the critical
Mpa
often ia not the same as for
ehronic exposure ; frequently
ef ingestion it is the gastroMR
(GI) tract, and in case of
fen it is either the respiratory or
GPwact.
ste
When a portion of the
is the critical tissue, the
BKM the radioisotope in thecritiA agin, @J2, 98 given by Eq. 1 is rewiitry the amount present at any
» critical portion of the GI
gt
te/T- and the average dose
, i8 integrated from the time
radioactive material from the
tion of the GI tract. The
D
In this.cace fyda the fegstion reaching
the critieal. portion of the GI tract and
8 ("Wat
100/,,
7
ia given by fe = (1~ fi) whee f. &
_, 93/100 J.Z(RBE)E fMO.eMtTr ot the
fraction going fromthe Gi tanat 4.
2.6 X 107? & 7m’
h
"
D- §1.1 To2(RBE)E (i — ho)
mG
(7)
(8)
where @ = 1 when the radioactive halflife T, >> 1. G is given by
G
0.693(A, _ ho)
= (e728695h0/Fr 7 0-698h1/?+) T,
(9)
If it is assumed the mass of the material, m’, in the critical portion of the
GI tract irradiates the intestinal wall
from half the solid angle for fraction
A, — hy of a day, the maximum permissible concentration in wateris given by
(MPC).0° =
No. 6 - June, 1954
_
22y
fo2,200
1.8 X 10-'m’DG
~ (hi — ho)fvZ(RBE)E
(MPC),@ =
2,200f~
(MPC) 2
2 xX 10"f,
2 X 10-*m’ DG
-G, ~hofzpee ‘)
where f, = 0.62 (1 — f,) is the fraction
retained in the critical GI tissue, and
the other terms are as defined prew(10)
ously.
In most cases, ic., where
T, > 34 day, the lower lange intestine
7
Moximum permissible Intake of a
radioisotope. in @ sibgle e.
the blood.
Usually, when a radiocisotepe ie inhaled, some of it is swallowed. If a
considerable portion enters the blood
stream from the GI tract and is deposited in some organ, Eq. 6 must be
used to find the (MPC),. If portion
of the GItract receives the largest dose
so that it is the critical tissue, Eq. 10
must be modified as follows
po
missible concentrationinalt and water
for the equilibriumgendition have been
given in the Internal Dose Hamdbeok
cam parminaleeigle ezpoedie gal
mum per
have been published by the Nasional
Committee on Radiation Predpatten.
Therefore, the single-cxposuse values published here—in the table-~@o aot
have official status. However, many
pereons are working with radicactive
materials under conditions in whieh an
accident couldlead to a single exposure;
it would be convenient to have available tables of values that apply in sack