to D, by
specific doses to the tissues of interest. The Dy is related
Di: =
_D.
|
results primarily from cosmic radiation
not included in the doses presented here.
The natural backer a.
(Sy {Sp}
where S$, and Sy are the stopping powers fortissue and bone respectively.
S1/Sp = 1.225
D,, = 0.2636 (mrad/d - pCi - g)
D,./Dy = 0.26
D./D, = 3.11.
Inhalation
Airborne concentrations of respirable °"'*?"’Pu and 7''Am are estimated from data developed in resuspension experiments conducted at
Bikini Atoll in May 1978. We briefly describe the resuspension meth-
odology here; further details can be found in a paper summarizing the
studies at Enewetak and Bikini Atolis [34]. Four simultaneous experiments were conducted: (1) a characterization of the normal (background) suspended aerosols and the contributions from sea spray off
the windward beach leeward across the island, (2) a study of resuspen-
Data Bases for Input Parameters in the Dose Models
External Pxposure
tn Sita Measurements
d
External exposure rates for ''Cs, “Co, and *‘'Am were obtaine
NMIRS
ofthe
t
aspar
EG&G
by
ed
perform
ements
from in situ measur
by
[33]. These measurements were made with 40 12.7-cm-diameter
pods
2
on
d
mounte
s
detector
ion
ntillat
iodidesci
sodium
ick
5 1-em-th
an
on a Sikorski SH-3 helicopter. Flight lines were on a 46-m grid at
this
of
tion
descrip
altitude of 38 m over the islands. For a detailed
methodology, see Ref. 11. The average external exposure for Bikini
Island is 31 pR/h for '"Cs, and 1.9 uR/h for "Co and for Eneu Island
it is 2.3 and 0.2 wR/h, respectively. In addition, external gamma
e
measurements were made at Eneu and Bikini Islands, using portabl
the
above
m
scintillation detectors [2]. Measurements were made |
Eneu
ground on a 30-m grid on Bikini Island and a 120-m grid on
with
ed
compar
was
r
Island. The response of the scintillation detecto
ent
uminesc
thermol
of
s
twotype
that of a pressurized ion chamber and
were
r
detecto
ation
scintill
the
from
ements
dosimeters. The measur
normalized to the pressurized chambers. Theaerial and ground surveys
are
agree quite well (33). The external gamma doses presented here
, the Marbased on the island average external exposure. However
shallese spend considerable time (30 to 50%) in or around the housing
the
area. As a result, the housing provides shielding that reduces
veh
meyer
.
ear
average outside expos
l
Marshal
the
in
practice
n
commo
a
houses,
spread 20 to 40 ft around
of 2 (see
Islands, can reduce the external exposure by another factor
Ref. 2).
The natural background at the atolls is 3.5 #R/h or 22 mrem/y and
ST ta
48
sion of radionuclides from a field purposely laid bare by bulldozers as
a worst-case condition, (3) a study of resuspension of radioactive
particles by vehicular and foot traffic, and (4) a study of personal
inhalation exposure using small dosimeters carried by volunteers
during daily routines.
The normal or background mass loading measured by gravimetric
methods for both atolls is approximately 55 ug/m". The Bikini Island
experiments show that 34 yg/m'of this total is from sea salt, which is
present across the entire island as a result of ocean, reef, and wind
action. The mass loading from terrestrial origins ts therefore about 21
ug/m'. The highest terrestrial mass loading observed was 136 yve/m'
immediately after bulldozing.
Concentrations of °*"*’'Pu have been determined for (1) collected
aerosols for normal ground cover and conditions in coconut groves
(2) in areas being cleared by bulldozers and being tilled, and (3)
stabilized bare soil in cleared areas after a few days of weathering. We
have defined an enhancement factor (EF) as the “""*?"’Pu concentration in the collected aerosol mass divided by the “""*“""Pu surface soil
concentration (0 to 5 cm).
. The EF of less than | for hi-vol data for normal, open-air conditions
is apparently the result of selective particle resuspension in which the
resuspended particles have a different plutonium concentration than
is observed in the total 0- to 5-cm soil sample. In addition, approximately 10% of the mass observed on thefilteris organic matter, which
has a much lower plutonium concentration than the soil. Similarly
the EF of 3.1 for high-activity conditions results from the increased
resuspension of particle sizes with higher plutonium concentration
than observed in the total 0- to 5-cm soil sample.
49