Table 2, External 137Cs gamma exposure-rate measurements in and around the houses ap village area
of Rongelap Island.
137Cs, wR hr!
Location |
~
Number
of sites
Mediana
Meana
Standard deviation
In house
12
0.79
0.83
0.32
Outside house
22
1.5
17
0.98
General village sites
16
2.2
2.4
85
a Decay corrected to 1995.
External Beta-Particle Exposure
Airborne Radionuclide Conadentrations
The unshielded beta contribution to the
external dose was estimated for Enjebi Island at
Enewetak Atoll in 1980 (Crase et al., 1982). The
Airborne concentrations of
241Am are estimated from data
resuspension experiments condu
external gamma dose in estimating the
whole-body dose. More recent studies at Bikini
listed.
average beta dose at 1-m height over open
ground was 29% of the externa] gamma dose. The
beta dose is delivered, for the most part, to the
first centimeter of tissue, the so-called “shallow
dose” and, therefore, should not be added to the
Atoll using new, thinner thermoluminescent
dosimeters (TLDs) indicate that the dose over
open ground at 1-cm height is about three times
that at 1-m height (Shingleton et al., 1987).
Thus, the unshielded beta dose at l-cm on
Rongelap Island could be equal to, or slightly
greater than, the external pamma dose. For some
portion of one day, people dosit or lie on the
ground where the 1-cm exposure maybe relevant.
However, for a significant part of the day, the
eyes, upper body, and gonads are at 0.8 m or more
in height above the ground surface.
Moreover, it is important to realize that the
beta dose to skin, for a number of reasons, will be
significantly less than that determined from the
unshielded TLDs placed over open ground. The
walls and floors of the houses and the crushed
coral customarily placed around houses and the
village area absorb most of the beta radiation.
Because people spend significant amount of
their time in these areas, their exposure to beta
particles is greatly reduced. In addition, any
clothing, shoes, zories, Pandanus mats, or other
coverings also greatly reduce exposure to beta
radiation.
297+240Pu and
developed in
at Enewetak
Atoll in February 1977, and at Bikini Atoll in
Our study conducted on Bikini
of 1978, provides a more comple
than ourpreliminary studies on E
set of data
i Island at
Enewetak Atoll in February of 1977. (Subsequent
studies were conducted on Eneu Is
Atoll.) The Bikini Island study
extensive soil sampling and in- itu gamma
spectroscopy to determine isotope
ncentrations
in soil and vegetation; (2) various ir-sampling
rticle-size
procedures to determine
distribution,
and
radioactivit ,
and
(3)
micrometeorological techniques t@. determine
aerosol fluxes.
Four simultaneous experiments
were
conducted: (1) a characterization of the normal
(background) suspended aerosofs and the
contributions of sea spray off th@ windward
beach leeward across the island, (2— a study of
resuspension of radionuclides frpm a field
purposely laid bare by bulldozers
provide a
worst-case condition, (3) a study of
spension
of radioactive particles by vehicul&r and foot
traffic, and (4) a study of personaj
inhalation
exposure using small air samplersj carried by
volunteers during daily routines. Less
complete
studies similar to those of (1) and (#) had been
LC