3. Island interior—0.059 mSvy-!
(5.9 mrem y-}).
4. Beaches and lagoon—0.50 pSv y~!
(0.050 mrem y~').
The average external effective dose rate
attributable to such a living pattern in 1995 on
Rongelap Island is about 0.11 mSv y~!
(11 mrem y~!). The natural external background
effective dose rate is about 0.22 mSv y—!
(22 mrem y-!).
Beta Radiation
It is impossible to predict precisely what
the beta dose to the skin will be, but it is clear
that the “shallow dose” due to both beta
particles and external gamma exposure will be
only slightly greater than the dose estimated
for external gamma whole-body exposure. This
higher “shallow dose” will occur primarily to
the most exposed parts of the body, usually the
arms, lower legs, and feet. The skin is a much
less sensitive organ to radiation than other
parts of the body; for example, the weighting
factor for stochastic risk recommended by the
ICRP for skin is 0.01, compared with 0.20 for
gonads, 0.12 for red bone marrow, colon,
stomach, and lungs, and 0.05 for breast, bladder,
dose for adults due to ingestion of P7Cs and Sr
can be used as a conservative |e
intake beginning in infancy. In
calculate only the doses to adults.
Strontium-90
Several models have been defeloped over
the years to estimate the cycling gnd retention
of 99Sr in the body as a functiqn of age to
calculate age-dependent dose] conversion
factors. We have previously uged both the
model developed at Environmental
MeasurementLaboratory (EML) (Rivera, 1967;
Bennett, 1973, 1977, 1978; Kluse&, 1979) and
that of Papworth and Vennart $1973, 1984).
The two models give very similarfresults, with
the biggest difference in results dccurring for
persons between the ages of 5 and 15 y. Both
models are empirical modelg based on
measurements of 99Sr in the diet and
corresponding measurements of “Br in autopsy
bone samples. The retentions and turnover
rates, and discrimination factors if the models
are determined by regression fanalysis or
equation solution fitting of the olfse
No particular correlation is made
liver, and thyroid (ICRP, 1990). Consequently,
the beta contribution to the total effective dose
is extremely small.
Internal Exposure
function of bone compartments fs generally
outlined in the ICRP model (ICRH, 1972, 1979,
Cesium-137
The conversion from the intake of137Cs to
the effective dose for the adult is based upon
the ICRP methods described in ICRP
Publications 30, 56, 61 (ICRP, 1979, 1990, 1991b),
which are based on Leggett's model (Leggett,
1986). We have combined the ICRP model for
charged-particle emissions for the betaparticle emissions (E = 0.51 meV) from 137Cs and
the methods of Leggett et al. (1984), and Cristy
and Ekerman (1987a and 1987b) for the photon
emission (E = 0.66 meV), associated with 137Cs
decay (137mBa) to generate the final dose
conversion factors. The biological half-life of
137Cs is determined as a function of mass (i.e.,
age) by the methods described in the Leggett
model. In a separate report, we estimated the
comparative doses between adults and children
(Robison and Phillips, 1989).
The results
indicate that the estimated integral effective
1990). The bone is assumed to be cbmposed of a
structural component associateq with bone
volume, which includes the compact cortical
bone, a large portion of tha@
(trabecular) bone, and a metabolif
associated with bone surfaces.
compartments are then identifiedi
cancellous
component
effect, three
two within
mechanical structure and integrity
of the bone,
the bone volume and one within the bone
surface. The bone volume is asspciated with
and the bone surface is involved with the
metabolic regulation of extracell@lar calcium.
Much use is made of general dat about age-
dependent bone formation
within these
compartments and, consequently, fhis modelis
not as dependent on radionuclidejspecific data
as the other models.
Wewill not discuss further ddtails of these
models, but refer the reader tojthe onginal
articles and their associated references for