Biomedical Engineering Reference
In-Depth Information
152
Eu and
154
Eu in rock and concrete,
60
Co in steel and granite,
36
Cl in granite and
concrete,
63
Ni in steel, and others). A number of improvements were made in all
aspects of the DS86 radiation computations for Hiroshima and Nagasaki. Calcu-
lations with newer cross-section values were made of the bomb-released radiation
and its air-over-land transport. The greatly advanced capabilities of computers per-
mitted three-dimensional calculations of the detonations and radiation transport.
Shielding by terrain and large buildings was upgraded. Differences between pre-
dicted and measured activations were resolved under the new dosimetry system,
as were other issues. The estimated yield of the Hiroshima weapon (uranium) was
revised from 15 to 16 kilotons (TNT), and the epicenter was relocated 20 m higher
than before and 15 m to the west. The 21-kiloton yield of the Nagasaki weapon
(plutonium) was confirmed with detonation close to its previously assigned site.
The new RERF dosimetry system, DS02, has effectively resolved all discrepancies
that existed with DS86. Results are now within expected uncertainties for this kind
of work. Analysis indicates that the major contribution to the error in doses deter-
mined for an individual are the uncertainty in his or her position and orientation
at the time of the explosion and the attenuation by surrounding structures. The
development of the DS02 system represents a major contribution to the Life Span
Study.
Statistically significant excess cancer deaths of the following types have appeared
among the atomic-bomb survivors: leukemia; all cancers except leukemia; and can-
cers of the stomach, colon, lung, female breast, esophagus, ovary, bladder; and
multiple myeloma. Mortality data on solid cancer and leukemia were analyzed
by using both DS86 and DS02 dose estimates. The new dosimetry system led to
only slight revisions in the effects of risk-modifying factors, such as sex, age at
exposure, and time since exposure. The risk per unit dose for solid cancers was
decreased by about 10%. Leukemia was the first cancer to be linked to radiation
exposure among the Japanese survivors. It also has the highest relative risk. The
following findings have appeared in some of the approximately 3,000 survivors ex-
posed
in utero
: reduction in IQ with increasing dose, higher incidence of mental
retardation among the highly exposed, and some impairment in rate of growth and
development.
Statistically significant radiation-related mortality is also seen for non-neoplastic
diseases, such as those associated with the heart, respiratory, digestive, and
hematopoietic systems. The effects of both cancer and non-cancer mortality are
reflected in a general life shortening. The median loss of life in one cohort with
estimated doses in the range 0.005 Gy to 1.0 Gy was about 2 months. With doses
of 1 Gy or more, the median was about 2.6 years.
Careful searches have been made for genetic effects in the exposed population.
Demonstration of such effects is made difficult by the background of naturally oc-
curring spontaneous mutations. Chromosome abnormalities, blood proteins, and
other factors have been studied in children born to one or both exposed parents. No
significant differences are found in still births, birth weight, sex ratio, infant mor-
tality, or major congenital abnormalities. The Japanese studies indicate, “
...
that
