wt
184
RADIOLOGICAL CLEANUP OF ENEWETAKATOLL
radioactive) which ultimately becomes stable again through radioactive
decay. The only induced radioactive isotope of significance remaining at
the time of cleanup was cobalt-60 (Co-60). Normally, cobalt is found in
small quantities in metals such as steel and iron; thus, the Co-60 on the
islands was generally associated with the metallic debris. Co-60 decays by
emission of energetic gamma rays accompaniedby beta particles.
The biological effects of all types of ionizing radiation are similar,
However, the probability that damage to the body may occur from
radiation varies among the types of ionizing radiation because of the
physical characteristics of each form. In addition, the degree of damage
that may occur depends upon factors such as the amountoftissue exposed
(whole-body versus partial-body), the quality and quantity of radiation
received (dose), and the time over whichit is received (dose rate).
Alphaparticles are relatively large and heavy and thus have a very short
range over which they can travel—about 3 cm in air, and fractions of a
millimeter in tissue. Thus, they ordinarily do not constitute an external
hazard to people because normal clothing and thé outer layers of skin
prevent the irradiation of any vital internal tissues. However, if alphaemitting material is deposited within the body in vital tissues (through
inhalation, ingestion, or entry into an open wound), the ensuing alpha
radiation can cause considerable localized cellular damage (within the
organ where located) becauseall the energy is dissipated over a very short
distance. For this reason, alpha-emitting materials such as the transuranic
elements are classed as internal hazards.
Beta particles are much smaller than alpha particles. They also can travel
over a greater range—tens of centimeters in air and a few millimeters in ©
tissue. Because of this, beta particles can be a moderate external hazard in
that the outer layer of skin can be penetrated and living tissues can be
exposed, resulting in ‘‘beta burns.’’ The burn produced is similar to the
burn caused by thermal energy (sun, fire) or chemicals, but it is not
accompanied by immediate pain. When deposited internally, beta-emitting
materials can also cause damageto the tissue in which they are located.
This damageis less localized than that caused by alpha particles because of
the greater range over which the energyis dissipated.
Gammaradiation, since it is a wave form with no mass, has great range
andis able to penetrate to all tissues of the body. It thus constitutes both
an external and internal hazard for the whole body. This is in contrast to
alpha andbeta particles, which are primarily partial-body or specific organ
hazards.
The characterization and extent of the potential problems at Enewetak
were well defined, both because of the extensive knowledge and detailed
records of the test period and because of the surveys done to characterize
ra,
the radiological environment. Based upon this understanding of the
asd
aA:
CNRMT
Rims 4 byt 8