Biomedical Engineering Reference
In-Depth Information
of Ionizing Radiation Course offered by the
Armed Forces Radiobiology Research Institute
at Bethesda, Maryland. In addition, the course
content is published in
The medical management
of radiological casualties
, which is available at
http://www.afrri.usuhs.mil.
materials are brought together in a controlled
fashion, i.e., nuclear reactor, then the energy is
released slowly preventing the explosive release
of energy. Certain man made and naturally occur-
ring atomic material such as uranium and pluto-
nium, spontaneously decay giving off radioactive
energy and particles, which can be harnessed for
various useful purposes. When humans are exposed
to gamma rays and atomic particles interactions
occur between the radioactive particles and DNA,
proteins, enzymes, and cell membranes causing
damage to the cells and organs. These particles
collide with atoms and molecules in the cells strip-
ping electrons, changing the surface charge of
enzymes and cell membranes and breaking strands
of DNA and RNA. It is this interaction that causes
acute radiation sickness (ARS).
The key principles in managing radiation casu-
alties are understanding the sources and effects
of radiation exposure. Radiation exposure can be
broken down into 2 categories: irradiation and
contamination. Irradiation occurs when radiation
from an external source interacts with an organism,
usually occurring in the first minute after a nuclear
accident, explosion or exposure to a radioactive
source. During a nuclear detonation, gamma and
neutron irradiation are the most serious radiation
threats (neutron damage was not detected after the
Chernobyl incident). While the residual gamma
radiation, which is similar to X-rays, is much less
intense than that emitted during the first minute
after a nuclear explosion, it is highly energetic,
passes through matter easily, and causes whole-
body exposure (Figure 5.2). Though exposure to
gamma irradiation may be short lived, if a signif-
icant dose is absorbed it can be rapidly fatal.
Radiation exposure may also come from external
and/or internalized radiation sources, such as dust
and fallout that is ingested, inhaled or deposited
on skin or clothes. Dust and weapons fragments
from a nuclear explosion or radiation dispersal
device constitute the most significant sources of
contamination as they continue to emit alpha,
beta, and gamma radiation. Contamination can
lead to on going radiation poisoning if decon-
tamination is not undertaken in a timely manner.
Alpha particles are a negligible external hazard,
5.2 Physics
A basic discussion on atomic structure helps one
to appreciate what occurs with radiation expo-
sure. All matter is composed of atoms, which
are themselves composed of protons (positively
charged), neutrons (no charge), and electrons
(negatively charged) held together by highly ener-
getic atomic forces. When atoms split, either
naturally (radioactive decay) or with the assis-
tance of man (fission), energy is released from
the atomic bonds (Figure 5.1). This energy is
in the form of heat, high energy gamma rays,
similar to X-rays, X-rays and atomic particles:
alpha and beta particles, and neutrons. Neutrons
are similar to protons except they have no charge.
Gamma and X rays are high energy electromag-
netic waves. Beta particles are free electrons which
have a negative charge, low mass and a high
reactivity. Alpha particles are helium nuclei (two
protons and two neutrons) stripped of electrons;
they are largest of atomic particles. When highly
radioactive material is brought together in suffi-
cient quantity and force, i.e., nuclear bomb, an
atomic chain reaction takes place causing a rapid
splitting of atoms and an exponential release of
the atomic energy: nuclear explosion. When these
Figure 5.1
Types of radiation released from atomic decay.
