RADIATION
AND ITS HAZARDS ON MAN
In general, radiation is a process where energy
emitted by one body travels in a straight line through a medium or through
space. Radiation comes from the sun, nuclear reactors, microwave ovens, radio
antennas, X-ray machines, and power lines, to name a few.
Radiation can be classified as either ionizing or
non-ionizing. Non-ionizing radiation is lower energy radiation that comes from
the lower part of the electromagnetic spectrum. It is called non-ionizing
because it does not have enough energy to completely remove an electron from an
atom or molecule. Examples include visible light, infrared light, microwave
radiation, radio waves, and long wave (low frequency) radiation. Ionizing
radiation has enough energy to detach electrons from atoms or molecules - the
process of ionization. It comes from both subatomic particles and the shorter
wavelength portion of the electromagnetic spectrum. Examples include
ultraviolet, X-rays, and gamma rays from the electromagnetic spectrum and
subatomic particles such as alpha particles, beta particles, and neutrons.
Subatomic particles are usually emitted as an atom decays and loses protons,
neutrons, electrons, or their antiparticles.
Radiation is a form of energy. It comes from man-made
sources such as x-ray machines, from the sun and outer space, and from some
radioactive materials such as uranium in soil. Radiation travels as rays, waves
or energetic particles through air, water or solid materials.
Radioactive materials are composed of atoms that are
unstable. As unstable atoms become stable, they release excess energy (called
"radiation") through a process called radioactive decay or
radioactivity. The time required for a radioactive substance to lose 50 percent
of its activity by decay is called its half-life.
The most common types of radiation emissions are
alpha, beta and gamma rays.
Alpha particles:
can be shielded by a sheet of paper or by human skin. But if materials that
emit alpha particles are inhaled, ingested or enter your body through a cut in
your skin, they can be very harmful.
Beta particles:
cannot be stopped by a sheet of paper. Some beta particles can be stopped by
human skin, but some need a thicker shield (like wood) to stop them. Just like
alpha particles, beta particles can also cause serious damage to your health if
they are inhaled or swallowed. For example, some materials that emit beta
particles might be absorbed into your bones and cause damage if ingested.
Gamma rays:
are the most penetrating of these three types of radiation. Gamma rays will
penetrate paper, skin, wood, and other substances. Like alpha and beta
particles, they are also harmful if inhaled, ingested or absorbed. To protect
yourself from gamma rays, you need a shield at least as thick as a concrete
wall. This type of radiation causes severe damage to your internal organs.
(X-rays fall into this category, but they are less penetrating than gamma
rays.)
HOW IS RADIATION
MEASURED?
Measuring radiation is complex and utilizes several
different units. Scientists measure the amount of radiation being emitted in
the conventional unit called the curie (Ci) or the SI unit called the becquerel
(Bq). These units express the number of disintegrations (or breakdowns in the
nucleus of an element) per second as the element tries to reach a stable or
nonradioactive state. One Bq is equal to one disintegration per second and one
Ci is equal to 37 billion Bq.
When measuring the amount of radiation that a person is exposed to or the
amount of energy absorbed by the body's tissues, two units are used: the
conventional Roentgen (or radiated) absorbed dose (rad) and the SI gray (Gy).
One Gy is equal to 100 rad. If a scientist is measuring a person's biological
risk of suffering health effects of radiation, the units of measurement are the
conventional Roentgen equivalent man (rem) or the SI sievert (Sv). One Sv is
equal to 100 rem.
HOW CAN I BE
EXPOSED TO RADIATION?
Small quantities of radioactive materials occur
naturally in the air we breathe, the water we drink, the food we eat, and in
our own bodies. People receive some background radiation exposure each day from
the sun, from radioactive elements in soil and rocks, from household appliances
(such as television sets and microwave ovens), and from medical and dental
x-rays. Even the human body itself emits radiation. These levels of natural and
background radiation are normal.
Radiation doses that people receive are measured in
units called "rem" or "sievert." (One sievert equals 100
rem.) Scientists estimate that the average person in the United States receives
a dose of about one-third of a rem per year. Eighty percent of typical human
exposure comes from natural sources, such as sunlight. The remaining 20% comes
from artificial radiation sources, primarily medical x-rays.
WHAT ARE THE
HEALTH EFFECTS OF EXPOSURE TO RADIATION?
Radiation's health effects can be mild, such as
reddening of the skin, or very serious, such as cancer or early death. Radioactive
materials dispersed in an urban area pose a serious health hazard. Strong
sources of gamma rays can cause acute radiation poisoning or even fatalities at
high doses. Long-term exposure to low levels of gamma radiation can cause
cancer. Alpha particles (such as americium) small enough to be inhaled can
damage people's lungs and lead to an increased risk of cancer.
The degree of damage to the human body depends on:
The amount of radiation absorbed by the body (the
dose)
The type of radiation
The route of exposure
The length of time a person is exposed
Exposure to very large doses of radiation may cause
death within a few days or months. Acute radiation syndrome (ARS), or radiation
sickness, is usually caused when much of the human body is exposed to a high
dose of radiation over the course of a few minutes. Survivors of the Hiroshima
and Nagasaki atomic bombs and firefighters responding to the Chernobyl nuclear
power plant event in 1986 experienced ARS. The immediate symptoms of ARS are
nausea, vomiting and diarrhea; later, bone marrow depletion may lead to weight
loss, loss of appetite, flu-like symptoms, infection and bleeding. The survival
rate depends on the radiation dose. For those who do survive, recovery may take
a few weeks to two years.
Exposure to lower doses of radiation may lead to an
increased risk of cancer, cataracts or decreased fertility. Radiation exposure,
like exposure to the sun, is cumulative. The damage from exposure to radiation
may not be apparent for many years.
Children are more sensitive to radiation than
adults. Exposure to human embryos or fetuses is of special concern because they
are extremely sensitive to radiation.
HOW CAN I
PROTECT MYSELF FROM RADIATION?
The longer a person is exposed to radiation and the
closer the person is to the source of radiation, the greater the risk. There
are three basic ways to reduce your exposure:
Time: Decrease the amount of time you spend near the
source of radiation.
Distance: Increase your distance from the radiation
source
Shielding: Increase the shielding between you and
the radiation source.
Shielding is anything that creates a barrier between
people and the radiation source. Depending on the type of radiation, effective
shielding can be something as thin as a plate of window glass or may need to be
as thick as several feet of concrete. Being inside a building or a vehicle can
provide shielding from some kinds of radiation.
Remember that any protection, however temporary, is
better than none at all. The more shielding, distance and time you can take
advantage of, the better. Although radiation cannot be detected by the senses
(sight, smell, etc.), scientists can detect even the smallest levels of
radiation with a range of instruments.
WILL POTASSIUM
IODIDE PROTECT ME?
Taking potassium iodide (KI) pills for protection
against a dirty bomb is not recommended. These tablets, now widely available,
are promoted by commercial companies for defense against everything from a
nuclear plant accident to a dirty bomb explosion. However, KI pills are not
likely to offer protection from the radiation spread by a dirty bomb and could
actually be harmful to people's health. KI pills help protect the thyroid gland
from the damaging effects of radioactive iodine, but they are of no help if the
dirty bomb contains any other form of ionizing radiation. There are many other
radioactive sources that could be used instead of, or along with, radioactive
iodine, and KI tablets would be useless against them. Many people could also be
harmed by the high concentration of iodine in KI because of allergies or other
conditions.
WHAT ARE SOME
SOURCES AND USES OF RADIOACTIVE MATERIALS?
Radioactive materials are widely used in hospitals,
research labs, industry and construction sites for such things as diagnosing
and treating illnesses, sterilizing equipment, and irradiating food.
Radioactive byproduct material in the United States is regulated by either
state or federal laws. The Nuclear Regulatory Commission, together with 32
states which regulate radioactive material, have over 21,000 organizations
licensed to use such materials for these purposes.
Other man-made radioactive materials come from
nuclear power and weapons sites. In the United States, radioactive waste is
located at more than 70 commercial nuclear power sites in 31 states. Enormous
quantities also exist overseas, especially in Europe and Japan.
Medical procedures, including diagnostic X-rays,
nuclear medicine and radiation therapy, make up the most significant source of
man-made radiation exposure to the general public. Other legal uses of
radioactive materials include industrial radiography, manufacture of gauging
devices, gas chromatography, and well logging. It is used in consumer products
such as smoke detectors (americium), "exit" signs, static
eliminators, and luminous watch dials. Some examples of radioactive materials
are cesium, americium, plutonium, and strontium.
HOW IS RADIATION
USED IN MEDICAL IMAGING?
There is a branch of medicine called radiology
that focuses on diagnosing and treating diseases using imaging technologies
based on radiation. Common imaging techniques include:
Projectional
Radiography - X-ray radiation is directed
through part of the body, which absorbs some of the radiation. Hard tissue such
as bone absorbs more than soft tissue such as muscle. The X-rays that are not
absorbed pass through the body and expose photographic film on the other side
of the body, creating a shadow effect. Different X-ray strengths are employed
depending on the part of the body that is being studied. Common projections
include a chest X-ray, breast X-ray (mammography), dental X-ray (dental
radiograph), and abdominal X-ray.
Fluoroscopy
(angiography, gastrointestinal fluoroscopy)
- These are X-rays that use a contrast (usually iodine- or barium-based) in
order to provide moving projections or images of movement inside the body.
Angiography is used to view the cardiovascular system and gastrointestinal
fluoroscopy is used to view the gastrointestinal tract.
Computed Tomography
(CT) :- a CT scan uses X-rays and
computers to create images that show slices of soft and hard tissues. Contrast
agents are often used during CT scans, and the result is a 3D reconstruction of
the part of the body being imaged. Widespread screening for the buildup of calcium
in the arteries using computed tomography scans would lead to an estimated 42
additional radiation-induced cancer cases per
100,000 men and 62 cases per 100,000 women, a study revealed.
Ultrasound:- Ultrasound
uses high-frequency sound waves to see soft tissues inside the body. Since the
test uses sound waves, no ionizing or potentially damaging radiation is
absorbed by the body. Ultrasounds can show images in real time, but they cannot
be used to image bones, lungs, bowel loops, or other air-filled body parts.
Magnetic Resonance
Imaging (MRI) :- An MRI
uses strong magnetic fields and a radio signal to take high quality 3D images
of the body. Although an MRI requires a patient to lie very still in a noisy
tube for a long period of time, the scan provided excellent visualizations of
soft tissue. MRIs do not use any damaging ionizing radiation, only strong
magnetic fields and non-ionizing radio frequencies.
Dual energy X-ray absorptiometry (DEXA or bone
densitometry) :- Commonly used to test for osteoporosis,
DEXA scans use two narrow X-ray beams to collect information on the density of
the bone. No images of the bone are created, and so this scan is not considered
projectional radiography.
Positron Emission
Tomography (PET) :- A PET scan
is a nuclear medicine imaging technique that uses a radioactive contrast agent
that is injected into the body. This tracer eventually begins to radioactively
decay and emits positron particles that are picked up by the PET scanner. A
computer is used to reconstruct 3D images.
HOW IS RADIATION
USED IN MEDICAL TREATMENT?
Many of the radiological imaging techniques
described above are used during diagnosis and treatment. For example,
ultrasounds and X-rays may be used to guide biopsy procedures, and ultrasounds
are used to break up kidney stones,
making them easier to pass. The branch of medicine that focuses on the use of
radiation for treatment (and imaging) is called nuclear medicine. Nuclear
medicine uses special pharmaceuticals called radiopharmaceuticals that have as
a component radionuclides - atoms with an unstable nucleus. Radiotherapy is the
practice of using these radioactive particles for the treatment of diseases.
Radiotherapy uses ionizing radiation to treat diseases such as cancer, coronary artery
disease, trigeminal neuralgia,
severe thyroid eye disease, and pterygium and to prepare the body for bone
marrow transplants.
Sometimes radiation can effectively help cancer patients who are not eligible
for surgery. A system called stereotactic body
radiation therapy may be effective in treating early-stage lung cancer,
scientists from the University of Kentucky's Markey Cancer Center found.
When a cure is not possible, radiotherapy or radiation treatment may be used
for palliative care, or the management of symptoms. In treating many types of
cancer, radiation therapy aims to damage the DNA of the cancer cells so that
they will commit suicide. A beam of radiation (photon, electron, proton,
neutron, or ion, but usually gamma rays from the Cobalt-60 isotope) is
carefully directed towards the malignant cancer cells with the goal of ionizing
or damaging the atoms that make up the DNA chain. This kills the cancer cells
and/or slows down their growth. Radiation treatments can result in the
absorption of several sieverts (Sv). Although radiotherapy is a painless
procedure, it carries side effects as the body absorbs this ionizing radiation.
Common side effects include skin damage, swelling, infertility,
fibrosis, hair loss,
fatigue,
cancer (radiation both causes and cures cancer), and dryness of the salivary
and sweat glands. The Society of Nuclear Medicine reports that the benefits of
medical imaging far outweigh the radiation risks.
Other types of radiation include the treatment involve swallowing a radioactive
isotope as a liquid or a capsule (Iodine-131 for thyroid cancer) or injecting
radioactive isotopes into the spaces near the damaged body part.
REFERENCES
Peter, C. (2009) Radiation and its Hazards on man
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