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RADIATION is powerful and very
dangerous rays that are sent out from radioactive substances.
Radioactive substances are elements
that have unstable nuclei. The instability of these nuclei causes them to
naturally decay, or deteriorate, over time. During this process, radiation is
produced and released from the substance.
The more potentially harmful types of
radiation include X-rays, high frequency ultraviolet rays, beta (ß) rays and
gamma (γ) rays, among others. Their danger lies in
the fact that they can penetrate through our body – and for some rays, even through concrete – and affect our cells.
Dr Ng Kwan Hoong, a Professor of
Medical Physics at University Malaya said, radiation has two effects on the DNA
in our cells. The rays can break the double-helix of DNA directly, or
indirectly produce free radicals that affect our DNA to create cancer cells. This
damage results in two consequences.
The first one occurs when someone is
exposed to high levels of radiation for a short time, and develops acute
radiation syndrome. An example of this would be the workers at the Chernobyl
Nuclear Power Plant, Ukraine, when the infamous nuclear accident occurred in 1986.
The high levels of radiation these workers were exposed to caused their cells
to die, and resulted in their deaths, within hours or days.
Regular radiation risks
The second one happens when someone
is chronically exposed to radiation, like the inhabitants of the areas around
Chernobyl, who continued to receive lower, but still dangerous, levels of
radiation over a long period of time.
In such cases, radiation causes
genetic mutations that increase the chances of developing cancers, or causes
physical or mental defects that are inheritable.
According to Bergonie and
Tribondeau’s law of radiosensitivity, undifferentiated cells that reproduce
themselves rapidly are the most radiosensitive, or vulnerable to these effects.
(See Radiosensitive cells)
The effects of radiation on these
cells result in the symptoms of radiation sickness. For example, the effect on
embryonic cells results in birth defects, the effect on epithelial cells (that
line most of our organs) results in nausea, vomiting and diarrhoea, and the
effect on white blood cells decreases our ability to fight off infections.
There is no cure for radiation
sickness. Once ingested, the (radioactive) particle remains inside the body.
There is no way to neutralise it.
Although the radioactive substance
will decay over time and disappear from the body, its effects will continue to
affect the body throughout that entire time, and beyond.
Away from the actual source of the
nuclear explosion, radioactive particles need to be swallowed or breathed in to
affect the body.
That is why in cases of exposure,
people are advised to remove their clothes and bathe themselves, as this will
remove most of the particles from their bodies.
The medical management for the
condition is supportive, meaning that doctors treat the symptoms of the
sickness to make the patient more comfortable and allow the body time to
recover itself, not the cause of it.
Prof Ng says that in the case of a
nuclear fallout, there are two main radioisotopes that people will be exposed
to – caesium-137 (Cs-137) and iodine-131 (I-131).
These are the two radioactive
elements that will spread the furthest because of their volatility, or ability
to change from solid or liquid to gas easily.
The danger from these two substances
comes not so much from direct exposure (unless you are on or near the plant
itself), but through consuming food and drinks that are contaminated with them
across a period of time.
For example, the substances can
settle on grass consumed by cows, which produce contaminated milk for human
consumption, or are themselves eaten as beef. This chain of events results in
the radioactive particles ending up in the human body, where it stays until it
decays.
Caesium-137 is water-soluble and
chemically toxic in small amounts. It has a long half-life of about 30 years. After
entering the body, caesium is quite uniformly distributed throughout the body,
with higher concentrations in muscles and lower in bones. The biological
half-life of caesium is rather short at about 70 days.
The half-life of a radioactive
substance is the amount of time taken for half of the amount of the substance
to decay.
Meanwhile, non-radioactive iodine in
our daily food is absorbed by the body and concentrated in the thyroid glands
for its proper functioning. When radioactive I-131 is present in high levels in
the environment from radioactive fallout, it can be absorbed through
contaminated food, and will also accumulate in the thyroid glands. As it
decays, the radiation emitted may cause damage to the thyroid. The main risk
from exposure to high levels of I-131 is the induction of radiogenic thyroid
cancer in one’s later life.
That is why the Japanese government
has supplied potassium iodide pills to the inhabitants nearest to the Fukushima
plant as a preventive measure.
The idea is to saturate the thyroid
gland with the non-radioactive iodine in the pills, so that the gland will not
be able to take up the radioactive iodine if the person consumes or inhales it.
However, Prof Ng adds that as iodine
is continually being excreted by the body, the pills need to be taken regularly
as long as the risk of exposure to radioactive iodine is present.
Constant exposure
The million-ringgit question is, of
course, will Malaysia be affected in the worst case scenario of a nuclear
meltdown at the Fukushima plant?
Based on the dilution principle, by
the time any radioactive particles get here, they will not pose a danger to the
population.The fact is, we are being exposed to radiation all the time.
We receive an average of two to three
millisieverts (mSv) of radiation a year from natural sources like the sun,
granite rock, natural radon gas and others. (A sievert is the SI unit measuring
the biological effect of radiation exposure by an ionising radiation source
undergoing an energy loss of one joule per kilogram of body tissue.)
Many medical imaging procedures, like
X-rays and CT scans, also involve the necessary exposure of patients to
radiation.
However, the risk of being negatively
affected by these procedures is far outweighed by the benefits of being able to
visualise the body parts necessary for diagnostic and therapeutic purposes.
Regular radiation risks
Prof Ng quoted Medical University of
South Carolina Professor of Radiology Dr G. Donald Frey, who once said: “It
would be a tragedy if someone did not have a medical imaging procedure that
might save his or her life, or alter the course of treatment, solely because of
concern over the effects of radiation.”
He adds that current radiation
protection recommendations are based on the Linear No Threshold (NLT)
hypothesis.
This hypothesis assumes that even the
lowest, near-zero dose of radiation can be detrimental, that the risk per unit
dose is constant and incremental, and that the risk can only increase with
dose; thus, erring on the side of caution.
For example, while the maximum
allowed limit for radiation exposure for those working with radioactive
materials is 20mSv per year, an investigation will be launched once a worker’s
dose badge shows signs of being exposed to one-third of that amount.
The chances of radiation workers
dying from exposure is about one in 20,000, as compared to one in 200 for those
who smoke 10 cigarettes a day and one in 10,000 from road accidents.
While the effects of high doses of
radiation are known through studies on those exposed to such levels by nuclear
accidents and atom bomb survivors, among others, the effects of low doses of
radiation are only extrapolations from the known data on high doses.
We usually assume that all doses of
radiation, no matter how small, increase the risk of stochastic effects such as
cancer; however, it is very difficult, perhaps impossible, to prove this.
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