This article compares the harm to human body caused by three different
types of ionizing radiations, i.e., alpha (α) particle, beta (β)
particle and gamma () ray. To learn more about the basics of ionizing
radiation, please visit the Observatory website:
1. Relative Vulnerability of
Alpha particle has greater mass, more electric charges and less
penetrating power in matter. Even though the range of penetration of
the most energetic alpha particle can be several centimeters in air, it
cannot go through the cuticle of human skin. As such, the vulnerability
to human body caused by external irradiation1 by
alpha particles is
comparatively less severe.
However, once alpha particle enters the human body, its characteristic
of depositing its energy over a short range becomes crucial. Under this
condition, the alpha particle is surrounded by the living tissue of
human body and the harm arising from such internal radiation exposure2
is mostly confined to the small area of tissue surrounding the alpha
particle source. If the alpha particles accumulate in a certain organ,
nearly all the energy released by the particles will be imparted to
that organ rather than distributed to a larger area around
it. Hence the damages to the cells of that organ by alpha
particles are substantially larger.
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Relative Vulnerability of Beta Particle
In contrast, the range of penetration of beta particles in air is
larger than that of alpha particles. Beta particles with higher energy
are capable of piercing the epidermis and penetrating several
millimeters deep into the skin tissue. Hence, exposure to beta
particles will cause more external irradiation hazard than alpha
particles. However, as the external irradiation brought by
beta particles is mostly confined to the epidermis and outer skin
tissue, such external irradiation hazard is not too severe.
Naturally, beta particles also cause internal radiation exposure hazard
but the hazard is relatively small when compared with that brought by
alpha particles. This is due to the fact that the penetrating power of
beta particles is greater than that of alpha particles. Thus, the
energy released by beta particles is absorbed by a larger volume of
tissue than that caused by alpha particles, bringing comparatively
smaller damages to that organ.
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Relative Vulnerability of Gamma Ray
Gamma ray is highly penetrating and has a relatively long range of
penetration in air and matter. Even if a gamma source is located far
away, it will still cause external irradiation hazard to the human
body. For a human body exposed to gamma ray, all of his/her organs and
tissues will probably be irradiated. Hence, the external irradiation
hazard brought by gamma ray is more severe than that brought by either
alpha or beta particles.
With high penetrating power, gamma rays may even penetrate through the
human body. As far as internal radiation exposure hazard is concerned,
the high penetrating power means that the energy released by gamma rays
and taken up by a small volume of tissue is comparatively smaller.
Hence the harm to the organ is also smaller. Therefore, the internal
radiation exposure hazard caused by gamma rays is not as severe as that
induced by alpha or beta particles.
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External Irradiation and Internal Radiation Exposure
Since the radioactive source causing external irradiation hazard is
outside human body, staying away from the source is the best way to
minimize the hazard. In addition, shortening the time of
exposure and shielding are also effective protective measures to reduce
the hazard caused by such external exposure.
Internal radiation exposure hazard is caused by radioactive source
inside the body. Radioactive material can get inside the body
through inhalation, ingestion or by passing through the wounds of your
skin. Once radioactive substances enter the human body, it
will produce radiation exposure the entire time they are inside the
body until the material is no longer radioactive (i.e. it decays) or
until it is removed naturally by the body through excretion.
For those radioactive substances with a long half-life or for those
materials of which only a small amount could be get rid of by the body
through excretion, the radioactive material will stay in the body for a
longer time. Furthermore, some radioactive nuclides have
affinity for certain human tissues or organs and will accumulate in the
organ, causing more damages. For example, iodine (beta particle and
gamma ray emitter) and strontium (beta emitter) tend to accumulate in
the thyroid gland and the bone respectively whereas plutonium (alpha
emitter) mainly accumulates in the bone and the liver.