Radiation is energy in transit in the form of high speed
particles and electromagnetic waves. We encounter
electromagnetic
waves every day. They make up our visible light, radio and
television waves, ultra violet (UV), and microwaves with a large spectrum
of energies. These examples of electromagnetic waves do not
cause ionizations of atoms because they do not carry enough
energy to separate molecules or remove electrons from atoms.
Ionizing radiation is radiation with enough energy so that
during an interaction with an atom, it can remove tightly bound
electrons from their orbits, causing the atom to become charged
or ionized. Examples are gamma rays and neutrons.
Non-ionizing radiation is radiation without enough energy to remove tightly bound electrons from their orbits around atoms. Examples are microwaves and visible light.
Health Physics is an interdisciplinary science and its application, for the radiation protection of humans and the environment. Health Physics combines the elements of physics, biology, chemistry, statistics and electronic instrumentation to provide information that can be used to protect individuals from the effects of radiation. For more on Health Physics, visit the
career section of the Health Physics Society
Radioactivity is the spontaneous transformation of an unstable
atom and often results in the emission of radiation. This process
is referred to as a transformation, a decay or a disintegrations
of an atom.
Radioactive Material is any material that contains radioactive
atoms.
Radioactive contamination is radioactive material distributed
over some area, equipment or person. It tends to be unwanted in
the location where it is, and has to be cleaned up or
decontaminated.
Gamma rays are electromagnetic waves or photons emitted from
the nucleus (center) of an atom.
A beta is a high speed particle, identical to an electron,
that is emitted from the nucleus of an atom
An alpha is a particle emitted from the nucleus of an atom,
that contains two protons and two neutrons. It is identical to
the nucleus of a Helium atom, without the electrons.
Neutrons are neutral particles that are normally contained in
the nucleus of all atoms and may be removed by various
interactions or processes like collision and fission
X Rays are electromagnetic waves or photons not emitted from
the nucleus, but normally emitted by energy changes in electrons.
These energy changes are either in electron orbital shells that
surround an atom or in the process of slowing down such as in an
X-ray machine.
These are the common units used in the United States in health
physics.
The roentgen is a unit used to measure a quantity called
exposure. This can only be used to describe an amount of gamma
and X-rays, and only in air. One roentgen is equal to depositing in dry air enough energy to cause 2.58E-4 coulombs per kg. It is a measure of the ionizations of the molecules in a mass of air. The main advantage
of this unit is that it is easy to measure directly, but it is
limited because it is only for deposition in air, and only for
gamma and x rays.
The rad is a unit used to measure a quantity called absorbed
dose. This relates to the amount of energy actually absorbed in
some material, and is used for any type of radiation and any
material. One rad is defined as the absorption of 100 ergs per
gram of material. The unit rad can be used for any type of
radiation, but it does not't describe the biological effects of
the different radiations.
The rem is a unit used to derive a quantity called equivalent
dose. This relates the absorbed dose in human tissue to the
effective biological damage of the radiation. Not all radiation
has the same biological effect, even for the same amount of
absorbed dose. Equivalent dose is often expressed in terms of
thousandths of a rem, or mrem. To determine equivalent dose
(rem), you multiply absorbed dose (rad) by a quality factor (Q)
that is unique to the type of incident radiation.
The curie is a unit used to measure a radioactivity. One curie
is that quantity of a radioactive material that will have
37,000,000,000 transformations in one second. Often radioactivity
is expressed in smaller units like: thousandths (mCi), one
millionths (uCi) or even billionths (nCi) of a curie. The
relationship between becquerels and curies is: 3.7 x 1010
Bq in one curie.
Note: These are the common units used throughout the world in
health physics.
The gray is a unit used to measure a quantity called absorbed
dose. This relates to the amount of energy actually absorbed in
some material, and is used for any type of radiation and any
material. One gray is equal to one joule of energy deposited in
one kg of a material. The unit gray can be used for any type of
radiation, but it does not't describe the biological effects of
the different radiations. Absorbed dose is often expressed in
terms of hundredths of a gray, or centi-grays. One gray is
equivalent to 100 rads.
The sievert is a unit used to derive a quantity called
equivalent dose. This relates the absorbed dose in human tissue
to the effective biological damage of the radiation. Not all
radiation has the same biological effect, even for the same
amount of absorbed dose. Equivalent dose is often expressed in
terms of millionths of a sievert, or micro-sievert. To determine
equivalent dose (Sv), you multiply absorbed dose (Gy) by a
quality factor (Q) that is unique to the type of incident
radiation. One sievert is equivalent to 100 rem.
The Becquerel is a unit used to measure a radioactivity. One
Becquerel is that quantity of a radioactive material that will
have 1 transformations in one second. Often radioactivity is
expressed in larger units like: thousands (kBq), one millions
(MBq) or even billions (GBq) of a becquerels. As a result of
having one Becquerel being equal to one transformation per
second, there are 3.7 x 1010 Bq in one curie.
Many units are broken down into smaller units or expressed as
multiples, using standard metric prefixes. As examples, a
kilobecquerel (kBq) in 1000 becquerels, a millirad (mrad) is 10-3
rad, a microrem (µrem) is 10-6 rem, a nanogram is 10-9
grams, and a picocurie is a 10-12 curies.
| 1018 |
exa |
E |
|
10-1 |
deci |
d |
| 1015 |
peta |
P |
|
10-2 |
centi |
c |
| 1012 |
tera |
T |
|
10-3 |
milli |
m |
| 109 |
giga |
G |
|
10-6 |
micro |
µ |
| 106 |
mega |
M |
|
10-9 |
nano |
n |
| 103 |
kilo |
k |
|
10-12 |
pico |
p |
| 102 |
hecto |
h |
|
10-15 |
femto |
f |
| 101 |
deka |
da |
|
10-18 |
atto |
a |
A Chronic dose means a person received a radiation dose over a
long period of time.
An acute dose means a person received a radiation dose over a
short period of time.
Somatic effects are effects from some agent, like radiation
that are seen in the individual who receives the agent.
Genetic effects are effects from some agent, that are seen in
the offspring of the individual who received the agent. The agent
must be encountered pre-conception.
Teratogenic effects are effects from some agent, that are seen
in the offspring of the individual who received the agent. The
agent must be encountered during the gestation period.
Stochastic effects are effects that occur on a random basis
with its effect being independent of the size of dose. The effect
typically has no threshold and is based on probabilities, with
the chances of seeing the effect increasing with dose. Cancer is
a stochastic effect.
Non-stochastic effects are effects that can be related
directly to the dose received. The effect is more severe with a
higher dose, i.e., the burn gets worse as dose increases. It
typically has a threshold, below which the effect will not occur.
A skin burn from radiation is a non-stochastic effect.
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