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2 Types of Radiation and Their Properties
2.2.3 Deep and Shallow Dose
Radiation is attenuated as it passes through tissue; some forms and energies of radiation are more attenuated than others. Beta radiation, for example, penetrates no
more than 1 cm into tissue; alpha radiation penetrates only a few microns; while
x-ray, neutron, and gamma radiation can penetrate through the entire body. Thus, a
person exposed to very high levels of external beta radiation might receive enough
exposure to give them skin burns while suffering no exposure at all to deeper tissues
and internal organs. For this reason, it is useful to measure (or calculate) radiation
exposure to the skin and shallow tissues as well as to deep tissues. These are called
shallow (or skin) dose and deep dose respectively (radiation dose to the lens of the
eye, which can cause cataracts, is usually tracked as well, but is not important for
the purpose of this discussion).
2.2.4 Calculating Radiation Exposure
Radiation exposure can be measured directly, but there might be times when it may
not be safe—or even possible—to make a direct measurement of radiation dose rates.
For example, if the theft of a high-activity source is reported, emergency responders
will not be able to make dose rate measurements on the source until it is located.
However, it can be useful to determine how close a responder can safely approach
and to distribute this information to the personnel who might be sent to try to interdict
the source or to those who might respond to its use in an attack to help them stay
safe as they work.
This process can also work in reverse; if the Radiological Health and Safety Officer
can measure radiation dose rate at a known distance from a source, they will be able to
determine how closely responders can approach without putting themselves at risk,
and might also be able to determine the amount of radioactivity present based on the
measured dose rate. For this reason, it is worth discussing some different methods
for calculating radiation exposure and how it is affected by various factors. At the
end of this section there will be an example problem demonstrating how all of these
factors can fit together.
2.2.5 Gamma Constant
Every gamma-emitting radionuclide gives off gamma photons with a unique set of
energies. Remembering that radiation dose (and dose rate) is a measure of energy
deposition and that radioactivity is a measure of the rate at which radioactive atoms
are decaying per unit of time, we can see that it is possible to add up the energies
of the gamma radiation emitted by a source of a given activity and the number of
2 Types of Radiation and Their Properties
2.2.3 Deep and Shallow Dose
Radiation is attenuated as it passes through tissue; some forms and energies of radiation are more attenuated than others. Beta radiation, for example, penetrates no
more than 1 cm into tissue; alpha radiation penetrates only a few microns; while
x-ray, neutron, and gamma radiation can penetrate through the entire body. Thus, a
person exposed to very high levels of external beta radiation might receive enough
exposure to give them skin burns while suffering no exposure at all to deeper tissues
and internal organs. For this reason, it is useful to measure (or calculate) radiation
exposure to the skin and shallow tissues as well as to deep tissues. These are called
shallow (or skin) dose and deep dose respectively (radiation dose to the lens of the
eye, which can cause cataracts, is usually tracked as well, but is not important for
the purpose of this discussion).
2.2.4 Calculating Radiation Exposure
Radiation exposure can be measured directly, but there might be times when it may
not be safe—or even possible—to make a direct measurement of radiation dose rates.
For example, if the theft of a high-activity source is reported, emergency responders
will not be able to make dose rate measurements on the source until it is located.
However, it can be useful to determine how close a responder can safely approach
and to distribute this information to the personnel who might be sent to try to interdict
the source or to those who might respond to its use in an attack to help them stay
safe as they work.
This process can also work in reverse; if the Radiological Health and Safety Officer
can measure radiation dose rate at a known distance from a source, they will be able to
determine how closely responders can approach without putting themselves at risk,
and might also be able to determine the amount of radioactivity present based on the
measured dose rate. For this reason, it is worth discussing some different methods
for calculating radiation exposure and how it is affected by various factors. At the
end of this section there will be an example problem demonstrating how all of these
factors can fit together.
2.2.5 Gamma Constant
Every gamma-emitting radionuclide gives off gamma photons with a unique set of
energies. Remembering that radiation dose (and dose rate) is a measure of energy
deposition and that radioactivity is a measure of the rate at which radioactive atoms
are decaying per unit of time, we can see that it is possible to add up the energies
of the gamma radiation emitted by a source of a given activity and the number of