4.6 Instrument Selection
37
4.6 Instrument Selection
While only your radiation instruments will indicate the presence of radiological
danger, excessive contamination, or other concerns, not every instrument is useful
in all situations. A GM detector, for example, is not sensitive to low-energy beta
and gamma radiation and does not display the correct dose rate in a mixed-energy
gamma radiation field. Even radiation professionals sometimes select the wrong
instrument or use the instrument they selected inappropriately. For this reason, it
seems appropriate to briefly discuss how to select radiation instruments that are
appropriate for the task at hand, and to summarize this information in a table.
4.6.1 Contamination surveys are best performed using a radiation detector with
a large cross-sectional area that is sensitive to the type of radiation thought to be
present.
• If multiple types of radiation are thought to be present, a “pancake” GM is useful,
although this is not sensitive to low-energy beta (e.g. tritium) or gamma (e.g.
125 I)
emitting radionuclides.
• Low-energy beta radiation can only be detected by performing a smear wipe that
can be counted using a liquid scintillation counter or through the use of a hand-held
proportional counter.
• Low-energy gamma contamination can only be detected by using a low-energy
gamma scintillation detector, such as a thin-crystal sodium iodide detector.
4.6.2 Radiation dose rate surveys must be performed using a survey instrument
sensitive to the type of radiation present and that is designed to accurately measure
energy deposition (as opposed to simply recording counts).
Gamma radiation dose rate can be accurately measured using an ionization
chamber or, at very low dose rates, using a pressurized ionization chamber.
Gamma radiation dose rate can also be measured fairly accurately using an
energy-compensated GM tube for gamma energies in excess of about 100 keV.
Beta radiation dose rate can be accurately measured using an ionization chamber
with a “beta window.”
Neutron radiation dose rate can only be accurately measured using a neutron
detector.
Radiation dose rate from alpha radiation is not normally measured as, due to their
very low penetrating ability, alpha particles typically do not exposure more than one
or two cells at a time.
These are summarized in Table 4.1.
37
4.6 Instrument Selection
While only your radiation instruments will indicate the presence of radiological
danger, excessive contamination, or other concerns, not every instrument is useful
in all situations. A GM detector, for example, is not sensitive to low-energy beta
and gamma radiation and does not display the correct dose rate in a mixed-energy
gamma radiation field. Even radiation professionals sometimes select the wrong
instrument or use the instrument they selected inappropriately. For this reason, it
seems appropriate to briefly discuss how to select radiation instruments that are
appropriate for the task at hand, and to summarize this information in a table.
4.6.1 Contamination surveys are best performed using a radiation detector with
a large cross-sectional area that is sensitive to the type of radiation thought to be
present.
• If multiple types of radiation are thought to be present, a “pancake” GM is useful,
although this is not sensitive to low-energy beta (e.g. tritium) or gamma (e.g.
125 I)
emitting radionuclides.
• Low-energy beta radiation can only be detected by performing a smear wipe that
can be counted using a liquid scintillation counter or through the use of a hand-held
proportional counter.
• Low-energy gamma contamination can only be detected by using a low-energy
gamma scintillation detector, such as a thin-crystal sodium iodide detector.
4.6.2 Radiation dose rate surveys must be performed using a survey instrument
sensitive to the type of radiation present and that is designed to accurately measure
energy deposition (as opposed to simply recording counts).
Gamma radiation dose rate can be accurately measured using an ionization
chamber or, at very low dose rates, using a pressurized ionization chamber.
Gamma radiation dose rate can also be measured fairly accurately using an
energy-compensated GM tube for gamma energies in excess of about 100 keV.
Beta radiation dose rate can be accurately measured using an ionization chamber
with a “beta window.”
Neutron radiation dose rate can only be accurately measured using a neutron
detector.
Radiation dose rate from alpha radiation is not normally measured as, due to their
very low penetrating ability, alpha particles typically do not exposure more than one
or two cells at a time.
These are summarized in Table 4.1.