12.5 Units of Radiation Dose
193
it is always better to experimentally measure the dose rate to get the real dose-rate.
Nevertheless, theoretical calculation does give some idea about the magnitude of
dose likely to be received by the isotope.
12.6 Protection from External Hazard
While working in radiochemical laboratory, it often happens that the dose-rate of the
sample is higher than the maximum permissible level, especially while dispensing
the highly active materials (like
82 Br). In such cases, the dose-rate is cut down by
one or more methods discussed in foregoing sections.
12.6.1 Distance
The intensity of radiations reaching the object is inversely proportional to the square
of the distance between the source and the object. Therefore, distance acts as a good
shielding. In the practical work, it is not possible to handle the radioactive material
at a long distance unless there are facilities, like remote control systems. However,
tweezers of six inches long are used to handle the radioactive sources in order to
reduce the dose-rate to some extent.
12.6.2 Shielding
It is possible to reduce the hazards of nuclear radiation by using a shield. Usually,
lead bricks are used for shielding γ -rays. One can use relatively thinner lead bricks as
compared to aluminum bricks to stop the β-particles to the same magnitude because
the latter element has low atomic weight.
Since γ -radiation may be scattered in all directions, care must be taken to see that
there is an adequate shielding from all the directions to prevent scattered radiations
reaching the person handling the radioactive material. However, for β-particles, elements of low atomic number such as aluminum, glass, polythene sheets etc., are used
for shielding purposes, because though the high atomic number nuclei would stop
the β-particles more effectively with a thinner sheet, but these materials increase
the Bremsstrahlung radiation for which we may need thicker lead bricks. Hence,
it is better to avoid the generation of Bremsstrahlung radiation by avoiding high
atomic weight elements. Unfortunately, there is no simple satisfactory method for
calculating the shielding thickness, taking due account of the scattered radiation. The
usual method is to check the dose-rate, at various distances from the shielding, by a
hand monitor, and if the dose-rate is higher than maximum permissible level, more
shielding has to be used.
193
it is always better to experimentally measure the dose rate to get the real dose-rate.
Nevertheless, theoretical calculation does give some idea about the magnitude of
dose likely to be received by the isotope.
12.6 Protection from External Hazard
While working in radiochemical laboratory, it often happens that the dose-rate of the
sample is higher than the maximum permissible level, especially while dispensing
the highly active materials (like
82 Br). In such cases, the dose-rate is cut down by
one or more methods discussed in foregoing sections.
12.6.1 Distance
The intensity of radiations reaching the object is inversely proportional to the square
of the distance between the source and the object. Therefore, distance acts as a good
shielding. In the practical work, it is not possible to handle the radioactive material
at a long distance unless there are facilities, like remote control systems. However,
tweezers of six inches long are used to handle the radioactive sources in order to
reduce the dose-rate to some extent.
12.6.2 Shielding
It is possible to reduce the hazards of nuclear radiation by using a shield. Usually,
lead bricks are used for shielding γ -rays. One can use relatively thinner lead bricks as
compared to aluminum bricks to stop the β-particles to the same magnitude because
the latter element has low atomic weight.
Since γ -radiation may be scattered in all directions, care must be taken to see that
there is an adequate shielding from all the directions to prevent scattered radiations
reaching the person handling the radioactive material. However, for β-particles, elements of low atomic number such as aluminum, glass, polythene sheets etc., are used
for shielding purposes, because though the high atomic number nuclei would stop
the β-particles more effectively with a thinner sheet, but these materials increase
the Bremsstrahlung radiation for which we may need thicker lead bricks. Hence,
it is better to avoid the generation of Bremsstrahlung radiation by avoiding high
atomic weight elements. Unfortunately, there is no simple satisfactory method for
calculating the shielding thickness, taking due account of the scattered radiation. The
usual method is to check the dose-rate, at various distances from the shielding, by a
hand monitor, and if the dose-rate is higher than maximum permissible level, more
shielding has to be used.