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of uranium 238 to spontaneously disintegrate, but only 24,000 years for half of the atoms in a mass
of plutonium 239 to spontaneously disintegrate. Iodine 131, commonly used in medicine, has a
half-life of only eight days.

There are following dose of ionizing radiation:

1) Еxposure dose.

The ionizing effects of radiation are measured by units of exposure.

 The coulomb per kilogram (C/kg) is the SI unit of ionizing radiation
exposure and measures the amount of radiation required to create 1 coulomb of
charge of each polarity in 1 kilogram of matter.

 The roentgen (R) is an older traditional unit that is almost out of use,
which represented the amount of radiation required to liberate 1 electrostatic unit
(esu) of charge of each polarity in 1 cubic centimeter of dry air. 1 Roentgen =
−4
2.58×10 C/kg.

dQ
D  .
exp
dm
2) Absorbed dose.

However, the amount of damage done to matter by ionizing radiation is more
closely related to the amount of energy deposited rather than the charge. This is
called the absorbed dose.

There are the following units of absorbed dose:

 The gray (Gy), with units J/kg, is the SI unit of absorbed dose, which
represents the amount of radiation required to deposit 1 joule of energy in 1
kilogram of any kind of matter.

 The rad (radioactivity absorbed dose), is the corresponding traditional
unit, which is 0.01 J deposited per kg. 100 rad = 1 Gy.

dE
D abs  c .
dm

3) Equivalent dose

Equal doses of different types or energies of radiation cause different amounts
of damage to living tissue.

For example, 1 Gy of alpha radiation causes about 20 times as much damage as
1 Gy of X-rays. Therefore, the equivalent dose was defined to give an approximate
measure of the biological effect of radiation.

It is calculated by multiplying the absorbed dose by a weighting factor W R,
which is different for each type of radiation (Table 13.3). This weighting factor is

4