3. The equivalent dose H is the absorbed dose
multiplied by a dimensionless radiation
weighting factor, WR which expresses the
biological effectiveness of a given type of
radiation
To avoid confusion with the absorbed dose,
the SI unit of equivalent dose is called the
sievert (Sv). The old unit was the “rem”
4. The SI unit: sievert (Sv)
HT (Sv) = WR x D (Gy)
Traditional (old) unit:
rem (roentgen equivalent man)
HT (rem) = WR x D (rad)
1 Sv = 100 rem
6. Radiation type and energy range WR
Photons (X-rays and gamma-rays) all
energies
Electrons, all energies
Neutrons
<10 keV
10-100 keV
>100 kev to 2 MeV
2-20 MeV
>20 MeV
Protons >20MeV
Alpha-particles, fission fragments
1
1
5
10
20
10
5
5
20
7. To account for differences in LET when measuring the
effect of radiation, each type of radiation has been
assigned a radiation weighting factor (WR).
This was done by measuring how much of each radiation
type it took to produce the same biological effect as 200-
keV X rays.
As shown, all photons, beta particles do the same
amount of damage.
Thermal neutrons do somewhat more damage, and fast
neutrons and alpha particles are extremely damaging.
9. The equivalent dose in each organ and tissue is
multiplied by a tissue weighting factor, WT, and the
results are summed over the whole body to give the
effective dose E
E=∑WT HT
12. These are multipliers used for radiation protection
purposes to account for the different sensitivities of the
organs and tissues to the induction of stochastic effects
of radiation.
The relationship between the probability of the
stochastic effect and equivalent dose varies with the
tissue irradiated.
Tissues which are at higher risk from radiation will
have higher weighting factors (WT)
The sum of the tissue weighting factors is equal to 1.
14. The collective dose refers to the amount
of radiation received by a group of people.
It is calculated by multiplying the average
effective dose received by the number of
persons exposed.
The collective dose is expressed in person-
sieverts (person-Sv).
15. S=∑Ei Ni
where Ei is the average effective dose in the
population subgroup i and Ni is the number of
individuals in the subgroup.
17. The quantity HT(tf), defined as:
HT (tt)=∫
t0+tf
t0 HT (t) dt
Where t0 is the time of intake and HT (t) is
the equivalent dose rate at time t in organ or tissueT
“ t “is the time elapsed after an intake of radioactive
substances.
When t is not specified, it will be taken to be 50
years for adults and to age 70 years for intakes by
children.
19. ALI is the derived limit for the amount of
radioactive material taken into the body of an
adult worker by inhalation or ingestion in a
year.
ALI is the smaller value of intake of a
given radionuclide in a year by the "reference
man" that would result in a committed
effective dose equivalent (CEDE) of
5 rems (0.05 sievert) to any individual organ or
tissue.
21. The DAC is the activity concentration in
air in Bq/m3 of the radionuclide
considered which would lead to an intake
of ALI assuming a breathing rate of the
ReferenceWorker of 1.2 m3 /hr and an
annual working time of 2000 hours
Then the DAC is given by:
DAC=ALI/2400
23. The personal dose equivalent ,Hp(d), is the operational
quantity for individual Monitoring
It is the dose equivalent in soft tissue (ICRU-sphere)
below a specified point on the body at an appropriate
depth ‘d’
This quantity can be used for measurements of
superficial and deep organ doses,
depending on the chosen value of the depth in tissue.
24. The depth d is expressed in millimetres, and ICRU
recommends that any statement of personal dose
equivalent should specify this depth.
For superficial organs, depths of 0.07 mm for skin and
3 mm for the lens of the eye are employed, and the
personal dose equivalents for those depths are denoted
by Hp(0.07) and Hp(3), respectively.
For deep organs a depth of 10 mm is frequently used,
with the notation Hp(10).
To account for differences in LET when measuring the effect of radiation, each type of radiation has been assigned a radiation weighting factor (WR). This was done by measuring how much of each radiation type it took to produce the same biological effect as 200-keV X rays.
As shown, all photons, beta particles, and electrons do the same amount of damage. Thermal neutrons do somewhat more damage, and fast neutrons and alpha particles are extremely damaging. Indeed, of the radiation types that we deal with, alpha particles and high-energy neutrons are the most damaging.
Collective effective dose accounts for the number of people exposed to a source by multiplying the average effective dose to the exposed group from the source by the number of individuals in the group.
Unit: man sievert (man Sv).
International commission on radiation units and measurements
International commission on radiation units and measurements
