Hall Book Ch 16 (Radiation Protection) Flashcards
The objectives of radiation protection are to prevent clinically significant ( ) by keeping doses below the practical threshold and to limit the risk of ( ) to a reasonable level in relation to societal needs, values, and benefits gained.
tissue reactions = deterministic effect
stochastic effects (cancer and heritable effects)
( ) is one of the basic principles of radiation protection; a practice involving exposure to radiation should produce sufficient benefit to the exposed individual or to society to offset the radiation detriment it causes.
( ) are approximate values of the RBE applicable to low doses and relevant to carcinogenesis and heritable effects.
Values of WR are chosen by the ICRP based on experimental RBE values with a large judgmental factor.
Justification, WR (Radiation Weighting Factor)
Equivalent dose is the product of ( ).
The unit is sievert for an absorbed dose in gray (Gy). ICRP has recommended a new name for this quantity—( )—and is considering a new name for the unit.
absorbed dose and WR (Radiation Weighting Factor)
radiation weighted dose
( ) reflect the susceptibility of different organs or tissues to carcinogenesis or heritable effects.
Effective dose is the sum of the weighted equivalent doses for all irradiated
tissues and organs multiplied by the appropriate WT.
Committed equivalent dose is the integral over 50 years of the equivalent dose
after the intake of a radionuclide.
Committed effective dose is the integral over 50 years of the effective dose in
the case of an incorporated radionuclide.
Collective effective dose is a quantity for a population and is the sum of
effective doses to all members of that population. The unit is person-sievert.
Collective committed effective doses applies to a population ingesting or
inhaling radionuclides and is the integral over 50 years of the effective dose
over the entire population.
All radiation exposures are governed by the ALARA principle.
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No occupational exposure should be permitted before 18 years of age.
The effective dose in any 1 year should not exceed 50 mSv (NCRP).
The individual worker’s cumulative lifetime effective dose should not exceed
age in years × 10 mSv (NCRP). However, to date, the NRC has not adopted
this cumulative limit.
To limit tissue reactions, the dose limit to the lens of the eye is 50 mGy per
year, and the dose limit to localized areas of the skin, hands, and feet is 500
mSv per year.
Once a pregnancy is declared, the NCRP recommends a monthly limit of 0.5
mSv to the embryo or fetus.
Specific controls for occupationally exposed women are no longer
recommended until a pregnancy is declared.
Internally deposited radionuclides pose a special problem for protection of the
embryo or fetus; particular care should be taken to limit intake.
Emergency occupational exposures normally justify doses in excess of the
recommended limits only if life-saving actions are involved. Volunteers from
among older workers with low lifetime accumulated effective doses should
be chosen in emergencies in which the exposure may be up to 0.5 Sv. If the
exposure may exceed 0.5 Sv, the worker should be counseled about the shortand long-term possible consequences.
For educational or training purposes, it may sometimes be desirable to accept
radiation exposures of persons younger than 18 years of age, in which case
the annual effective dose limit of 1 mSv should be maintained.
The annual effective dose limit for members of the public is 1 mSv, except for
infrequent exposures in which the limit may be 5 mSv. Medical x-rays are
excluded from these limitations because they are assumed to confer personal
benefit.
For tissue reactions (deterministic effects), the dose limit for members of the
general public is 50 mSv to the hands and feet and to localized areas of the
skin and 15 mSv to the lens of the eye.
Indoor radon is perceived to be the most important problem involving radiation
exposure of the general public to naturally occurring radiation. Remedial
action in homes is recommended by the EPA if the radon concentration
exceeds 148 Bq/m3
.
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Negligible individual dose is the dose below which further expenditure to
improve radiation protection is unwarranted. The negligible individual dose
is an annual effective dose of 0.01 mSv, which carries a risk of between 10−6
and 10−7 of carcinogenesis or heritable effects.
ICRP introduced the concept of “detriment” to quantify the harmful effects of
radiation exposure in different parts of the body, taking account of the
severity of the disease in terms of lethality, loss of quality of life, and years of
life lost.
A uniform whole body equivalent dose of 1 Sv to an adult radiation worker is
assumed to result in a total detriment of about 5.7% per Sv. This is made up
of a risk of fatal and nonfatal cancer together with a small contribution from
severe heritable effects.
The average annual equivalent dose to monitored radiation workers is about 2
mSv. This involves a total detriment of about one in 10,000, which is
comparable to the annual risk of a fatal accident in a “safe” industry such as
trade or government service.
The NCRP and ICRP differ in two important recommendations:
1. The effective dose limit for occupational exposure (stochastic effects).
The NCRP recommends a lifetime cumulative limit of age × 10 mSv, with
a limit in any year of 50 mSv. The ICRP recommends a limit of 20 mSv
per year averaged over defined periods of 5 years, with a limit in any year
of 50 mSv.
2. The dose limit to the developing embryo or fetus once a pregnancy is
declared. The NCRP recommends a monthly limit of 0.5 mSv to the
embryo or fetus. The ICRP recommends a limit of 2 mSv to the surface of
the woman’s abdomen for the remainder of pregnancy.
WT (Tissue Weighting Factor)
