Radiation protection Flashcards
What is health physics?
Why do we need to define radiation protection protocols?
Why is dosimetry not enough to build protocols on radiation protection?
Health physics is the discipline of public health that concerns itself with radiation protection.
It involves physics, biology and health policy as it considers both effects of physical dose and radiobiology + tries to build protocols and norms for the safety of the community.
Physics alone, dosimetry in particular, is not enough to build appropriate protocols on radiation protection because, although the physical absorbed dose is very precisely measurable, it doesn’t account for the biological effects of the radiation.
- The biological target is the chromosomal DNA. The organ response to the damages caused by radiation can become visible and appreciable only after weeks or years from the exposure.
The dose response is determined by both deterministic and stochastic effects. The firsts are in principle predictable and are assigned to a specific probability. The stochastic effects are not predictable because there’s no relation between the observed effects and the dose.
–> Health physics tries to develop models to quantify the biological damage through:
- dosimetry (physical method)
- in vitro experiments (biological method)
- epidemiological studies (statistical method, requires a large cohort of people
Give the definition of radiation exposure
Exposure to radiation is the collection of all the events during which dose can be absorbed, either from the outside or the inside of the body. 3 cathegories of radiation exposure have been identified:
- Occupational
- Public
- Medical
Explain what are the principles of radiation protection and give examples of how they can be put in practice for the specific case of external exposure.
PRINCIPLES OF RADIATION PROTECTION
1) dose limits: are defined by the ICRP for specific groups of people. They are not applicable to medical or natural exposures.
2) justification: the benefit of the intentional exposure should be greater than the risks related to the exposure.
3) optimization: ALARA principle
Protection from external exposure:
1) maximization of the distance from the radiation source
2) minimization of the exposure time
3) shieldings
What is the dose limit defined for public exposure? What is the one for occupational exposure?
PUBLIC: 1 mSv/a
OCCUPATIONAL: 20 mSv/a
What are the quantities we refer to when talking about radiation protection from external exposure?
Not measurable, but defined for the only purpose of quantifying dose limits.
1) EQUIVALENT dose: Obtained by the product of the physical dose with correction factors that account for the different effectiveness of radiation in causing biological harm. The weighting factor depends then on the radiation (beam energy and quality).
2) EFFECTIVE dose: Obtained by the product of the equivalent dose with weighting factors accounting for the different organ sensitivities to the radiation. The weighting factor depends then on the tissue.
What are the operational quantities? What are they used for?
Since the radiation protection quantities are nor measurable, their quantification has to be obtained with the help of other quantities: so-called operational quantities.
These are:
PDE) equivalent dose in a soft tissue below a specified point of the body at an appropriate depth d.
ADE) dose delivered to a depth of d (mm) in the ICRU sphere under condition of broad beam and parallel irradiation
What is the quantity we refer to when talking about internal exposure?
In case of internal contamination the dose is delivered by the injested radionuclides. The contamination time span t is given by the death of the host or the decay of the radionuclide.
The quantity is the COMMITTED DOSE. This is defined as the integral over the contamination time span of the dose delivery rate: dD0/dt e^(-lambda_e t)
Cite some exposure values for natural radiation sources.
Compare the dose rates of natural and medical radiation.
Space+Terrestrial: 1.8/1.9 –> mSv
Food/water + everyday activities –> < 5.5 mSv
Nuclear + Industries/Research/Hospitals –> < 1.65 mSv
The dose rate of diagnostics medical images is 10^6 times larger than that of natural radiation. Lower doses and dose rates have lower biological effectiveness than high dose/dose rates. Quantified by the DDREF.
