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''Effective dose'' in particular is a central feature of radiological protection. It sums up any number of different exposures into a single number that reflects, in a general way, the overall risk. The concept may be complex, but it makes radiological protection practical to implement.
'''Dose limits help ensure that no person is exposed to an excessive amount of [[ICRPædia Guide to the Basics of Ionising Radiation|radiation]] in normal, planned situations.'''
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→Dose Limits
Radiation dose is a measure of the amount of exposure to radiation. There are three kinds of dose in radiological protection. ''Absorbed dose'' is a measureable, physical quantity, while ''equivalent dose'' and ''effective dose'' are specifically for radiological protection purposes.
===Absorbed Dose===
Effective dose = sum for all organs of (equivalent dose to the organ times the appropriate tissue weighting factor)
The tissue weighting factors are needed because different organs have different levels of sensitivity to radiation, even if the equivalent dose is the same. Effective dose is expressed in sieverts (Sv), or, more frequently, millisieverts (mSv) which are 1/1000th of a sievert. This is the most frequently used dose in radiological protection. Unless you see mention of a specific organ, a "dose" in Sv or mSv is the effective dose. In the simplest cases, for uniform whole-body exposure to gamma (photon) or beta (electron) radiation, the radiation weighting factor is 1, and the tissue weighting factors add up to 1, and therefore, for example, an absorbed dose of 1 mGy equals an effective dose of 1 mSv.
''Effective dose'' in particular is a central feature of radiological protection. It sums up any number of different exposures into a single number that reflects, in a general way, the overall risk. The concept may be complex, but it makes radiological protection practical to implement.
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==Dose Limits==
They are the strongest form of restriction on dose to an individual. Exceeding a dose limit is contrary to regulations in most countries.
===Dose Limits Recommended by ICRP===
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Dose limits alone are not enough to ensure adequate protection. They function in combination with the [[System_Of_Radiation_Protection_Overview#Fundamental Principles of Radiological Protection | fundamental principles]] of justification and optimisation. These limits apply only to doses received above the normal local [[Sources of Radiation Exposure | natural background radiation]]. Limits on [[System_of_radiation_protection_module_2#Effective Dose | effective dose]], combined with optimisation of protection, are designed to avoid a risk of [[Effects of Exposure | stochastic effects]] that would be considered intolerable in a [[System_of_radiation_protection_module_2#Exposure Categories and Situations | planned exposure situation]]. Limits on [[System_of_radiation_protection_module_2#Equivalent Dose | equivalent dose to an organ]], combined with optimisation of protection, are designed to prevent the occurance of [[Effects of Exposure | deterministic effects]]. Dose limits apply only in [[System_of_radiation_protection_module_2#Exposure Categories and Situations | planned exposure situations]]. In other situations, restrictions on individual dose are called reference levels. They provide the additional flexibility needed in [[System_of_radiation_protection_module_2#Exposure Categories and Situations | emergency and existing exposure situations]] to make sure protection is optimised.
Dose limits apply only in [[System_of_radiation_protection_module_2#Exposure Categories and Situations | planned exposure situations]]. In other situations, restrictions on individual dose are called reference levels. They provide the additional flexibility needed in [[System_of_radiation_protection_module_2#Exposure Categories and Situations | emergency and existing exposure situations]] to make sure protection is optimised. Dose limits do not apply to [[System_of_radiation_protection_module_2#Exposure Categories and Situations | medical exposures]]. If they did, the effectiveness of diagnosis or treatment might be reduced, doing more harm than good for the patient. The emphasis is on justification of medical procedures and optimisation of protection.
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