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D

dose:
1.   A measure of the energy deposited by radiation in a target.
For definitions of the most important such measures, see dose quantities and dose concepts.

2.    Absorbed dose, committed equivalent dose, committed effective dose, effective dose, equivalent dose or organ dose, as indicated by the context.

• committed dose: committed equivalent dose or committed effective dose.

dose concepts:

• annual dose:The dose due to external exposure in a year plus the committed dose from intakes of radionuclides in that year.
  The individual dose, unless otherwise stated.

! This is not, in general, the same as the dose actually delivered during the year in question, which could include doses from radionuclides remaining in the body from intakes in previous years, and could exclude doses delivered in future years from intakes during the year in question.

• avertable dose: The dose that could be averted if a countermeasure or set of countermeasures were to be applied.
• averted dose: The dose prevented by the application of a countermeasure or set of countermeasures, i.e. the difference between the projected dose if the countermeasure(s) had not been applied and the actual projected dose.
• collective dose: The total radiation dose incurred by a population.
  This is the sum of all of the individual doses to members of the population.  If the doses continue for longer than a year, then the annual individual doses must also be integrated over time.  Unless otherwise specified, the time over which the dose is integrated is infinite; if a finite upper limit is applied to the time integration, the collective dose is described as ‘truncated’ at that time.
  Unless otherwise specified, the relevant dose is normally effective dose (see collective effective dose for the formal definition).
  Unit: man sievert (man Sv).  This is, strictly, just a sievert, but the unit man sievert is used to distinguish the collective dose from the individual dose which a dosimeter would measure (just as, for example, ‘man hours’ are used to measure the total effort devoted to a task, as opposed to the elapsed time that would be shown by a clock).
  Contrasting term: individual dose.

! The BSS definition states that the collective dose is "defined as the product of the number of individuals exposed to a source and their average radiation dose."  Strictly, it would be more accurate to say that the collective dose can be expressed in this way, but it is not defined as such — indeed, in order to calculate the average dose it would normally be necessary to calculate the collective dose (by summing the individual doses, and integrating over time if necessary) and divide it by the number of individuals.

• committed dose:The lifetime dose expected to result from an intake.
  This term partially supersedes dose commitment.
• dose commitment: The total dose that would eventually result from an event (e.g. a release of activity), a decision or a finite portion of a practice.
  More specific and precise terms, such as committed dose or collective dose should be used as appropriate.
• individual dose: The dose incurred by an individual.
  For contrast with collective dose.
• lifetime dose: The total dose received by an individual during his/her lifetime.
  In practice, often approximated as the sum of the annual doses incurred.  Because annual doses include committed doses, some parts of some of the annual doses may not actually be delivered within the lifetime of the individual, and therefore this may overestimate the true lifetime dose.
  For prospective assessments of lifetime dose, a lifetime is normally interpreted as 70 years.
• projected dose: The dose that would be expected to be incurred if a specified countermeasure or set of countermeasures — or, in particular, no countermeasures — were to be taken.
  The BSS definition [40] refers only to the dose that would be received if no countermeasures were to be taken.
• residual dose: In a chronic exposure situation, the dose expected to be incurred in the future after intervention has been terminated (or a decision has been taken not to intervene).

dose and dose rate effectiveness factor (DDREF):
The ratio between the risk or radiation detriment per unit effective dose for high doses and/or dose rates and that for low doses and dose rates.
Used in the estimation of risk coefficients for low doses and dose rates from observations and epidemiological findings at high doses and dose rates.
Supersedes dose rate effectiveness factor (DREF).

dose equivalent:
The product of the absorbed dose at a point in the tissue or organ and the appropriate quality factor for the type of radiation giving rise to the dose.
A measure of the dose to a tissue or organ designed to reflect the amount of harm caused.
A quantity used by the International Commission on Radiation Units and Measurements (ICRU) in defining the operational quantities ambient dose equivalent, directional dose equivalent and personal dose equivalent (see dose equivalent quantities).  The quantity dose equivalent has been superseded for radiation protection purposes by equivalent dose. [40]

• effective dose equivalent, H_E: A measure of dose designed to reflect the risk associated with the dose, calculated as the weighted sum of the dose equivalents in the different tissues of the body.
  Superseded by effective dose.

dose equivalent quantities:

• ambient dose equivalent, H*(d): The dose equivalent that would be produced by the corresponding aligned and expanded field in the ICRU sphere at a depth d on the radius opposing the direction of the aligned field.
  Defined at a point in a radiation field.  Used as a directly measurable proxy for effective dose for use in monitoring of external exposure.
  The recommended value of d for strongly penetrating radiation is 10 mm.
• directional dose equivalent, Hc(d,W): The dose equivalent that would be produced by the corresponding expanded field in the ICRU sphere at a depth d on a radius in a specified direction W.
  Defined at a point in a radiation field.  Used as a directly measurable proxy for equivalent dose in the skin for use in monitoring of external exposure.
  The recommended value of d for weakly penetrating radiation is 0.07 mm.
• individual dose equivalent, penetrating, H_p(d): See personal dose equivalent.
• individual dose equivalent, superficial, H_s(d): See personal dose equivalent.
• personal dose equivalent, H_p(d): The dose equivalent in soft tissue below a specified point on the body at an appropriate depth d.
  Used in the BSS as a directly measurable proxy for equivalent dose in tissues or organs or (with d = 10 mm) for effective dose, in individual monitoring of external exposure.
  The recommended values of d are 10 mm for strongly penetrating radiation and 0.07 mm for weakly penetrating radiation.  ‘Soft tissue’ is commonly interpreted as the ICRU sphere.
  Recommended by ICRU [49], [50] as a simplification of the two separate terms, individual dose equivalent, penetrating, Hp(d), and individual dose equivalent, superficial, Hs(d) defined in ICRU 39 [63].

dose limit:
See limit.

dose quantities:

• absorbed dose, D: The fundamental dosimetric quantity D, defined as:
  
  where d is the mean energy imparted by ionizing radiation to matter in a volume element and dm is the mass of matter in the volume element. [40]
  The energy can be averaged over any defined volume, the average dose being equal to the total energy imparted in the volume divided by the mass in the volume.
  Absorbed dose is defined at a point; for the average dose in a tissue or organ, see organ dose.
  Unit: J/kg, termed the gray (Gy) (formerly, the rad was used).
• collective effective dose, S: The total effective dose S to a population, defined as:
  
  where E_i is the average effective dose in the population subgroup i and N_i is the number of individuals in the subgroup. It can also be defined by the integral:
  
  where  is the number of individuals receiving an effective dose between E and E+dE. [11]
  
  The collective effective dose S_k committed by an event, a decision or a finite portion of a practice k is given by:
  
  
  where  is the collective effective dose rate at time t caused by k. [40]
• committed effective dose, E(t): The quantity E(t), defined as:
  
  where H_T(t) is the committed equivalent dose to tissue T over the integration time t and w_T is the tissue weighting factor for tissue T.  When t is not specified, it will be taken to be 50 years for adults and to age 70 years for intakes by children. [40]
• committed equivalent dose, H_T(t): The quantity H_T(t), defined as:
  
  where t₀ is the time of intake,  is the equivalent dose rate at time t in organ or tissue T and 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. [40]
• effective dose, E: The quantity E, defined as a summation of the tissue equivalent doses, each multiplied by the appropriate tissue weighting factor:
  
  where H_T is the equivalent dose in tissue T and w_T is the tissue weighting factor for tissue T.  From the definition of equivalent dose, it follows that:
  
  where w_R is the radiation weighting factor for radiation R and D_T,R is the average absorbed dose in the organ or tissue T. [40]
  • The unit of effective dose is J/kg, termed the sievert (Sv).  The rem, equal to 0.01 Sv, is sometimes used as a unit of equivalent dose and effective dose.  This should not be used in Agency documents except when quoting directly from other documents, in which case the value in sieverts should be added in parentheses.
  • Effective dose is a measure of dose designed to reflect the amount of radiation detriment likely to result from the dose.
  • Values of effective dose from any type(s) of radiation and mode(s) of exposure can be compared directly.
• equivalent dose, H_T: The quantity H_T,R, defined as:
  
  

  where D_T,R is the absorbed dose delivered by radiation type R averaged over a tissue or organ T and w_R is the radiation weighting factor for radiation type R.  When the radiation field is composed of different radiation types with different values of w_R the equivalent dose is:
  [40]

  • The unit of equivalent dose is J/kg, termed the sievert (Sv).  The rem, equal to 0.01 Sv, is sometimes used as a unit of equivalent dose and effective dose.  This should not be used in Agency documents except when quoting directly from other documents, in which case the value in sieverts should be added in parentheses.
  • A measure of the dose to a tissue or organ designed to reflect the amount of harm caused.
  • Values of equivalent dose to a specified tissue from any type(s) of radiation can therefore be compared directly.
• organ dose: The mean absorbed dose D_T in a specified tissue or organ T of the human body, given by:
  
  where m_T is the mass of the tissue or organ and D is the absorbed dose in the mass element dm.

dose rate:

! Although dose rate could, in principle, be defined over any unit of time (e.g. an annual dose is, technically a dose rate), in Agency documents the term dose rate should be used only in the context of short periods of time, e.g. dose per second or dose per hour.

dose rate effectiveness factor (DREF):
The ratio between the risk per unit effective dose for high dose rates and that for low dose rates.
Superseded by dose and dose rate effectiveness factor (DDREF).