Effective amount

In Nuclear physics, the effective amount is a physical Grandeur measuring the impact on the biological fabrics of an exposure to a Ionizing ray, in particular with a source of Radioactivité. It is defined as the absorptive Dose , namely the energy received by Unité of Masse, corrected of a factor without dimension taking of account the relative dangerosity of the radiation considered and the sensitivity of irradiated fabric.

The unit of the effective amount is the Sievert (Sv), in the honor of the Physicien Rolf Sievert, and can be expressed in effective equivalent of Joule by Kilogram (J/kg). The old unit, the Rem, is worth 10 mSv (100 rem = 1 Sv).

Use

The effective amount is a unit used in Radioprotection to predict the risks Stochastique S related to a chronic irradiation. It is not adapted to envisage the effects of a acute irradiation.

The effective amount

General calculation

Starting from the absorptive amounts D R, T delivered by various radiations R on various fabrics T the effective amount is calculated according to:

E = \ sum_ \ mathrm {T} \ sum_ \ mathrm {R} w_ \ mathrm {T} w_ \ mathrm {R} D_ \ mathrm {R, T} \, .
where the W T are the factor loadings of the fabrics and the W R the factor loadings of the radiations.

One can also write E according to the equivalent amounts H T delivered on the fabrics T:

E = \ sum_ \ mathrm {T} w_ \ mathrm {T} H_ \ mathrm {T} \, .

In practice, the effective amount is the sum of the directly measured external Dose by a Dosimètre and estimated internal Dose by the doctor starting from the activity incorporated in the organization.

Factor loading of fabrics

The external amount

See also: Dosimeter

The Internal amount

It is given starting from the measurement of the activity of the organization or of excreted.

The first stage consists in determining the built-in activity thanks to models biocinetic. This built-in activity associated with tables of the CIPR makes it possible to evaluate the committed amount.

Models of entry

Before determining to become it of each radio operator isotope in the organization, it should be known if the inhaled or introduced substance will be transferred in the blood system.

To study that, the CIPR developed two models of entry:

  • the respiratory model : it consists of five thoracic areas, 2 extra sectors (ET1 and ET2) and 3 thoracic sectors (BB, bb and AI). The risk of incorporation by inhalation is most important in the workers, this model is thus used the most. It is closely related to the granulometry particles like with the chemical form of the radioisotope and the solubility of the substance. Three types of particles were thus defined:

  • the food model : It was recently corrected by the CIPR. the introduced particles are absorbed according to a gastro-intestinal factor of absorption . This factor, like in the case of inhaled particles, depends on the physicochemical form of the introduced radionuclides.

  • a model of transfer for the wounds also exists.

Incorporated activity, function of retention

The estimate of the built-in activity (AI) is based for each individual over the physical period and the biological half-life of each isotope.

It can be given by the company doctor to leave:

  • Is activity present in the organization thanks to a measurement direct, known as in vivo , radioactivity of the individual: the rays emitted through the body are directly measured by Anthroporadiamétrie;
  • Is biological sample thanks to an indirect measurement of biological samples eliminated by the organization (urines…).

AI = \ tfrac {M} {m (T)}

If M is the measured activity of the organization, m (T) is the value of the function of retention R (T) for a time t
Si M is the measured activity of the biological sample, m (T) is the value of the function of excretion E (T) for a time T (since incorporation).

The functions of retention depend on certain elements such as:

  • the type of exposure: acute or chronic
  • modes of incorporation (S)
  • contaminant radioisotopes like their forms physico - chemical
  • the physiology of the subject (age, morphology, retention of the radioisotopes in the bodies…)
  • lifestyle (deprives of iodine)
  • emergency treatments (ex: iodine catch) and the drugs

These various variables, studied in the systemic models, are generally badly identified, especially those which depend on the physiology of the subject. The CIPR recommends nevertheless the use of average values of reference, described in its publications.

Moreover, the date of the exposure is necessary to go back with the built-in activity and the amount. It is a data often difficult to determine with precision.

Committed effective amount

The internal component of the effective amount can be given starting from the built-in activity (AI, in Bq or Bq/jour), by using DPUI (effective amount engaged per unit of incorporation, in Sv.Bq-1) . This coefficient takes into account the two factor loadings (Wr and wt) as well as the functions of retention.

Thus, for an acute exposure the effective amount committed over 50 years is: E_ {50} = AI \ times DPUI

And for a chronic exposure, during I days: E_ {50} = AI \ times I \ times DPUI

The values of reference of the DPUI by ingestion and inhalation are defined by the CIPR and are proposed in the French decree of September 1st, 2003

See too

Internal bonds

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