P

• Parent

  In a decay process, a nuclide that decays; in a decay chain, the first nuclide in the chain. (See "Daughter".)

• Particle accelerator

  Electrical radiation generator in which the speed of a stream of charged particles (electrons, protons, etc.) is increased. Depending on the type of acceleration, they are divided into circular (betatrons, cyclotrons, etc.) or linear (linacs) accelerators. In radiotherapy, charged particles can be used directly (electrotherapy, proton therapy, etc.) or through a target which, on receiving the particle beam, emits high-energy X-rays (over 5 MeV) or neutrons (neutrotherapy).

• Particle flow or fluence

  Number of particles that enter a small sphere every unit of time, divided by the area of the sphere's maximum circle.

• Population at large

  For the purpose of radiological protection, the entire population including the members of the public and the professionally exposed workers and trainees and students during their usual working hours.

• Positron

  Antiparticle of the electron; it has the same mass and the same electric charge, but in the positron this charge is positive instead of negative, as happens with the electron.

• Precursor

  In a decay chain, the radionuclide preceding the one being considered.

• Primary coolant

  Fluid used to extract the heat produced in the core of a nuclear reactor.

• Primary cooling circuit

  Closed system through which a nuclear reactor's coolant flows (in most reactors, water), in order to extract the heat formed in the core by the nuclear reaction. It is therefore the circuit that contains the fluid which comes into direct contact with the fuel elements.

• Professionally exposed worker

  Person who works in the presence of ionising radiation and may receive more than one tenth of the dose limits established for workers. If it is possible that the worker may receive more than 1/10, but it is very unlikely that he or she may receive more than 3/10 of the dose limits (more than 5 and less than 15 mSv), the worker is classified as category B. If it is possible that the worker may receive more than 3/10 of the established limits (15 mSv), he or she is classified as category A and will be required to use an individual dosimetry system.

• Protected area

  An area established around the area under the operator's control where means are provided to protect the population in the event of an accident at the site.

• Proton

  Elementary particle whose electric charge is positive and equal to that of the electron, and whose mass is 1.67 E-27 g. It is found in the nucleus of atoms.