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A symbol for proton.
A symbol for pico.

A symbol for phosphorus.
A symbol for pressure.
A symbol for peta.

A symbol for protactinium.

Packaging together with its radioactive contents as presented for transport.

Reference: 10CFR71.
Related to fissile material package.
Related to type B package.

The assembly of components necessary to ensure compliance with the packaging requirements in 10CFR part 71. It may consist of one or more receptacles, absorbent materials, spacing structures, thermal insulation, radiation shielding, and devices for cooling or absorbing mechanical shocks. The vehicle, tie-down system, and auxiliary equipment may be designated as part of the packaging.

Reference: 10CFR71.

A chemical element with atomic number 46. Palladium was discovered in 1803 by William Hyde Wollaston in deposits of platinum. The name palladium was derived from the asteroid Pallas. Pallas is also the Greek goddess of wisdom.

Symbol: Pd.
Related to transition metals.

para positronium
An atom-like system composed of a positron and an electron whose spins are antiparallel, in a singlet state. The mean life of para positronium is 10-10 s.

Symbol: p-Ps.
Related to ortho positronium.
Related to positronium.

A synonym for parent nuclide.

The relationship of a nuclide to a second nuclide through a single radioactive decay. The initial nuclide is known as the parent and the product nuclide is known as the daughter.

Related to daughter nuclide.
Related to decay chain.
Related to parent nuclide.

parent nuclide
The first of two nuclides linked by radioactive decay. A parent decays to a daughter nuclide.

Synonym: parent.
Related to daughter nuclide.
Related to decay chain.

particle accelerator
A synonym for accelerator.

A symbol for lead.

A symbol for picocurie.

A symbol for palladium.

A synonym for fuel pellet.

performance assessment
A systematic analysis of the potential risks posed by waste management systems to the public and environment, and a comparison of those risks to established performance objectives.

Reference: DOE Order 5820.2A.
Acronym: PPA.

performance-based regulations
Regulations that are outcome-oriented rather than procedure-oriented.

periodic table
A table showing the chemical elements ordered by atomic number and grouped roughly according to the electron structure of the last valence electron.

Related to actinides.
Related to alkali metals.
Related to alkaline earth metals.
Related to cerium earths.
Related to chart of nuclides.
Related to halogens.
Related to lanthanides.
Related to noble gases.
Related to rare earths.
Related to terbium earths.
Related to transition metals.
Related to yttrium earths.

personal dose equivalent
A synonym for dose equivalent.

personnel monitoring
Measuring and tracking the radiation dose received by personnel.

A unit prefix equivalent to 1015.

Symbol: P.

An object constructed to duplicate the size, density, and composition of a human body. Phantoms are used in radiological protection studies.

phantom material
A synonym for tissue equivalent material.

A chemical element with atomic number 15. Phosphorus was discovered in 1669 by Hennig Brand while he was conducting experiments on urine. The name phosphorus is derived from phosphoros, Greek for bearing light. Phosphorus is also the ancient name for the planet Venus.

Symbol: P.

photoelectric absorption
A synonym for photoelectric effect.

photoelectric effect
An interaction mechanism for x-rays and gamma-rays with matter. The photon is completely absorbed by an atomic electron. The electron is ejected from the atom and it carries an energy of E = Eg - Eb, where Eg is the original photon energy and Eb is the binding energy of the electron. Photoelectric effect is dominant at low photon energies.

Synonym: photoelectric absorption.

Nuclear fission induced by high energy photons.

Related to fission.
Related to fission fragment.
Related to fission neutron.
Related to fission product.
Related to spontaneous fission.
Related to ternary fission.

A quantum of electromagnetic radiation such as a gamma ray or an x-ray. It is a boson and has a mass of 0, a charge of 0 and a spin of 1.

Related to electromagnetic radiation.
Related to gamma ray.
Related to X-ray.

pick-off annihilation
Annihilation of a positron that is bound to a positronium with an electron that is bound to a colliding molecule.

A unit prefix equivalent to 10-12.

Symbol: p.

A unit of radioactivity equivalent to 1.0x10-12 curie. The becquerel has replaced the curie as a unit of radioactivity.

Symbol: pCi.
Related to becquerel.
Related to curie.
Related to megacurie.
Related to microcurie.
Related to millicurie.
Related to nanocurie.

A heavily shielded container designed to safely store or transport radioactive materials.

Related to cask.
Related to cave.
Related to coffin.

A nuclear reactor constructed by stacking graphite blocks and uranium.

Synonym: atomic pile.

A uranium-containing mineral that has concentrations of U3O8 on the order of 50-80%. It has a black, grayish or greenish color; a pitch-like, earth, dull, or glassy luster; and a specific gravity of 6-9.

planned special exposure
An infrequent exposure to radiation, separate from and in addition to the annual dose limits.

Reference: 10CFR20.

plant capacity factor
A synonym for capacity factor.

plant efficiency
The fraction of the energy content of the power plant fuel that is converted into electricity. It is generally expressed as a percentage.

plant factor
A synonym for capacity factor.

A chemical element with atomic number 78. Platinum was used by pre-Columbian Indians, but it was not until 1735 that Ulloa discovered, isolated, and named the element. The name platinum is derived from platina, Spanish for silver.

Symbol: Pt.
Related to transition metals.

A chemical element with atomic number 94. Plutonium was discovered in 1940 by Seaborg, McMillan, Wahl and Kennedy at the University of California, Berkeley. The group irradiated uranium with deuterons in a 60-inch cyclotron. The name plutonium was given in honor of the planet Pluto. Seaborg often said he and his colleagues assigned the symbol Pu for plutonium as a prank as it stood for something that smelled bad. They never believed the community would accept Pu as the adopted symbol.

Symbol: Pu.

A symbol for promethium.

A symbol for polonium.

pocket dosimeter
A small ionization detector that is generally used to monitor whole body exposure.

A synonym for fission poison.

A chemical element with atomic number 84. Polonium was discovered in 1898 by Marie Sklodowska Curie. The name polonium was given in honor of Poland, the homeland of its discoverer, Marie Curie.

Symbol: Po.
Related to metalloids.

pool reactor
A synonym for swimming pool reactor.

positive electron
A synonym for positron.

positive ion
A synonym for cation.

An early proposed name for the positron. It was proposed by the Cosmic Ray Commission of the International Union of Physics at their annual meeting in October 1947.

A synonym for positron.

The antiparticle of the electron. Its mass and spin are identical to that of the electron but it has a charge of +1.

Symbol: e+.
Symbol: β+.
Synonym: positive electron.
Synonym: positon.
Related to beta particle.
Related to electron.
Related to exotic atom.

positron decay
Disintegration by emission of a positron. A neutrino is also emitted in this type of decay and the decay results in the nucleus converting a proton into a neutron.

Synonym: β+ decay
Synonym: positron emission
Related to β- decay.
Related to beta decay.
Related to positron.

An atom-like system formed between an electron and a positron. One of the two particles acts as a nucleus with the other particle orbiting around it. The positronium is unstable and annihilates forming two photons each with an energy of 511 keV, the rest mass of the electron.

Related to ortho positronium.
Related to para positronium.

A chemical element with atomic number 19. Potassium was discovered in 1807 by Sir Humphry Davy who conducted experiments on potash. The name potassium is derived from the English words potash ore.

Symbol: K.
Synonym: kalium.
Related to alkali metals.

power coefficient
The change in reactor reactivity with an increase in power.

Related to reactivity.

power reactor
A reactor designed to produce electricity.

power rod
A synonym for control rod.

An acronym for performance assessment.

A symbol for para positronium.

A symbol for praseodymium.

A synonym for praseodymium.

A chemical element with atomic number 59. Praseodymium first isolated in 1885 by Karl Auer von Welsbach who isolated praseodymium and neodymium from the mineral dydimia. The name praesodymium is derived from prasios and didymos, Greek for green and twin.

Symbol: Pr.
Synonym: praeseodymium.
Related to cerium earths.
Related to lanthanides.
Related to rare earths.

pressure vessel
Acronym: PV.
A synonym for reactor vessel.

pressurized water reactor
A reactor design in which water flows through the core at very high pressures. The water is not allowed to boil in the core but flows to a steam generator.

Acronym: PWR.
Related to boiling water reactor.

primary fission product
A synonym for fission fragment.

primary radiation
Radiation in a system that was not produced as a result of the action of another radiation on that system.

Related to secondary radiation.

For gaseous isotope diffusion it is the material enriched in a given isotope.

Related to feed.
Related to waste.

product nuclide
The nucleus that is formed a nuclear reaction. It is used in the context of a nuclear reaction where the projectile interacts with a target nucleus, producing a product nucleus and an ejectile.

Related to ejectile.
Related to projectile.
Related to target nuclide.

A radiation, particle or ion incident on a target nuclide. It is used in the context of a nuclear reaction where the projectile interacts with a target nucleus, producing a product nucleus and an ejectile.

Related to ejectile.
Related to nuclear reaction.
Related to product nuclide.
Related to target nuclide.

A chemical element with atomic number 61. Promethium was discovered in 1945. The name promethium was is derived from the mythological creature Prometheus who stole fire from the heavens, giving it to humans.

Symbol: Pm.
Related to cerium earths.
Related to lanthanides.
Related to rare earths.

prompt fission neutron
A neutron emitted during fission in the formation of the fission fragments.

Related to beta-delayed neutron.
Related to delayed fission neutron.
Related to fission neutron.

proportional counter
A counting system with a gas ionization detector operated in the voltage region where the pulse height is proportional to the energy of the incident particle.

A chemical element with atomic number 91. Protactinium was discovered in 1913 by Kasimir Fajans although he named it brevium. In 1918, the elements name was permanently changed to protactinium when Otto Hahn and Lise Meitner identified the nuclide 238Pa. The name protactinium is derived from protos, Greek for first.

Symbol: Pa.
Synonym: (obsolete) brevium.
Synonym: (obsolete) protoactinium.
Related to actinides.

protective barrier
A material or a set of materials that absorbs radiation and is designed to reduce exposure.

(obsolete term)

An early proposed name for the nuclide 1H, hydrogen.

A synonym for hydrogen.

(obsolete term)

A synonym for protactinium.

A basic constituent of the atomic nucleus. The proton is a fundamental particle, has a mass of 1.007276470 ± 0.000000012 atomic mass units (938.27231 ± 0.00028 MeV). Chemical elements are defined by the number of protons in the nucleus, which is equal to the atomic number of that element. Free, unbound protons are stable with respect to radioactive decay with the lower limit of their half life as 1.1x1025 yr. The proton is a hadron that is composed of three quarks, uud, and it has a spin-parity of 1/2+ and a magnetic moment of +2.792847386 ± 0.000000063.

Symbol: p.
Related to atomic number.
Related to electron.
Related to neutron.
Related to nucleon.

proton binding energy
A synonym for proton separation energy.

proton number
A synonym for atomic number.

proton separation energy
The energy required to remove one proton from a nucleus.

Symbol: Sp.
Synonym: proton binding energy.
Related to binding energy.
Related to neutron separation energy.
Related to separation energy.

A symbol for platinum.

A symbol for plutonium.

public dose
The dose received by a member of the public from exposure to radiation or to radioactive material released by a licensee, or to any other source of radiation under the control of a licensee. Public dose does not include occupational dose or doses received from background radiation, from any medical administration the individual has received, from exposure to individuals administered radioactive material and released under section 35.75, or from voluntary participation in medical research programs.

Reference: 10CFR20.1003.

An acronym for pressure vessel.

A synonym for pressurized water reactor.

An acronym for pressurizer.
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