 [P]- PAA Photon activation analysis. See instrumental photon activation analysis.
- PAC Perturbed angular correlation.
- PACKING FRACTION The mass excess of a nucleus divided by the mass number; that is, the average mass excess per nucleon.
- PAES Positron-annihilation-induced Auger-electron emission spectroscopy.
- PAIR ATTENUATION COEFFICIENT The attenuation coefficient when only the pair production process is taken into account.
- PAIR PRODUCTION The simultaneous formation of an electron and a positron as a result of the interaction of a photon of sufficient energy (> 1.02 MeV) with the field of a charged particle.
- PARALYSIS TIME See dead time.
- PARENT A nuclide which is a precursor to another nuclide in a decay chain.
- PARITY A symmetry property of a spatial wave function. The parity is said to be even (or +) if the wave function is left unchanged by reversing the sign of all the coordinates, odd (or -) if the sign of the wave function is thereby changed. NM.
- PARTIAL CROSS SECTION The portion of the total cross section corresponding to a particular final reaction channel, that is, to a distinct set of reaction products.
- PARTIAL DECAY CONSTANT For a radionuclide , the probability in unit time for the decay of one of its nuclei by one of several modes of decay.
- PARTICLE A nuclear or an elementary particle.
- PARTICLE DENSITY The number of particles divided by the containing volume.
- PARTICLE FLUX DENSITY See flux density, particle.
- PARTICLE-INDUCED DESORPTION MASS SPECTROMETRY Time-of-flight mass analysis of a sample that is desorbed from a surface as a result of bombardment by microbeams of charged particles , most often heavy-ions, for instance with a nuclide decaying by spontaneous fission.
 PARTICLE-INDUCED GAMMA EMISSION Charged particle activation analysis in which the gamma radiations are detected on line) from the electromagnetic de-excitation of the product nuclei. CRC.- PARTICLE-INDUCED PROMPT PHOTON SPECTROMETRY See particle-induced gamma emission.
- PARTICLE-INDUCED X-RAY EMISSION SPECTROSCOPY Any technique in which a specimen is bombarded with a focused beam of high-energy particles (protons, aparticles, or heavier ions) and the characteristic x-ray spectrum generated in the specimen is recorded. C.
- PARTICLE, NUCLEAR A nucleus or any of its constituents in any of their energy states.
- PARTICLE, ELEMENTARY A particle in which, at the present, no structure can be observed at moderate energies.
- PARTITION COEFFICIENT Distribution ratio of a radionuclide between two phases.
- PASSIVE ASSAY OR INTERROGATION A non-destructive measurement of nuclear material content or element or isotopic concentration of an item carried out by observing spontaneous radiations. SAFE.
- PDMS Particle-induced desorption mass spectrometry.
- PEAK ANALYSIS The extraction of relevant peak parameters (i.e., position, area) from a measured spectrum.
- PEAK AREA METHOD A method of peak analysis in which a peak area is calculated by subtracting an estimate of the underlying continuum in a relevant part of a measured spectrum.
- PEAK FITTING A method of peak analysis in which a relevant part of a spectrum is fitted with a theoretical response function.
- PEAK-TO-COMPTON RATIO In a gamma-ray spectrum, the relative heights of the full energy peak to the broad continuum that lies below its Compton edge. It is a measure of a detector's ability to distinguish full energy peaks from the general smooth background in a complex spectrum.
- PELLICLE In nuclear emulsions , the thin layer or film of photographic emulsion material.
- PENETRATION FACTOR The fraction of particles (or probability per particle) which pass through a classically forbidden barrier. The barrier can be due to centripetal and Coulomb effects, for example.
- PERTURBED ANGULAR CORRELATIONS Angular correlations between coincident radiations in which the angular correlation coefficients have a time-dependent factor which depends on the lifetime of the intermediate state and on the interaction of the nuclear electromagnetic moments with the local atomic or molecular electric field.
- PESA See proton elastic scattering analysis.
- PET Positron emission tomography
- PGAA Prompt gamma-ray activation analysis. See prompt gamma-ray neutron activation analysis.
- PGNAA Prompt gamma-ray neutron activation analysis.
- PHA Pulse height analysis or analyzer.
- PHOTOACTIVATION Activation induced by photons, that is, by electromagnetic radiation.
- PHOTOEFFECT See photoelectric effect.
- PHOTOELECTRIC ATTENUATION COEFFICIENT The attenuation coefficient when only the photoelectric process is taken into account.
- PHOTOELECTRIC EFFECT The complete absorption of a photon by an atom with the emission of an orbital electron. Synonymous with photoeffect.
- PHOTOELECTRIC PEAK Of a spectrum of gamma radiation , the part of the spectral response curve corresponding to the absorption in the radiation detector by the photoelectric effect of the detected gamma energy. In most cases the peak also contains the events caused by multiple processes and use of the expressions total absorption peak or full energy peak is to be preferred. Synonymous with photopeak.
- PHOTOELECTRON The electron ejected from an atom which completely absorbs a photon in the photoelectric effect.
- PHOTOFRACTION The fraction of detected gamma-rays that produce output signals in the photopeak region. NM.
- PHOTOMULTIPLIER TUBE A vacuum tube containing a photosensitive layer which serves as the cathode for an electron multiplier.
- PHOTON A quantum of electromagnetic radiation.
- PHOTON ACTIVATION See activation.
- PHOTONEUTRON A neutron which is ejected from a nucleus as a consequence of the absorption of a photon.
- PHOTONUCLEAR REACTION A nuclear reaction induced by absorption of a photon.
- PHOTOPEAK See photoelectric peak.
- PHOTOPEAK EFFICIENCY, ABSOLUTE Of a gamma-ray spectrometer , the counting efficiency when only considering the events recorded in the photopeak.
- PHOTOPEAK EFFICIENCY, INTRINSIC The detector efficiency when only considering counts resulting from the photoelectric effect.
- PIG A small shielding container for storing or carrying radioactive material or for housing a detector system for measuring radioactivity.
- PIGE Particle-induced gamma emission.
- PIGME See particle induced gamma emission.
- PILE Obsolete term for a nuclear reactor. NM.
- PILE-UP The processing by a radiation spectrometer of pulses resulting from the simultaneous absorption of independent particles or photons in a radiation detector. As a result they are counted as one single particle or photon with energy between the individual energies and the sum of these energies.
- P.I.N SEMICONDUCTOR DETECTOR See semiconductor detector, P.I.N.
- PIPPS Particle-induced prompt photon spectroscopy.
- PIXE Particle-induced x-ray emission.
- PLASMA DESORPTION MASS SPECTROMETRY See Particle-induced desorption mass spectrometry.
- PLATEAU The plot of counting rate against voltage applied to a Geiger counter in the presence of a constant source of radiation. As the voltage is increased from zero, this counting rate first rises sharply to a plateau several hundred volts long. Over the plateau the counting rate rises very slowly, and at the end it increases rapidly as instability sets in. NM.
- PM Photomultiplier tube.
- PNEUMATIC TUBE A cylindrical pipe for transporting a rabbit (sample) by means of compressed air.
- POCKET ION CHAMBER A small dosimeter having a physical appearance similar to a fountain pen, used to monitor the amount of radiation to which an individual is exposed. NM.
- POPOP diphenyloxazolbenzene, used in liquid scintillation spectroscopy as a wavelength shifter.
- POSITION SENSITIVE DETECTOR A radiation detector which records not only physical properties of the radiation, but also where it impinges on the detector surface.
- POSITRON A positively charged electron.
- POSITRON ANNIHILATION The conversion of a positron and its antiparticle, the electron, into annihilation radiation.
- POSITRON DECAY Radioactive decay in which the emission of a positron by the decaying nucleus occurs, accompanied by an emitted neutrino.
- POSITRON EMISSION TOMOGRAPHY An external technique for the rapid serial reconstruction of the spatial distribution of any positron-emitting radioisotope that has been administered in vivo. J.
- POSITRON-ANNIHILATION-INDUCED AUGER-ELECTRON EMISSION SPECTROSCOPY A form of Auger electron emission spectroscopy based on the use of thermalized positrons whose annihilation excites the Auger emission. The surface analysis technique is particularly sensitive to the outermost few ngstroms layer.
- POSITRONIUM The short-lived atom consisting of a positron and electron.
- POSTLABELING A method for determination and measurement of covalent DNA adducts based on enzymatic incorporation of 32P into DNA nucleotides.
- POWER, STOPPING See stopping power.
- PPO 2,5-diphenyloxalol, used in liquid scintillation spectrometry as a primary scintillator.
- PRA Prompt radiation analysis. Use prompt gamma neutron activation analysis.
- PREAMPLIFIER An amplifier whose primary function is boosting the output of a lowlevel frequency source to an intermediate level so that the signal may be further processed without appreciable degradation of the signal-to-noise ratio of the system. M.
- PRECISION A measure for the reproducibility of measurements within a set, that is, of the scatter or dispersion of a set about its central value.
- PRECONCENTRATION In trace analysis: a process resulting in an increase in the concentration or the amount of the components of interest. As a synonym, enrichment is not recommended.
- PRECURSOR Of a nuclide , any radioactive nuclide which precedes that nuclide in a decay chain.
- PROJECTILE A particle in a beam being used for irradiation.
- PROMPT GAMMA A gamma ray which is emitted from an excited state of a nucleus immediately upon formation of that excited state by a previous decay step or reaction.
- PROMPT GAMMA NEUTRON ACTIVATION ANALYSIS Neutron activation analysis in which the radiation of the neutron capture gamma-ray cascade is detected online , that is, simultaneously with the production. KE.
- PROMPT NEUTRON ACTIVATION ANALYSIS See prompt gamma neutron activation analysis.
- PROMPT RADIATION ANALYSIS See prompt gamma neutron activation analysis.
- PROOFREADER "A malefactor who atones for making your writing nonsense by permitting the compositor to make it unintelligible." Ambrose Bierce in The Devil's Dictionary.
- PROPORTIONAL COUNTER (TUBE) See counter tube, proportional.
- PROTON A single nucleon, of mass number one, which is the nucleus of the hydrogen atom.
- PROTON ELASTIC SCATTERING ANALYSIS Elastic recoil detection analysis using a proton beam.
- PROTON NUMBER See atomic number.
- PROTON MICROBEAM A highly collimated and focused beam of protons. KE.
- Ps The symbol for positronium used to emphasize the analogy of positronium to atomic hydrogen.
- PSEUDOCYCLIC ACTIVATION ANALYSIS A variation of cyclic activation analysis in which a delay is introduced between irradiation and spectrum acquisition. FR.
- PSEUDO-RADIOCOLLOID An inactive colloid which incorporates radionuclides.
- PULSE AMPLITUDE ANALYZER A sub-assembly for determining the distribution function of a set of pulses in terms of their amplitudes. Synonymous with pulse height analyzer.
- PULSE AMPLITUDE SELECTOR A circuit which gives an output pulse for each input pulse whose amplitude lies within a chosen interval. Synonymous with single channel pulse height analyzer.
- PULSE HEIGHT ANALYSIS The process of determining the spectrum of radiation energies through use of a pulse height analyzer.
- PULSE HEIGHT ANALYZER See pulse amplitude analyzer.
- PULSE HEIGHT ANALYZER, MULTICHANNEL A pulse amplitude analyzer which includes a storage function to record the number of pulses received per channel.
- PULSE HEIGHT ANALYZER, SINGLE CHANNEL See pulse amplitude selector.
- PULSED NEUTRONS Neutrons of transient high flux density produced in certain reactors when control rods are removed. KE.
- PULSED REACTOR ACTIVATION ANALYSIS Activation analysis using pulsed neutrons. KE.
- PUREX PROCESS A separation scheme for recovering plutonium and uranium from fission products in reactor fuel. The process is based on the efficient partitioning of Pu and U into TBP. Ch.
- PURITY, ISOTOPIC See abundance, isotopic.
- PURITY, RADIOCHEMICAL For a material, the fraction of the stated isotope present in the stated chemical form.
- PURITY, RADIONUCLIDIC Of a material, that fraction of the total activity which is present in the form of the stated radionuclide (including its daughter products).
- PWR Pressurized water reactor.
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