Nuclear Physics Fundamental Principles - Glossary
ABSORBED DOSE
Absorbed dose is the amount of energy deposited in any material by
ionizing radiation. It is a measure of energy absorbed per gram of
material. The SI unit of absorbed dose is the gray.
The special unit of absorbed dose is the rad.
ACCURACY
The degree of agreement between an individual measurement or average
of measurements and the accepted reference value of the quantity being
measured. See also precision.
ACTIVATION ANALYSIS
A method of chemical analysis (for small traces of material) based on
the detection of characteristic radionuclides in a sample after it has
been subjected to nuclear bombardment.
ADC
Analog to Digital Converter. A device which changes an analog signal
to a digital signal.
AIM
Acquisition Interface Module: a type of
multichannel analyzer.
ALARA
Since exposure to radiation
always carries some risk, the exposure should be kept
"As Low As Reasonably Achievable", as defined by 10 CFR 20.
ALGORITHM
A set of well-defined rules for solving a problem.
ALPHA PARTICLE [Symbol: a]
A particle made up of two neutrons
and two protons; it is identical to
a helium nucleus and is the least
penetrating of the three common types of
radiation(the other two are beta particles
and gamma rays), being stopped
by a sheet of paper or a few centimeters of air. An alpha-emitting substance
is generally not dangerous to a biological system, such as the human
body, unless the substance has entered the system.
See decay.
AMPLIFICATION
The process by which weak signals, such as those from a
detector
are magnified to a degree suitable for measurement.
ANALOG MULTIPLEXER
An electronic instrument that accepts several inputs and stores
each one in a separate section of MCA
memory. Also called a mixer/router.
ANNIHILATION RADIATION
Radiation produced by the annihilation of a
positron
and an electron. For particles at
rest, two photons with an energy of
511 keV each are produced.
ANTICOINCIDENCE CIRCUIT
A circuit with two inputs. The circuit delivers an output pulse
if one input receives a pulse within a predetermined time interval,
usually on the order of milliseconds, but not if both inputs receive
a pulse. A principle used in
pulse height analysis.
See also
coincidence circuit.
AREA
The number of counts in a given region of a
spectrum
that are above the continuum level.
ASCII
An acronym for American Standard Code for Information Interchange,
a method for encoding alphabetical, numeric, and punctuation characters
and some computer control characters.
ATTENUATION CORRECTION
Correction to the observed signal for the attenuation of
radiationin a material between the sample and the
detector
or within the sample itself.
BACKGROUND RADIATION
radiationdue to sources other
than the sample, such as
cosmic rays, radioactive materials
in the vicinity of a detector or
radioactive components of the detection system other than the sample.
BACKGROUND SUBTRACTION
The statistical process of subtracting the background level of
radiationfrom a sample count.
BACKSCATTERING
The process of scattering or deflecting into the sensitive volume
of a measuring instrument radiationthat originally had no motion in that direction. The process is dependent
on the nature of the mounting material, the shield surrounding the sample
and the detector, the nature of the sample, the type of energy of the
radiation, and the geometry. See
also scattering.
BASELINE
In biology, a known base state from which changes are measured.
In electronics, a voltage state (usually zero volts) from which a pulse
excursion varies.
BECQUEREL [Symbol: Bq]
The SI unit of activity, defined as one
disintegration
per second (dps).
BETA PARTICLE [Symbol: ]
An elementary particle emitted from a nucleus
during radioactive decay with a single
electrical charge and a mass equal to 1/1837 that of a
proton. A negatively charged beta particle is
identical to an electron.
A positively-charged beta particle is called a
positron.
BIOLOGICAL HALF-LIFE [Symbol: Tb]
The time required for a biological system to eliminate half of
the amount of a substance (such as radioactive material) by natural
processes. Compare effective
half-life and half-life.
BLUETOOTH
Bluetooth is a wireless protocol utilizing short-range communications technology facilitating data transmissions over short distances from fixed and/or mobile devices, creating wireless personal area networks (PANs).
BREMSSTRAHLUNG
radiationproduced by the
sudden deceleration of an electrically charged particle when passing
through an intense electrical field.
CASCADE SUMMING
Also referred to as true coincidence summing,
it occurs when two or more pulses from the same decay are
summed because they deposit energy in the detector at
the same time. It is a function of the measurement efficiencies and occurs
only with susceptible cascading nuclides (60Co, 88Y, 152Eu, 133Ba,
etc.)
CENTROID
The center of a peak; usually not
an exact channel number.
CHANNEL
One of an MCA's
memory locations for storage of a specific level of energy or division
of time.
CHERENKOV RADIATION
Photons emitted from polarized molecules when
returning to their ground state following excitation by charged particles
traveling faster than the speed of light in a transparent medium.
CHI-SQUARE TEST
A general procedure for determining the probability that two different
distributions are actually samples of the same population. In nuclear
counting measurements, this test is frequently used to compare the observed
variations in repeat counts of a radioactive sample to the variation
predicted by statistical theory.
COINCIDENCE CIRCUIT
A circuit with two inputs. The circuit delivers an output pulse
if both inputs receive a pulse within a predetermined time interval,
usually on the order of milliseconds, but not if just one input receives
a pulse. A principle used in
pulse height analysis. See also
anticoincidence circuit.
COINCIDENCE SUMMING
A process where the signal from two or more
gamma rays emitted by a single
decay
of a single radionuclide occur within the resolving time of the
detector
end up being recorded together as a single event so that the recorded
event is not representative of the original decay. Typically causes
counts to be lost from the full energy peaks,
but may also cause addition to the full energy peaks. Coincidence summing
is a function of the sample-to-detector geometry,
and the nuclide's
decay
scheme. It is not a function of the overall count rate.
COLLECT
An MCA function
that causes storage of data in memory.
COMPTON SCATTERING
Elastic scattering of photons
in materials, resulting in a loss of some of the photon's energy.
CONFIDENCE FACTOR
It is common practice when reporting results to assign them a confidence
level: the value plus or minus one
standard deviation.
radiationprotection
measurements are usually reported at the 95% confidence level, meaning
that the results would be expected to be within plus or minus that range
95 out of 100 times. Also called Confidence Level.
CONTINUUM
A smooth distribution of energy deposited in a gamma detector caused
by the partial absorption of energy from processes such as
Compton scattering or
bremsstrahlung.
CONVERSION GAIN
The number of discrete voltage levels (or channels)
that the ADC's full scale input is divided
into.
CONVERSION TIME
The time required to change an input signal from one format to
another, such as analog to digital, or time difference to pulse amplitude;
contributes to dead time.
COSMIC RAYS
radiation, both particulate
and electromagnetic, that originates outside the earth's atmosphere.
COUNT
A single detected event or the total number of events registered
by a detection system.
CRITICAL LEVEL (Lc)
The level below which a net signal cannot reliably be detected.
See also detection level.
CROSSOVER ENERGY
In some efficiency calibration
models, the energy at which one calibration curve is
changed into a second calibration curve. This is used in the Dual Efficiency
Calibration in Genie software.
CURIE [Symbol: Ci]
The (approximate) rate of decay
of 1 gram of radium; by definition equal to 3.7 x 1010
becquerels
(or disintegrations per second). Also, a quantity of any
nuclide
having 1 curie of radioactivity.
DATASOURCE
A hardware device or a file which stores data acquisition parameters and spectral data.
DAUGHTER NUCLIDE
A radionuclide produced by the decay
of a parent nuclide.
DEAD TIME
The time that the instrument is busy processing an input signal
and is not able to accept another input; often expressed as a percentage.
See also live time.
DECAY
The disintegration of the nucleus
of an unstable atom by spontaneous fission, by the spontaneous emission
of an alpha particle or
beta particle, isomeric transitions,
or by electron capture.
DEFAULT
The value of a parameter used
by a program in the absence of a user-supplied value.
DERIVED AIR CONCENTRATION (DAC)
The concentration (Bq/m3) of a radionuclide in air that
if breathed by Reference Man for a working year (2000 hours) under light
activity conditions would result in the annual limit on intake (ALI)
by inhalation.
DETECTION LEVEL
The level of net signal that can be predicted to be detectable.
See also critical level.
DETECTOR
A device sensitive to radiationwhich produces a current or voltage pulse which may or may not correspond
to the energy deposited by an individual photon
or particle.
DIGITAL STABILIZATION
The monitoring of one or two reference peaks
in a spectrum, one for gain and
one for zero, to correct for drift in the system electronics.
DISCRIMINATOR
An electronic circuit which distinguishes signal pulses according
to their pulse height or voltage so that unwanted counts can be excluded.
DISINTEGRATION
See decay.
DPM
Disintegrations per minute. One DPM equals 60 becquerels.
DOSE
The radiationdelivered to
the whole human body or to a specified area or organ of the body. This
term is used frequently in
whole body counting applications.
DOUBLE ESCAPE PEAK
See escape peak.
EFFECTIVE HALF-LIFE [Symbol: Teff]
The time required for a radioactive element in a biological system,
such as the human body, to be reduced by one-half as a result of the
combined action of radioactive decay
and biological elimination. Compare half-life
and biological half-life.
EFFICIENCY
The fraction of decay events from
a standard sample seen by a detector
in the peak corresponding to the
gamma ray energy of the emission,
and stored by a detection system. Also called Peak Efficiency. Used to
calibrate the system for quantitative analyses. Also used to specify
germanium detectors, where the relative efficiency of the germanium detector
is compared to a standard (3 x 3 in.) NaI(Tl) detector. Compare
total efficiency.
EFFICIENCY CALIBRATION
A function, a lookup table, or series of functions, which correlate
the number of counts seen by the detection system in specific
peaks with known activity corresponding
to such emission energies in a radioactive sample.
ELASTIC SCATTERING
See scattering.
ELECTRODEPOSITION
A process for coating the surface of samples being prepared for alpha spectroscopy
and alpha/beta counting.
ELECTROMAGNETIC RADIATION
A general term to describe an interacting electric and magnetic
wave that propagates through vacuum at the speed of light. It includes
radio waves, infrared light, visible light, ultraviolet light,
X rays and
gamma rays.
ELECTRON [Symbol: e]
An elementary particle with a unit negative electrical charge and
a mass 1/1837 that of the proton.
Electrons surround the positively charged
nucleus
and determine the chemical properties of the atom.
ELECTRON VOLT [Symbol: eV]
The amount of kinetic energy gained by an
electron
as it passes through a potential difference of 1 volt. It is equivalent
to 1.602 x 10-19 joules per second. It is a unit of energy,
or work, not of voltage.
ENERGY CALIBRATION
A function which correlates each channel
in the displayed spectrum with a
specific unit of energy. Allows peaks
to be identified by their location in the calibrated spectrum.
ESCAPE PEAK
A peak in a
gamma ray
spectrum resulting from the
pair production process,
the subsequent annihilation
of the photons produced, and escape
from the detector of the annihilation
photons. If both annihilation photons escape, and the rest of the original
gamma energy is fully absorbed, a double escape peak is produced at
an energy equal to the original
gamma ray energy minus 1.022
MeV. If only one of the photons escapes, a single
escape peak is produced at an energy equal to the original gamma ray energy
minus 511 keV.
EXCITED STATE
The state of molecule, atom, or nucleus
when it possesses more than its ground
state energy. Excess molecular or atomic energy may be reduced through
emission of photons or heat. Excess
nuclear energy may be reduced through emission of
gamma rays or conversion
electrons
or by further decay of a radionuclide.
eV
See electron volt.
FACTORS
The parameters used by an
algorithm
for its calculations.
FIPS 140-2
The Federal Information Processing Standard (FIPS) Publication 140-2, FIPS PUB 140-2, is a U.S. government computer security standard used to accredit cryptographic modules.
FULL ENERGY ABSORPTION
The absorption and detection of all of the energy of an incident
photon. May take place as a direct
photoabsorption or as a result of multiple
Compton scatterings
of the incident photons within the
resolving time of the detection system.
FULL ENERGY PEAK
The peak in an energy spectrum of
X-ray
or gamma-ray
photons
that occurs when the full energy of the incident photon is absorbed
by the detector.
FWHM (Full Width at Half Maximum)
The full width of a peak measured at one-half
of its maximum amplitude with the continuum
removed. Defines the resolution of a
spectroscopy system.
GAIN, ADC
See conversion gain.
GAIN, AMPLIFIER
The ratio of the amplifier's output signal to its input signal.
GAIN CONTROL
A control used to adjust the height of a pulse received from the
detecting system.
GAMMA RAY [Symbol: ?]
A photon or high-energy
quantum
emitted from the nucleus of a
radioactive atom. Gamma rays are the most penetrating of the three
common types of radiation(the other two are alpha particles
and beta particles) and are best
stopped by dense materials such as lead.
GAUSSIAN FIT
Calculating the parameters of a Gaussian (or Normal) function to best match
a set of empirical data (in spectroscopy, the acquired photopeak histogram).
This calculation is typically performed using a least squares method after
subtracting the Compton continuum underlying the peak.
GAUSSIAN PULSE SHAPE
A pulse shape resembling a statistical bell-curve, with little
or no distortion.
GEOMETRY
The detector to sample distance, the sizes
and shapes of the detector, the sample, and any shielding, all of which
affect the radiationseen by the detector.
The geometry helps define the efficiency of
the detector.
GIS
A geographic information system (GIS), also known as a geographical information system, is an information system for capturing, storing, analyzing, managing and presenting data which are spatially referenced.
GRAY [Symbol: Gy]
The SI unit of absorbed dose, defined as one joule per kilogram
of absorbing medium.
GROUND STATE
The state of a nucleus, atom or molecule
at its lowest energy level.
HALF-LIFE [Symbol: Tl/2]
The time in which one half of the atoms of a particular radioactive
substance decay to another nuclear form.
Half-lives vary from millionths of a second to billions of years.
HISTOGRAM
A representation of data by vertical bars, the heights of which
indicate the frequency of energy or time events.
INELASTIC SCATTERING
See scattering.
ION
An atom or molecule that has become electrically charged by having
lost or gained one or more electrons. Examples
of an ion are an alpha particle, which
is a helium atom minus its two electrons, and a
proton, which is a hydrogen atom minus
its single electron.
INDEX
An MCA function that jumps the cursor from one
region of interest to another.
INPUT/OUTPUT
The process of loading data into or copying data from an
MCA
or computer using a peripheral device, such as a computer, a floppy
disk, or a printer.
IN SITU COUNTING
Measurement and analysis of radioactivity
performed at the sample's location.
INTEGRAL
The total sum of counts in the region
of interest.
INTENSIFY
To change the contrast of a displayed
region of interest to set it off from
data regions of lesser importance.
INTERACTIVE PEAK FIT
The process of refining and verifying the quality of a peak fit.
The fitting parameters, such as the centroid location
and the way the continuum is defined, can be changed.
The change in the quality of the fit is displayed.
INTERFERING PEAK
A peak due to background radiation
which is produced at the location of a peak in the sample spectrum or
due to a peak produced by a radionuclide in the sample at the location
of another radionuclide's peak.
IN VIVO COUNTING
In vivo counting refers to directly measuring and analyzing radionuclide
activity levels in a living body.
IN VITRO COUNTING
In vitro counting refers to samples, such as tissue or blood, being
analyzed for radionuclide activity levels in an artificial environment
(outside of a living body).
I/O
See input/output.
IONIZATION
The process by which an electrically neutral atom acquires a charge
(either positive or negative).
IONIZING EVENT
Any process whereby an ion or group of ions is produced. As applied
to nuclear spectroscopy, this refers to the passing of
radiationthrough a gas, a crystal, or a semiconductor.
ISOMERIC TRANSITION
The de-excitation of an elevated energy level of a
nucleus
to the ground state of the same nucleus
by the emission of a gamma ray or a conversion
electron.
ISOTOPE
One of two or more atoms with the same atomic number (the same
chemical element) but with different atomic weights. An equivalent statement
is that the nuclei of isotopes have the same number of
protons
(thus the same chemical element) but different numbers of
neutrons
(thus the different atomic weight). Isotopes usually have very nearly
the same chemical properties, but somewhat different physical properties.
See also nuclide and
stable
isotope.
keV (kiloelectron volt)
One thousand electron volts.
KEY LINE
Designated in nuclide libraries for reporting
purposes only. It is intended to indicate the highest abundance photopeak energy
for nuclides with multiple energy lines, or the line
that is the least likely to have interferences.
LAN
Local area network: a network of two or more computers connected
together.
Lc
See critical level.
LIBRARY DIRECTED PEAK SEARCH
Method of designating the location of peaks using all of
the lines from the specified nuclide library.
All of the nuclide library energies are assumed to have photopeak present
and the peak analysis is typically required to verify or reject each peak.
This limits the peak search to the nuclides in the library
but allows for greater sensitivity than with typical unknown peak searches.
See also second difference peak search.
LIMIT OF DETECTION
The minimum amount of the characteristic property being measured
that can be detected with reasonable certainty by the analytical procedure
being used under specific measuring conditions. If the conditions change,
the limit of detection will also change, even if the analytical procedure
remains the same. See also
lower limit of detection.
LIVE TIME
The time that the ADC is not busy processing a signal. See also
dead time and
real time.
LIVE TIME CORRECTION
In an MCA, the process of stopping the live time clock whenever
the processing circuits are busy and cannot accept further information.
Commonly used to extend the collection time by accounting for the
dead time.
LOWER LIMIT OF DETECTION (LLD)
The smallest net signal that can reliably be quantified. LLD is
a measure of the performance of a system in terms of activity.
LOWER LEVEL DISCRIMINATOR (LLD)
An SCA's minimum acceptable energy level. Incoming
pulse amplitudes below this limit will not be passed. See also
upper level discriminator.
MARINELLI BEAKER
A standard sample container that fits securely over a
detector
cryostat's endcap and is used when calibrating voluminous samples (usually
soil or water solutions).
MASS NUMBER
The sum of the neutrons and
protons
in a nucleus. It is the nearest whole number
to an atom's atomic weight. For instance, the mass number of 235U
is 235.
MAXIMUM PERMISSIBLE CONCENTRATION (MPC)
The concentration limit for a given radionuclide in
air or water in determining possible inhalation, ingestion or absorption for
health physics controls.
MCA
See multichannel analyzer.
MCS
See multichannel scaling.
MDA
Minimum detectable activity. See
lower limit of detection.
MEAN
The average of a group of numbers.
METASTABLE ISOTOPE
A long-lived energy state of a particular nuclide
that is not its ground state. Some nuclides
have more than one isomeric state. An isomeric state has the same
mass number and atomic number as the ground
state, but possesses different radioactive properties.
MeV (megaelectron volt)
One million electron volts.
MIXER/ROUTER
See analog multiplexer.
MONITORING, PERSONNEL
Periodic or continuous observation of the amount of
radiationor radioactive contamination present in or on an individual.
MULTICHANNEL ANALYZER (MCA)
An instrument which collects, stores and analyzes time-correlated or
energy-correlated events. See also multichannel
scaling and pulse height analysis.
MULTICHANNEL SCALING (MCS)
The acquisition of time-correlated data in an
MCA.
Each channel is sequentially allocated a dwell
time (a specified time period) for accumulating counts until all the
memory has been addressed. MCS is useful for studying rapidly decaying
radioactive sources.
MULTISPECTRAL SCALING
Multispectral scaling acquisition mode, also called ping-pong mode, alternately collects data in two separate memory regions, quickly collecting many spectra with extremely low latency between acquisitions.
MULTIPLET
Peaks in a spectrum which overlap each other. Compare
singlet.
NATURALLY OCCURRING RADIOACTIVE MATERIAL (NORM)
Radioactivity that is naturally present in the earth.
NEUTRON [Symbol: n]
An uncharged elementary particle with mass slightly greater than
that of the proton, and found in the
nucleus
of every atom heavier than hydrogen.
NEUTRON ACTIVATION ANALYSIS (NAA)
The process of activating materials by neutron absorption
then measuring the emission of characteristic photons on
decay to determine the relative abundance of elements in an object.
NID
Nuclide Identification, the process of identifying radionuclides
by comparing peak energies detected with entries
in a nuclide library.
NIM
Nuclear Instrumentation Module. A nuclear instrument conforming
to the DOE/ER-00457T standard.
NOISE
Unwanted signals on or with a useful signal which can distort its
information content.
NON-DESTRUCTIVE ASSAY
An analysis method that does not destroy the sample. For example:
gamma spectroscopy, X-ray fluorescence and neutron activation.
NUCLEAR SAFEGUARDS
The general topic of maintaining control and accountability of special nuclear
materials.
NUCLEUS
The positively charged core of an atom, which contains nearly all
of the atom's mass. All nuclei contain both protons
and neutrons, except the nucleus of ordinary
hydrogen, which consists of a single proton.
NUCLIDE
A general term applicable to the isotopes of all elements,
including both stable and radioactive forms (radionuclides).
NUCLIDE LIBRARY
A file listing nuclides, their names, half-lives, types,
energies/lines, and line abundances. These files are used with library
directed peak searches, nuclide identification (NID)
and as aids in performing calibrations.
PAIR PRODUCTION
Creation of an electron-
positron
pair by gamma ray interaction in the field
of a nucleus. For this process to be possible,
the gamma ray's energy must exceed 1.022 MeV, twice
the rest mass of an electron.
PARAMETER
A variable that is given a constant value for a specific application.
PARENT NUCLIDE
A radionuclide that produces a daughter
nuclide during decay.
PASSIVE NON-DESTRUCTIVE ASSAY
A method that uses radiation emitted by the sample itself, without
increasing the emission by bombarding the sample with something, such
as neutrons. The sample itself is not changed
in any way in the course of passive assay.
PEAK
A statistical distribution of digitized energy data for a single energy.
PEAK CHANNEL
The channel number closest to the centroid of
a peak.
PEAK FIT
The optimization of parameters to match an expected model shape to empirical
data (see also gaussian fit). This optimization
is typically performed using a least squares method.
PEAK-TO-TOTAL RATIO
The ratio of the observed counts in a full
energy peak to the counts in the entire
spectrum, caused by the interaction of
radiationwith the
detector at that emission energy only.
PERCENT SIGMA [Symbol: s]
An expression of the standard deviation
as a percentage. It is numerically equal to 100 times the standard deviation
divided by the mean.
PERSONAL AREA NETWORK
A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet.
PHA
See pulse height analysis.
PHOTOELECTRIC ABSORPTION
The process in which a photon interacts with
an absorber atom, the photon disappears completely, and the atom ejects
a photoelectron (from one of its bound
shells) in place of the photon.
PHOTOELECTRON
An electron released from an atom or molecule
by means of energy supplied by radiation,
especially light.
PHOTOMULTIPLIER TUBE (PMT)
A device for amplifying the flashes of light produced by a
scintillator.
PHOTON
In quantum theory, light is propagated in discrete packets of energy
called photons. The quantity of energy in each packet is called a
quantum.
PHOTOPEAK
See Peak.
PHYSICAL HALF-LIFE
See half-life.
POLE/ZERO
A method of compensating the preamplifier's output signal fall-time and the
amplifier's shaping time constant. Its use improves the amplifier's high count
rate resolution and overload recovery.
PMT
See photomultiplier tube.
POSITRON [Symbol: +]
An elementary particle, an "anti-electron" with the mass
of an electron but having a positive charge.
It is emitted by some radionuclides and is also created in
pair production by the interaction of
high-energy gamma rays with matter.
POSITRON ANNIHILATION
A process where a positron combines with an electron,
producing two annihilation photons of 511 keV each.
PRECISION
The degree of agreement between several measurements of the same
quantity under specific conditions. See also
accuracy.
PRIMORDIAL NUCLIDE
A nuclide as it exists in its original state.
PROGENY
See daughter nuclide.
PROMPT GAMMA ANALYSIS
A form of neutron activation
analysis where gammas, emitted during
capture of neutrons, are used for analysis instead
of gammas of subsequent beta decay.
PROTON
An elementary particle with a single positive electrical charge
and a mass approximately 1837 times that of the
electron.
The atomic number (Z) of an atom is equal to the number of
protons
in its nucleus.
PROTON INDUCED X-RAY EMISSION (PIXE)
The emission of X rays when a sample is bombarded
by protons. The X rays emitted are characteristic
of the elements present in the sample. Used for trace analysis.
PULSE HEIGHT ANALYSIS (PHA)
The acquisition of energy-correlated data in the
MCA.
Each channel, defined as an energy window, is
incremented by one count for each event that falls
within the window, producing a spectrum which
correlates the number of energy events as a function of their amplitude.
PULSE PAIR RESOLUTION
The ability to discriminate between two pulses close together in time.
PULSE PILEUP
A condition, where two energy pulses arrive at nearly the same
time, which could produce false data in the
spectrum.
PULSE PILEUP REJECTOR (PUR)
An electronic circuit for sensing the
pulse pileup condition and
rejecting these pulses so that only single pulses are counted.
QUANTUM
The unit quantity of energy according to quantum theory. It is
equal to the product of the frequency of the
electromagnetic radiation
and Planck's constant (6.626 x 10-34 J/s).
RAD
A special unit of absorbed dose. Equal to
0.01 gray.
RADIATION
The emission or propagation of energy through matter or space by
electromagnetic disturbances which display both wave-like and particle-like
behavior. Though in this context the "particles" are known as
photons, the term radiation has been extended
to include streams of fast-moving particles. Nuclear radiation includes
alpha particles,
beta particles,
gamma rays and free
neutrons
emitted from an atomic nucleus during
decay.
RADIOACTIVITY
The emission of radiationfrom the spontaneous
disintegration (decay) of an unstable
nuclide.
RADIONUCLIDE
A radioactive isotope. See also nuclide.
RANDOM SUMMING
A process where the signal from two or more separate
decays
of the same radionuclide or different radionuclides that occur within
the resolving time of the detector
end up being recorded together as a single event so that the recorded
event is not representative of the original decays. Typically causes
counts to be lost from the full energy
peaks. Random summing is a function of
the overall count rate, or the activity of the sample being measured.
RANDOM SUMMING LOSS
The loss of counts from the full energy
peaks due to
random summing.
RANGE, ADC
The full-scale address (number of channels)
of the ADC's assigned memory segment.
REAL TIME
Elapsed clock time; also called true time. Compare
live time.
RECOILING NUCLEUS
A nucleus that gains significant kinetic energy from
its decay.
REGION OF INTEREST (ROI)
A user-defined area of the spectrum which
contains data of particular interest, such as a peak.
REM (Roentgen Equivalent Man)
A unit of dose equivalency; equal to 0.01 sievert.
See also Roentgen.
RESOLUTION
The ability of a spectroscopy system to differentiate between two
peaks that are close together in energy. Thus, the
narrower the peak, the better the resolution capability. Measured as
FWHM.
ROENTGEN
The Roentgen, the international unit of X radiation or
gamma radiation, is the amount
of radiation producing, under ideal conditions in one
cc ionization of either sign
equal to one electrostatic unit of charge.
ROI
See region of interest.
SCA
Single Channel Analyzer. A device which recognizes events (pulses)
occurring between the settings of the
lower level discriminator
and the
upper level discriminator.
In an MCA,
each event within these limits is counted; events outside of these limits
are discarded.
SCATTERING
A process that changes a particle's trajectory. Scattering is caused
by particle collisions with atoms, nuclei and
other particles or by interactions with electric or magnetic fields.
If there is no change in the total kinetic energy of the system, the
process is called elastic scattering. If the total kinetic energy changes
due to a change in internal energy, the process is called inelastic
scattering. See also backscattering.
SCINTILLATOR
A type of detector which produces a flash
of light as the result of an ionizing event.
See also photomultiplier tube.
SECOND DIFFERENCE PEAK SEARCH
A technique for locating photopeaks by calculating
the second difference for each channel in a spectrum,
then locating areas of negative concavity. See also library
directed peak search.
SEGMENTED GAMMA SCANNER
A gamma spectroscopy system that analyzes a sample by counting
it in discrete segments.
SELF ABSORPTION
Absorption of the photons emitted by the
radioactive nuclides in the sample by the sample
material itself.
SHADOW SHIELD
An attenuating enclosure that shields the detector from
direct background radiationwithout being a 4p shield.
Typically used in whole body counting.
SHAPE CALIBRATION
The process of establishing a relationship between the expected
peak shape and energy. A shape calibration can be
established by using two or more peak FWHM/energy
(or FWHM/channel) pairs or by using a least squares
fit algorithm.
SIEVERT [Symbol: Sv]
The SI unit of dose equivalency (a quantity used in radiation protection).
The sievert is the dose equivalent when the absorbed dose of ionizing
radiationmultiplied by the dimensionless factor
Q (quality factor) and N (product of any other multiplying factors)
stipulated by the International Commission on Radiological Protection
is one joule per kilogram.
SINGLE CHANNEL ANALYZER
See SCA.
SINGLE ESCAPE PEAK
See escape peak.
SINGLET
A single peak in a
spectrum,
well separated from other peaks. Compare
multiplet.
SMOOTHING
To decrease the effects of statistical uncertainties in computerized
spectrum analysis, the content of each channel
is replaced by a weighted average over a number of adjacent channels.
SPECIFIC ACTIVITY
The quantity of radioactivity
per unit mass; for example, dpm/g or
Bq/g.
SPECIAL NUCLEAR MATERIAL (SNM)
Material containing fissionable isotopes
suitable for nuclear weapons.
SPECTRUM
A distribution of radiationintensity
as a function of energy or time.
SPECTROMETER
A device used to count an emission of radiationof a specific energy or range of energies to the exclusion of all other
energies. See also
multichannel analyzer.
STABLE ISOTOPE
An isotope that does not undergo radioactive decay.
STANDARD DEVIATION [Symbol: s]
A measure of the dispersion about the mean
value of a series of observations expressed in the same units as the
mean value.
STRIPPING
Subtracting a specified fractional part of the data in one section
of memory from the data in another section of memory.
SYSTEM BUSY TIME
The dead time of an entire spectroscopy
system.
TOTAL DETECTOR EFFICIENCY
All pulses from the detector are accepted,
TOTAL EFFICIENCY
The ratio of all pulses recorded in the
MCA's memory
(in all channels) to the gamma
quanta
emitted by the sample. Compare efficiency.
TRANSURANIC (TRU)
Possessing an atomic number higher than that of uranium (92).
TRUE COINCIDENCE SUM PEAK
A spectral peak, the energy of which equals
the sum of the energies of two or more gamma rays
or X rays from a single nuclear event.
TRUE TIME
See real time.
UNCERTAINTY
In a nuclear decay measurement, uncertainty
refers to the lack of complete knowledge of a sample's decay rate due
to the random nature of the decay process and the finite length of time
used to count the sample.
UPPER LEVEL DISCRIMINATOR (ULD)
An SCA's maximum acceptable energy level. Incoming
pulse amplitudes above this limit will not be passed. See also
lower level discriminator.
WHOLE BODY COUNTING (WBC)
In vivo determination of radionuclide activity levels in the human
body. Used to determine compliance with the regulations of various governmental
bodies regarding radiationexposure.
Wi-Fi
A term developed by the Wi-Fi Alliance to describe WLAN products that are based on the IEEE 802.11 standards. (See also: Wi-Fi CERTIFIED)
.
Wi-Fi CERTIFIED
The certification standard designating IEEE 802.11-based WLAN
products that have passed interoperability testing requirements
developed and governed by the Wi-Fi Alliance. (See also:
Wi-Fi)
Wi-Fi Alliance
A non-profit organization that certifies the interoperability of
802.11 wireless LAN products. Products bearing the Wi-Fi CERTIFIED
logo have been proven to work with Wi-Fi products from other
vendors. The Alliance also makes sure that certain security and
performance features are interoperable, to improve the Wi-Fi user
experience.
WINDOW
A term describing the upper and lower limits of
radiationenergy accepted for counting by a
spectrometer.
X RAY
A penetrating form of
electromagnetic radiation
emitted during electron transitions
in an atom to a lower energy state; usually when outer orbital electrons
give up some energy to replace missing inner orbital electrons.
