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LSC GLOSSARY
Accuracy:
An expression of the correctness of a measurement when compared to the true value of the quantity being measured. Radioactive decay is a random event, hence the true value cannot be stated. It is preferable to refer to uncertainity.
Becquerel:
The basic unit of radioactivity in the international system of units. One becquerel is equal to one disintegration per second. One Curie is 3.7 * E10 DPS or 3.7 E10 Becquerels.
Cerenkov Radiation:
Light emitted when charged particles pass through a transparent material at a speed greater than that of light in this material.
Chi-Square Test:
A general procedure for determining the probability that two different distributions are actually samples of the same population. This test is used in nuclear counting to compare the observed variations in repeat counts of a radioactive sample with the variation predicted by the theoretical nuclear statistics.
Coincidence Time:
The maximum time interval allowing between two or more input signals for the production af an output signal. The coincidence resolving time is typically 18 nsec.
Coincidence Circuit:
Section of the electronic analysis system of an LS counter which acts to reject pulses which are not received from two PMTs within the coincidence time.
CPM:
Counts per Minute
Dead Time:
The time immediately following the sensing of a signal pulse that the instrument remains insensitive and unable to handle another pulse.
Discriminator:
Electronic circuit which distinguishes signal pulses as per their pulse height or voltage. It is used to exclude background and other radiation in order to maximize sensitivity of the given isotope.
DPM:
Disintegrations per Minute.
External Standard:
Radioactive gamma source used in a LSC only and placed adjacent to the vial to produce scintillations in order to determine the level of quenching. External standards are: 133Ba (18 µCi) / 137Cs / 152Eu.
Figure of Merit:
A numerical value used to characterize the performance of an LSC, e.g. E2/B or C2/B
Gross Counts:
The total number of accumulated counts within a defined counting time and counting window.
Photomultiplier Tube:
The PMT is a device for detecting low levels of light. The photons are converted into electrons multiplied (amplified) by the dynodes present in the tube in order to produce a measurable output signal.
Percent Sigma:
Expression of the theoretical standard deviation as a percentage. (100 times the SD divided by the mean).
Quench Indicating Parameter:
The QIP is a number indicating the level of quenching in a sample, e.g. tSIE / SIS / tSIS / H# etc.
Specific Activity:
The radioactivity per mass unit, e.g. mCi/g or DPM/mg
Scintillation:
Flash of light produced in a scintillator by an ionizing event, e.g. (alpha- beta-, gamma-, x-ray emitters)
Terminators:
Parameters used to end the sample measurement based on either preset time or preset counts.