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Counts is the number of events detected, but dose rate relates to the amount of ionising energy deposited in the sensor of the radiation detector. The conversion calculation is dependent on the radiation energy levels, the type of radiation being detected and the radiometric characteristic of the detector.
It is often indicated in micrograys per hour (μGy/h) [1] or as an equivalent dose rate Ḣ T in rems per hour (rem/hr) or sieverts per hour (Sv/h). [ 2 ] [ 3 ] Dose and dose rate are used to measure different quantities [ 1 ] in the same way that distance and speed are used to measure different quantities.
The rad is a unit of absorbed radiation dose, defined as 1 rad = 0.01 Gy = 0.01 J/kg. [1] It was originally defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by one gram of matter.
Specific activity (symbol a) is the activity per unit mass of a radionuclide and is a physical property of that radionuclide. [ 1 ] [ 2 ] It is usually given in units of becquerel per kilogram (Bq/kg), but another commonly used unit of specific activity is the curie per gram (Ci/g).
There are two types of detected radiation readout: counts and radiation dose. The counts display is the simplest, and shows the number of ionizing events detected, displayed either as a count rate, such as "counts per minute" or "counts per second", or as a total number of counts over a set time period (an integrated total).
The rate of a reaction is the concentration of substrate disappearing (or product produced) per unit time (mol L −1 s −1). The % purity is 100% × (specific activity of enzyme sample / specific activity of pure enzyme). The impure sample has lower specific activity because some of the mass is not actually enzyme.
It was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium (element)", [1] but is currently defined as 1 Ci = 3.7 × 10 10 decays per second [4] after more accurate measurements of the activity of 226 Ra (which has a specific activity of 3.66 × 10 10 Bq/g [5]).
A number of electronic devices known as Electronic Personal Dosimeters (EPDs) have come into general use using semiconductor detection and programmable processor technology. These are worn as badges but can give an indication of instantaneous dose rate and an audible and visual alarm if a dose rate or a total integrated dose is exceeded.