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Measurement of a variable is determined by comparison with a primary standard, which is designated or widely acknowledged as having the highest metrological qualities, and whose value is established without reference to other standards for the same variable. All measurements with respect to the manufacturing or monitoring of LEA products are assessed via comparison with this standard. Standards manufacturing by LEA are used for calibration of customers' instruments.
The International System of Units (SI unit system) is universally
acknowledged and applied as the reference system within scientific
Natural radioactivity, discovered by Henri Becquerel in 1896, is often contrasted with artificial radioactivity. In fact, there is no difference between the two phenomena: quite simply, radioactive isotopes are either natural, having been present in the soil and atmosphere since the formation of the Earth, or artificial, having been created in nuclear reactors or particle accelerators since the 1930's. However, natural sources generally exhibit only low levels of activity.
In physical terms, radioactivity arises when the atoms which make up a given material are unstable. Some of these atoms undergo spontaneous transformations, thereby emitting radiation.
There are three main types of radiation, corresponding to the three forms of radioactivity:
A standard for radioactivity
The unit of radioactivity adopted under the SI system is the
becquerel (Bq). This unit measures the transformation (or
disintegration) of nuclei, with associated emission of ionizing
One becquerel (Bq) is equal to one disintegration per second.
Variables and units
The definitions given below are taken from the standard NF ISO 31-10:
A = dN/dt • Unit : Bq (Becquerel). 1Bq = 1s-1.
• Decay constant
• Radioactive half-life
T1/2 = (ln2)/
• Specific activity
Am = A/m
• Activity concentration
Av = A/V
Note : Note: this variable is mainly used to characterize gaseous standards. It is considered under STP reference conditions (T = 273.16 K, P = 101.325 kPa).
• Particles flux
F = dN/dt
Remarque : Note: this variable is identical to the “emission rate”. The particles considered must be specified. The solid angle within which emission is considered must also be stated.
For example : Flux particle flux within 2 pi sr : F = 3,5 x 103 s-1.
• Particle mass flux
Unité : s-1.kg-1, s-1.g-1.
• This variable is identical to “mass emission rate”.
Another unit, the curie (Ci), corresponds to the number of nuclei
that disintegrate in a gram of radium in one second. The curie was
formerly the standard unit, and is still in use.
Tableau de conversion Becquerel/Curie
T = Téra (1012) m = milli (10-3)