169
edits
Changes
mLine 362:
Line 362: + + + + + + + + + + + + + + + + + + + + + + + + + + +
no edit summary
Reference transfer equipment which CNSC uses for periodic verification of a and b emission rates and gamma activity measurements of traceable calibration sources includes a large area planar NaI(Tl) planar detector, small diameter dual phosphor ZnS(Ag), a large area ZnS(Ag) scintillator detector for alpha and beta counting and a large area sealed gas proportional counter. Appendix on measurement traceability and secondary measurement standards provides details of the program for maintaining traceability of reference equipment.
Reference transfer equipment which CNSC uses for periodic verification of a and b emission rates and gamma activity measurements of traceable calibration sources includes a large area planar NaI(Tl) planar detector, small diameter dual phosphor ZnS(Ag), a large area ZnS(Ag) scintillator detector for alpha and beta counting and a large area sealed gas proportional counter. Appendix on measurement traceability and secondary measurement standards provides details of the program for maintaining traceability of reference equipment.
{| class="wikitable"
|The corrected meter reading ''M'' is given by:
(3)
where ''M<sub>raw</sub>'' is the uncorrected meter reading as read directly from the instrument.
''P<sub>TP</sub>'' is the correction factor for air density, required when the temperature and pressure of the air in the cavity of the ionization chamber differ from the reference values of 22°C and 760.0 mm of Hg (101.325 kPa). At a temperature ''T'' (in degrees Celsius) and pressure ''P'' (in mm of Hg) the correct ion factor can be calculated from:
(4)
The air in the ionization chamber is assumed to be moist with the relative humidity in the range of 20% to 75%.
''P<sub>leak</sub>'' is the correction factor to take into account any leakage or drift of the instrument readings in the absence of the radiation to be measured. If the instrument reading is represented by ''M<sub>raw</sub>'' (Coulomb/s) and the leakage rate by ''B'' (Coulomb/s), ''P<sub>leak</sub>'' has the effect of replacing ''M<sub>raw</sub>'' by ''M<sub>raw</sub>'' - ''B''. The factor ''P<sub>leak</sub>'' may be calculated from:
(5)
The only correction factors applied at the time of calibration are ''P<sub>TP</sub>'' and ''P<sub>1eak</sub>''. The remaining factors, as discussed below, are not generally applied because these factors are not applicable under the circumstances of the calibration and the quantity of interest.
''P<sub>ion</sub>'' is the correction factor to take into account the incomplete collection of charge from an ionization chamber. ''P<sub>ion</sub>'' is taken to be unity because measurements with the reference standard are conducted under the same configuration (including the bias voltage) as those applied at NRC.
''P<sub>pol</sub>'' is the correction factor used to take into account that, in general, changing the polarity of the charge being collected results in a change in its absolute value. Calibrations are performed at the same polarity as that used in the calibration of the reference standard at NRC.
''P<sub>elec</sub>'' is the electrometer calibration coefficient. Calibration of the reference standard is performed at NRC for the ionization chamber and electrometer as a complete system so there is no separate electrometer factor and therefore no associated uncertainty.
''P<sub>rp</sub>'' is the correction factor to account for radial variation in the intensity profile of the radiation field over the sensitive volume of the ionization chamber. ''P<sub>rp</sub>'' is taken to be unity under the circumstances of the calibration.
|}