UNITS OF RADIATION MEASUREMENT
The curie is the number of particles
per second from 1 gram of Radium = 3.7 x 10 E10 counts/second =
37 billion cps. = 37 billion Becquerel.
1 Becquerel (Bq) = 1 count per
second = 1 event per second
1 microcurie = 1 uCi =
37,000 Bq = 37,000 cps.
1 microcurie = 2.22 x
10E6 disintegrations / minute = 2,220,000 cpm.
1 nanocurie = 1 billionth
of a curie = 2,220 disintegrations / minute.
1 picocurie = 2.2 disintegrations
/ min.
Dosage units:
Gray (Gy) = 1 Joule/kg
Sievert (Sv) = Gray x
QF, where QF is a "quality factor" based on the type of
particle.
QF for electrons, positrons,
and xrays = 1 QF = 3 to 10 for neutrons, protons dependent upon
the energy transferred by these heavier particles.
QF = 20 for alpha particles
and fission fragments.
The Sievert is a measure of
biological effect.
Converting older units:
1 rad = 1 centigray = 10 milligrays
( 1 rad = 1cGy = 10 mGy )
1 rem = 1 centisievert = 10
millisieverts ( 1 rem = 1cSv = 10 mSv )
1 mrad = 10 uGy
Nominal background radiation
absorbed dose of 100 mrad/year = 1 mGy/yr.
Nominal background radiation
dose biological equivalent of 100mrem/year = 1mSv/yr.
Occupational whole body limit
is 5 rem/yr = 50 mSv/yr. ( Recently proposed that levels be reduced
to 2 rem/yr.)
2.5 mrem/hr or
25 uSv/hr is maximum average working level in industry.
Exposure rate from
Naturally Occurring Radioactive Material (NORM) ; an empirically
derived conversion factor for Ra-226 decay series:
1.82 microR/ hour = 1 picoCurie/gram.
