Operating Manual

3.1 Units
Until 1978 the “International Commission of Radiation Units and Measurements” (ICRU)
used the conventional radiation units of roentgen (R), rad (rd), and curie (Ci). Since 1978
the ICRU has recommended the use of the international system units (SI) with special
new units for radiation quantities; the Becquerel, Gray and Sievert.
Table 1-3 shows the relationships of these new units to the older units.
In radiography and radiation safety, units are preceded by prefixes.
Table 2-3 shows the ones mostly used.
3
Units
and definitions
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Table 1-3. Overview of new and old units
* disintegrations per second C = Coulomb = A.s J = Joule
** RBE = Relative Biological Effect A = Ampère
Table 2-3. Prefixes
SI –units Formerly used Conversion
Designation of quantity Name Unit Name Unit Old to SI
Designation Designation
Activity (A) Becquerel 1/s* Curie Ci 1 Ci = 37 GBq
(Bq)
Ionisation dose Coulomb (C) C/kg Röntgen R 1 R=2.58 x 10
-4
C/kg
Ionisation dose rate Coulomb (C) C/kg.s R/s
Ampère (A) or A/kg
Absorbed energy Gray J/kg Rad Rad 1 Rad = 0.01 Gy
dose (D) (Gy)
Equivalent dose (H) Sievert J/kg Rem Rem 1 Rem = 0.01 Sv
H=D x RBE** (Sv)
Prefix Meaning Value Notation
p pico 0.000000000001 10
-12
n nano 0.000000001 10
-9
μ micro 0.000001 10
-6
m milli 0.001 10
-3
- 11 1
k kilo 1000 10
3
M Mega 1000000 10
6
G Giga 1000000000 10
9