Physics Athens 2016

Ionometric standard

standard dosimetry: dose measurement with i.c. in 60 Co:

 (s w,air

D w,Co D air,Co

= D air,Co = E air,Co

) Co

/m, E air,Co

is energy deposited in air by electrons

D air,Co )/m - Q = charge formed in air cavity (measured with electrometer) - W air,Co = average energy expended in air per coulomb - m = mass of air in cavity = (Q  W air,Co

air

P

i.c

= ((Q  W air,Co

)/m)  (s w,air

D w,Co

) Co

water

TRS398: - W air,Co

Refinements needed e.g. to correct for deviations Bragg-Gray (in TRS398)

= 33.97 J/C

- (s w,air

) Co

= 1.134

used in standard laboratory to assess dose with their ionometric standard: D w,Co = ((Q  W air,Co )/m)  (s w,air ) Co  f i