Date:    Tue, 22 Apr 1997 10:04:59 +0200
From:    Hilde Olerud <Hilde.Olerud@NRPA.NO>
Subject: Re: Roentgen to absorbed dose conversion factor
 
Dear Bijan,
 
In ICRU report 31, a value of W/e=33.85 J/C is recommended (the mean
energy expected in air per ion pair formed). However, recommended
changes in stopping-power values (ICRU report 37) influence the value of
W/e, and CCEMRI(I) has therefor recommended a value of W/e=33.97 J/C for
dry air :
 
CCEMRI (Section I), Effect of a change of stopping-power values on the W
value recommended by ICRU for electrons in dry air. Rep. CCEMRI(I) 85-8
Bureau International des Poids et Mesures, Sevres (1985).
 
You will also need to convert R into SI units: 1R=0.258 mC/kg x 33.97
J/C = 8.76 mJ/kg = 8.76 mGy
 
You might also use the conversion factor 8.77 mGy/R applied in the CEC
intercomparison programme for diagnostic dosemeters : European
intercomparison of diagnostic dosemeters. Radiat. Prot. Dosim. Vol 43,
No 1-4, page 75-91. This conversion factor is used by the PTW, Freiburg.
This is the most up to date I have found.
 

