Radiography Formulas1

Useful Radiography Formulas HVT(Steel ) of Ir192

EXPOSURE FACTOR

= 13.0 mm

Film Density 

Thickness (mm)

2.00

2.50  

3.175 6.350 9.525 12.700 15.880 19.050 22.230 25.400 28.575 31.750 34.925 38.100 41.275 44.450 47.625 50.800

0.072 0.082 0.099 0.125 0.150 0.180 0.200 0.240 0.280 0.340 0.390 0.465 0.557 1.650 0.777 0.905

0.091 0.110 0.130 0.150 0.180 0.210 0.250 0.295 0.350 0.410 0.495 0.595 0.702 0.810 1.030 1.250

Exposure Time = [EF x D2( inch) x FF] Curies

Where: EF = Exposure Factor  D = Distance in inches FF = Film Factor  Agfa D7 FF = 1 Kodak MX FF = 2.5

HVT ( Lead ) of IR 192 = 5.5 mm HVT ( Concrete) of IR 192 = 43.0 mm

Radioactive Isotope Decay Formula Cp = Co / 2n Where: n = t 74.4 days t = no. of days Cp = Curies after t number of days Co = Original Curies 74.4 days = Half life of IR 192

Safe Distance Formula SD =

Curie x 130 x 37 7.5

meters

Geometrical Un-sharpness Ug = Focal size x Material Thickness Distance Max. Req’d = 0.020 inch or 0.503 mm .

Inverse Square Law I1 D1 2 = I2 D2 2

Exposure Time - Distance Relationship Half Value Thickness

T1 D2 2 = T2 D12

I = IO 2n

Where: Io = Initial Intensity I = Second Intensity

Curie – Exposure Time Relationship C1T1 = C2T2

n = number of HVT

Conversion Factors Tenth Value Thickness I = IO 10 n Where:

1.0 Curie Curie = 37 37 Gbq Gbq = 37 x 10 12 Bq 1.0 1.0 Gray Gray = 100 100 Rad Rads s 1.0 1.0 Sv = 100 100 Rems Rems

Io = Initial Intensity I = Second Intensity n = number of TVT

Output @ 1.0 meter IR 192

Alternative HVT Formula

= 130 microSv/hr/GBq microSv/hr/GBq

No. of HVT = Log I – Log Io Log 2

= 0.48 R/hr/ Ci