Scrata Calculator

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Scrata Calculator

The Scrata Gamma Exposure Calculator is designed to provide rapid and precise exposure times for gamma radiography of ferrous materials for Cobalt 60, Ytterbium 169 and Iridium 192. Tabular data accompanying radiographic film, in the density range from 1.0 to 4.0 are available with instructions.

The plastic scrata calculators are used to indicate the exposure time of x-ray film and are supplied with a case.

Instructions for use:

Before starting on any calculations first (a) which isotope, i.e. Iridium 192, Cobalt 60 or Ytterbium 169 and (b) the film factor appropriate to the x-ray film in use

Fuji	IX	150	20
		100	30
		80	65
		50	120
		25	250
Kodak	Industrex	CX	20
		AX	30
		B	75
		MX	115
AGFA	Structurix	D8	22
		D7	35
		D5	50
		D4	120
		D2	250

 

Use the front of the scrata calculator when using Iridium and Cobalt and the back of the scrata calculator for Ytterbium.

1. To calculate an exposure time for a given source to film distance
2. Position the lower slide to bring the film factor into line with the required film density.
3. Holding the calculator so these two readings do not move in relation to each other, adjust the top slide so that the source film distance comes into line with the source strength.
4. Read off the exposure time adjacent to the Steel thickness being radiographed for the selected isotope.

Example:                         Film Density –                      2.0

Film Factor –                          25

Isotope – Iridium                   30ci

Source Film Distance         100cm

Steel thickness                     3cm

The exposure time required would be 13 minutes

1. To calculate the source to film distance for a given exposure
2. Position the lower slide to bring the film factor into line with the known film density
3. Position the top slide to bring the known exposure time into line with the Steel thickness being radiographed
4. Read off the source film distance adjacent to the source strength
5. To re-adjust a calculated exposure time or source to film distance, whilst maintaining the same film density
6. Using the top two scales on the front of the calculator, position the top slide so that the original source film distance is in line with the original exposure time.
7. Any point on the exposure time scale will give the required distance on the source film distance scale or vice-versa.
8. To determine the equivalent Steel thickness to be employed when examining materials other than Steel
9. Using the top two scales on the back of the calculator, adjust the top slide so that the index mark of the appropriate material on the material density scale is in line with the thickness of the section to be radiographed on the material thickness scale
10. Read off the material thickness scale the equivalent thickness scale the equivalent thickness of the Steel indicated by the point marked Steel equivalent.

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