Kamran,
You have to make an optimized decision in selecting a combination of film and gamma source.
- Films range from medium grain to ultra fine grain and sources differ in scatter of gamma radiations
- D-4 films have very fine grain and are suitable for Ir-192 having medium scatter
- D-7 films have fine grain and are very effective with Se-75 (having lesser scatter) saving time, cost and giving high contrast
- So, combination of D-7 and Se-75 is better than D-4 and Ir-192 in result as well as in time and cost value
- Yes you can get time advantages by using D-7 with Ir-192 but the contrast would be lesser (not significantly) than D-4
- There is no limitation in using D-7 with Ir-192 but you have to make a wise decision considering your application
- In Petrochemical plants, D-4 and Ir-192 combination is preferred to ensure high quality welding. But at some instances like for higher thicknesses, D-7 is also used to save time as D-7 has lower exposure time than D-4
Go through this document, select your application and make a wise decision:
http://www.geinspectiontechnologies.com ... ochure.pdf
Hope this would help.