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Technical Discussions
V.JAGADISH
NDT Inspector
heisco, Kuwait, Joined Aug 2006, 7

V.JAGADISH

NDT Inspector
heisco,
Kuwait,
Joined Aug 2006
7
03:50 Aug-21-2006
back scatter radiation

I am Jagadish who feel free to express my doubt in practical conventional gamma radiography using Ir-192 regarding backscatter radiation. If a lead letter B is placed on the back of the casette is the image B is formed in every case. As Per my observation i observed in 100% where the letter is used. Can
anybody please explain how the letter B appears on the radiograph if there is no back scatter at all that is the back of film facing the
open atmosphere towards the sky. In this case which secondary
radiation tends to expose the letter B. I request to the group to
provide me with sufficient technical knowledge to solve the technical problem for which i may be thank ful


    
 
 
RT Guy
RT Guy
04:02 Aug-21-2006
Re: back scatter radiation
----------- Start Original Message -----------
: I am Jagadish who feel free to express my doubt in practical conventional gamma radiography using Ir-192 regarding backscatter radiation. If a lead letter B is placed on the back of the casette is the image B is formed in every case. As Per my observation i observed in 100% where the letter is used. Can
: anybody please explain how the letter B appears on the radiograph if there is no back scatter at all that is the back of film facing the
: open atmosphere towards the sky. In this case which secondary
: radiation tends to expose the letter B. I request to the group to
: provide me with sufficient technical knowledge to solve the technical problem for which i may be thank ful
------------ End Original Message ------------

Is the image of the Letter B white or is it a dark image on the film?
If it is white then you have back scatter. If it is dark it is merely the radiation either being reflected from the lead onto the film or the lead emmitting electrons after absorbing the primary radiation.


    
 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
01:12 Aug-21-2006
Re: back scatter radiation
Many years back when we were doing radiography with Cobalt-60 source of about 70 Curies strength inside an underground pit with concrete walls, naturally we had to put the back side 'B', for ascertaining the presence of back scatter. Indeed, we were protecting the cassette on the back side from the backscatter from pit walls etc.

First time when we saw a dark 'B' on the developed film we were perplexed.We had the same result when we repeated the shot. We understood that the lead 'B' placed on the back side is giving off secondary soft radiation resulting in the dark 'B'. It is unlikely that the elctrons from the 'B'travel through the cassette wall and the back side lead screen, to affect the film.

We had the same problem with our (initially 100 Curies) Ir-192.

We called this "the case of the black 'B'" and further investigated.

We did use various combinations of front side Copper/Brass screens etc.and heavier protection on the back side to mitigate the problem of so called black'B'as well as to improve penetrameter sensitivity in case of long exposures of about 6" thick steel.( with Co-60 source)

----------- Start Original Message -----------
: : I am Jagadish who feel free to express my doubt in practical conventional gamma radiography using Ir-192 regarding backscatter radiation. If a lead letter B is placed on the back of the casette is the image B is formed in every case. As Per my observation i observed in 100% where the letter is used. Can
: : anybody please explain how the letter B appears on the radiograph if there is no back scatter at all that is the back of film facing the
: : open atmosphere towards the sky. In this case which secondary
: : radiation tends to expose the letter B. I request to the group to
: : provide me with sufficient technical knowledge to solve the technical problem for which i may be thank ful
: Is the image of the Letter B white or is it a dark image on the film?
: If it is white then you have back scatter. If it is dark it is merely theradiation either being reflected from the lead onto the film or the lead emmitting electrons after absorbing the primary radiation.
------------ End Original Message ------------




    
 
 

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