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Technical Discussions
Suresh
Suresh
07:04 Sep-22-2008
RT Back Scattering

Hi,
How does a letter B appears black in RT film, when it is placed at the back of film ?

I find some procedures mentioning,

"If a dark image "B" appears on a lighter background then this is not a cause for rejection"

thanks for replies,


Suresh


    
 
 Reply 
 
ezio
Other, Retired ex Laboratory Technical Manager
OMECO Research Centre, Italy, Joined Sep 2008, 273

ezio

Other, Retired ex Laboratory Technical Manager
OMECO Research Centre,
Italy,
Joined Sep 2008
273
07:44 Sep-22-2008
Re: RT Back Scattering
----------- Start Original Message -----------
: Hi,
: How does a letter B appears black in RT film, when it is placed at the back of film ?
: I find some procedures mentioning,
: "If a dark image "B" appears on a lighter background then this is not a cause for rejection"
: thanks for replies,
:
: Suresh
------------ End Original Message ------------

It is correct: if B appears darker, back scatterig radiation is irrelevant.


    
 
 Reply 
 
DJ Kallhof
DJ Kallhof
09:16 Sep-22-2008
Re: RT Back Scattering
The reason it shows up on the film dark is from scatter between the "B" itself and the film.
----------- Start Original Message -----------
: Hi,
: How does a letter B appears black in RT film, when it is placed at the back of film ?
: I find some procedures mentioning,
: "If a dark image "B" appears on a lighter background then this is not a cause for rejection"
: thanks for replies,
:
: Suresh
------------ End Original Message ------------




    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
00:57 Sep-23-2008
Re: RT Back Scattering - slight edit
Hi Suresh

A light image "B" on the film against a darker background means less radiation is reaching the film immediately under the "B" than is reaching the surrounding area. The lead letter is SHIELDING the film from scattered radiation from materials behind the film which lie in the radiation path. UNACCEPTABLE.

If the density of the surrounding film is less than that of the image of the "B", i.e. the "B" is a dark image against a lighter film background, then the scatter effect is weaker from the background than backscatter and/or emission from the lead "B". ACCEPTABLE.


Thoughtful set-up and use of lead sheet will minimise backscatter.

Good shooting.

Nigel

----------- Start Original Message -----------
: : Hi,
: : How does a letter B appears black in RT film, when it is placed at the back of film ?
: : I find some procedures mentioning,
: : "If a dark image "B" appears on a lighter background then this is not a cause for rejection"
: : thanks for replies,
::
: : Suresh
: It is correct: if B appears darker, back scatterig radiation is irrelevant.
------------ End Original Message ------------




    
 
 Reply 
 

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