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Technical Discussions
gowrishankar
R & D, scientist
ISRO, India, Joined Nov 2008, 34

gowrishankar

R & D, scientist
ISRO,
India,
Joined Nov 2008
34
09:37 Apr-22-2008
radiography

sir
1. i have read an equation that Linear absorption coefficient= log2/HVL. I think this is related to gamma sources.Similarly is there any relation exists with respect to x-ray energies? please give me answer.

2. Is there any research paper related to defect depth estimation in radiography ( here depth is third dimension of defect .anyway we can measure length and width of the defect)


 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
08:17 Apr-27-2008
Re: radiography
Dear Gowrishankar,

I would like to respond to your second question. Triangulation method is a well developed technique for determination of depth of a discontinuity. However, with thin sections, it is limited in accuracy. If you need any more information about the method, pl. get in touch.

S.V.Swamy

----------- Start Original Message -----------
: sir
: 1. i have read an equation that Linear absorption coefficient= log2/HVL. I think this is related to gamma sources.Similarly is there any relation exists with respect to x-ray energies? please give me answer.
: 2. Is there any research paper related to defect depth estimation in radiography ( here depth is third dimension of defect .anyway we can measure length and width of the defect)
------------ End Original Message ------------




 
 Reply 
 
gowrishankar
R & D, scientist
ISRO, India, Joined Nov 2008, 34

gowrishankar

R & D, scientist
ISRO,
India,
Joined Nov 2008
34
00:40 May-06-2008
Re: radiography
----------- Start Original Message -----------
: Dear Gowrishankar,
: I would like to respond to your second question. Triangulation method is a well developed technique for determination of depth of a discontinuity. However, with thin sections, it is limited in accuracy. If you need any more information about the method, pl. get in touch.
: S.V.Swamy
: : sir
: : 1. i have read an equation that Linear absorption coefficient= log2/HVL. I think this is related to gamma sources.Similarly is there any relation exists with respect to x-ray energies? please give me answer.
: : 2. Is there any research paper related to defect depth estimation in radiography ( here depth is third dimension of defect .anyway we can measure length and width of the defect)
------------ End Original Message ------------

Thank you sir,
please send some useful data/ site addresses for academic interest.actually my interest resticted to 6mm max thickness of aluminum alloys
regards.
gowrishankar





 
 Reply 
 
Nandeesh
Nandeesh
01:18 May-14-2008
Re: radiography
Can u pls tell me how to estimate the beam spread in Gamma radiography when using A COLLIMATOR?


 
 Reply 
 
Gowri santhosh Palika
NDT Inspector,
Royscan engineering pte ltd, Singapore, Joined May 2008, 52

Gowri santhosh Palika

NDT Inspector,
Royscan engineering pte ltd,
Singapore,
Joined May 2008
52
06:47 May-15-2008
Re: radiography
----------- Start Original Message -----------
: Can u pls tell me how to estimate the beam spread in Gamma radiography when using A COLLIMATOR?
------------ End Original Message ------------

Hi,
This is Gowri from GJ. First of all we have to know that collimator is used to guide the radiation and for safe practice in dangerous Radiography. collimators are made up of high density metals eg. tungsten and heavy alloys to absorb the non required ionising radiation for safety. I think so there is no any change in beam spread when using collimators, rather than as usual.


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

Nigel

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
08:26 May-15-2008
Re: radiography
"No any change in beam spread"? What would be the purpose of collimators if they dont restrict the beam spread, Gowri? Perhaps you misunderstood Nandeesh's question.

Nandeesh, the collimator supplier should have provided a data sheet at the time of purchase detailing material, dimensions and beam spread. If you dont have that then theoretically you could make a set-up using a 40 x 30 film and precisely measure the source to film distance, expose for a couple of seconds to the collimated beam and measure the dimensions of the significant exposure on the developed film. At least it would give you a qualitative idea of the beam cone.

Hope that helps. Safe (as possible) shooting!

Nigel

----------- Start Original Message -----------
: : Can u pls tell me how to estimate the beam spread in Gamma radiography when using A COLLIMATOR?
: Hi,
: This is Gowri from GJ. First of all we have to know that collimator is used to guide the radiation and for safe practice in dangerous Radiography. collimators are made up of high density metals eg. tungsten and heavy alloys to absorb the non required ionising radiation for safety. I think so there is no any change in beam spread when using collimators, rather than as usual.
------------ End Original Message ------------




 
 Reply 
 
DJ Kallhof
DJ Kallhof
04:14 May-15-2008
Re: radiography
I performed industrial radiography for 8 years before settling into aerospace. I may be able to offer some insight. The source size of your typical Ir 192 source is app. 0.100" X 0.100" (.00393mm X .00393mm) yielding an effective source size of 0.141" (.0055mm). If memory serves me, the portal on most collimators was app. somewhere between .250" -.375" (.0098mm - .01476mm). The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur. The source simply floats somewhere in the opening of the much larger collimator portal. The function of the collimator is for the safety of the radiographer and anyone outside the ropes.
----------- Start Original Message -----------
: "No any change in beam spread"? What would be the purpose of collimators if they dont restrict the beam spread, Gowri? Perhaps you misunderstood Nandeesh's question.
: Nandeesh, the collimator supplier should have provided a data sheet at thetime of purchase detailing material, dimensions and beam spread. If you dont have that then theoretically you could make a set-up using a 40 x 30 film and precisely measure the source to film distance, expose for a couple of seconds to the collimated beam and measure the dimensions of the significant exposure on the developed film. At least it would give you a qualitative idea of the beam cone.
: Hope that helps. Safe (as possible) shooting!
: Nigel
: : : Can u pls tell me how to estimate the beam spread in Gamma radiography when using A COLLIMATOR?
: : Hi,
: : This is Gowri from GJ. First of all we have to know that collimator is used to guide the radiation and for safe practice in dangerous Radiography. collimators are made up of high density metals eg. tungsten and heavy alloys to absorb the non required ionising radiation for safety. I think so there is no any change in beam spread when using collimators, rather than as usual.
------------ End Original Message ------------




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

Nigel

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
07:19 May-16-2008
Re: radiography
David

Could you clarify your sentence:

"The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur."

In my opinion the source size is (almost) irrelevant in determining the geometric beam spread as the uncollimaed source emits omnidirectional radiation. Collimating attenuates radiation which travels into the body of the collimator - but the collimator's aperture emits essentially uncollimated radiation, the aperture dimensions will determine the extent of the beam spread.

The beam spread of a collimated source CANNOT be the same as that of an uncollimated dosurce. The collimator effectively turns an almost spherical radiation distribution from an uncollimated source into an approximately conical radiation beam


Also something is wrong with your Imperial to metric conversions. 0.1" is 2,5mm. therefore the effective source size is the direct equivalent of 0.141", namely 3.54mm

Cheers

Nigel


----------- Start Original Message -----------
: I performed industrial radiography for 8 years before settling into aerospace. I may be able to offer some insight. The source size of your typical Ir 192 source is app. 0.100" X 0.100" (.00393mm X .00393mm) yielding an effective source size of 0.141" (.0055mm). If memory serves me, the portal on most collimators was app. somewhere between .250" -.375" (.0098mm - .01476mm). The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur. The source simply floats somewhere in the opening of the much larger collimator portal. The function of the collimator is for the safety of the radiographer and anyone outside the ropes.
: : "No any change in beam spread"? What would be the purpose of collimators if they dont restrict the beam spread, Gowri? Perhaps you misunderstood Nandeesh's question.
: : Nandeesh, the collimator supplier should have provided a data sheet at the time of purchase detailing material, dimensions and beam spread. If you dont have that then theoretically you could make a set-up using a 40 x 30 film and precisely measure the source to film distance, expose for a couple of seconds to the collimated beam and measure the dimensions of the significant exposure on the developed film. At least it would give you a qualitative idea of the beam cone.
: : Hope that helps. Safe (as possible) shooting!
: : Nigel
: : : : Can u pls tell me how to estimate the beam spread in Gamma radiography when using A COLLIMATOR?
: : : Hi,
: : : This is Gowri from GJ. First of all we have to know that collimator is used to guide the radiation and for safe practice in dangerous Radiography. collimators are made up of high density metals eg. tungsten and heavy alloys to absorb the non required ionising radiation for safety. I think so there is no any change in beam spread when using collimators, rather than as usual.
------------ End Original Message ------------




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

Nigel

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
07:23 May-16-2008
Re: radiography
As an afterthought, David you seem to be describiing image shadow formation (penumbra) or geometric unsharpness (Ug), which DOES depend on source size (as well as the set-up geometry) and IS affected by the source size. Different phenomenon from beam spread.

----------- Start Original Message -----------
: David
: Could you clarify your sentence:
: "The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur."
: In my opinion the source size is (almost) irrelevant in determining the geometric beam spread as the uncollimaed source emits omnidirectional radiation. Collimating attenuates radiation which travels into the body of the collimator - but the collimator's aperture emits essentially uncollimated radiation, the aperture dimensions will determine the extent of the beam spread.
: The beam spread of a collimated source CANNOT be the same as that of an uncollimated dosurce. The collimator effectively turns an almost spherical radiation distribution from an uncollimated source into an approximately conical radiation beam
:
: Also something is wrong with your Imperial to metric conversions. 0.1" is 2,5mm. therefore the effective source size is the direct equivalent of 0.141", namely 3.54mm
: Cheers
: Nigel
:
: : I performed industrial radiography for 8 years before settling into aerospace. I may be able to offer some insight. The source size of your typical Ir 192 source is app. 0.100" X 0.100" (.00393mm X .00393mm) yielding an effective source size of 0.141" (.0055mm). If memory serves me, the portal on most collimators was app. somewhere between .250" -.375" (.0098mm - .01476mm). The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur. The source simply floats somewhere in the opening of the much larger collimator portal. The function of the collimator is for the safety of the radiographer and anyone outside the ropes.
: : : "No any change in beam spread"? What would be the purpose of collimators if they dont restrict the beam spread, Gowri? Perhaps you misunderstood Nandeesh's question.
: : : Nandeesh, the collimator supplier should have provided a data sheet at the time of purchase detailing material, dimensions and beam spread. If you dont have that then theoretically you could make a set-up using a 40 x 30 film and precisely measure the source to film distance, expose for a couple of seconds to the collimated beam and measure the dimensions of the significant exposure on the developed film. At least it would give you a qualitative idea of the beam cone.
: : : Hope that helps. Safe (as possible) shooting!
: : : Nigel
: : : : : Can u pls tell me how to estimate the beam spread in Gamma radiography when using A COLLIMATOR?
: : : : Hi,
: : : : This is Gowri from GJ. First of all we have to know that collimator is used to guide the radiation and for safe practice in dangerous Radiography. collimators are made up of high density metals eg. tungsten and heavy alloys to absorb the non required ionising radiation for safety. I think so there is no any change in beam spread when using collimators, rather than as usual.
------------ End Original Message ------------




 
 Reply 
 
DJ Kallhof
DJ Kallhof
01:14 May-16-2008
Re: radiography
Actually, the name is Dennis. Thank you for the math correction. I don't typically work with metric, the USA has caught up there yet, I mistakenly divided by 25.4 rather than multiplied. My bad. The point I was trying to make, is unless the collimator is the same size or smaller then the effective source size, it will not affect the beam spread. I didn't consider 360 degree beam spread being cut down to under 180 degrees as collimating, but I guess it is.

----------- Start Original Message -----------
: As an afterthought, David you seem to be describiing image shadow formation (penumbra) or geometric unsharpness (Ug), which DOES depend on source size (as well as the set-up geometry) and IS affected by the source size. Different phenomenon from beam spread.
: : David
: : Could you clarify your sentence:
: : "The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur."
: : In my opinion the source size is (almost) irrelevant in determining the geometric beam spread as the uncollimaed source emits omnidirectional radiation. Collimating attenuates radiation which travels into the body of the collimator - but the collimator's aperture emits essentially uncollimated radiation, the aperture dimensions will determine the extent of the beam spread.
: : The beam spread of a collimated source CANNOT be the same as that of an uncollimated dosurce. The collimator effectively turns an almost spherical radiation distribution from an uncollimated source into an approximately conical radiation beam
: :
: : Also something is wrong with your Imperial to metric conversions. 0.1" is 2,5mm. therefore the effective source size is the direct equivalent of 0.141", namely 3.54mm
: : Cheers
: : Nigel
: :
: : : I performed industrial radiography for 8 years before settling into aerospace. I may be able to offer some insight. The source size of your typical Ir 192 source is app. 0.100" X 0.100" (.00393mm X .00393mm) yielding an effective source size of 0.141" (.0055mm). If memory serves me, the portal on most collimators was app. somewhere between .250" -.375" (.0098mm - .01476mm). The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur. The source simply floats somewhere in the opening of the much larger collimator portal. The function of the collimator is for the safety of the radiographer and anyone outside the ropes.
: : : : "No any change in beam spread"? What would be the purpose of collimators if they dont restrict the beam spread, Gowri? Perhaps you misunderstood Nandeesh's question.
: : : : Nandeesh, the collimator supplier should have provided a data sheet at the time of purchase detailing material, dimensions and beam spread. If you dont have that then theoretically you could make a set-up using a 40 x 30 film and precisely measure the source to film distance, expose for a couple of seconds to the collimated beam and measure the dimensions of the significant exposure on the developed film. At least it would give you a qualitative idea of the beam cone.
: : : : Hope that helps. Safe (as possible) shooting!
: : : : Nigel
: : : : : : Can u pls tell me how to estimate the beam spread in Gamma radiography when using A COLLIMATOR?
: : : : : Hi,
: : : : : This is Gowri from GJ. First of all we have to know that collimator is used to guide the radiation and for safe practice in dangerous Radiography. collimators are made up of high density metals eg. tungsten and heavy alloys to absorb the non required ionising radiation for safety. I think so there is no any change in beam spread when using collimators, rather than as usual.
------------ End Original Message ------------




 
 Reply 
 
tj
tj
04:17 May-29-2008
Re: radiography
----------- Start Original Message -----------
: Actually, the name is Dennis. Thank you for the math correction. I don't typically work with metric, the USA has caught up there yet, I mistakenly divided by 25.4 rather than multiplied. My bad. The point I was trying to make, is unless the collimator is the same size or smaller then the effective source size, it will not affect the beam spread. I didn't consider 360 degree beam spread being cut down to under 180 degrees as collimating, but I guess it is.
: : As an afterthought, David you seem to be describiing image shadow formation (penumbra) or geometric unsharpness (Ug), which DOES depend on source size (as well as the set-up geometry) and IS affected by the source size. Different phenomenon from beam spread.
: : : David
: : : Could you clarify your sentence:
: : : "The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur."
: : : In my opinion the source size is (almost) irrelevant in determining the geometric beam spread as the uncollimaed source emits omnidirectional radiation. Collimating attenuates radiation which travels into the body of the collimator - but the collimator's aperture emits essentially uncollimated radiation, the aperture dimensions will determine the extent of the beam spread.
: : : The beam spread of a collimated source CANNOT be the same as that of an uncollimated dosurce. The collimator effectively turns an almost spherical radiation distribution from an uncollimated source into an approximately conical radiation beam
: : :
: : : Also something is wrong with your Imperial to metric conversions. 0.1" is 2,5mm. therefore the effective source size is the direct equivalent of 0.141", namely 3.54mm
: : : Cheers
: : : Nigel
: : :
: : : : I performed industrial radiography for 8 years before settling into aerospace. I may be able to offer some insight. The source size of your typical Ir 192 sourceis app. 0.100" X 0.100" (.00393mm X .00393mm) yielding an effective source size of 0.141" (.0055mm). If memory serves me, the portal on most collimators was app. somewhere between .250" -.375" (.0098mm - .01476mm). The beam spread in industrial radiography is dictated by the effective source size of the isotope, the portal of the collimator simply allows that to occur. The source simply floats somewhere in the opening of the much larger collimator portal. The function of the collimator is for the safety of the radiographer and anyone outside the ropes.
: : : : : "No any change in beam spread"? What would be the purpose of collimators if they dont restrict the beam spread, Gowri? Perhaps you misunderstood Nandeesh's question.
: : : : : Nandeesh, the collimator supplier should have provided a data sheet at the time of purchase detailing material, dimensions and beam spread. If you dont have that then theoretically you could make a set-up using a 40 x 30 film and precisely measure the source to film distance, expose for a couple of seconds to the collimated beam and measure the dimensions of the significant exposure on the developed film. At least it would give you a qualitative idea of the beam cone.
: : : : : Hope that helps. Safe (as possible) shooting!
: : : : : Nigel
: : : : : : : Can u pls tell me how to estimate the beam spread in Gamma radiography when using A COLLIMATOR?
: : : : : : Hi,
: : : : : : This is Gowri from GJ. First of all we have to know that collimator is used to guide the radiation and for safe practice in dangerous Radiography. collimators are made up of high density metals eg. tungsten and heavy alloys to absorb the non required ionising radiation for safety. I think so there is no any change in beam spread when using collimators, rather than as usual.
------------ End Original Message ----------
Hello,
You can think of the source as a light bulb on a lamp. If left bare you get radiation in 360 degrees.
When you put a shade on the lamp the radiation, as you can see, is attenuated in areas covered by lamp shade. You can also see that the "beam" not attenuated by the shade is directly proportional to the dimensions of the shade or collimator. If you change the size of the lightbulb the effect remains the same (as long as the bulb fits in the shade!). Use a narrow lampshade for a narrow beam and vice/versa.


 
 Reply 
 

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