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Technical Discussions
IClampers
IClampers
03:09 Jul-06-2005

31. (1) Every person who operates an exposure device shall
(b) when an external sealed source assembly guide tube is being
used, have immediately available the following items:
(i) material that can be used to attenuate, by a factor of at
least 100, the radiation from the sealed source,

This is an exerpt from the Canadian CNSC regulation pertaining to radiography. My question is, when they say attenuate by a factor of 100, does that mean 100 times less. So if the source unshielded is giving off 20000mrem/h at 1 metre then does an attenuator of 100 bring that down to 20000/100=200mrem/h? or does it mean half? I'm a little confused by the statement.

Appreciate it if someone could clarify this for me . Thanks.

Jim Knowles
Jim Knowles
01:01 Jul-08-2005
Re: RT Attenuation Factor (Lead Tunnel)
----------- Start Original Message -----------
: 31. (1) Every person who operates an exposure device shall
: (b) when an external sealed source assembly guide tube is being
: used, have immediately available the following items:
: (i) material that can be used to attenuate, by a factor of at
: least 100, the radiation from the sealed source,
:
: This is an exerpt from the Canadian CNSC regulation pertaining to radiography. My question is, when they say attenuate by a factor of 100, does that mean 100 times less. So if the source unshielded is giving off 20000mrem/h at 1 metre then does an attenuator of 100 bring that down to 20000/100=200mrem/h? or does it mean half? I'm a little confused by the statement.
: Appreciate it if someone could clarify this for me . Thanks.
------------ End Original Message ------------

Essentialy Yes, it can be more,so can be made up of bags of lead shot, sheet, but what it is trying to relay is that it gives more time to think, assess and recover the situation.
Aimed at reducing the dose to the person who has to approach the source to recover to a safer condition.

John Woollven
John Woollven
08:34 Jul-08-2005
Re: RT Attenuation Factor (Lead Tunnel)
----------- Start Original Message -----------
: 31. (1) Every person who operates an exposure device shall
: (b) when an external sealed source assembly guide tube is being
: used, have immediately available the following items:
: (i) material that can be used to attenuate, by a factor of at
: least 100, the radiation from the sealed source,
:
: This is an exerpt from the Canadian CNSC regulation pertaining to radiography. My question is, when they say attenuate by a factor of 100, does that mean 100 times less. So if the source unshielded is giving off 20000mrem/h at 1 metre then does an attenuator of 100 bring that down to 20000/100=200mrem/h? or does it mean half? I'm a little confused by the statement.
: Appreciate it if someone could clarify this for me . Thanks.
------------ End Original Message ------------

I was a bit surprised to see that the same wording has been in use since at least 1983, when it appeared in Section 18 of the (Canadian) Atomic Energy Control Regulations. In those days the rules for industrial radiography in Canada were contained in one thin section of the Regulations, instead of being spread over a number of more complex documents as they are today.

To help us understand these Regulations, in 1983 AECB published Regulatory Document R-62 which provided guidance in layman's terms as to what was really meant by some of the official words. Unfortunately the 'attenuation by a factor of at least 100' was not covered, but I have always taken it to mean reduce the radiation level to 1/100 of its unshielded value, and we usually satisfy this requirement by carrying around a lead tunnel. For the definitive answer you should contact your licensing specialist at CNSC.

Do any other Canadian readers remember the little booklet RPD-SC-1 published in 1968 by the Radiation Protection Division of the National Health & Welfare department? This spelled out in simple language everything you needed to know about industrial radiography in 1968 and was a great study guide for exams. I keep hoping that CNSC will come out with an updated version but no doubt there are legal implications that would prevent it.

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