Building lead wall of roofing lead rolls ?

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reteb1
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Building lead wall of roofing lead rolls ?

Post by reteb1 »

I can buy a considerable quantity of lead in rolls of 2mm thick.
They were for roofing material.

My questions :

1.
Is this kind of roofing lead suitable for shielding against X-rays and gamma's ?
Or is another particular kind of lead more desirable ?

2.
I could get enough to build small walls of up to 2" thick.
Does it matter that small air gaps will remain there between the 2 mm thick windings ?
I intend to wind e.g. 20 windings in order to get a ~ 1 3/4 " thick wall around the x-ray generating devices ( at present 40-80 kV X-ray tubes ).

3.
I also need lead for shielding my alpha beta probes and alpha PMT 's against gamma background.
How thick should the lead be for shielding against background gamma ?

Thanks,
Peter.
davidtrimmell
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Re: Building lead wall of roofing lead rolls ?

Post by davidtrimmell »

Soft lead is the easiest to work with, so yes. 40 mm should do the job as the tenth value for 85KeV X-Rays is 0.52mm, see:
http://www.hc-sc.gc.ca/hecs-sesc/ccrpb/ ... endix2.htm
Table 4 (note that that the TVL for 70 and 85KeV x-rays are interposed.)

I have used two layers of 1mm lead sheeting around a 'home made' x-ray head and it drops the dose rate from around 200R/Hr. to nearly 20mr/Hr. You have to be real careful about cracks or any hole in the shielding as a small one can let out a lethal beam of shine that may be real easy to miss in a survey.

Lead works real well also to shield your beta/gamma detectors. For real low gamma readings often a depleted Uranium composite is used with lead on the inside (to shield the low energy gammas from the U). Alpha detectors should not need any real shielding, but confounders can be Radon/Thoron daughters in the air. Also if you are trying to create a really low gamma/cosmic ray background (for low level gamma spec. etc.), good old concrete with a lead lining works very well.

Be careful with those x-rays.

Regards,

David Trimmell
raneyt
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Re: Building lead wall of roofing lead rolls ?

Post by raneyt »

Peter,

Richard Hull wrote a brief article about attenuating gamma rays with lead. He may have posted it under the references forum. If not, I'm sure he'd send you a copy, if you ask him.

I'm sure there are some good industrial hygiene websites with data on lead thickness for a given x-ray tube energy. One reference I have (Clark, 1927) mentioned 0.25" for 150kV. And he also mentions a 2 mm thick lead sheet will absorb about 99.4% of a 120kV x-ray beam.

This is dated data & I only include it here for reference & to give you a "ball park" feeling for how much lead you'll need.

Warm Regards,

TIM RANEY
raneyt
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Re: Building lead wall of roofing lead rolls ?

Post by raneyt »

Peter,

Just a little update. "Radiology Physics" (Robertson, 1941), has a table of lead thicknesses to absorb an x-ray of a given energy.

For example, 1mm for 75kV, 2mm for 125kV, 4mm for 200kV, etc. Again, it's probably better to check current health physicists guidelines for this type of project.

Warm Regards,

TIM RANEY
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Richard Hull
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Re: Building lead wall of roofing lead rolls ?

Post by Richard Hull »

For your 80kev x-rays, I would think that about 1cm would be more than enough.

To reduce cosmics to a dull roar a lead castle is usually the thing with 20cm thick walls. Most castles weigh one quarter ton or more and are about the size of a very small office trash can. The interior is normally very small (about the size of a juice can). These rarely reduce background by more than 80%, but that can be significant in many counting experiments. They cost a fortune (>$1000) due to the need to use rather rare, certified, 100+ year old lead.

Richard Hull
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