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old TV CRT used for radiation shielding

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pauleddy

Sat Sept 04 2010, 10:18PM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

not too high, all i would like to do is be able to veiw an x-ray of something in real time or build a electron beam to make those cool lighting glass things

Adam Munich

Sat Sept 04 2010, 10:31PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I still think that's a bad idea. It all depends on the amount of radiation though. If you plan on using a coolidge tube, don't do it.

Proud Mary

Sat Sept 04 2010, 11:39PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

pauleddy wrote ...

not too high, all i would like to do is be able to veiw an x-ray of something in real time or build a electron beam to make those cool lighting glass things

Fluoroscopy is best done when the intensifying screen is imaged with a video camera inside the shielded enclosure, and the video signal exported for viewing in safety elsewhere.

pauleddy

Sun Sept 05 2010, 12:53AM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

not that i have an x-ray tube, im just pondering, so theoretically how much radiation does the averge tv screen block

Adam Munich

Sun Sept 05 2010, 01:26AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Not much. A TV tube doesn't generate many x-rays, and the little bit that it does make are of low energy. The lead is just mainly there to make the glass much more clear. Blocking any soft rays that just happen to get produced is a bonus.

A superb radiation shield a CRT is not.

IntraWinding

Sun Sept 05 2010, 12:00PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

If you want to view live x-ray images, how about a 45 degree mirror to put you out of the beam path, and the rest shielded conventionally?

Proud Mary

Sun Sept 05 2010, 02:02PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

IntraWinding wrote ...

If you want to view live x-ray images, how about a 45 degree mirror to put you out of the beam path, and the rest shielded conventionally?

A bad idea! Not only are X-rays reflected - though to a far lesser degree than optical wavelengths, except at very low angles - they are also scattered by air molecules.

IntraWinding

Sun Sept 05 2010, 08:48PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

What percentage of the x-ray beam would reflect/scatter 90 degrees?

Adam Munich

Sun Sept 05 2010, 10:01PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

It's hard to tell.

Also, don't forget about compton scattering and backscatter. Even without the mirror, x-rays will still go all over the place.

Proud Mary

Sun Sept 05 2010, 10:44PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

IntraWinding wrote ...

What percentage of the x-ray beam would reflect/scatter 90 degrees?

The percentage of the beam energy undergoing complex processes of reflection, refraction, and scattering, such that X-rays were emitted through an aperture at 90 degrees to the primary beam would have to be determined empirically.

If we assume a typical dental tube 75kVp/5mA, the dose rate at 1000mm would be about 80 Sv/hr. So if we placed this 'viewing aperture' at 1 metre from the tube, and allowed that 1% of the beam energy escaped through the 'viewing aperture.' that would still be 800 mSv/hr.

If the 'viewing port' were located at only 50cm from the tube, then 1% of the dose would >3.0 Sv/hr.

These percentages are conjectures on my part, but I include them to give some idea of the order of the dose rates that might be encountered if this most ill-advised proposal were to be followed through.

By contrast, in the United Kingdom, the estimated total radiation dose from all sources natural and otherwise to members of the general population is 2.7 mSv/yr. (Source: HPA-RPD-001 - Ionising Radiation Exposure of the UK Population: 2005 Review)

Current ICRP recommendations (ICRP, 2007) for radiation protection assume an overall fatal cancer risk from low dose ionising radiation of about 5% per Sv.(Source: HPA-RPD-055 - An Introduction to the Estimation of Risks Arising from Exposure to Low Doses of Ionising Radiation)

The UK Ionising Radiation Regulations 1999 stipulate maximum annual effective doses for workers in industry as follows:

1. for employees aged 18 years or over, 20 millisieverts in a calendar year (except that in special cases employers may apply a dose limit of 100 millisieverts in 5 years with no more than 50 millisieverts in a single year, subject to strict conditions);
2. for trainees, 6 millisieverts in a calendar year; and
3. for any other person, including members of the public and employees under 18 who cannot be classed as trainees, 1 millisievert in a calendar year.

An ancient paper, "The Shoe-Fitting Fluoroscope as a Radiation Hazard" (Calif Med. 1950 January; 72(1): 26â€“30) touches upon many of the issues raised in this thread - X-ray leakage through lead glass, X-ray scattering through an aperture at 90 deg to the beam, and so on, that much may be learned from it even sixty years later:

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