At 07:49 PM 7/21/03 +0100, Peter Fairbrother wrote:
a_b_sorbed. Absorb is a widely used word meaning 3to drink in, to soak up,2 both literally and figuratively. Adsorb is a specialized technical term, meaning only 3to collect a condensed gas or liquid on a surface.2
Thank you. Have a hard time keeping them straight. Probably a textual clue that will undermine my pseudo-anonymity some day :-)
The glass of CRT's absorbs so much of the X-rays that it might be hard to detect a signal at all at any distance, but then the signal is not swamped by noise from the not-immediately-illuminated areas, unlike the optical
emissions.
"0.5 milliroentgens per hour at a distance of five (5) centimeters from any point on the external surface of the receiver" is the US legal
Yes but anything that picks up the weak X-ray will be sensitive to other normal background ionizing. With a proportional counter like a scintillator/PMT combo, where you could discriminate different types of radiation on the basis of pulse height, but you'll be down in the photomultiplier tube's noise. And as a cosmic ray secondary slows down it can generate x-rays. Maybe if the Adversary is allowed cryogenic detectors in the next room over... he still has to deal with the attenuating coefficient for drywall, etc. And again, I think basically nothing gets through the glass. limit[*], and
low voltage (and thus very low x-ray emission) crt monitors are common now, if not a de-facto standard.
That's pretty hot, actually. A glass vial of 5 gms U Acetate is only twice that, a few mm from the alpha-window of a GM detector. And the broad face of a CRT means 1/R^2 doesn't apply until you get some distance away... more like 1/R for an infinite slab.
However, I expect shot noise to be a limiting factor here. Unfortunately, the Roentgen is such a wierd unit it's not that easy to convert it to photons and do the math!
Since the signal is rastering at MHz, you can't very well integrate ionizing radiation over long times, as you could to say detect the betas coming out of a jar of salt substitute (potassium). Roentgens are defined as producing a certain amount of ionization in dry air. The photons doing the ionizing would range from the 10's of keV for X-rays to MeV for gammas. (Careful with that brightness control Eugene!) An ion pair takes about 37 eV to form. Compare with visible light's very small range, blue to red.
I use 180:210:210[**] (r:g:b) text on a 255:255:255 window background at present, with very light wallpaper, though I speckle both slightly. It's a little hard to read, but much better than some other suggested combinations.
I hope you don't do this all the time...
[*]< Probably far too high for safety! Originally for TV's, where the viewing distance is much higher. But most modern monitors will emit much less than that. I hope! >
As do TVs. Nowadays its the Radon daughters attracted to the charged glass that will be giving you your RDA (Radiation Daily Allowance.. RDA is a Yank FDA pun) Also some of the TV radiation was from HV tubes inside the box; that was solved by first using leaded glass (hack!) and then more elegantly by getting rid of tubes.