On Thu, 7 May 1998 07:54:21 +1000 "Paul B. Webster VK2BZC" writes: >Gordon Couger wrote: > >> From time to time I have thought soft x-rays should erase OTP chips. > > The concept has merit. > >> Has anyone tried it. It erases the chips alright, but it also ruins them. X-ray generating devices are not new, and neither are plastic OTP EPROM chips. Many people have tried. Some have claimed success. They have only erased their chip once and it is likely not fully up to specifications because of radiation damage. If it really did work, there would be little reason to sell window EPROM chips. Instead, small x-ray generators would be used instead of UV lamps. >> A soft x-ray source can be made from a vacuum tube. > An X-ray tube consists of an electron gun similar to that in a CRT >(TV, oscilloscope) *except* that it generates from five (dental, II) >to >200 times the beam current, focussed onto an oblique tungsten anode >such >that all the X-rays come out *in one direction*. Such a complicated tube is used for X-ray photography because in order to produce a good image, the X-rays need to effectively come from a "point source". An X-ray picture is essentially a shadow of the more inpenetrable parts of the object being X-rayed, cast onto the film. If the X-rays came from a large diffuse area, the shadow would be blurred. So the tube is built to focus the electrons to one spot on the anode. The anode needs to be made of tungsten or similar material because very concentrated heat (as well as a few X-rays) is generated by electrons striking the focus point. I remember something about tungsten also working better than most metals at converting the energy from colliding electrons into X-rays. Obviously, setting the target at an angle makes it easier for the X-rays to get out of the tube since they don't have to pass through the target first. Ordinary tubes with thin metal anodes should allow some X-rays to pass to the outside of the anode, then out through the glass. The tube's anode will likely overheat before producing any significant amount of X-radiation. I have seen high-voltage TV diode tubes with lead/rubber shields on the outside and dire warnings about not messing with the shield. I suspect the level of X-rays produced from these tubes even without the shields was miniscule. But the government was concerned about having any measurable source of X-rays so close to millions of people for such a long time. The problem with >X-ray emission from TV tubes and the old EHT shunt regulators is that >it >comes out *all over the place*! This is not a problem, as long as the extra X-rays are kept from irradiating anyone. Of course using a concentrated powerful source would reduce the damage/erasure time. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]