>> Hello Markus, >> >> sounds veeeeery strange to me. >>
MR> Hello Jan and all the others, MR> yes, this article is quite extraordinary, but PIN-Diodes ARE INDEED used MR> to detect radiation. I don't know whether they are directly coated by a MR> szintillation substance. The author replaced the glass window with a 10� MR> Al-coated foil to keep the light outside (but I don't know wheter this MR> foil also acts as a szintillatior). I would really like to give this MR> circuit a try before looking for such a special detection diode. MR> Further researches about the author braught up the following results: MR> The article was published in "Electronics Designer's Casebook No.3 for MR> the period Feb 16, 1978 to Jan 4, 1979". The author doesn't work for the MR> indicated institute in poland any more, not quite a surprise. So I can't MR> contact him directly. MR> But this tells us that the diodes are at least 25 years old and probably MR> of eastern europe type (former CCCP I think, but not sure). So if anyone MR> of the list members has an old data book on the shelf, please take a MR> look ... MR> Today's photodiodes should have a higher performance/sensitivity, so MR> would a general purpose type (which one?) be ok for a simple test of the MR> circuit? MR> Best Regards MR> Markus May I clean up a bit? Indeed any pn junction is sensitive to ionizing radiation, independent of the type of radiation. alpha, beta and gamma do all create electron-hole pairs in the semiconductor material, while loosing some energy themselves. The energy loss per created eletron-hole pair is about 3x the band gap energy of the material, i.e. 3x 1.2eV in the case of silicon. If the electron-hole pair is created in or near the depletion region of the junction, the external field will separate electrons and holes and accelerate them towards the oppositely charged electrodes. These carriers appear then as an electric current through the diode. There are special diodes for these purposes around which have an extremely wide depletion region by the in-diffusion of lithium into the semiconductor material - they can even fully stop an alpha particle in the active region and the full energy of the particle will be converted. This allows an accurate measurement of the energy of the incoming alpha particles. A normal pn or even pin diode will only absorb part of the energy in the sensitive region and can still be used to detect the presence of radiation. For Markus' project _any_ pn or pin diode will do if he can expose the junction to the incoming radiation. As described in the article a diode in a metal can with glass window is easiest to use, since you can remove the front window and replace it by an alpha-transparent material, such as the mylar foil described in the article - of course it has to be really light-tight, otherwise you will detect anything else as well. Gamma and X-ray radiation has very little energy loss in most semiconductor materials, requiring very thick depletion regions to be detected. Since these are hard/impossible to manufacture and also very sensitive to thermal noise, scintillator materials are used to convert the incoming radiation into visible light which is easily absorbed in the junction. Just a rough estimation of the absorption depth in semiconductors: alpha 1-10um beta 5-50um gamma several mm Uwe. -- Author: Uwe Zimmermann INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
