neal@lynx.uucp (Neal Woodall) (04/26/89)
I have recently decided to purchase a geiger counter, for general use and for possible survival applications. I have seen several different types of devices offered for sale, including some that are old US Civil Defense surplus, some that are based on solid-state sensors that are obviously commercial-grade units, and some that are advertised as being European/NATO surplus (brand new, never opened). Now for questions/confusion: I believe that the geiger counters that I have seen can be broadly classed "radiological health" units (measure in the .5 to 500 milli-roentegen/hour range and are not "hardened" or weather-proof) and those that are intended for military/war conditions (measure in the 1-500 roentgen/hour range and are "hardened" and weather/water proof). How exactly is a "roentgen" defined? Is it in terms of energy dose, or just in terms of "counts" (ie, gamma striks regardless of energy, also do beta/alpha strikes count, even though they are obviously not as bad as high-energy gammas)? What is considered normal "background radiation" in roentgens? Also, do any of these detectors count neutrons (which are very bad)? Is a geiger tube detector better than solid-state (or vise versa) and under which conditions/uses is either "better" than the other? How is a roentgen (one measure of radiation) related to a REM (which I believe stands for Radiation Effective to Man)? What dose of roentgens/REMs in bad/worse/fatal? (I have been told that more than 350 roentgens is bad/fatal) As you can tell, I have lost of questions that perhaps one of you can answer for me. I have used a solid-state commercial-grade unit (belongs to a friend) and it was quite interesting to use. One of the "funniest" things occured when we tested another friend's rock/mineral collection....we found that two of his rocks (uranannite and cuprosklodouskite (both probably spelled wrong)) gave off MUCH more radiation than the normal background. This device measured the radiation in "counts" or "events" (which I understand to be the detection of an alpha/beta/gamma of greater than some threashold energy). Normal background was about 12 counts/minute....these rocks were on the order of 7000 counts/minute! The rocks now reside in a metal box in the garage. My friend's wife went through a nite of severe depression when she was just sure that they would never have kids! She has completely forgotten the whole episode now. Anyway, all practical answers/info is appreciated. I undertand the difference between alphas (ionized helium nuclei), betas (high energy electrons) and gammas (very high energy photons) and why fast neutrons are so VERY bad (affect the nucleus of an atom, rather than just the electron shell). Any info concerning the "practical" aspects of radioactivity, radiologcal health, geiger counters, etc. will be appreciated. All follow-ups have been directed to sci.electronics. Thanx in advance! Neal
bourland@godot.radonc.unc.edu (J. Daniel Bourland) (04/26/89)
A geiger-muller counter (GM) will count any ionizing radiation that is able to penetrate the wall of the detector. This includes gamma and x rays down to 10's of keV, higher energy beta (not from tritium) and few alphas. Some GMs have a thin window in the end of the tube (a thin- end window GM) which allow much more beta and more alphas to enter the tube and be counted. In terms of hazard, gamma, x, beta, alpha, and neutrons can all be of sufficient danger if the exposure route is the "right" one as well as the dose rate. For instance, with gammas the risk is for external exposure although internal exposures can occur. With alphas the risk is for internal exposure of the lung through inhalation. So it can vary - you should be careful about saying this one is safe and this one is bad. The roentgen is a measurement of ionization per mass of air, specifically 2.58 x 10^-4 coul/kg of air (a coulomb is a lot of charge) and is valid only for photons. Your GM counter's output is one click per ionizing event, regardless of the amount of energy deposited, thus the GM really just gives you counts per minute or hour or something like that. The GM does not discriminate between photon, beta or alpha radiation in terms of output - if the particle makes and ionizing event in the GM, it is counted. For this reason, the R/hr scale is true only for the isotope for which the GM is calibrated (usually Cs-137, Co-60 or Ra-226), but it is still accurate for isotopes having energies near to that of the calibration isotope. With regard to the rem, the rem is a unit for radiation protection purposes, and is the dose in rads times the quality factor (QF) for the radiation in question. QF is an indicator of biological effect, relative to the effect for photons or electrons (which have a QF of 1). For neutrons QF = 10, for alhpas QF = 10 to 20. As it turns out, 1 rad is about 1 roetgen. So a rem about equals a roetgen if the QF is 1, which works for photons and electrons. For alphas and neutrons, it will depend on the QF, which does vary with energy. Your GM will detect neutrons if the interact in the wall of the detector. Neutron detectors are usually surrounded by a sphere of plastic to stop the neutrons for counting - it is very tricky dosimetry. All for now. For those participating in this mini-series on radiation instrumentation and dosimetry, please send $10.00 to the address below. The honor code is in effect. Thank you. Dan Bourland, Physicist bourland@godot.radonc.unc.edu Dept of Radiation Oncology CB 7512 Chapel Hill, NC 27599
martens@wasatch.utah.edu (William G Martens) (04/26/89)
> I have recently decided to purchase a geiger counter, for general use and for > possible survival applications. I have seen several different types of devices Heath kit sells a general purpose radiation monitor that features a small geiger-mueller tube with a mica window. It is suppose to detect soft x-rays, alpha, beta and gamma rays, (will not detect neutrons). It comes as a built it yourself kit, (piece of cake to put together), and resales for around $130.00, (the exact same model is featured, pre-built, from Edmunds Sci. for another $100.00 if money is no object). William Martens UofUtah Comp Sci
henry@utzoo.uucp (Henry Spencer) (04/27/89)
In article <5499@lynx.UUCP> neal@lynx.UUCP (Neal Woodall) writes: >How exactly is a "roentgen" defined? Is it in terms of energy dose, or just >in terms of "counts"... >How is a roentgen (one measure of radiation) related to a REM (which I >believe stands for Radiation Effective to Man)? There are actually three units involved. The roentgen is simply a unit of radiation energy, as I recall. The rad is, I think, "roentgen absorbed dose", which is more related to how much of that energy gets absorbed. And the REM is "roentgen equivalent [for] man", which corrects absorbed energy for the biological effectiveness of different types of radiation. REMs are what you really want to know about for health purposes, but the instruments usually measure roentgens or rads and you have to know the type of radiation to get REMs. > What dose of roentgens/REMs >in bad/worse/fatal? (I have been told that more than 350 roentgens is >bad/fatal) Background levels are very small, normally measured in milliREMs. Hundreds of REMs are very bad news. Humans vary, so the most you can get is a statistical measure, the LD50 -- how big a dose will be lethal to 50% of a population. That's something like 250-300 REMs, as I recall. Some sources give a tentative rule of thumb that it is reasonable to accept a once-in-a-lifetime dose of 100 REMs in an emergency with human life at stake. That is unlikely to kill you but likely to make you sick (later). All this is based on rather fuzzy memory; corrections welcome. -- Mars in 1980s: USSR, 2 tries, | Henry Spencer at U of Toronto Zoology 2 failures; USA, 0 tries. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
mandel@uxe.cso.uiuc.edu (04/27/89)
> /* Written 5:49 pm Apr 25, 1989 by neal@lynx.uucp in uxe.cso.uiuc.edu:sci.physics */ > /* ---------- "Radiation Detectors/Counters" ---------- */ > > > I have recently decided to purchase a geiger counter, for general use and for > possible survival applications. I have seen several different types of devices > offered for sale, including some that are old US Civil Defense surplus, some > that are based on solid-state sensors that are obviously commercial-grade > units, and some that are advertised as being European/NATO surplus (brand new, > never opened). > > Now for questions/confusion: > > I believe that the geiger counters that I have seen can be broadly classed > "radiological health" units (measure in the .5 to 500 milli-roentegen/hour > range and are not "hardened" or weather-proof) and those that are intended > for military/war conditions (measure in the 1-500 roentgen/hour range and are > "hardened" and weather/water proof). This is basically correct. The high range instruments will not be useful to you unless you happen to be near a nuclear explosion :-) > > How exactly is a "roentgen" defined? Is it in terms of energy dose, or just > in terms of "counts" (ie, gamma striks regardless of energy, also do > beta/alpha strikes count, even though they are obviously not as bad as > high-energy gammas)? What is considered normal "background radiation" in > roentgens? The Roentgen is defined as the amount of x or gamma radiation which will produce 1 E.S.U. of ionization in a cc of air at STP. The Roentgen is NOT DEFINED FOR beta, neutron or alpha radiation. Normal background radiation depends on where you live. An average for the U.S. is about 50 milliroentgens per year, but that's only from external gamma and x-rays. > > Also, do any of these detectors count neutrons (which are very bad)? Is a > geiger tube detector better than solid-state (or vise versa) and under which > conditions/uses is either "better" than the other? > G-M detectors are insensitive to neutrons. G-M are best for detecting > beta radiation. Solid detectors such as NaI are best for x and gamma rays. > How is a roentgen (one measure of radiation) related to a REM (which I > believe stands for Radiation Effective to Man)? What dose of roentgens/REMs > in bad/worse/fatal? (I have been told that more than 350 roentgens is > bad/fatal) > One roentgen (1 R) of x or gamma radiation deposits about 87 ergs per gram of air. The same exposure will deposit about 93 ergs per gram of soft tissue. The roentgen is a unit of EXPOSURE. In order to relate x or gamma exposure to ABSORBED DOSE, we use the rad unit (Radiation Absorbed Dose). ANY type of ionizing radiation dose can be characterized by the amount of energy deposited per unit mass of material (ANY material). One RAD is equal to an absorbed dose of 100 ergs per gram. Since some type of radiation are more effective than gamma rays in producing biological effects, we need a way to "normalize" the absorbed dose units. We do this by converting the absorbed dose in RADS into a "dose equivalent" in REMS. In general, it is assumed that 1 RAD of x or gamma ray dose yields 1 REM of dose equivalent. On the other hand 1 RAD of thermal neutron dose yields 3 REM of dose ezuivalent. 1 RAD of fast neutron dose yields 10 REM dose equivalent. One RAD of alpha dose yields 20 REM of dose equivalent. One RAD of beta dose yields 1 REM of dose equivalent. The conversion factor used for converting from RADS to REMS is called the Quality Factor (QF). The QF is defined in terms of the linear energy transfer of the type of radiation in question (amount of energy transfered to the medium per unit path length). Regardless of the type of radiation in question or the means of exposure, a REM produces the same amount of risk. (Actually there may be other "modifying factors" which might be applied in the conversion of absorbed dose to dose equivalent in certain situations, but it would be beyond the scope of this note to discuss them here.) Great care should be excercised when using geiger counters for determination of dose or dose equivalent. G-M's are, by nature, only flux-measuring devices- they do not measure energy deposition. G-M's should only be used for qualitative assessments such as contamination surveys unless specifically calibrated (or "energy-compensated") for specific situations. The LD-50 dose (lethal within 30 days in 50% of those exposed) is about 400 rads (can vary greatly depending on the individual and medical attention). The average annual NATURAL background dose equivalent is on the order of 300 millirem per year (this includes RADON).
ron@hpfcmgw.HP.COM (Ron Miller) (04/27/89)
> > How exactly is a "roentgen" defined? Is it in terms of energy dose, or just > in terms of "counts" (ie, gamma striks regardless of energy, also do > beta/alpha strikes count, even though they are obviously not as bad as > high-energy gammas)? What is considered normal "background radiation" in > roentgens? REM is Roentgen Equivalent Man which is a correction factor for health affecting dosage. For example, if you were a worker in a plutonium handling facility, your exposure to gammas would be predictable via a Roentgen measuring device and the exposure calculated by a correction factor for the known energy of the gammas from Pu. (if any, I don't have references handy) Nuclear powerplants utilize enough dosimeters that the correction factor is already scaled in and many of the personal dosimeters read in REM. BTW, the Federal limit for exposure for Radiation Workers is 5 REM per year accumulation. The maximum allowable for lifetime dosage is 5 REM per year for every year of age over 18. Extremely localized body parts have their own limits but 5 REM is the whole-body allowed dosage. (Hands and fingers have higher limits because the risk to bone marrow and blood producing organs is reduced.) Alpha strikes in a G-M detection are non-events. The particle can't get into the tube! Beta can be screened from alpha if you insert a piece of paper between the radiation source and the counter. (paper stops beta, counter is a scintillation detector with a mylar window) > > Also, do any of these detectors count neutrons (which are very bad)? Is a > geiger tube detector better than solid-state (or vise versa) and under which > conditions/uses is either "better" than the other? Neutrons are very hard to count. Typically they are "fast" and can't be counted until they are slowed. Polyethylene is used to slow (thermalize) fast neutrons and then typically a boron-triflouride detector is used. My training was with G-M detectors so I don't know about "solid state" types. > > How is a roentgen (one measure of radiation) related to a REM (which I > believe stands for Radiation Effective to Man)? What dose of roentgens/REMs > in bad/worse/fatal? (I have been told that more than 350 roentgens is > bad/fatal) 350 REM in a single exposure ought to be fatal. 100 induces radiation sickness for most people. Of course these are statistical conclusions. Your exposure may vary! (Makes you wonder what happened to the statistical people) > > > All follow-ups have been directed to sci.electronics. > > > Neal I used to know a lot more when I was a practicing Nuke. Of course my knowlege was simply about the conditions and equipment in the powerplant. Given a nuclear attack, I'd be only slightly more knowlegeable than anyone else about what radiological problems exist. Ron Miller
strong@tc.fluke.COM (Norm Strong) (04/29/89)
In article <1667@wasatch.utah.edu> martens@wasatch.utah.edu (William G Martens) writes: }> I have recently decided to purchase a geiger counter, for general use and for }> possible survival applications. I have seen several different types of devices } }Heath kit sells a general purpose radiation monitor that features a small }geiger-mueller tube with a mica window. It is suppose to detect soft x-rays, }alpha, beta and gamma rays, (will not detect neutrons). It comes as a built }it yourself kit, (piece of cake to put together), and resales for around }$130.00, (the exact same model is featured, pre-built, from Edmunds Sci. for }another $100.00 if money is no object). I was unaware that Beta particles would penetrate mica. Incidentally, how does one measure neutron radiation? -- Norm (strong@tc.fluke.com)
neal@lynx.uucp (Neal Woodall) (04/29/89)
In article <1240005@hpfcmgw.HP.COM> ron@hpfcmgw.HP.COM (Ron Miller) writes: >Alpha strikes in a G-M detection are non-events. The particle can't >get into the tube! I have seen Geiger tubes with mica end windows for detecting alphas...the alphas will indeed pass through the mica. Neal