Quick and Dirty Film Dosimeter

With all the talk of radiation in the media today [freddysam] posted a quick Instructable about using standard camera film as a radiation dosimeter. Film is sensitive to other forms of radiation other than visible light, and high speed films are even more susceptible due to their chemistry, which has caused all sorts of headaches to travelers before most people went digital. This uses that headache as a simple way to see if you have been exposed to abnormal amounts of radiation in a  3 step process.

  1. Get some film. Yes they still sell it, it can still be found just about anywhere.
  2. In a dark room unroll a little out of the metal can and put it back in its black plastic container.
  3. Develop it if you think you have been exposed.

The idea is to let a few frames of film to be exposed to normal background radiation and develop it so you have something to compare with in the future, then you can unroll a bit more, and if you think your going into a hot area you can develop that newly exposed film to see roughly how much more radiation there was, maybe helping you sleep better at night.

Comments

  1. Cameron says:

    This is a terrible idea. Millions of dollars go into developing accurate dosimeters because the dose response of something simple like camera film is not linear. This means differentiating between dose slightly above background but not dangerous(flying in a plane for example) and something actually dangerous is not possible. The only thing this does is increase paranoia about radiation.

  2. stunmonkey says:

    not only is it not linear, but the fogging from any actual radiation exposure is probably not anywhere near as large as the fogging from simply handling the film.

    there is a difference between a true darkroom and a ‘dark room’, and people have no idea how easily fogged film is. it also has a spectral sensitivity well beyond the visible in both directions.

  3. lwatcdr says:

    Talk about shameful fear mongering. Really HAD this is not only useless but could scare the living crap out of any poor fool that uses it.
    All it would take is for somebody to have a light leak and mess up the film. Next thing you know they are sure the are sick and are in the ER for no good reason.
    In the US that would be just an annoyance in Japan it could mean someone that really needs help will not get it!
    If you want to try this out for fun have at it but if you think it is useful then you are just wrong.

  4. uC says:

    Interesting idea. This could be fun to use as a simple experiment on a weather balloon.

    Any one know of any calibrated (or -able) dosimeters worth of HAD?

  5. asheets says:

    The Kearney Fallout Meter is infinitely more reliable as a dosimeter than this film trick, and is more worthy of publishing on HaD since its primary components are drywall, thread, and foil.

    http://www.ki4u.com/free_book/s60p792.htm

    Or, if you are lazy like me, grab a hundred or so of CD-era dosimeters off of eBay (along with a charger, of course). This is a good example, though I didn’t pay nearly this much for mine: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290546036180

  6. not_mine says:

    I used to work for a major railroad and had to know where we could place carload of dangerous substances.

    I believe very explosive loads had to be placed more than 4 cars away from an occupied engine or caboose. Couldn’t place these cars next to cars with shiftable loads like a flatcar.

    Cars with radioactive loads only had one restriction. We couldn’t place them next to a load of undeveloped film.

  7. Cameron says:

    I think your best bet would be to find an old civil defense pen dosimeter and make your own charger. With that and a source(maybe Am from a smoke detector) to calibrate it you may be able to make something HAD worthy. I am in no way saying this would work only that it may be possible.

  8. uC says:

    @asheets I’d never heard of the “Kearney Fallout Meter”

    That’s quite a simple design very HAD worth. Charge foil leaves with static and measure separation. Then calculate how fast the charge leaves the foil.

    Would a weak source such as a smoke alarm be detectable. Sounds like its time to do some science!

  9. JS says:

    Am (Americium) is a alpha emitter and alpha particles are easily blocked.

    In a proper setup the emissions will never reach the film.

  10. Luke says:

    Film badge dosimeters used to be quite common – I haven’t worked in the field in ages, so I don’t know about today’s usage.

    This will work, but realistically, if you don’t have a means of calibrating the exposure, you don’t know what level of radiation you’ve been exposed to. The use of a shield over part of the film will allow you do determine the difference between radiation exposure and other film fogging.

    Short of a means of determining the proper shielding and a densitometer to read the relative densities of the exposed and non-exposed areas (plus a calibration to know what that difference means) this is a useless toy.

  11. BR says:

    I worked as an x-ray tech for many years, the key to the arguments against it due to fogging can be solved very simply. Most badge holders contain a stepped set of shielding so you can see different levels of penetration. You can ignore the fogging because you can compare the overall background color against each steps difference to see the overall exposure and type of exposure. The lowest step consists of an open film area.

    I believe the steps are made from aluminum but you would have to do some absorption calculations based on the shielding you choose. By measuring the difference between steps you can quickly tell how much actual radiation you have received vs defects on the film or development.

  12. BR says:

    I forgot to mention the other nice thing about this type of dosimeter is that it will keep track over a months time. Meaning you can even be sure you are aware of your absorption after you have turned off your device for the night.

  13. BR says:

    For those wanting to make stepped shielding there is a nice guide on the attenuation math here: http://www.ehow.com/how_7630142_calculate-xray-absorption.html

    It would be nice to hear from a radiation physicist if this calculation would compare favorably to attenuation of iodine and cesium isotopes.

  14. Cameron says:

    @JS Am also emits 59 keV gammas and yes these are very low energy but it MAY be possible to do some sort of calibration with them.

    @Luke Film badge != photography film. Photography film is thin film for measuring visible light that also is sensitive to other forms of radiation. A film badge usually contains either multiple films or a specially designed film so that the energy of the radiation is proportional to the exposure of the film. For comparison visible light photons have an energy range of 1.65 – 3.1eV(electron volts). Typical “radiation” that could pose a health threat to people is 50kev-2MeV. This is a much larger range and 4 orders of magnitude higher energy than visible light.

  15. lwatcdr says:

    The plastic container will probably block Alpha and possibly low energy beta. As an experiment this is fine but it really is terrible fear mongering to post it at this time IMHO.

  16. Cameron says:

    @BR Using attenuators is more complicated than just using the NIST mass attenuation coefficient because one incident Cs-137 decay gamma(for example) can produce several lower energy photons(from compton scatter and subsequent x-ray production) when it interacts in your attenuator. I must stress again that photography film is not designed for measuring nuclear radiation accurately.

  17. Just had an idea about those itty bitty Russian “mini” geiger tubes.
    I have two of them + the datasheet here, they are just small enough to fit inside a cheap poundland “step” counter which only needs a simple power supply based on a MPSA42 and two 180V zeners for voltage feedback.

    If it is built correctly the battery life should be several weeks, and for safety you would want to use a separate battery for the tube.

    Another related idea is to use a surplus piece of mica or pyrolytic graphite, epoxied into a thin wall metal tube with a length of 40 gauge wire through the centre but insulated from the metal casing, aka homemade Geiger tube.
    Vacuum down to 0.1atm with 50/50 butane/argon with a drop of alcohol and you should be able to detect alpha and beta particles without major problems at 4-700V input.

    A related hack is any old surplus B/W CMOS camera with its window removed , edge connectors epoxied in place and a mica sheet coated with lamp black placed over the chip.
    If you have any surplus x-ray intensifier screen a thin strip can be placed near the edge of the chip to detect the type of radiation.

  18. BR says:

    Ahh good point, I forgot about Compton scatter. Plus there is always the control film used that is locked in a lead container at the time the films are sealed and later developed. Without a good control it will be hard to filter as well. I did see quite a few badge companies that supply dental facilities for about $100-$200 which would give you everything you need for a fairly affordable price. But then again, everyone who is going to catch the plume isn’t going to see much in terms of exposure anyway.

    For fun there are quite a few geiger counter parts available from http://www.goldmine-elec.com/ Meuller tubes and the like. This would be a fun project but ultimately everyone in the US who is worried about the “Plume” is going to be very disappointed when nothing happens. It would be far more fun to try and measure a plane ride or another source of common radiation that we all receive regularly.

  19. Whatnot says:

    @BR indeed you’d need to take one film and clad half in lead to have a reference.
    As for geiger counters, those are bulky and will be so distrusted at the airport security I imagine, especially home-made versions, don’t expect to be without delays trying to take that on board.
    Oh and old geiger counter tubes are fragile I hear, being glass and having a thin glass front.

  20. BR says:

    @Whatnot Fortunately I have already been through the hell of bringing a case worth of custom electronics on a plane. I had to do a presentation and brought with me 4 of my experiments. I can say this took about 40 minutes of discussion with TSA and eventually after a small demonstration and a good demeanor I was able to bring the devices on board. It was an AVR Dragon, 10 or so random AVR chips, an arduino, 3 battery packs and a grand assortment of various breadboards and wires. I think it has to do with your showmanship at that point so the key is to bring charm. I expect with a smaller device it may be a bit easier to explain but if you are going to do this it would be best to talk to the stewardess about it since she may see the gieger counter and freak out. Perhaps a nice custom enclosure would make things a bit less exciting for everyone as well. Maybe a sticker or two for authenticity :)

  21. Jeditalian says:

    that’s why i never get a good photograph of a UFO?
    better go digital.

  22. haxwithaxe says:

    sorry to raise the dead :P
    any reason why you couldn’t just roll up the film with an aluminium strip thus creating an aluminium+film onion which is progressively shielded?

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