Radioactive dose unit conversion

Discussion in 'Supporting Physics' started by mike wilson, Jul 10, 2019.

  1. I'm looking to dispose of most of our old, tired (and otherwise - see elsewhere) sources but have run into a slight difficulty.

    The units in L93 are microCuries but all of our activity measurements are in millisieverts. Does anyone have a proeperly referenced conversion factor? The only one I can find online suggests that a Sievert is about 1000 Curies but it is not referenced at all.
  2. To my understanding sieverts and curies would not have a direct conversion factor as they are measurements of different properties of radiation

    Curies are a measurement of activity in the radioactive material and sieverts are the measurement of dose received in the absorbing material
  3. Exactly. So I'm stumped as to how to evaluate if sources can be disposed of in the normal waste.
  4. Nick Mitchener

    Nick Mitchener COMMITTEE

    The sources are in Microcuries, but the legislation is in Bq isn't it? Sources below 200 kBq can be grouted. Higher than that you need a contractor.
    Andrew Goloskof likes this.
  5. Nick Mitchener

    Nick Mitchener COMMITTEE

    that's cup sources btw, Under 40 kBq is even easier. We grouted our radium paint sources last year.
    Andrew Goloskof likes this.
  6. I would suggest they've just put down the wrong units as god alone knows how they think they managed to measure the equivalent dose of radiation received by a radioactive source.......
  7. Interesting how are you going to get rid of them? Its just that i do believe the disposal method that CLEAPSS recommends is changing!
  8. To be fair the CLEAPSS method on the website is "raise a contact form and we'll advise you directly" so if you're doing that you'll always have the up to date advice
  9. This source may be of interest which gives 1 mSv is equivalent to 27 nCi :)
  10. Same one that I found. Looks like it will have to do.
  11. There is so much wrong here. For a start you should not be deciding how sources should be disposed of. Anything beyond the CLEAPPS advice means consulting your Radiation Protection Advisor [RPA] this may be done through your Local Authority Radiation Protection Officer [RPO]. In any case, this is not a job for a technician, it should all be done by your School Radiation Protection Officer [RPO(Schools)].

    If you do not have this chain in position (RPO only applies to Local Authority Schools) then the school should not have any radioactive sources.

    Now, units:

    The SI unit of Activity is the becquerel [Bq] which represents one nucleus decaying each second; so this is the figure marked on the radioactive source when new.

    There is another unit, the grey [Gy] which is the measure of the quantity of energy absorbed by a target; it represents joules per kilogram. It is not important in this discussion but another unit, the sievert [Sv] which is a measure of the biological effect of radiation on the human body is encountered frequently. It represents the absorbed dose in greys multiplied by a complicated fiddle-factor which takes into account the type of radiation, its energy, and the organs affected. Like the grey it has the dimensions J/kg.

    It is quite impossible to convert activity in becquerels to absorbed dose in sieverts. For a start, the sievert is a measure of accumulated dose whereas the becequerel is an instantaneous value.

    The site which GeorgetheScienceTech cites looks rather dodgy; but the main point is the table referred to above. It is poorly laid out and catches the unwary: apart from being wrong there are actually three separate tables; rem to sieverts, rad to greys, and curies to becquerels; reading across from sieverts to becquerels is totally inadmissible.

    The old cgs units are still in use in the US and are found in older texts and markings on sources; curies to becquerels is probably all that you need.
    PhysicsSimon likes this.
  12. Nick Mitchener

    Nick Mitchener COMMITTEE

    I agree with all of that, but it starts with the technician who assesses what can and can't go and reads the regulations and advice from CLEAPSS on what must go. (you think teachers read all that?)

    We proposed then what to do and that went to our RPO. We also informed our RPS (Schools) what we were doing.

    Having got agreement from our RPO we then went ahead following the CLEAPSS instructions in the latest L93, and as requested informed our RPO when we had completed the work. The grouted items stayed in my preproom for 28 days for a full cure of the cement and site team kindly put them in the eurobin just before the refuse contractor collected it. We then informed the RPO it had left the preimises and updated our own paperwork.
  13. The disposal has been agreed with our RPA. I am the joint RPS for the College.
    Where did you get that from?
  14. Nick Mitchener

    Nick Mitchener COMMITTEE

    I said in that posting. Have you got a copy of L93?

    EDIT> No I didn't, but I inferred from your original you had read L93
  15. My mistake. We have a number of copies of L93 and I thought I had disposed of the out of date ones. Turns out I was looking at the only old copy in the place....
  16. Nick Mitchener

    Nick Mitchener COMMITTEE

    it would help if they changed the front cover each time.
  17. I've been told that Cleapss have temporarily withdrawn GL220 disposing of waste sealed sources via grout/dustbin. It is all to do with how your local authority deals with the waste - if black bag waste undergoes mechanical and biological treatment (MBT) then you can not do it. You need to check with your RPO, Council Health and Safety Officer (the same person for us) who should advice you on this. Obviously it would be a good idea to check with Cleapss too. This change was made in the last couple of months! I can no longer use the dustbin route because of the way the waste is treated in Powys
  18. Nick Mitchener

    Nick Mitchener COMMITTEE

    We did well disposing of what we wanted when we did. There has been talk of getting shot of our radium source before but after it nearly became a pag we decided to keep it. You never know when they are going to change the specs again.
  19. I've already checked that there is a route to get the packaged sources to landfill without being treated.

    I added some packing to the source in the sample pot before I encapsulated it. Both because I can't think of anything more likely to cause investigation than a lump of mortar that rattles and because I think the impacts with the hard sides of the pot will be more likely to release small pieces of foil. If someone does then investigate, the chances of becoming contaminated are much higher.
    Lesley Newcombe likes this.
  20. Wish I had one of those routes, good idea with the packaging too!