Yup, another 'am I screwed?' thread by yours truly.
I recently came into possession of an old bottle of thorium nitrate, 1oz. Really old, around 50 years. As I was given this at university, I carried
it around with me for a bit, and sat a couple feet away from it for an hour or so. Middle of that hour class the thrill of getting it was replaced
with a 'just how hot is this thing?' feeling. I improvised some shielding for half the class with my jacket being between me and the bottle. After, I
took it to a geiger counter, and the clicks were pretty constant, it was almost a constant buzz coming out of it. This was through the thick glass
bottle mind you. So I got nervous, and left it in a lab with someone I know for the rest of the day. It is there now almost completly wrapped in
<1mm thick lead foil. Now I went and did some research, thorium is normally an alpha emitter, but old thorium compounds contain enough decay
products(radium and daughters to make it much more radioactive). The LANL docs (which Polverone is so gracious to host ) state that back then they
recommended treating thorium like "a more active alpha emitter" in a similar way to the treatment of plutonium.
Anyway, I am pretty sure I am perfectly fine, but my arms and legs are tingling in what I believe to be a negative placebo effect(I hope).
Anyway, I guess I am just looking for some reassurance that sitting a couple feet from it for just over an hour won't do any harm. I got paranoid
about this sort of thing in the lab over the summer.
PS the geiger counter I used had the meter broken, it just did the clicking thing. So exact ammount of radiation is ambiguous.
[Edited on 16-9-2006 by rogue chemist]Eclectic - 15-9-2006 at 20:21
The half life of the major thorium isotope is 14 billion years.
50 years is not really that "old" for a purified thorium sample.
I think you will be ok. (Try counting a bag of 0-0-60 potassium fertilizer if you want to scare yourself).
[Edited on 16-9-2006 by Eclectic]not_important - 15-9-2006 at 20:48
Once I owned a crucible made of ThO2, weighing close to 2 Kg. It would tickle a counter, but the flux was low and consists of 4 MeV alphas. With the
long half life there won't be much of the daughter isotopes built up, doubt they're of any concern.
Try putting it in a heavy walled plastic containter and taking a reading. Normally a sheet of paper will pretty well screen out alphas, but you can
get a bit of secondary radition from collisions.
As Eclectic said, the real concern is inhalation of thorium compounds. A few layers of skin cells stops most of the alphas; this is OK wken it is
outer skin that is constantly being shed, but when it's cells that hang around longer problems can arise. Likewise thorium compounds should not be
used as condiments.
Enough radiation to give a tingling would be more than fast clicks on a counter, it would be well past "the counter screamed" stage. Howver if you
are concerned I will gladly take it off your hands.JohnWW - 15-9-2006 at 21:21
What about the ThO2 mantles in kerosene lamps? Has anyone tested them out with a geiger counter, especially if there is any possibility of
contamination with shorter-lived isotopes like those of uranium?not_important - 16-9-2006 at 02:33
The isotope Th232 is considered to be the natural isotope. In its decay chain is Th228, with a half life of 1,9 years; Ra228 at 5,8 years comes before
it.
The following states that a fresh preparation of thorium will loose activity over 5 years, as the Th228 decays out. After that it will grow to about 2
and a half times the original at 20 years out as decay daughters build up.
[Edited on 16-9-2006 by not_important]pantone159 - 16-9-2006 at 08:31
Quote:
Originally posted by JohnWW
What about the ThO2 mantles in kerosene lamps? Has anyone tested them out with a geiger counter
I have three of them in a glass vial, they give around 1000 counts/minute in the vial, 6500 CPM removed from the glass, compared to 30-40 CPM for
background radiation.
Most of the mantles you find now (at least in USA) are not radioactive, though.unionised - 17-9-2006 at 12:00
To a rough aproximation. because of the potassium you contain, you are about as radioactive as a gram of thorium.Jdurg - 21-9-2006 at 18:02
I wouldn't be worried about it at all. Also, don't take the clicks from a geiger counter all too seriously. The clicking just tells you a decay has
happened. It doesn't tell you how strong the decay is. If you have 1000 CPM of very weak radiation it's not nearly as bad as 100 CPM of very strong
radiation, yet the clicking will be more intense on the higher CPM sample.
I've got about 2 grams of pure thorium metal foil that is perfectly safe in a sealed glass ampoule under argon which is stored in a lead cylinder made
of about 5 layers of 2mm thick lead sheet. It's stored along with the rest of my elements and isn't posing any serious radiation hazards. I got more
exposure on a cross-atlantic flight than I do by being in the same room as my thorium and uranium. woelen - 21-9-2006 at 23:01
Funny to read about such a strong placebo effect. But indeed it only exists between your ears.
A 1 hour exposure of this level is not bad at all (see response of others).
I only want to add, that _if_ it were harmful, then the effect could not be noticed, unless several years have passed by. Being irradiated for such a
short time with such a weak exposure really does not have noticeable effects in days or weeks.
Things become different if you are exposed to very strong radiation. Then in weeks you can notice things, but that definitely is not the case in your
situation. I would, however, worry about the chemical toxicity of thorium. It is a heavy metal, and its toxicity is at the same level as Hg, Pb and
U.
