[chris (OP)]

This is not a post evidencing an intention to commit a crime!

A friend has approached me regarding a novel he is writing. One of his plot lines involves a manner of a person dying (possibly killing themself, I'm not sure) through ingestion of a radioactive source that will be delivered to their home, do the deed and cast the die, setting in train a death spiral, but then decay to an undetectable state so no one would know.

We were discussing what isoptopes, if any, would fulfil these criteria?

I guess we're looking for something that is an alpha source (strongly ionising, but poorly penetrating so the postman wouldn't get harmed and it would be easier to conceal), soluble, and with a short half life.

Thoughts...

[alancalverd]

You'd have a job to find a better candidate than Po210 as a pure alpha emitter, but it has a significant halflife of 138 days. The trick, then, would be to use a very small dose and wait - ask a Komodo dragon!

Not recommended for suicide (slow and painful) therefore, but would any prospective suicide care whether the cause of his death was discovered?

[evan_au]

He could try ⁷⁵As. It leaves no radioactive residue, and is not a danger to the postman...

https://en.wikipedia.org/wiki/Isotopes_of_arsenic 

[paul cotter]

How quick does it need to be? You may remember thorium was once used as a radiocontrast medium, under the trade name thorotrast,  as it gave excellent visualisation, far better than iodine based compounds. Natural thorium is a low level α source and had to be abandoned when patients developed problems. I can't think of anything active enough that would not leave traces. I think I would forget radionuclides and go for something like abrin or ricin. Amatoxin is another obscure possibility and could be ascribed to natural contamination.

[Bored chemist]

This is weird...
I'm sure I once saw a TV "murder mystery" where the deed was done using an industrial Xray machine from the room next door.
(An Xray source that will send a beam through metal to look at the welds  is not a healthy thing to get in the way of).

The key to unravelling the mystery was that the beam had also killed the fish in the victim's aquarium.

In my memory, it was an episode of Columbo.

But a bit of googling doesn't seem to show any trace of it.
Does anyone else recall anything like it?

Incidentally, 32P might fit the bill. You can certainly detect it from outside the body, but the range of the beta particles in a person is only a few  mm.
So if you could arrange for it to be bound to the heart or brain or something deep seated, you wouldn't spot it.
The short half life (a few days iirc) is small enough that "the authorities" would need to recognise and test for radiation quickly.
It has the advantage of being a real available thing.
Gold-198 has much the same properties (in this context) and is more glamorous.

There's an alternative approach.
Just call the stuff "the isotope". Never specify what it is.
That way, nobody accuses you of publishing how to commit a murder.

[alancalverd]

P32 half life is about 2 weeks, but the absence of primary gamma radiation might indeed keep it secret for a while.

It occurred to me that tritium is a real nasty beta-emitter, will find its way into pretty much every cell, and wouldn't be the first thing a pathologist would look for. You'd need a lot as its halflife is 12.3 years  but T₂O is chemically indistinguishable from water so you could brew some pretty toxic beer and quaff a few pints without anyone taking much notice.

Industrial x-rays (up to 400 kV) are penetrating but usually only used at quite low dose rates over an extended period (our "patients" don't move or breathe much!), as the main problem is getting rid of 95% of the input power as heat. The inverse square law militates against firing from an adjacent building, and if your subject built the source in his own house somebody might notice the 50 kg tube shield and similar electronics box. Then comes the pathology bit: a huge  dose delivered over a short time will produce characteristic external burns, and over a long period will induce various cancers indistinguishable from natural ones but taking some years to become fatal.

[paul cotter]

Iodine(131?) would localise to the thyroid and wreck it just like p32 as phosphate could localise to the bones, depending on the victims phosphate balance at the time.

[Petrochemicals]

You could try any of the istopes found in various food sources, it may have already been done. As i remember radioactive brazil nuts where a thing a few years ago, only for it to come to nothing, I wonder what brought that on. Find where your victim has been, do they live for example in cornwall, where a good dose of radon could be passed off, or been to Norway areas contaminated by Chernobyl.

[alancalverd]

Brazil nuts are indeed radioactive, and occasional consignments have tripped the alarms at Heathrow and East Midlands airports. Principal nuclide is radium, which will eventually induce a cancer or even an acute burn but you'd need a hell of a lot of nuts and the gamma radiation plus a pile of nut shells would be a bit of an easy giveaway.

I131 will indeed damage the thyroid but hypothyroidism isn't rapidly lethal. P32 looks like a good contender, particularly for a young person, as it could destroy bone marrow.

But there is no doubt that Putin's contractors have done plenty of research on the subject and Po210 is their weapon of choice. If it's being delivered by Evri, you'll need the 4 month half life and at least six complaint letters. 

[Bored chemist]

its halflife is 12.3 years  but T2O is chemically indistinguishable from water

I think the biological half life is a lot shorter (and rather variable) so it's not a viable option (unless you can add lots of it to the victim's water supply over a long period). Given the price of tritium, I think buying the apartment next door and paying for the electricity supply and the cooling system needed for an  Xray source might be easier.

[alancalverd]

The short biological half life is due to its indistinguishability from the hydroxylated protons that folk normally ingest and excrete in huge quantities. This permits rapid and even distribution through the blood and uptake by every organ including  those most crucial to sustaining life (heart, liver, lungs, kidneys).

Assuming that our suicide is suffering from immediate or inevitable distress (why else kill himself?) he wants to die in fairly short order, so my advice would be to quaff umpteen gallons of 95% tritium oxide beer, and as soon as the symptoms of internal  bleeding and organ failure appear, wash it out with something decent like 8 pints of Marstons Mild, thus flushing the evidence down the toilet and passing away on a cloud of happiness.  Or maybe walking in front of a bus whilst drunk.

Nonalcoholic beers are improving all the time, so New Tritium Speckled Hen or Guinness H3 Zero can be substituted to avoid problems with life insurance or religious authorities.

The cost is immaterial. Use Amex Platinum. Especially if that was the cause of the problem!

[chris (OP)]

Thanks, all, for these helpful suggestions, which I shall pass on.

Incidentally, the point about firing an X-ray beam through the wall made me think of this trip we made to UCLA 16 years ago to visit Carlos Camara, who'd recently published the findings that unreeling sticky tape in a vacuum produces a beam of X-rays through triboluminescence.

His apparatus was pointing at the ceiling, prompting me to ask, "who is on the floor above?"

We all looked skyward and someone said, "not sure, but by now they're probably infertile!"

https://www.thenakedscientists.com/get-naked/experiments/glowing-tape

[vhfpmr]

wouldn't be the first thing a pathologist would look for.

From an episode of Silent Witness:

"How would you commit the perfect murder?"

"First find out what ails them, then use that to kill them."

[Petrochemicals]

The problem with using radioisotopes is that they need to exist long enough from their production site to the victim but dissapear withing 24 hours of their remains being handed to a pathologist. Polonium used to kill alexander litvinenko left a radioactive trail all the way back to Moscow.

An element like francium has a half life of minutes, there are 1440 minutes in a day, so that may have worked, but if francium actually existed in a large enough quantity to be gathered together it would vapourise itself due to its own radioactivity.

[paul cotter]

Again not what Chris' friend is looking for but I suggest an overdose of insulin, administered subcutaneously with a fine guage needle. Nothing extraneous will be found at post mortem(autopsy) unless an insulin titre is done which is certainly not a routine test.

[Bored chemist]

commit a crime!

...(possibly killing themself, I'm not sure)

Suicide isn't a crime.
Doing it undetectably in order to ensure you kin benefit from life insurance probably is, but it would be too late to prosecute.

A suicide that looks like an accident isn't that rare.

" He took to drugs and drink and died because of it" is a tragedy; but it would be hard to prove intent.

Incidentally, if anyone is looking at this for ideas, try these folks.

https://www.samaritans.org/how-we-can-help/contact-samaritan/

[vhfpmr]

Incidentally, if anyone is looking at this for ideas, try these folks.

https://www.samaritans.org/how-we-can-help/contact-samaritan/

They don't have any ideas either.

[alancalverd]

Not officially, but they have dealt with most of the standard methods.