Tuesday 11 June 2013

Questions From Friends (Part 2) - Radiation & Radioactivity

Another slightly-cheaty post from me, unashamedly based on an email conversation with a friend who writes Fan-Fiction.  If you're unfamiliar with the genre, it's generally an extension of an established fictional world, for example Harry Potter or Clarke's Space Odyssey series - anything you want in fact, it's a fan-driven and fan-written culture that has sprung up because people love the characters and setting, and want to explore it further.  Sadly, lawyers love getting involved, even when (as is normal) it's all done on an amateur basis and for free, which is why you're not getting a link to the final fictional result of this discussion.

I received an email containing the following request:

[Let's imagine] a new processing chip has flooded the's actually
radioactive, but a thin coating of plastic has disguised this fact.
(Yeah yeah, point is, it will leak eventually.)

However, by a series of improbable coincidences, the radioactivity is
discovered a week after launch by a scientific gentleman, actually
scanning for evidence of radioactivity from a difference source.

What, exactly, does the scan pick up? I mean, I know it picks up
radioactivity - like a Geiger counter - but if I want to refer to that
radioactivity in scientific muttering, what do I say? Unstable
isotopes? Fission activity? Help!! Is there useful vocabulary I can
drop in?

Cool.  I wish all fiction authors would put so much thought into their technowaffle, as it's officially called.  I'll point out that, much as I love it, Star Trek in all its forms is one of the worst perpetrators of Bad Technowaffle.  (Red Dwarf, on the other hand, is one of the best.)

So, my reply, which was written as an informal email if you spot any glaring errors in style or content:


[General personal salutations deleted]
 There are three basic types of radiation, alpha, beta and gamma.  All are produced by the decay of atomic nuclei, according to some very beautiful quantum mechanical magic which I'd love to go into but will omit for brevity (give me a shout if it's useful).  Particular nuclei (eg Carbon 14 or Uranium 235) omit a particular type or types of radiation when they break up (decay) and produce "daughter products" which are themselves radioactive, so they decay producing their own particular type or types and so on, until you have stable isotopes left (or just ones with a very long half-life).

An isotope is simply an atomic nucleus with a particular number of neutrons.  Carbon, for example, is defined as any nucleus with six protons, and the normal stable form has another six neutrons, hence Carbon 12. Carbon 14 has eight neutrons, and according to quantum wibbly stuff is more unstable and likely to decay.

Alpha radiation is simply a Helium 4 nucleus, the most common low-mass "chip off an atom" that is produced.  It's by far the biggest and heaviest lump that's ejected when a nucleus decays, and it is generally fired off at very, very high speed.  It can do a hell of a lot of damage to entire cells when it smashed into them, so it's very dangerous in the body.  However, because it's so big it's fairly easy to stop.  A sheet of paper, or indeed a thin film of plastic/resin, will stop it in its tracks.  This is what all the decontamination showers are about, washing off the contamination which produces the alpha before you can accidentally ingest or inhale it, it's relatively harmless on the dead outer skin layers (you can safely hold a piece of refined uranium in your hand), but when the source gets into the living cells inside the body it really kicks off.

Beta radiation is a high speed electron. It's not an electron that existed in the atoms in the first place though, it's made out of the leftover energy from an atom breaking up, and some of that leftover energy also gives it a hefty kick of kinetic energy.  Beta is the more benign of the three in some ways - it can be stopped by a thin piece of metal, an inch or so of wood, that kind of thing.  Beta will mess with atoms when it hits them, so it can cause mutations and hence cancers, and as it can penetrate a few millimetres of flesh you don't want to have any long term exposure - however, that's never stopped us worrying about cathode TV screens - cathode literally means "spits out electrons at high speed" - they're just electrically created beta radiation, and if you leave a Sellafield radiation badge sellotaped to a TV screen overnight and leave it playing it will detect enough radiation to get you removed from your job while they investigate! (My dad did it with his old badge when he left - you'd probably face a real risk of cancer if you did it for a month solid. As long as you're an inch or so from the screen you're fine for centuries.)

Gamma is the odd one out - it's not even matter, it's just a photon of light.  Just like radio, infra red, light, UV and so on, but with particularly high energy (in other words, a very short wavelength).  Different isotopes produce gamma with different energies, it's a very direct E=mc^2 demonstration: The energy (and therefore wavelength) depends directly on the amount of mass the nucleus loses when it splits, and that depends on which isotope it is - I'm getting quantum again...
Gamma can penetrate anything up to a few inches of lead, it's insidious, nasty stuff that's very difficult to escape.  It carries so much energy that it can kick electrons out of atoms, which changes their chemistry and really screws with the body's functions.  If you want to kill a lot of people in a nasty way with very little defence against it then gamma rays are what you want.  (Although SF would suggest at this point you would face an army of very big, very muscular and exceedingly pissed off green people...)

(There is a fourth kind, high energy neutrons as released in neutron bombs, but I've only just realised this and won't comment until I've read up on it and found it was first published in the 1920s!)

So...relevance to Silicon chips with a coating of plastic.  If your geiger counter picks up anything significant it won't be alpha.  You also need something which has a long enough half life to be of danger to the consumer, and most of the unstable Silicon isotopes decay in milliseconds, so they're out.  What is a good candidate, however, is Silicon 32.  It has a half life of 153 years, so it's going to be "live" for several human lifetimes.  It decays by beta, so you've got something which would be hindered by a plastic layer, but could be a danger with a little poetic license (eg silicon carrying current, ie a chip, boosts the beta).  Alternatively, people could be exposed in another way, like exploding chips (would only need to be a puff of Magic Blue Smoke) or, as Gerry suggests, "people licking them - there's nothing geeks like more than fission chips" - he says you're free to pinch that if you aren't already using it as the title)

First article on Si32 that popped out was one on geochronology - it's produced by cosmic ray impacts in the atmosphere.


So there you go.  That's how much thought and research goes into what ended up being about 1% of the storyline of an amateur piece of fiction done purely for fun.  There are certain science fiction books that you can pay actual money for which don't do the job half so well.

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