Half-life

Just finished watching a generally pleasing Horizon programme by Jim Al-Khalili about the Fukushima nuclear plant disaster, its consequences to date and the likely effect on nuclear power more widely. It had a lot of interesting stuff about how minimal the radioactive effects of the disaster have been (and are likely to continue being). And there was a nice section on how the most deleterious effects of the Chernobyl disaster of 1986 are, arguably, the psychological effects of worrying about radiation, rather than the radiation itself. Al-Khalili also made the same, oft-repeated point about how most of the socio-political problems faced by the nuclear industry can be traced back to its early association with the military.

It did, however, finish with a rather confusing item about a developing technology for dealing with nuclear waste that transmutes radioisotopes with long half-lives into others that decay much more quickly. This sounds like a good idea when you first hear it - get rid of pollution faster - but it doesn't quite make sense. Paradoxically, the longer a radioisotope takes to decay, the safer it is since it gives off less radiation per unit time. When one hears of nuclear waste that will take tens of thousands of years (or more) to decay, you're really hearing about something that's not very radioactive. By contrast, elements that decay in short periods of time - days, weeks, months - kick off a huge amount of potentially dangerous radiation in that time. Of course, if you store them safely during this period, this isn't a big problem, but they're still far from safe.

It may be that what Al-Khalili was getting at was this latter point, namely that one has to look after nuclear waste carefully for less time. Or that, in the case of radioactive elements that are also chemically toxic, they're quickly turned into elements with less conventionally undesirable properties. But it would help if he'd said, since I can't help but think that a shorter half-life isn't all sweetness and light.