(no subject)

[chess]

Oh, and there was the small matter of a Physics exam sometime in the morning. I think it went kinda okay, although there was an annoying question on radiation - I could think of all kinds of reasons why the count rate might have been *lower* than it was meant to be, but they were all higher, so my answer was a bit pathetic really. I *hate* 5-mark questions, I think they just have something against me.

Looking through the moods I think this is a particularly good one for me going on about not being good enough at Physics...

Comments

Higher counts ...

[passage.livejournal.com]

Background radiation:
Solar radiation,
Radioactive ores in the ground

If one of the decay products is also radioactive

err, that's three marks ... broken detector?

Oh, what if each disintegration gave two forms of radiation (eg Alpha and Gamma, both of which the detector caught).

Neil

Re: Higher counts ...

[chess]

I muttered about background radiation, but it didn't say anything about whether it was included in the original count and not included in the others and I'm not sure why it'd have been in one but not the others. It didn't actually tell us how it decayed (although I presume from context it was a gamma source, and we're not meant to know why some stuff is just a gamma source and doesn't throw other stuff around too, or at least we're not meant to know what a gamma source that isn't also an alpha source decays into). And it couldn't really have been a source of another type (it was a 'tracer inside the body' thing) and anyway that'd have been caught in the initial count too. (they had an initial count then said 'after an hour the readings were this, according to a half-life calculation they should have been 50 (about 20-30 lower), why')

Re: Higher counts ...

[passage.livejournal.com]

True Gamma source only emitters are pretty rare (read: they bascially don't exist) as they are not really involved in decays, only in changing the energy of the nucleus. Thus gamma decay typically occurs during alpha or beta decay if the nucleus produced is too energetic.

However, that is a strange question as I would have also expected to read lower, did it say how detection was carried out (the calultion is mathematical so I still think background radiation is the value they're after).

Neil

Re: Higher counts ...

[chess]

It didn't say anything at all about how detection was carried out either time - it said that the tracer was being used to measure blood flow in the heart.