Quick Advert:
Tomorrow (Wednesday 19th May), a free public physics lecture is being given in Lecture Theatre M at the University of Surrey at 7pm. It's being given by Prof David Sanderson of SUERC - the Scottish Universities Environmental Research Centre, and it's about how to detect irradiated food, a technique which the SUERC group developed and is now a European standard.
I picked up a delivery today of some equipment that the speaker wants to use in the talk - and am intrigued!
No booking is required - just turn up to Lecture Theatre M for a 7pm start
Tuesday, 18 May 2010
Sunday, 9 May 2010
What if everyone were a nucleus?
In a series of tweets this evening Jim Al-Khalili pointed out that there has been a small disagreement between him in his Atom series and Michael Mosley in the Story of Science. They each illustrated the ratio of occupied space to empty space in atoms by saying that if all the empty space were taken out of the entire human population then we would occupy a volume the size of an apple (Jim's calculation) or a sugarcube (Michael's calculation).
In either case, the analogy makes clear that atoms have a whole lot of empty space, but in terms of volume, there's a fair bit of difference between a sugarcube (around 1 cm3) and an apple (around 200 cm3). So who is right?
The population of the world is around 7 billion. The average mass of people is usually taken to be around 70kg so the mass of the human population is 7×109×70 kg = 490 000 000 000 kg. Let's call that 5×1011 kg. Now, if all the space were taken out of all these atoms, we would essentially be left with an enormous nucleus (as Jim says, a pulsar). The density of nuclear matter (i.e. of the inside of an enormous nucleus) is 0.16 nucleons per cubic femtometer. A nucleon weighs 1.7×10-27 kg.
So: The number of nucleons in total is 5×1011 / 1.7×10-27 = 3×1038 nucleons, giving a volume of 3×1038/0.16 = 2×1039 fm3 = 2 cm3.
Looks like I agree with Michael, more or less... unless I've guessed the size of a sugarcube wrongly. I mean, I haven't seen a sugarcube for years.
In either case, the analogy makes clear that atoms have a whole lot of empty space, but in terms of volume, there's a fair bit of difference between a sugarcube (around 1 cm3) and an apple (around 200 cm3). So who is right?
The population of the world is around 7 billion. The average mass of people is usually taken to be around 70kg so the mass of the human population is 7×109×70 kg = 490 000 000 000 kg. Let's call that 5×1011 kg. Now, if all the space were taken out of all these atoms, we would essentially be left with an enormous nucleus (as Jim says, a pulsar). The density of nuclear matter (i.e. of the inside of an enormous nucleus) is 0.16 nucleons per cubic femtometer. A nucleon weighs 1.7×10-27 kg.
So: The number of nucleons in total is 5×1011 / 1.7×10-27 = 3×1038 nucleons, giving a volume of 3×1038/0.16 = 2×1039 fm3 = 2 cm3.
Looks like I agree with Michael, more or less... unless I've guessed the size of a sugarcube wrongly. I mean, I haven't seen a sugarcube for years.
Wednesday, 5 May 2010
Nuclear Physics and the Election
I've not blogged at all about the forthcoming election. Nuclear physics is a pretty minor issue in the election, but not completely non-existent. The amount of overall science funding will be a factor in determining how much money will be spent on nuclear physics research, and the commitment to nuclear power (or otherwise) of the parties will be a factor in determining how much the UK is interested in keeping a knowledge base in nuclear science and engineering on a broader scale. These two facts are ironically approximately inversely correlated in the three main parties. I don't think I'd ever vote on a single issue alone, but there doesn't seem to be a completely obvious choice from a nuclear physics point of view. I think Martin Robbins' article in the Guardian sums things up pretty well, though, from an overall science perspective.
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