Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 02/10/2007 20:15:29

Title: I'm puzzled by Helium4
Post by: DoctorBeaver on 02/10/2007 20:15:29

How can it be bosonic? I thought all conventional matter was fermionic  [???]

Title: I'm puzzled by Helium4
Post by: Bored chemist on 02/10/2007 20:41:05

Among other interesting things, fermions can get together in pairs and pretend to be bosons.

Title: I'm puzzled by Helium4
Post by: DoctorBeaver on 02/10/2007 20:43:13

That's sneaky

Title: I'm puzzled by Helium4
Post by: another_someone on 02/10/2007 20:43:45

A boson is matter with integral spin, where as a fermion has half integral spin.

Electrons, protons, and neutrons, all half half integral spin.  On the other hand, if you have an even number of fermions, then the halves combine to create a composite body that has an integral net spin (this is not to change the fact that the component parts of that entity remain fermions, but the combined behaviour of the composite body is now that of a boson).

Title: I'm puzzled by Helium4
Post by: another_someone on 02/10/2007 20:44:34

OK - Bored chemist got there first - and shorter.

Title: I'm puzzled by Helium4
Post by: DoctorBeaver on 02/10/2007 20:45:31

So are there lots of isotopes that are bosons?

Title: I'm puzzled by Helium4
Post by: another_someone on 02/10/2007 21:05:13

Quote from: DoctorBeaver on 02/10/2007 20:45:31

So are there lots of isotopes that are bosons?

I would imagine so - ¹⁶O would be one, as would ⁸Be.

Title: I'm puzzled by Helium4
Post by: DoctorBeaver on 02/10/2007 21:17:57

 [:o]

So do they behave differently from fermionic isotopes? (apart from climbing walls at low temps, that is)

Title: I'm puzzled by Helium4
Post by: Bored chemist on 03/10/2007 20:31:30

I seem to remember that they do make a difference if you are worried about the intensity of emision lines in spectra or some such.
This sort of thing
http://www.thch.uni-bonn.de/pc/PHIP/parahydrogen.html
is different with deuterium.

Title: I'm puzzled by Helium4
Post by: DoctorBeaver on 03/10/2007 20:55:51

Their spectral lines are different? Why would that be?

Title: I'm puzzled by Helium4
Post by: Soul Surfer on 03/10/2007 21:56:28

It is very easy to forget the vast number of spin isomers that exist.  they all have slightly different energy levels abnd spectral frequencies.  there are even nuclear spin isomers.  for example a hydrogen atom with its nuclear and electronic spin aligned has different energy levels from a hydrogen atom with them antiparralell to each other.  the switch between these two states produces the 21cm microwave hydrogen spectral line that is so valuable for inderstanding the flow of hydrogen gas within galaxies.

Title: I'm puzzled by Helium4
Post by: DoctorBeaver on 03/10/2007 21:59:38

So it would just be emission lines, not absorption lines. That's understandable.