# Calculating the amount of time for recombination

1. Aug 1, 2012

### Eagle9

Imagine that we have got some vessel under standard temperature and pressure filled with atomic Hydrogen inside and the electrons of these atoms have got the same spin and therefore they cannot join into Hydrogen molecules, so the process of recombination does not occur. But I was told that due to atoms’ collision to each other the spin of some electrons will be “overturned” and therefore the recombination will still occur slowly. Could you please tell me how to calculate the amount of time needed for complete recombination? That is when there will be no atoms of Hydrogen but molecules only. What this time depend on? On pressure inside the vessel? Temperature? Something else?

2. Sep 14, 2012

### Eagle9

Is it so difficult to calculate?

3. Sep 15, 2012

### M Quack

In ³He the relaxation time can quite long. Even after 1-2 days you still have >70% polarization. The excitation is usually done with lasers and a magnetic field.

The big difference to hydrogen is that for ³He we are talking about nuclear magnetic moments. And of course He will not form molecules if left alone.

slightly OT:

Polarized ³He is used to detect polarized neutrons - only neutrons with their spin antiparallel to the He nucleus will be absorbed to form ⁴He which has no nuclear spin.

4. Sep 17, 2012

### Eagle9

Well, this is very interesting, but what can you tell me about Hydrogen?

5. Sep 17, 2012

### M Quack

Hmmm, let's see...

The electron's magnetic moment is about 2000 times as large as that of the nucleus.

In the absence of any better estimate, you could imagine that the sensitivity to collisions etc, is then about 2000 times higher, and hence the life time could be expected to be smaller by the same factor. So instead of a day for ^3He you would get less than a minute for H. Note that this is waving hands - or rather flailing arms.

6. Sep 19, 2012

### Eagle9

M Quack
Very bad.....is it somehow possible to increase this timespan? :uhh: