The Naked Scientists

The Naked Scientists Forum

Author Topic: question or few about tritium water  (Read 3811 times)

Offline McKay

  • Sr. Member
  • ****
  • Posts: 148
  • Thanked: 1 times
    • View Profile
question or few about tritium water
« on: 31/03/2014 10:07:06 »
Generally about what happens when a radioactive isotope transmutates while in a chemical compound, but this case about tritium water. That is - water where hydrogen is replaced by tritium.

If tritium decays to helium-3 - does the helium detatch from the OH part and create a two opositely charged ions (negtive OH and positive He) that cannot recombine orthe helium atom (ion, actually) stay with the OH part/ instantly recombine and make some weird water like molecule that has helium in it (Helium is not supposed to react   chemically,isnt it?


 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8669
  • Thanked: 42 times
    • View Profile
Re: question or few about tritium water
« Reply #1 on: 31/03/2014 16:39:56 »
Something like
 2 HTO --> 2 He  + H2O2

Though actually you get a mess of H2, water, O2, ozone, etc.
 

Online evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 247 times
    • View Profile
Re: question or few about tritium water
« Reply #2 on: 31/03/2014 21:11:39 »
Tritium breaks down via the beta decay process, releasing the fairly low energy (compared to most nuclear reactions) of 18.6keV. However, nuclear reactions carry a lot of energy compared to chemical reactions; the electron and Helium recoil is probably* enough to totally disintegrate the water molecule (and some nearby water molecules).

Note that natural water H2O is always naturally breaking down to H+ and OH-, and then reforming. At any one time, about 1 in 10 million water molecules is in this dissociated state. So an extra OH group floating around would not be very unusual.

Helium has a very high ionisation energy, so I suspect that it would quickly end up as a neutral atom.

* I don't have time now to estimate how many water molecules could be disintegrated by a 5 keV electron (and a similar amount of energy in the He+ ion). Another component of the energy is carried away by the ghostly neutrino, which doesn't really interact with anything, much.
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: question or few about tritium water
« Reply #3 on: 01/04/2014 09:09:02 »
Everything will technically remain neutral as the 3H will loose an electron through beta decay, and the 3He will pick up a nearby electron.

However, it is likely not the same electron. 

As BC mentioned, you will likely get a mix of ions, free radicals, and etc as various chemical bonds are broken, and molecules either gain or loose electrons, or have their electrons blasted away.

There are a few helium compounds, generally not very stable, but none equivalent to water. 
 

Online evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 247 times
    • View Profile
Re: question or few about tritium water
« Reply #4 on: 01/04/2014 10:12:55 »
PS: I estimate that around 2000 water molecules will be disrupted by the decay of one tritium atom (give or take an order of magnitude).

Rationale as follows:
A) 1 eV = 1.6E-19 Joules
B) NA = 6E23 /mol
C) Electron energy from beta decay: 5.7 keV = 9.1E-16 J
D) Enthalpy change of formation for water: -2.4E5 J/mol = -4E-19 J per molecule
E) Number of water molecules potentially disrupted by a beta particle from tritium = C/D = 2300 molecules

While this beta particle can travel about 6mm through air, it does not have enough energy to get through human skin.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8669
  • Thanked: 42 times
    • View Profile
Re: question or few about tritium water
« Reply #5 on: 01/04/2014 12:44:15 »
The voltage needed to split water in an electrolytic cell is about 1 volt so it must take about 1 eV to split a water molecule. That's consistent with an estimate of a few thousand messed up molecules per beta decay.
Though some of the energy will be converted to heat rather than producing radiolysis.


It's interesting to note that the first proof of the existence of the perbromate ion relied on beta decay not breaking up a molecule.

http://en.wikipedia.org/wiki/Perbromate
 

Offline McKay

  • Sr. Member
  • ****
  • Posts: 148
  • Thanked: 1 times
    • View Profile
Re: question or few about tritium water
« Reply #6 on: 02/04/2014 06:20:53 »
Something like
 2 HTO --> 2 He  + H2O2

Though actually you get a mess of H2, water, O2, ozone, etc.

Ahh, of course, the newly formed helium ion will probably just rip the electron from something negative that is close enough and wont simply stick together with a negative ion, right?
Hmm, ok, seems fine.
Then another question - if a decay of tritium in a compound will (most probably) cause the compound to brake up and be in a higher energy state (a gas will be formed and, if in enclosed system, pressure will build up), then that is [the braking up part], essentially, an endothermic process, isnt it?
The radioactive brake down will release energy and heat up the system, but the braking up part will take some heat in and cool [ a bit] the system?
« Last Edit: 02/04/2014 06:23:30 by McKay »
 

Offline McKay

  • Sr. Member
  • ****
  • Posts: 148
  • Thanked: 1 times
    • View Profile
Re: question or few about tritium water
« Reply #7 on: 15/04/2014 01:04:26 »
A vial filled with tritium water will, gradually, have a pressure build up inside it, right? Such a vial would have more energy producing stuff (decaying tritium) in it than a regular tritium gas vial, right? And the pressure build up would threaten to brake the vial?
What if the container is made to be porous - with holes in it large enough to let helim-3 escape, but small enough for other particles (compounds containing tritium) to escape? Is that feasible?
Where I am going with this is - having tritium as a battery. I red that someone simply used regular photo voltaic panels stacked around a glowing tritium vial to produce some 7 miliwatts of power..
 

Online evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 247 times
    • View Profile
Re: question or few about tritium water
« Reply #8 on: 15/04/2014 11:45:29 »
1 mole of water occupies 18ml.
18ml of 100% tritiated water weighs 22g. As it breaks down, it will release 2 moles of Helium 3.
After 12 years (the half-life of tritium), it will release about 24 liters of He3, or enough to inflate a few party balloons.
Add some other reaction products like O2 and T2, and you might get enough to inflate a few more party balloons.

This seems a fairly inefficient generator, given that this 18ml of water will release around 5x108 Joules.

You may get more energy by igniting a balloon containing O2 and T2.
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3823
  • Thanked: 19 times
    • View Profile
Re: question or few about tritium water
« Reply #9 on: 15/04/2014 17:26:03 »
I would be interested to know what does Tritium cost I can well imagine that it would be a very expensive source of power.
 

Online evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 247 times
    • View Profile
Re: question or few about tritium water
« Reply #10 on: 15/04/2014 21:42:07 »
Tritium has been used in microscopic quantities in luminous watch dials.
However, it is quite dangerous - if it is ingested, it gets incorporated in the body, and irradiates the body from the inside.

I imagine that Tritium supplies are very tightly controlled, since it is a component of nuclear weapons.
This may change if someone develops a practical fusion reactor, since a Tritium/Deuterium mixture makes a good fuel.

In practice, thermoelectric generators used in spacecraft tend to use Plutonium 238 (as an oxide, as it is much less reactive than the metal).
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: question or few about tritium water
« Reply #11 on: 16/04/2014 04:45:30 »
You can purchase Tritium exit signs.  I assume it is come kind of scintillation bath around the tritium, perhaps in solid form, but it would work much like a scintillation counter. 

Just THO or T2O would be more or less transparent, I think.

The light produced would be very dim, so your power generation would be low.

I don't think the tritium decays are picked up by ordinary "Geiger counters", or their equivalent.  However, perhaps you could figure out how to capture those errant electrons directly, for example coating your solar cells with a tritiated compound.  Or, as BC mentioned, you'd probably create a shower of electrons with each decay.

 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3823
  • Thanked: 19 times
    • View Profile
Re: question or few about tritium water
« Reply #12 on: 16/04/2014 09:11:38 »
No answer to the question what does Tritium cost but I have seen suggestions that it should be mined on the Moon but knowing what it cost to collect a few kilo's of rocks I would think quite a lot.
As far as I can tell about $100m/Kg although nano grams can be useful
« Last Edit: 16/04/2014 09:55:07 by syhprum »
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: question or few about tritium water
« Reply #13 on: 16/04/2014 10:28:49 »
One of the labs I worked in used tritium labeled neuro translators which we then exposed to photographic film, and eventually analyzed with a computer software.  Unfortunately I don't know the company it was purchased from, but we probably had about 1ml of labeled neuro transmitter for the project.

I noticed that Sigma Aldrich sells D2O, but not T2O.

I don't think it was that expensive for small quantities of tritium labeled organic compounds, but the waste would increase a lot as anything it touched had to be treated as radioactive waste, and everything was tracked by the NRA.

Waste from shorter half-life substances like Phosphorous-32 can be stored onsite for a year or two until it is mostly decayed, then disposed as ordinary lab waste.

While relatively rare in nature, the tritium is made in our nuclear reactors.

I'm seeing tritium exit signs for about $225, which could probably be used for one's solar cell experiments.  The signs would still have to be treated as a radioactive hazard.
« Last Edit: 16/04/2014 10:41:57 by CliffordK »
 

Online evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 247 times
    • View Profile
Re: question or few about tritium water
« Reply #14 on: 16/04/2014 12:47:11 »
Quote
I don't think the tritium decays are picked up by ordinary "Geiger counters"
The fairly low energy of tritium decay means that it's decay particles only travel about 6mm through air - and would not pass through a glass or plastic cover over the tritium - or the cover of the Geiger tube.
 

The Naked Scientists Forum

Re: question or few about tritium water
« Reply #14 on: 16/04/2014 12:47:11 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums