Re: nonconservation of hydrogen

[John Denker <jsd@MONMOUTH.COM>]

At 08:51 PM 3/16/00 +0100, Paolo Cavallo wrote:

> > If I have a box that is impermeable to
> > hydrogen, I can turn hydrogen atoms into something else (e.g. neutrons)
> > that silently escape from the box;  the net result is that hydrogen atoms
> > disappear from the interior without ever passing (as such) through the
> > walls.
>
> This is a trick, isn't it? By the way, how do you do that?

It wasn't meant to be a trick.  Let's discuss the n-->H reaction, because
it is a lot easier to carry out than the H-->n reaction.  There are lots of
places we can get thermal neutrons.  We send them into the box, where they
decay.  We then capture the decay products inside the box and let them
recombine to form hydrogen.  This is 100% real.

Operationally it is easy to make a box that is more permeable to neutrons
than to hydrogen atoms.  Metal walls have this property.  Filling the
interior with liquid helium will help make the neutrons stay a while
(diffusion) and will keep the decay products from escaping too easily.

The reaction is reversible in principle, but the H-->n direction is
strongly disfavored.  Either direction suffices to demonstrate that there
is no local conservation law for hydrogen atoms per se, which was the point.