NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/sci/physics/fusion/1799

Internet Message Format | 1992-07-23 | 5.1 KB

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From: [e-mail] (Richard Long)
Newsgroups: sci.physics.fusion
Subject: Re: Why Ying?
Message-ID: <[e-mail]>
Date: 23 Jul 92 23:02:08 GMT
References: <[e-mail]>
Sender: [e-mail] (News system)
Organization: University of Central Florida
Lines: 101

In article <[e-mail]>
[e-mail] (Rolfe G. Petschek) writes:
> In article <[e-mail]>
[e-mail] (Dieter Britz) writes:
>
> >Something bothers me about the Ying experiment. I'm just a humble
> >electrochemist, so maybe some physics expert out there can enlighten
me:
> >The Ying theory says, correctly, that one of the branches of d-d fusion
is
> >d + d --> (4)He + gamma (23.x MeV); this is in fact the controversial
minor
> >branch, with a probability of 1E-07 times the other two, with the
infamous
> >50:50 branching ratio, yielding neutrons or tritium. OK. Ying now
proposes
> >to enhance this minor branch by tickling it with gamma rays at just
that
> >energy, 23.x MeV.
> >
> >I understand that quantum physics is not like chemistry but I still
can't
> >shake the thought that this is the wrong way around. In chemistry, if
you
> >have a reaction like
> >
> >A + B + C + ... ---> O + P + Q + ...
> >
> >then if you add, to a mixture of all these, one of the products O, P, Q
..,
> >you drive the reaction backwards. This is Le Chatelier's Principle, and
we
> >understand it today in terms of thermodynamics, equilibrium constants
etc.
>
> All correct.  However:
>
> Think about a laser.  A laser has a population inversion (many more
> atoms in an excited state than in a lower level state) and this can be
> thought of as a system with a *negative* temperature.
etc.

Rolfe's analysis of the thermodynamics is very clear.  However, he does
not mention the quantum mechanical properties of bosons that makes not
only lasers, but superfluid He4 and superconductivity, as well as lasers,
possible.
My naive understanding (having never done the wavemechanical calculations
myself, but instead borrowing from Feynman's more intuitive descriptions)
is that when two bosons are within a wavelength or so of one another,  (so
that the uncertainty principle makes the two completely
indistinguishable), we have two possible pathways for a process like.  One
is the process itself, the second is the two bosons are exchanged along
with the process.  Boson wavefunctions are even, so the total wavefunction
is the sum of the two.  Since the wavefunctions are identical, the
probability is simply doubled.  For N bosons, there are N possible
exchanges and the probability is multiplied by N.
For this boson coupling to work, we need the bosons to be within a
wavelength or so of one another, and in very nearly the same quantum state
(within the uncertainty relations).  This means that, in the case of a
laser, the emitted photon will be in very nearly the same quantum state as
the neighbors (with a probability proportional to N) which is why laser
light is coherent.
In the case of liquid He4, we have the same argument.  The uncertainty
relations say that our needed distance between He4 nuclei should be on the
order of the wavelength.  For liquid helium, this is about 2 angstroms.
The uncertainty relations say that:
    2e-10 m = h_bar/p = h_bar/(sqr(2mE)) = h_bar/(sqr(2mkT))

Solving for T gives a critical temperature of about 3 degrees kelvin for
superfluid he4.

By the same token, we would expect that photons will behave as a
superfluid when the photon density puts the average photon within a
wavelength of the others.  Materials that are opaque would then become
transparent.  The reason is that, if a photon scatters to a new direction
and frequency, the probability of it rescattering back to the same
direction and frequency is increased by the number of photons within one
wavelength.
Also, the very short wavelengths of gamma rays would be what makes a gamma
ray laser so difficult make, I imagine, since the interaction
cross-section is so much smaller.
Which brings me to Ying's hypothesis.  The alpha penetration (the distance
of closest approach) is proportional to 1/E, and the wavelength is
proportional to 1/(sqr(E)).  The energy where these two match is in the
tens of MeV range, so energetic alphas would work I guess, but the
interaction cross-section would be so small that I don't see how it would
work.  Maybe the virtual alpha from fusion is so spread out as to make
this cross-section very large, and at the same time allow the wavelength
to be longer (lower energy).  Otherwise, its probably better to just put
the whole thing in a superfluid He4 bath, but then there would be other
more mundane physical problems to overcome ;)



--
Richard Long
Institute for Simulation and Training
University of Central Florida
12424 Research Parkway, Suite 300, Orlando, FL 32826
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