On Dec 9, 2009, at 3:06 PM, Steven Krivit wrote:
Jones,
and how about ultra-low momentum neutrons?
Steve
Quoted from:
http://arxiv.org/pdf/cond-mat/0509269v1
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"In terms of the ultra
low momentum neutron wave length λ = (2π¯h/p), Eq.(7)
implies:
mfp = 1/(2 * n * lambda * b)
The ultra low momentum neutron is created when a
heavy electron is absorbed by one of many protons participating
in a collective surface oscillation. The neutron
wave length is thus comparable to the spatial size of the
collective oscillation, say λ ∼ 10−3 cm."
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end quote
The above is a rather arbitrary estimate of momentum by W&L, on which
is based the mean free path estimate, etc. Proceeding on with that
anyway we have:
lambda = h/p
p = h/lambda = h/(10^-3 cm) = 6.626x10^-29 kg m/s
p = m * v
v = p/m = (6.626x10^-29 kg m/s)/(1.675x10^-27 kg)
v = 3.96x10^-2 m/s = 0.0396 m/s
Given a half-life of 886 seconds about half the neutrons move (0.0396
m/s)*(886 s) = 35 meters or less. Half of those move another 35
meters or less, etc. Freed into a vacuum, about 1 in a million
neutrons could move 20*35 m = 700 meters before disintegrating into a
proton, beta, and anti-neutrino. However, based on the huge
wavelength chosen, and lattice density, W&L say the neutron will
quickly react, and can only move typically less than a nano-meter.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
