NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/physics/fusion/3089

Internet Message Format | 1992-12-23 | 8.1 KB

Path: sparky!uunet!gatech!destroyer!sol.ctr.columbia.edu!hamblin.math.byu.edu!yvax.byu.edu!physc1.byu.edu!jonesse
Newsgroups: sci.physics.fusion
Subject: Replies to D. Blue/Original BYU Expts.
Message-ID: <[e-mail]>
From: [e-mail]
Date: 23 Dec 92 13:25:07 -0700
Distribution: world
Organization: Brigham Young University
Lines: 129

Dear Colleagues,

Dick Blue has challenged the original BYU experiments on cold fusion in
recent postings.  While I have responded (e.g.,"Original BYU expts/reply
to D. Blue" posted 15 Dec), others at BYU have also written answers which
I now post in their behalf.

In article posted 9 Dec. by D. Blue, "Rehash of Jones' Results," we find:
"If you refer to the paper describing the detector used in the original BYU
experiment, take from that paper the stated gamm-ray rejection ratio, and
incorporate information as to the nature of the radiation background such
detectors would respond to in a normal laboratory environment, you will be
led to the conclusion that the pulse height spectra recorded by Jones was
dominated by gamma rays, NOT NEUTRONS.  Second point is that there were some
few net counts left after subtraction of a background only because of a
renormalization of the background.  And thirdly, while the detector had some
capability for determination of neutron energy if the signals had been
employed in one possible mode of operation, the mode used in the Jones
experiment was such that energy information would be washed out due to the
adding of a signal (with a finite noise width) that was not dependent on
neutron energy.  In short the results of that experiment should be ignored."

BYU Professor Gary Jensen replies:
First point:  The background included mostly cosmic-ray neutrons and some
gamma rays; we knew this when the paper was published.  [As we stated in
our Nature paper, only about 1/4 of background was due to gammas.]
Second point:  The background HAD to be normalized [approx. 4 times more
background than foreground hours], but the background was featureless and
could not generate a peak.
Third point:  The only mode used in the experiment was the standard
spectrometer mode.  Nothing was added to the signal.  The "capture-spectrum"
mode was not developed until after the data used in the Nature paper were
taken.  We did use it to investigate the nature of the background.

The spectrometer is a COINCIDENCE spectrometer.  The pulse from the liquid
scintillator that carries energy information is rejected unless a capture
pulse from the glass is also produced within the coincidence gate time.
Monoenergetic neutrons therefore produce a peak that correlates with neutron
energy.  From the calibration data at 5.5 MeV and 2.9 MeV, a reasonable
extrapolation shows where the 2.45 MeV peak should occur.
In short, the comments in paragraph 1 [Dr. Blue's comments cited above] should
be ignored.
[End of Prof. Jensen's comments.]

In his posting of 18 Dec "The first S. Jones low-level CF result", Dick cites
the Nuclear Instruments and Methods paper of Gary Jensen and Bart Czirr (A284:
365 [1989]) and states:
"this paper does indicate that this spectrometer was used in the "capture-
spectrum mode" for the 'recent cold-fusion experiments'". ... "With these facts
in mind I want Steve Jones to explain how a peak corresponding to 2.45 MeV gets
generated in this detector and what the calibration method was that determined
the peak shape and position.  I am aware of the Figure 6 in the Czirr and
Jensen paper which shows an experimentally determined peak shape for 2.9 MeV
neutrons, but it also shows the response going off scale as it rises toward
channel zero."  [Please see Dr. Blue's posting for further details.]

Gary Jensen answered some of these points above.  In particular, the "capture-
spectrum mode" was NOT used in collecting the foreground data for the Nature
paper, but was used to investigate the nature of the background spectrum.  I
hope this clarifies an evident misunderstanding of Dr. Blue's, that
the "capture-spectrum mode" was used for foreground data collection.

I will now quote from BYU Professor Paul Palmer's reply to Dr. Blue:

Our neutron spectrometer is a delayed-time-coincidence spectrometer.  When a
slowed neutron is captured in the 6Li-containing scintillator glass, the light
flash produced by the resulting triton/slpha pair is characteristic of the
process.  This pulse does not give neutron-energy information.  It is a confir-
mation pulse indicating that a NEUTRON stopped inside the detector.  Any
neutron leaking out of the system does not produce this confirmation pulse
and is lost.  This reduces the efficiency of this capture process to about 25%
in detectors of the size which we commonly use now.  In our original
spectrometer, this efficiency was less than 10%.
If this characteristic pulse is seen, a search is then made for the preceeding
pulse which was generated by a high-energy neutron being thermalized in a
hydrogenous scintillator material.  This early pulse contains the energy
information about the neutron.  This pulse must occur prior to the 6Li-glass
confirmation pulse, within a couple of neutron mean-capture-times in the
particular detector.  If the properly timed and sized pulses do not appear, the
event is rejected, as being caused by an ambient thermal neutron wandering into
the system or by accidental gamma events.
The probability of the proper thermalization pulse occurring is about 50% in
our present detectors.  It was less than 10% in our original detector.
Our current spectrometer designs have an overall efficiency of about 12% in
detecting fusion-energy neutrons.  The original detector had an efficiency of
about 0.6%.

Current designs reduce the accidental gamma coincidence rate by a factor of 10
E6.  In a tunnel to shield against high-energy cosmic rays and with modest
shielding (copper and bags of salt) to shield against gammas, and with timing
and pulse-shape and pulse-size discrimination to reduce muons and ambient
gammas, the rate of false background events is about one every three hours.

Monoenergetic calibration neutrons produce a peak in pulse-size distribution
that correlates neutron energy.  From the calibration data at 5.5 MeV and
2.9 MeV a reasonable extrapolation shows where the 2.45 MeV peak should be.
The capture-spectrum mode was not well developed until the data used in the
Nature paper were taken.  The nature of the background began to be investigated
prior to publication of the paper.  The signal data produced a broad bump
above background in the proper energy region.
[End of reply by Paul Palmer,BYU.]

I might add that the peak in the energy spectrum arises since all the light
generated by a neutron slowing in the liquid scintillator (BC 505) is added
to determine the neutron energy, not just the light from the first recoil
proton.  A delayed coincidence of the scintillator pulse with a distinctive
pulse from the 6Li-doped glass is required to complete the event trigger.

The low energy response in Figure 6 in the Czirr/Jensen paper arose
due to the presence of low-energy neutrons from unwanted deuteron-beam
interactions, evidently in the beam line.  Since then, we have succeeded in
generating a clean, monoenergetic neutron beam using one of the Van de Graaf
accelerators at BYU.  This beam produces a peak in the neutron spectrometer
(we now have about four working spectrometers, two of which are in the new
Tunnel Lab in Provo Canyon near BYU, and the neutron beam is used to calibrate
each detector), whose shape is similar to that of the spectral peak generated
by D2O-electrolytic cells in the original BYU paper published in Nature.
The roughly 2.5-MeV energy corresponding to this peak suggests a d-d fusion
origin.  We still stand by this claim, having found no combination of portable
sources or noise-events or backgrounds that produce such a distinctive peak.

The reported RATE of neutron production was approximately 10 E13 below that
required to produce one watt of excess power and thus does not support claims
by some that xs heat produced in (ostensibly) similar cells originates from
d-d fusion.

Respectfully,
Steven Jones  - with submissions also from Profs. Jensen and Palmer at BYU