Professor Werner Tornow served as the Director of TUNL from 1996 - 2006. He is an active researcher in many areas of nuclear physics including few-nucleon studies and neutrino physics. A summary of research efforts he has been involved with in 2007 is given below.
A. Neutrino Physics
a) Neutrino oscillations: In
the first half of 2007 the KamLAND Collaboration continued
its $20M liquid scintillator purification task to
convert the KamLAND anti-neutrino detector into a
low-threshold solar neutrino detector. At the end of July the purification
effort had to be halted due to blasting in the Kamioka
mine (for a new cave for a xenon based dark matter experiment). In the Spring
of 2007 I spent 10 days in
A draft for a PRL with the
title “Precision Measurement of Neutrino Oscillation Parameters with KamLAND” is currently being circulated amongst the KamLAND collaboration members.
b) Double-beta decay: In 2007 we leased from DOE
about 50 grams of Nd-150 (95% enriched) at a cost of $30,000. After 100 days of double-beta decay studies
to excited states of the daughter nucleus we concluded that the purity of the
Nd-150 sample was not sufficient for a successful measurement. We returned the
sample to Oak-Ridge National Laboratory where efforts are now underway to
remove or reduce the thorium impurities. Gamma-ray lines from decay products of
the thorium chain interfere with our transitions of interest. It is not clear
at the present time by how much Ra-228 can be removed which is responsible for
the Ac-228 lines which almost coincide with the Nd-150 lines of interest. We
expect to have the purified Nd-150 sample back at TUNL in early 2008. Our 8’ x
20’ mobile laboratory will then be moved to the Kimballton
mine (VA) where we will continue the Nd-150 measurements at the 1700 ft level. These
measurements are part of the thesis project of Mary Kidd.
While we were waiting for a purified Nd-150
sample we started a feasibility study of a promising alternative to neutrinoless double-beta decay: neutrinoless
double electron capture. There seem to exist one or two nuclei for which this
process can proceed through an excited state of the daughter nucleus which is
degenerate with the parent nucleus, resulting in zero phase space for the
two-neutrino double-electron capture, and providing in principle a severable order
of magnitude enhancement of the capture rate. We acquired 4 g of Sn-112
enriched to 90% (natural abundance ~1%) from Livermore National Laboratory and
during 100 days of measuring time at TUNL we obtained not a single count in the
energy region of interest (not even a background count!). This result gives very
useful information on how to design a larger scale experiment based on our
coincidence approach.
In support of the Majorana
Project we continued our measurement program at TUNL to determine the neutron
induced background in a typical Ge-76 based double-beta decay experiment. This
background becomes crucial once the other known background sources have been
reduced to the level envisioned for the Majorana
Project. Here, gamma rays from neutron induced reactions on lead and copper,
and of course 76Ge, are of special interest. After studying lead and copper at
two incident neutron energies in 2006, we took data on Ge-76 in 2007. These
data are currently being analyzed .
B. Few-Nucleon Physics
a) Two-body
system: In 2007 we submitted our paper
on the analyzing power in neutron-proton scattering for publication. The
associated data are the most accurate data ever obtained in polarized neutron scattering
off any hadron or nucleus. The data disagree
significantly from nucleon-nucleon potential model predictions and global nucleon-nucleon
phase-shift analyses. The concluding sentence of our manuscript reads: “Perhaps
the impass comes because we are at the point where
the precision of our data and the development of our low-energy theoretical
models has pushed the paradigm of meson-exchange based nucleon-nucleon
potential models beyond its limit.”
Our Russian colleagues from the DIANNA
Collaboration made quite some progress in 2007 toward our goal of measuring the
neutron-neutron scattering length in a direct neutron-neutron collision
experiment using the pulsed high-flux reactor JAGUAR in
b) Three-body system: We continued our
neutron-deuteron elastic analyzing power measurements at 21.9 MeV, where the three-nucleon analyzing power puzzle is expected
to be less pronounced than at lower energies. However, our new data support the
two proton-deuteron data points at 22.7 MeV, which
indicate an increased discrepancy and resonance-like behaviour.
Again, this observation is not understood at all, and I have to admit that I
didn’t trust the two proton-deuteron data points either, but nevertheless
decided to check on these data with neutrons as a probe due to the lack of a polarized
proton beam in the energy range of interest. This new spin to the three-nucleon
analyzing power puzzle will keep us busy for the foreseeable future. We plan to
submit a proposal
to RCNP (
c) Four-body
system: In 2007 we completed our
measurements of the analyzing power in elastic neutron-He-3 scattering at low
energies. This experimental program is part of the thesis project of James Esterline. Here the goal is to obtain information needed to
resolve the so-called analyzing power puzzle, the largest discrepancy (25-50%)
known to exist in low-energy nuclear physics between data and rigorous
theoretical calculations. To the great surprise of the few-body community our
data are in much better agreement with theoretical predictions than those previously
obtained for proton-He-3 scattering in the same energy region. This result,
although still unpublished, triggered quite some activity in the theoretical
few-body community. With our help it was found that proton-triton analyzing
power data are also in much better agreement with theory than the proton-He-3
data. These observations may point to a completely unexpected isospin dependence of three-nucleon forces in the four-body
system.
Our recent observations have earned me
invitations to present talks at international conferences in
C. Nuclear Physics for
Society
a) (n,2n)
measurements: We completed our (n,2n) measurements on U-238 and U-235 which
constitute the thesis project of Tony Hutcheson. We also completed our Am-241(n,2n)Am-240 cross-section measurements. This project is
headed by Anton Tonchev. In 2008 we will pursue
measurements of the Pu-239(n,2n) Pu-238 cross section
These data will be obtained with collaborators from LANL and LLNL who also will
provide the 239Pu targets. Very stringent safety procedures are in place to
handle this special nuclear material on a university campus. We are working
with the Duke University Radiation Safety Office and the State of
b) Transmutation of
radioactive waste: We have not done any experimental work during 2007.
D. Nuclear Physics for Fun
a) Neutron production with a pyroelectric
crystal: In 2005 Naranjo,
Gimzewski and Putterman
(Nature 434, 115, 2005) and in 2006 Geuther, Danon and Saglime (Phy. Rev. Lett. 96, 054803, 2006)
showed that a pyroelectric crystal operated in a
dilute gas of deuterium and augmented with a nanotip
and a deuterated target foil can be used to produce
neutrons via the fusion reaction 2H(d,n)3He. In contrast to the "cold fusion" days of
Pons and Fleischman back in 1986, the findings of
these two research groups regarding "hot fusion" are generally being
considered as plausible. Here, the pyroelectric
crystal acts as a miniature particle accelerator. Although I managed to produce
neutrons with a LiTaO3 crystal operated in 3 mTorr of
deuterium gas, I could not reproduce the high neutron flux reported in the
references given above. I think these experiments are flawed. A manuscript
about my experimental work is almost completed.
b) Manipulating the decay rate of radioactive
nuclei: Ever since
We are trying to reproduce these
effects, but so far, have not seen a decay-time change of Cu-64 ( emitter) and
Zn-65 ( emitter) between samples at room temperature and samples cooled to12 –
13 K. Our radioactive samples were produced at TUNL by bombarding natural
copper with proton and deuteron beams, respectively. There was no need to
implant the radioactive nuclei in a metallic environment, because they were
produced already in a metallic environment.