308 research outputs found
Neutrino-induced deuteron disintegration experiment
Cross sections for the disintegration of the deuteron via neutral-current
(NCD) and charged-current (CCD) interactions with reactor antineutrinos are
measured to be 6.08 +/- 0.77 x 10^(-45) cm-sq and 9.83 +/- 2.04 x 10^(-45)
cm-sq per neutrino, respectively, in excellent agreement with current
calculations. Since the experimental NCD value depends upon the CCD value, if
we use the theoretical value for the CCD reaction, we obtain the improved value
of 5.98 +/- 0.54 x 10^(-45) for the NCD cross section. The neutral-current
reaction allows a unique measurement of the isovector-axial vector coupling
constant in the hadronic weak interaction (beta). In the standard model, this
constant is predicted to be exactly 1, independent of the Weinberg angle. We
measure a value of beta^2 = 1.01 +/- 0.16. Using the above improved value for
the NCD cross section, beta^2 becomes 0.99 +/- 0.10.Comment: 22pages, 9 figure
Investigation of the chemical vicinity of crystal defects in ion-irradiated Mg and AZ31 with coincident Doppler broadening spectroscopy
Crystal defects in magnesium and magnesium based alloys like AZ31 are of
major importance for the understanding of their macroscopic properties. We have
investigated defects and their chemical surrounding in Mg and AZ31 on an atomic
scale with Doppler broadening spectroscopy of the positron annihilation
radiation. In these Doppler spectra the chemical information and the defect
contribution have to be thoroughly separated. For this reason samples of
annealed Mg were irradiated with Mg-ions in order to create exclusively
defects. In addition Al- and Zn-ion irradiation on Mg-samples was performed in
order to create samples with defects and impurity atoms. The ion irradiated
area on the samples was investigated with laterally and depth resolved positron
Doppler broadening spectroscopy (DBS) and compared with preceding
SRIM-simulations of the vacancy distribution, which are in excellent agreement.
The investigation of the chemical vicinity of crystal defects in AZ31 was
performed with coincident Doppler broadening spectroscopy (CDBS) by comparing
Mg-ion irradiated AZ31 with Mg-ion irradiated Mg. No formation of
solute-vacancy complexes was found due to the ion irradiation, despite the high
defect mobility.Comment: Submitted to Physical Review B on March 20 20076. Revised version
submitted on September 28 2007. Accepted on October 19 200
Final results from the Palo Verde Neutrino Oscillation Experiment
The analysis and results are presented from the complete data set recorded at
Palo Verde between September 1998 and July 2000. In the experiment, the
\nuebar interaction rate has been measured at a distance of 750 and 890 m
from the reactors of the Palo Verde Nuclear Generating Station for a total of
350 days, including 108 days with one of the three reactors off for refueling.
Backgrounds were determined by (a) the technique based on the difference
between signal and background under reversal of the positron and neutron parts
of the correlated event and (b) making use of the conventional reactor-on and
reactor-off cycles. There is no evidence for neutrino oscillation and the mode
\nuebar\to\bar\nu_x was excluded at 90% CL for \dm>1.1\times10^{-3} eV
at full mixing, and \sinq>0.17 at large \dm.Comment: 11 pages, 8 figure
Components of Antineutrino Emission in Nuclear Reactor
New scattering experiments aimed for sensitive searches of
the magnetic moment and projects to explore small mixing angle
oscillations at reactors call for a better understanding of the reactor
antineutrino spectrum. Here we consider six components, which contribute to the
total spectrum generated in nuclear reactor. They are: beta
decay of the fission fragments of U, Pu, U and
Pu, decay of beta-emitters produced as a result of neutron capture in
U and also due to neutron capture in accumulated fission fragments
which perturbs the spectrum. For antineutrino energies less than 3.5 MeV we
tabulate evolution of spectra corresponding to each of the four
fissile isotopes vs fuel irradiation time and their decay after the irradiation
is stopped and also estimate relevant uncertainties. Small corrections to the
ILL spectra are considered.Comment: LaTex 8 pages, 2 ps figure
Sensitivities of Low Energy Reactor Neutrino Experiments
The low energy part of the reactor neutrino spectra has not been
experimentally measured. Its uncertainties limit the sensitivities in certain
reactor neutrino experiments. The origin of these uncertainties are discussed,
and the effects on measurements of neutrino interactions with electrons and
nuclei are studied. Comparisons are made with existing results. In particular,
the discrepancies between previous measurements with Standard Model
expectations can be explained by an under-estimation of the low energy reactor
neutrino spectra. To optimize the experimental sensitivities, measurements for
\nuebar-e cross-sections should focus on events with large (1.5 MeV)
recoil energy while those for neutrino magnetic moment searches should be based
on events 100 keV. The merits and attainable accuracies for
neutrino-electron scattering experiments using artificial neutrino sources are
discussed.Comment: 25 pages, 9 figure
Production of Ultra-Cold-Neutrons in Solid \alpha-Oxygen
Our recent neutron scattering measurements of phonons and magnons in solid
\alpha-oxygen have led us to a new understanding of the production mechanismen
of ultra-cold-neutrons (UCN) in this super-thermal converter. The UCN
production in solid \alpha-oxygen is dominated by the excitation of phonons.
The contribution of magnons to UCN production becomes only slightly important
above E >10 meV and at E >4 meV. Solid \alpha-oxygen is in comparison to solid
deuterium less effcient in the down-scattering of thermal or cold neutrons into
the UCN energy regime.Comment: 4 pages, 5 figuer
Is the Unitarity of the quark-mixing-CKM-matrix violated in neutron -decay?
We report on a new measurement of neutron -decay asymmetry. From the
result \linebreak = -0.1189(7), we derive the ratio of the axial vector
to the vector coupling constant = = -1.2739(19). When
included in the world average for the neutron lifetime = 885.7(7)s, this
gives the first element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix . With this value and the Particle Data Group values for and
, we find a deviation from the unitarity condition for the first row of
the CKM matrix of = 0.0083(28), which is 3.0 times the stated error
Reactor-based Neutrino Oscillation Experiments
The status of neutrino oscillation searches employing nuclear reactors as
sources is reviewed. This technique, a direct continuation of the experiments
that proved the existence of neutrinos, is today an essential tool in
investigating the indications of oscillations found in studying neutrinos
produced in the sun and in the earth's atmosphere. The low-energy of the
reactor \nuebar makes them an ideal tool to explore oscillations with small
mass differences and relatively large mixing angles.
In the last several years the determination of the reactor anti-neutrino flux
and spectrum has reached a high degree of accuracy. Hence measurements of these
quantities at a given distance L can be readily compared with the expectation
at L = 0, thus testing \nuebar disappearance.
While two experiments, Chooz and Palo Verde, with baselines of about 1 km and
thus sensitive to the neutrino mass differences associated with the atmospheric
neutrino anomaly, have collected data and published results recently, an
ambitious project with a baseline of more than 100 km, Kamland, is preparing to
take data. This ultimate reactor experiment will have a sensitivity sufficient
to explore part of the oscillation phase space relevant to solar neutrino
scenarios. It is the only envisioned experiment with a terrestrial source of
neutrinos capable of addressing the solar neutrino puzzle.Comment: Submitted to Reviews of Modern Physics 34 pages, 39 figure
Accelerator and Reactor Neutrino Oscillation Experiments in a Simple Three-Generation Framework
We present a new approach to the analysis of neutrino oscillation
experiments, in the one mass-scale limit of the three-generation scheme. In
this framework we reanalyze and recombine the most constraining accelerator and
reactor data, in order to draw precise bounds in the new parameter space. We
consider our graphical representations as particularly suited to show the
interplay among the different oscillation channels. Within the same framework,
the discovery potential of future short and long baseline experiments is also
investigated, in the light of both the recent signal from the LSND experiment
and the atmospheric neutrino anomaly.Comment: uuencoded compressed tar file. Figures (13) available by ftp to
ftp://eku.sns.ias.edu/pub/lisi/ (192.16.204.30). Submitted to Physical Review
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