Showing papers by "Werner Tornow published in 2010"

Production of radioactive isotopes through cosmic muon spallation in KamLAND

Abstract: Radioactive isotopes produced through cosmic muon spallation are a background for rare-event detection in ν detectors, double-β-decay experiments, and dark-matter searches. Understanding the nature of cosmogenic backgrounds is particularly important for future experiments aiming to determine the pep and CNO solar neutrino fluxes, for which the background is dominated by the spallation production of ^(11)C. Data from the Kamioka liquid-scintillator antineutrino detector (KamLAND) provides valuable information for better understanding these backgrounds, especially in liquid scintillators, and for checking estimates from current simulations based upon MUSIC, FLUKA, and GEANT4. Using the time correlation between detected muons and neutron captures, the neutron production yield in the KamLAND liquid scintillator is measured to be Y_n=(2.8±0.3)×10^(-4) μ^(-1) g^(-1) cm^2. For other isotopes, the production yield is determined from the observed time correlation related to known isotope lifetimes. We find some yields are inconsistent with extrapolations based on an accelerator muon beam experiment.

Spectral structure of the pygmy dipole resonance.

Abstract: High-sensitivity studies of $E1$ and $M1$ transitions observed in the reaction $^{138}\mathrm{Ba}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},{\ensuremath{\gamma}}^{\ensuremath{'}})$ at energies below the one-neutron separation energy have been performed using the nearly monoenergetic and 100% linearly polarized photon beams of the $\mathrm{HI}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}\mathrm{S}$ facility. The electric dipole character of the so-called ``pygmy'' dipole resonance was experimentally verified for excitations from 4.0 to 8.6 MeV. The fine structure of the $M1$ ``spin-flip'' mode was observed for the first time in $N=82$ nuclei.

Substantial increase in acceleration potential of pyroelectric crystals

Abstract: We report on a substantial increase in the acceleration potential achieved with a LiTaO3 pyroelectric crystal. With a single 2.5 cm diameter and 2.5 cm long z-cut crystal without electric field-enhancing nanotip we produced positive ion beams with maximal energies between 300 and 310 keV during the cooling phase when the crystal was exposed to 5 mTorr of deuterium gas. These values are about a factor of 2 larger than previously obtained with single pyroelectric crystals.

Measurement of the Am241(γ,n)Am240 reaction in the giant dipole resonance region

Abstract: The photodisintegration cross section of the radioactive nucleus $^{241}\mathrm{Am}$ has been obtained using activation techniques and monoenergetic $\ensuremath{\gamma}$-ray beams from the HI$\ensuremath{\gamma}$S facility. The induced activity of $^{240}\mathrm{Am}$ produced via the $^{241}\mathrm{Am}$$(\ensuremath{\gamma},n)$ reaction was measured in the energy interval from 9 to 16 MeV utilizing high-resolution $\ensuremath{\gamma}$-ray spectroscopy. The experimental data for the $^{241}\mathrm{Am}$$(\ensuremath{\gamma},n)$ reaction in the giant dipole resonance energy region are compared with statistical nuclear-model calculations.

Determination of the proton and alpha-particle light-response functions for the KamLAND, BC-501A and BC-517H liquid scintillators

Abstract: A cylindrical 5.1 cm×5.1 cm scintillator cell filled with the KamLAND liquid scintillator has been exposed to monoenergetic neutron beams produced via the 2H(d,n)3He reaction to measure the proton light-response function for energies up to 10 MeV. Using Birks’ recipe, the α -particle light-response function was derived from these data. The same method was applied to the BC-501A and BC-517H liquid scintillators to check on the systematic accuracy of the present data. The proton and α -particle light-response functions are needed to correct the KamLAND antineutrino prompt energy spectrum for background effects caused by the reaction C 13 ( α , n ) O 16 . Especially, the geo-antineutrino energy regime measured in the KamLAND experiment is contaminated by background events from this reaction.

GEMSTAR: The Alternative Reactor Technology Comprising Graphite, Molten Salt, and Accelerators

Abstract: The technology of nuclear power could be quite different from today’s if it had been practical in the beginning to supplement fission neutrons with accelerator-produced neutrons. The purpose of this chapter is to illustrate the possible benefits of implementing supplementary neutrons from accelerators in an optimized reactor. GEMSTAR (Green Energy MultiplierSubcritical Technology for Alternative Reactors developed by Accelerator Driven Neutron Applications (ADNA Corp) is a subcritical thermal-spectrum reactor operating with molten salt fuel in a graphite matrix and in a continuous flow mode initially at keff = .. The model described is able to use natural uranium as fuel and generate twice as much electric power as a light water reactor (LWR) generates from the same mined uranium. GEM∗STAR at keff = . also can be fueled with unreprocessed LWR spent fuel, and it can generate as much electricity as the LWR had generated from the same fuel. Because GEMSTAR uses liquid fuel, it can recycle its own fuel at keff = . without any operations on the fuel. This recycle can be repeated severalmore times, always without reprocessing, as accelerator or fusion neutron generation technology development reduces the cost of neutrons. GEMSTAR therefore increases the electricity frommined uraniummany times while avoiding the serious problems of current nuclear-power technology arising from enrichment, reprocessing, fast reactor deployment, and near term high-level waste storage. GEM∗STAR also offers technology for nuclear energy generation that promises reductions in nuclear electricity cost and eliminates major proliferation concerns. The technology can use a modest source of intermittent “green” electricity such as wind or solar as input power to drive an accelerator that, in effect,multiplies the green energy by a factor of about  with – continuity and without compromising any environmental objectives of green energy sources. This chapter is not a complete history of molten salt, graphite, and accelerator technologies, but a description of how these orphan elements of nuclear power development may be integrated for a GEMSTAR solution to the main barriers that constrain the full deployment of today’s nuclear power technology.

Neutron production with a pyroelectric double-crystal assembly without nano-tip

Abstract: Two cylindrical LiTaO3 crystals facing each other's deuterated circular face were exposed to deuterium gas at an ambient pressure of a few mTorr With a distance of about 4 cm between the z+ and z− cut crystal faces, neutrons were produced via the 2H(d,n)3He fusion reaction upon the heating and cooling of the crystals The 25 MeV neutrons were detected with organic liquid scintillation detectors equipped with neutron-gamma pulse-shape discrimination electronics to reject pulses generated by the intense X-ray flux During the cooling phase of naked crystals, deuterium ion-beam (D2+) energies of up to 400 keV were obtained as deduced from the associated electron bremsstrahlung end-point energy The highest electron-beam energy observed during the heating phase was 360 keV With a layer of deuterated polyethylene evaporated on the front face of the crystals, the maximal energies were about 10% lower In contrast to earlier studies, an electric-field enhancing nano-tip was not employed Neutron yields up to 500 per thermal cycle were observed, resulting in a total neutron production yield of about 16×104 neutrons per thermal cycle Our approach has the potential of being substantially improved by reducing the frequency of the discharges we are currently experiencing with our geometry, which was not designed for the unprecedented high potentials produced in the presentwork

Enhanced Constraints on $\theta_{13}$ from A Three-Flavor Oscillation Analysis of Reactor Antineutrinos at KamLAND

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Differential cross section for neutron scattering from Bi209 at 37 MeV and the weak particle-core coupling

Abstract: Differential scattering cross-section data have been measured at 43 angles from ${11}^{\ifmmode^\circ\else\textdegree\fi{}}$ to ${160}^{\ifmmode^\circ\else\textdegree\fi{}}$ for 37-MeV neutrons incident on $^{209}\mathrm{Bi}$. The primary motivation for the measurements is to address the scarcity of neutron scattering data above 30 MeV and to improve the accuracy of optical-model predictions at medium neutron energies. The high-statistics measurements were conducted at the China Institute of Atomic Energy using the $^{3}\mathrm{H}$($d,n$)$^{4}\mathrm{He}$ reaction as the neutron source, a pulsed deuteron beam, and time-of-flight (TOF) techniques. Within the resolution of the TOF spectrometer, the measurements included inelastic scattering components. The sum of elastic and inelastic scattering cross sections was computed in joint optical-model and distorted-wave Born approximation calculations under the assumption of the weak particle-core coupling. The results challenge predictions from well-established spherical optical potentials. Good agreement between data and calculations is achieved at 37 MeV provided that the balance between surface and volume absorption in a recent successful model [A. J. Koning and J. P. Delaroche, Nucl. Phys. A 713, 231 (2003)] is modified, thus suggesting the need for global optical-model improvements at medium neutron energies.

Neutron-deuteron analyzing power data at 19.0 MeV

Abstract: Measurements of neutron-deuteron (n-d) analyzing power A y (θ) at E n = 19.0 MeV are reported at 16 angles from θ c.m. = 46.7 to 152.0°. The objective of the experiment is to better characterize the discrepancies between n-d data and the predictions of three-nucleon calculations for neutron energies above 16.0 MeV. The experiment used a shielded neutron source, which produced polarized neutrons via the 2 H(d,n) 3 He reaction, a deuterated liquid scintillator center detector (CD) and liquid-scintillator neutron side detectors. A coincidence between the CD and the side detectors isolated the elastic-scattering events. The CD pulse height spectrum associated with each side detector was sorted by using pulse-shape discrimination, time-of-flight techniques, and by removing accidental coincidences. A Monte Carlo computer simulation of the experiment accounted for effects due to finite geometry, multiple scattering, and CD edge effects. The resulting high-precision data (with absolute uncertainties ranging from 0.0022 to 0.0132) have a somewhat lower discrepancy with the predictions of three-body calculations, as compared to those found at lower energies.

Spin and parity assignments to dipole excitations of the odd-mass nucleus 207Pb from nuclear resonance fluorescence experiments with linearly-polarized γ-ray beams

Abstract: Pb(,γ') photon scattering reactions were studied [1] with the nearly monochromatic, linearly polarized photon beams at the High Intensity γ-ray Source (HIγS) at the DFELL. Azimuthal scattering intensity asymmetries measured with respect to the polarization plane of the beam have been used for the first time to assign both the spin and parity quantum numbers of dipole excited states of 206,207,208Pb at excitation energies in the vicinity of 5.5 MeV. Evidence for dominant particle-core coupling is deduced from these results along with information on excitation energies and electromagnetic transition matrix elements.

Improved Results for the 2H(d, n)3He Transverse Vector Polarization-Transfer Coefficient {K^{y'}_{y}(0^{\circ})} at Low Energies

Abstract: Measurements of the 2H(d, n)3He transverse vector polarization-transfer coefficient $${K^{y'}_{y}}$$ at 0° are reported for 29 outgoing neutron energies between 3.94 and 8.47 MeV. Our new results determine $${K^{y'}_{y}(0^{\circ})}$$ more accurately than previous data, especially for neutron energies below 5 MeV. Low-energy data for this reaction are important both as a high-intensity source of highly polarized neutrons for nuclear physics studies with polarized neutron beams, and as a test of the emerging theoretical descriptions of the four-body system, where recently substantial progress has been made.

Corrections for the polarization-dependent efficiency and new neutron-proton analyzing power data at 7.6 MeV

Abstract: We present new corrections for the polarization-dependent efficiency (PDE), which introduces a false asymmetry into measurements of $n\text{\ensuremath{-}}p$ analyzing power ${A}_{y}(\ensuremath{\theta})$ caused by double scattering in the neutron side detectors. To accomplish this, we created a new database of $^{12}\mathrm{C}$$(\mathrm{nP\vec},n)$ ${A}_{y}(\ensuremath{\theta})$ by using a combination of fits to data, phase-shift analysis, and $R$-matrix analysis. Our recorrection for PDE of previously reported $n\text{\ensuremath{-}}p$ ${A}_{y}(\ensuremath{\theta})$ data at 7.6 and 12.0 MeV and new data at 7.6 MeV indicate that we have achieved a superior representation of $^{12}\mathrm{C}$$(\mathrm{nP\vec},n)$. Our results continue to suggest a possible charge dependence of the pion-nucleon coupling constant.