135661547
Summary of the radiation damage studies of the SDC dopants in polystyrene
Approximately 80 commercially available fluorescent organic compounds were studied as dopants in a polystyrene matrix for possible use in wavelength shifting (WLS) fibers. The goal was to find a new green- emitting WLS fiber which would outperform in light yield and decay time the currently available fiber doped with K-27. Therefore the fluorescent compounds of interest should exhibit the following spectroscopic characteristics in polystyrene: {lambda}{sub abs} = 400--450 nm,{lambda}{sub em} = 450--550 nm, {tau} = 3--7 ns and quantum efficiency of minimum 0.7. Polystyrene samples doped with different fluorescent compounds were prepared and characterized. Of all the compounds tested, only a series of coumarins exhibited the spectroscopic characteristics of interest. Radiation damage studies had to be performed on these samples in order to condusively determine if they were better candidates than K-27 for green WLS fibers. AU samples except those showing opacity or deep coloration were irradiated. They were, however, separated in two sets. Radiation damage set No. 20 was mainly formed by the coumarin derivatives. Radiation damage set No. 22 was based on the remaining samples. The irradiations were performed at the Phoenix Memorial Laboratory using a {sup 60}Co source. Both sets were exposed to a total dose ofmore » 10 Mrad in air, at a dose rate of 1.8 Mrad/h. Transmittance measurements were recorded before and after irradiation, and after annealing. After irradiation, the samples were annealed in oxygen to accelerate the recovery process.« less
55019383
Gamma-irradiation of coumarins in a polystyrene matrix
Abstract Polystyrene samples doped with commercially available coumarin derivatives were prepared and tested as wavelength shifters for plastic scintillation applications. Radiation damage studies were performed utilizing a 60 Co source. Transmittance and light yield measurements were recorded before and after irradiation (100 kGy), and after annealing of the samples. All samples experienced losses in transmittance and light yield as a result of radiation-induced damage to the polymer and in some cases, the dopant. None of the coumarins examined in this study outperformed the commonly-used green wavelength shifter, K-27, after irradiation.
118575585
QCD evolutions of twist-3 chirality-odd operators
We study the scale dependence of twist-3 distributions defined with chirality-odd quark-gluon operators. To derive the scale dependence we explicitly calculate these distributions of multi-patron states instead of a hadron. Taking one-loop corrections into account we obtain the leading evolution kernel in the most general case. In some special cases the evolutions are simplified. We observe that the obtained kernel in general does not get simplified in the large-N-c limit in contrast to the case of those twist-3 distributions defined only with chirality-odd quark operators. In the later, the simplification is significant. (C) 2012 Elsevier B.V. All rights reserved.
119224580
Gauge invariance and QCD twist-3 factorization for single spin asymmetries
A bstractThe collinear factorization at twist-3 for Drell-Yan processes is studied with the motivation to solve the discrepancy in literature about the single spin asymmetry in the lepton angular distribution, and to show how QCD gauge invariance is realized in the hadronic tensor. The obtained result here agrees with our early result derived with a totally different approach. In addition to the asymmetry we can construct another two observables to identify the spin effect. We show that the gauge invariance of different contributions in the hadronic tensor is made in different ways by summing the effects of gluon exchanges. More interestingly is that we can show that the virtual correction to one structure function of the hadronic tensor, hence to some weighted SSA observables, is completely determined by the quark form factor. This will simplify the calculation of higher order corrections. The corresponding result in semi-inclusive DIS is also given for the comparison with Drell-Yan processes.
119215240
Neutron energy spectrum measurements with a compact liquid scintillation detector on EAST
A neutron detector based on EJ301 liquid scintillator has been employed at EAST to measure the neutron energy spectrum for D-D fusion plasma. The detector was carefully characterized in different quasi-monoenergetic neutron fields generated by a 4.5 MV Van de Graaff accelerator. In recent experimental campaigns, due to the low neutron yield at EAST, a new shielding device was designed and located as close as possible to the tokamak to enhance the count rate of the spectrometer. The fluence of neutrons and ?-rays was measured with the liquid neutron spectrometer and was consistent with 3He proportional counter and NaI(Tl) ?-ray spectrometer measurements. Plasma ion temperature values were deduced from the neutron spectrum in discharges with lower hybrid wave injection and ion cyclotron resonance heating. Scattered neutron spectra were simulated by the Monte Carlo transport Code, and they were well verified by the pulse height measurements at low energies.
118079649
Cross-section measurement and analysis for the Sm-149 (n, alpha) Nd-146 reaction at 6.0 MeV
We have measured the $^{149}\mathrm{Sm}(n,\ensuremath{\alpha})^{146}\mathrm{Nd}$ cross section at 6.0 MeV to be $0.12\ifmmode\pm\else\textpm\fi{}0.018$ mb. This is the first reported result for this cross section in the MeV region and so should be helpful for constraining nuclear data evaluations (which differ by a factor of 40 for this reaction at this energy) and for testing and improving nuclear models. The experiment was performed at the at the 4.5-MV Van de Graaff accelerator of Peking University. Neutrons were produced via the $^{2}\mathrm{H}(d,n)^{3}\mathrm{He}$ reaction using a deuterium gas target, and absolute neutron flux was determined with a small $^{238}\mathrm{U}$ fission chamber. Alpha particles were detected using a two-section gridded ionization chamber in which two large-area $^{149}\mathrm{Sm}{}_{2}{\mathrm{O}}_{3}$ samples were placed back-to-back so that the cross section and forward/backward ratio were measured for nearly the entire 4$\ensuremath{\pi}$ solid angle. The data were compared to statistical-model predictions using the code talys. Good agreement between the measured and theoretical cross sections could be obtained with a small modification of the $\ensuremath{\alpha}$-optical potential parameters from their default values in talys. However, we were not able to reproduce the measured forward/backward ratio. In addition, using the previously reported $^{147}\mathrm{Sm}(n,\ensuremath{\alpha})^{144}\mathrm{Nd}$ cross section at 6.0 MeV together with our new result, good agreement was found between the measured and predicted cross-section ratio for these two isotopes. Finally, none of the existing evaluated data libraries are in agreement with our new data to within the experimental uncertainties.
53552875
QCD corrections of all structure functions in transverse momentum dependent factorization for Drell-Yan processes
A bstractWe study the one-loop correction in Transverse-Momentum-Dependent(TMD) factorization for Drell-Yan processes at small transverse momentum of the lepton pair. We adopt the so-called subtractive approach, in which one can systematically construct contributions for subtracting long-distance effects represented by diagrams. The perturbative parts are obtained after the subtraction. We find that the perturbative coefficients of all structure functions in TMD factorization at leading twist are the same. The perturbative parts can also be studied with scattering of partons instead of hadrons. In this way, the factorization of many structure functions can only be examined by studying the scattering of multi-parton states, where there are many diagrams. These diagrams have no similarities to those treated in the subtractive approach. As an example, we use existing results of one structure function responsible for Single-Spin-Asymmetry, to show that these diagrams in the scattering of multi-parton states are equivalent to those treated in the subtractive approach after using Ward identity.