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Neutron-Emission Measurements at a White Neutron Source
R. C. Haight 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
Data on the spectrum of neutrons emitted from neutron-induced reactions are important in basic nuclear physics and in applications. Our program studies neutron emission from inelastic scattering as well as fission neutron spectra. A ``white'' neutron source (continuous in energy) allows measurements over a wide range of incident neutron energies all in one experiment. We use the fast neutron source at the Los Alamos Neutron Science Center for incident neutron energies from 0.5 MeV to 200 MeV. These experiments are based on double time-of-flight techniques to determine the energies of the incident and emitted neutrons. For the fission neutron measurements, parallel-plate ionization or avalanche detectors identify fission in actinide samples and give the required fast timing pulse. For inelastic scattering, gamma-ray detectors provide the timing and energy spectroscopy. A large neutron-detector array detects the emitted neutrons. Time-of-flight techniques are used to measure the energies of both the incident and emitted neutrons. Design considerations for the array include neutron-gamma discrimination, neutron energy resolution, angular coverage, segmentation, detector efficiency calibration and data acquisition. We have made preliminary measurements of neutron emission spectra from neutron-induced fission of ^(235)U, ^(238)U, ^(237)Np and ^(239)Pu. Neutron emission spectra from inelastic scattering on iron and nickel have also been investigated. The results obtained will be compared with evaluated data.
Generation of 193-nm Femtosecond Light Pulses and Their Application to Photomask Repair
D. Lim,R. Haight 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Femtosecond laser pulses at 193 nm were generated from visible Ti:sapphire amplified pulses by using an Ar filled capillary tube as four-wave mixing medium. We could identify the dominant generation mechanism by experimenting with 3 different femtosecond pump pulses, the 772-nm fundamental and its second and third harmonics. To take advantage of the improved resolution at a shorter wavelength, we used the 193-nm output for photomask repair. Clean ablation of Cr on glass photomasks was demonstrated. Clean ablated lines as narrow as 175-nm could be obtained. The threshold pulse energy for ablation was less than 2 nJ, which is much smaller than the generated pulse energy, making it possible to extend the ablation wavelength to even deeper vacuum ultraviolet (VUV) wavelengths. The damage to the quartz substrate was found to be minimal. Our results show that high resolution VUV femtosecond photomask repair can play an important role in highly scaled semiconductor fabrication.
A. B. Laptev,R. C. Haight,R. A. Arndt,W. J. Briscoe,M. W. Paris,I. I. Strakovsky,R. L. Workman 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
The absolute total cross sections for np and pp scattering below 1000 MeV are determined based on partial-wave analyses (PWAs) of nucleon-nucleon scattering data. These cross sections are compared with the most recent ENDF/B-VII.0 and JENDL-3.3 data files, and the Nijmegen PWA. Systematic deviations from the ENDF/B-VII.0 and JENDL-3.3 evaluations are found to exist in the low-energy region. Comparison of the np evaluation with the result of most recent np total and differential cross section measurements will be discussed. Results of those measurements were not used in the evaluation database. A comparison was done to check a quality of evaluation and its capabilities to predict experimental observables. Excellent agreement was found between the new experimental data and our PWA predictions.
Koo, Bonhyeong,Nam, Sung-Wook,Haight, Richard,Kim, Suncheul,Oh, Seungtaeg,Cho, Minhyung,Oh, Jihun,Lee, Jeong Yong,Ahn, Byung Tae,Shin, Byungha American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.6
<P>We report on the photoelectrochemical (PEC) performance and stability of Cu(In,Ga)Se-2 (CIGS)-based photocathodes for photocatalytic hydrogen evolution from water. Various functional overlayers, such as CdS, TiO2, ZnxSnyOz, and a combination of the aforementioned, were applied on the CIGS to improve the performance and stability. We identified that the insertion of TiO2 overlayer on p-CIGS/n-buffer layers significantly improves the PEC performance. A multilayered photocathode consisting of CIGS/CdS/TiO2/Pt exhibited the best current-potential characteristics among the tested photocathodes, which demonstrates a power-saved efficiency of 2.63%. However, repeated linear sweep voltammetry resulted in degradation of performance. In this regard, we focused on the PEC durability issues through in-depth chemical characterization that revealed the degradation was attributed to atomic redistribution of elements constituting the photocathode, namely, in-diffusion of Pt catalysts, out-diffusion of elements from the CIGS, and removal of the metal-oxide layers; the best-performing CIGS/CdS/TiO2/Pt photocathode retained its initial performance until the TiO2 overlayer was removed. It was also found that the durability of CIGS photocathodes with a TiO2-coated metal-oxide buffer layer such as ZnxSnyOz was better than those with a TiO2-coated CdS, and the degradation mechanism was different, suggesting that the stability of a CIGS-based photocathode can be improved by careful design of the structure.</P>
T. Kajimoto,N. Shigyo,K. Ishibashi,D. Moriguchi,Y. Nakamura,H. Arakawa,S. Kunieda,T. Watanabe,R. C. Haight 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
We measured neutron-production double-differential cross-sections by neutron incidence from 50 to 150 MeV. A ^(238)U fission ionization chamber was set to take the incident-neutron flux. Six NE213 liquid scintillators which had a thickness of 12.7 cm and 12.7 cm in diameter, were placed at 15˚, 30˚, 60˚, 90˚, 120˚, and 150˚ to detect neutrons emitted from a sample. The energy of incident neutron was determined by the time of flight (TOF) technique. The energy spectra of neutron emitted from the sample were derived by the unfolding their light output spectra with the response functions of the detectors. The response functions were measured with the spallation neutrons above 25 MeV. In the unfolding process, we assumed that neutron energy spectra reproduced the shape by the moving source model. The neutron-induced neutron-production double-differential cross sections were parameterized with the moving source model by the least-square method. The experimental results were compared with calculations of the PHITS and the TALYS codes.
J. L. Ullmann,A. J. Couture,A. L. Keksis,D. J. Vieira,,J. M. ODonnell,J. M. Wouters,M. Jandel,R. C. Haight,R. S. Rundberg,T. A. Bredeweg,T. Kawano,C. Y. Wu,J. A. Becker,A. Chyzh,B. Baramsai,G. E. Mitc 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
A careful new measurement of the ^(238)U(n,γ) cross section from 10 eV to 100 keV has been made using the DANCE detector at LANSCE. DANCE is a 4π calorimetric scintillator array consisting of 160 BaF^2 crystals. Measurements were made on a 48 mg/cm^2 depleted uranium target. The cross sections are in general in good agreement with previous measurements. The gamma-ray emission spectra, as a function of gamma multiplicity, were also measured and compared to model calculations.