Velocity driving system for an in-field Mössbauer spectrometer

The velocity driving system for an in-field Mössbauer spectrometer with a constant acceleration mode is described. The driving system uses a digital proportional-integral-derivative velocity controller based on the Field Programmable Gate Array in the National Instruments CompactRIO system. This novel approach is able to drive the transducer in wide range of measurement conditions and eliminates external magnetic field disturbances. The frequency characteristics of stray fields of 5 T and 8 T were measured and analyzed. The nonlinearity of the velocity scales is better than 0.2%.     

Production cross-sections of residual radionuclides from proton-induced reactions on Ag up to 40 MeV

We measured the cross-sections of the ^{104g,105,106m}Ag and ^104,107Cd radionuclides produced by proton-induced reactions on natural silver by using a stacked-foil activation technique in the energy range from a threshold energy to 40 MeV at a MC50 cyclotron. The results showed generally good agreement with available data as well as the theoretical data. The integral yields for thick targets were also deduced using the measured cross-sections and the stopping power of ^natAg over the energy range from a threshold energy to 40 MeV, taking into account that the total energy is absorbed in the targets. The production cross-sections for the ^104gAg and the ¹⁰⁴Cd radionuclides from natural silver were measured for the first time.     

ZnTe/Si heterostructures grown by isothermal closed space sublimation

ZnTe films with different thickness were grown onto (001) Si substrates using isothermal closed space sublimation by alternated sublimation of Zn and Te sources. As a result ZnTe polycrystalline films were obtained with a strong [111] orientation as revealed by X-ray diffraction patterns. The reason for this polycrystalline nature of the samples comes from incomplete removal of SiO₂ from the Si substrate surface. A preferential adsorption of Te in the first stages of the growth was concluded from Rutherford backscattering spectra analysis.     

Determining Pu isotopic composition and Pu content of PuBe sources by neutron coincidence technique

The paper describes a pure neutron method for determining both Pu content and Pu isotopic composition of PuBe neutron sources by neutron coincidence technique, without using gamma-spectrometry. The new procedure based on the R/T-T relationship is a developed version of the R/T-method based on R/T-M_Pu calibration curve described in [C.T. Nguyen, J. Bagi, L. Lakosi, A novel method of quantitative assay of PuBe neutron sources by neutron coincidence technique, Nucl. Instr. and Meth. B 246 (2006) 409], utilizing Pu isotopic correlations; here R, T, M_Pu are double count rate, single count rate and total Pu content, respectively. Accuracy of the method was found to be about 2-3% and 15% for ²³⁹Pu component and Pu content, respectively. Measurement time as a function of detector efficiency is treated in detail. It is shown that in a system of frame, a transuranium neutron source can be characterized by a pair of co-ordinates [R/T,  T].     

Elaboration and characterization of hydrogen standard stable under heavy ion irradiation: Application to nuclear astrophysics

A hydrogen standard has been carried out by ion implantation in silicon. The silicon wafer was implanted with hydrogen at different energies and fluences to provide a ∼100 nm flat distribution to the specimen. The samples obtained were characterized by mean of elastic recoil detection analysis (ERDA) and resonant nuclear reaction analysis (RNRA). All important properties of the hydrogen standard have been controlled: isotopic purity, depth profile, stability under ion irradiation and reproducibility. The standards were validated by the measurement of the resonant cross-section of the ¹³C(p,γ)¹⁴N reaction. The similarity of the resonance energy, the resonance width and the resonance strength measurements with those reported in literature confirms the validity of the proposed procedure for hydrogen standards. Therefore, this kind of target could be used to investigate all nuclear reactions in which a proton is involved, from reactions with astrophysical interest to the ones with concern in material analysis.     

Growth and photoluminescence of ZnO thin films on Si(1 1 1) by PLD in oxygen adequate ambient

Polycrystalline ZnO thin films were synthesized on Si(1 1 1) substrates by pulsed laser deposition (PLD) under oxygen sufficient condition at temperatures ranging from 550 to . The results of in situ reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) show that the (0 0 2) orientation of ZnO thin films is deteriorated, but the full-width at half-maximum (FWHM) of (0 0 2) peak decreases as the substrate temperature (T_s) increases. In photoluminescence (PL) spectra at room temperature (RT), all the ZnO thin films show small ultraviolet (UV) peak FWHMs in the range of 83-95 meV. The thin film prepared at exhibits the narrowest UV peak FWHM of 83 meV and the biggest intensity ratio (122) of UV emission (UVE) to deep-level emission (DLE). When the T_s increases to , a low-energy peak in the UV region at around 381 nm (3.25 eV) appears, which maybe result from a donor-acceptor-pair (DAP) transition and be a signal of excess incorporation of oxygen in the thin film.