We propose a new method for modeling the instrumental resolution of time-of-flight neutron spectrometers based on an improved version of the Violini approach. The key improvements are a switch from an instrument based approach to a neutron distribution one, to take into account a non-perfect beam collimation along the entire neutron path and a finite sample size. We tested the methods on both elastic and inelastic, coherent and incoherent examples. The present model agrees well with the measured resolution and provides a better estimation than Violini’s method. The sample size is especially important for incoherent scattering at large neutron wave-vector. Similarly, the proper modeling of the beam collimation is important at large wavelengths.
As a radiation detection material, CdZnTe (CZT) exhibits excellent performance at room temperature. With the development of CZT detectors, unipolar charge sensitive technology has effectively reduced the influence of incomplete hole collection on the energy resolution. In order to achieve high-resolution and high efficiency for MeV gamma-ray astronomy observation, a capacitive Frisch-grid CZT detector with dimensions of 5 & times;5 & times;20 mm3 has been fabricated and systematically tested. Its leakage current is 3.6 nA at 3000 V, and the energy resolution (FWHM) is 1.20% at 662 keV (2800 V). Additionally, the electron mobility lifetime product ((& micro;z)e) has been evaluated. The comparison of simulation and experimental results suggest that the (& micro;z)e is close to 1.0 & times; 10-1 cm2/V, which is significantly higher than the value obtained using the Hecht equation and the optimized direct measurement method.
This paper presents a novel digital cusp-flat-top shaping algorithm aimed at improving both the counting rate and the imaging quality of capacitive anode detectors. The method is developed as an enhancement of conventional cusp shaping, combining the advantage of cusp filtering in approximating an infinite impulse response with the noise-suppression capability of trapezoidal shaping. Compared with conventional trapezoidal shaping, the proposed algorithm effectively mitigates pulse pile-up, thereby satisfying detection requirements under high counting-rate conditions. The algorithm was implemented on a field-programmable gate array (FPGA) using the System Generator and Vivado platforms, and its performance was validated through software simulation, FPGA-based verification, and a benchtop imaging experiment using a capacitive anode detector with a low-pressure mercury lamp as the input light source and a dense pinhole-array mask as the test target. The results demonstrate that the algorithm achieves significant suppression of electronic noise and effective reduction of pulse pile-up. A minimum resolvable pulse interval of 0.4 mu s was obtained, corresponding to a maximum counting rate of 2500 kcps, while the reconstructed images achieved an averaged spatial resolution of 17.62 +/- 1.73 line pairs per millimeter. These findings indicate that the proposed algorithm offers a practical and efficient solution for digital signal processing in high-performance capacitive anode detectors.
The design of the compact gantry is critical for reducing the footprint and construction costs of proton therapy facilities. In this study, a compact gantry using FeCo-alloy magnets was designed with a short source-to-axis distance (SAD). A downstream scanning layout is implemented, with the beam optics optimized and verified through error analysis and orbit correction. A hybrid lamination strategy, combining FeCo pole tips with silicon steel yoke, was implemented to reduce the material costs of dipole magnets. This approach achieved a maximum magnetic field of 1.72 T and a reduced bending radius of 1.35 m, while maintaining an integrated field uniformity of +/- 3.8 & times; 10-4. The beam quality was validated through Monte Carlo simulations using BDSIM, which incorporated a detailed beamline model and a realistic nozzle with helium-filled chamber. Despite the emittance growth induced by beam-material scattering in the nozzle, the transverse beam spot size increase at the isocenter was limited to be less than 60% for 70 MeV protons. Furthermore, the beamline maintained a transmission efficiency above 94% across the entire 70-230 MeV energy range. With an estimated total weight of approximately 80 tons and a length of 8 m, this gantry design provides a reference for the development of compact proton therapy systems.
Accurate neutron spectrum measurement is vital for nuclear energy and nuclear medicine applications. While iterative unfolding methods are favored for their efficiency and accuracy, their precision critically depends on the initial guess spectrum. Without prior information of the measured field, a non-informative "all-ones flat spectrum" is typically used, limiting further accuracy improvements. This paper proposes a method to construct preset spectra based on analytical neutron spectrum models (Watt, Maxwell-Boltzmann, moderation, evaporation spectra), incorporating physical characteristics to provide more instructive initial values for iterative unfolding. Numerical validation using IAEA-403's PTB multi-sphere response functions and 251 radiation-protection scenario spectra shows that the moderation-model-based preset spectrum reduces average relative deviation by similar to 20% compared to the flat preset spectrum, achieving superior accuracy in 80.1% of scenarios and comparable accuracy in 17.1%. The method also suppresses spurious structures from uneven energy-group division, enhancing spectral restoration. Cf-252 neutron source experiments confirmed a 26.4% reduction in deviation and improved restoration using the moderation preset spectrum. The proposed method offers a clear, versatile approach compatible with various unfolding algorithms, supporting high-accuracy broad-energy neutron spectrometry. (c) 2001 Elsevier Science. All rights reserved.
