Counting-loss correction for X-ray spectra using the pulse-repairing method

Facing the technical problem of pulse distortion caused by frequent resetting in the latest high-performance silicon drift detectors, which work under high-counting-rate conditions, a method has been used to remove false peaks in order to obtain a precise X-ray spectrum, the essence of which eliminates distorted pulses. Aiming at solving the problem of counting-loss generated by eliminating distorted pulses, this paper proposes an improved method of pulse repairing. A 238Pu source with activity of 10 mCi was used as the measurement object, and the energy spectrum obtained by the pulse repairing method was compared with that obtained by the pulse elimination method. The ten-measurement results show that the pulse repairing method can correct the counting-loss caused by the pulse elimination method and increase peak area, which is of great significance for obtaining a precise X-ray energy spectrum.

Counting-loss correction for X-ray spectroscopy using unit impulse pulse shaping

High-precision measurement of X-ray spectra is affected by the statistical fluctuation of the X-ray beam under low-counting-rate conditions. It is also limited by counting loss resulting from the dead-time of the system and pile-up pulse effects, especially in a high-counting-rate environment. In this paper a detection system based on a FAST-SDD detector and a new kind of unit impulse pulse-shaping method is presented, for counting-loss correction in X-ray spectroscopy. The unit impulse pulse-shaping method is evolved by inverse deviation of the pulse from a reset-type preamplifier and a C-R shaper. It is applied to obtain the true incoming rate of the system based on a general fast–slow channel processing model. The pulses in the fast channel are shaped to unit impulse pulse shape which possesses small width and no undershoot. The counting rate in the fast channel is corrected by evaluating the dead-time of the fast channel before it is used to correct the counting loss in the slow channel.

Multi-tube area detector developed for reactor small-angle neutron scattering spectrometer SANS-J-II

A newly developed multi-tube area detector for a small-angle neutron scattering (SANS) spectrometer (SANS-J-II) at the research reactor JRR-3 in Tokai, Japan, has been implementedviathe use of one-dimensional position-sensitive3He detectors (tubes). Ninety-six active tubes of 8 mm in diameter and 650 and 580 mm in length were filled with 15 atm (1.52 MPa) of3He and aligned vertically parallel in order to cover a sufficiently large area for small-angle scattering measurement. These tubes are enclosed in an air chamber together with neutron encode and GATENET modules (VME boards), which compose a standard data acquisition system for the spallation neutron source of the Japan Proton Accelerator Research Complex. This system facilitates the acquisition of time-of-flight neutron event data. The multi-tube detector is mounted on a truck moving in a vacuum chamber of the SANS spectrometer. After discriminating noise originating from γ-rays, and calibrating the positions and sensitivities of individual tubes, the resolution was determined (i.e.channel widths along parallel and vertical directions along a tube). The counting rate of one tube was determined to be 1.4 × 103counts per second with a counting loss of 1%. This implies that the new detector, composed of 96 tubes, can detect more than 105neutrons per second with a counting loss of 1%. To demonstrate its use, small-angle scattering originating from a diblock copolymer film with a highly oriented lamellar microdomain was observed. The data acquisition in event mode has a great advantage in time-resolved measurements that are synchronized with external stimuli imposed on a sample.

Statistical properties of measured X-ray intensities affected by counting loss

The statistical properties of X-ray intensities measured with counting systems have been experimentally investigated. A formula of statistical variance for the intermediately extended dead-time model is proposed and compared with the experimentally evaluated variance obtained from repeated measurements based on Chipman's foil method applied to X-ray detection systems of laboratory and synchrotron powder diffractometers. It has been found that the variance of the observed intensities is smaller than the average of count, as has been suggested by conventional theoretical models for counting loss. It is shown that the statistical errors can be predicted by applying an intermediately extended dead-time model including dead-time τ and degree of extension ρ as fixed parameters.

Monte Carlo simulation of the effect of counting losses on measured X-ray intensities

The statistical properties of intensities affected by counting loss based on conventional non-extended and extended dead-time models are examined by a Monte Carlo method. It has been confirmed that the variance of the counted pulses for the non-extended dead-time model with the rate of generated pulsesr and the dead-time τ is given by \sigma_{\rm non}^2 = \mu_{\rm non}/(1+r \tau)^2, while that for the extended dead-time model is given by \sigma_{\rm ext}^2 = \mu_{\rm ext} [1 - 2r\tau \exp(-r \tau)], as proposed by Laundy & Collins [(2003).J. Synchrotron Rad.10, 214–218], for the mean values of counted pulses μnonand μext, respectively. Practical formulae to estimate the statistical errors of the corrected intensities are also presented.