MULTICHANNEL PULSE HEIGHT ANALYSER USING FPGA FOR DATA ACQUISITION

This document gives the description of a multichannel pulse height analyser which is implemented using FPGA technology for high speed data acquisition and analysis. Multichannel analysers (MCA) are used globally in various laboratories in the application of nuclear spectroscopy. The most common use of a MCA is to plot the energy spectrum or to find the decay rate of the radio material under test. In the following context we have described the designing of an open source multichannel pulse height analyzer which uses a high speed ADC for data acquisition and displays the output on a graphical user interface designed using labVIEW in a computer.

Correction for counting losses in X-ray diffractometry

Non-extended and extended dead-time models, a pulse-height analyser (PHA) windowing model, and a model intermediate between the non-extended and extended models for losses in counting methods are compared. The validities of the methods are examined by application to the analysis of powder diffraction peak intensity profiles measured by a foil method. The intermediate model including parameters for the dead-time and degree of extension can reproduce both the non-extended and the extended models and also intermediate dependence between the two models. A convenient approximate formula for the intermediate model, the maximum relative deviation of which is 0.0003, is also proposed. The determination of the parameters and a correction for the measured intensities can easily be achieved by applying the approximate model, because it provides simple formulae for the correction function expressed as a combination of elementary functions. Experimental and analytical methods for precise evaluation of the parameters to specify the counting losses are also presented. Systematic deviations of the observed dependence from the non-extended and extended dead-time models have been detected by the precise analyses of experimental data, while the PHA windowing model, intermediate model and its approximation have reproduced the observed dependence within the experimental errors.

The Damage Capacity of Cavitating Flow From Pulse Height Analysis

Digital pulse amplitude acquisition systems are reviewed and an analogue pulse height analyser (PHA) is described. Cavitation experiments are reported in which pressure pulses in the liquid (water) are picked up by a flush mounted pressure transducer and measured using the PHA. Tests were carried out on two cavitation sources: a 60 deg symmetric wedge and a circular cylinder. Despite generating similar r.m.s. noise levels the wedge is 21 times as damaging as the circular cylinder at peak noise flow conditions (at V = 16 m/s). By imposing thresholds on the spectra parameters it had been possible to find a linear calibration beween noise and erosion applicable to both cavitation sources over a range of flow velocities. A good correlation between cavitation noise and erosion was found by simply measuring the number of pulses above a suitable threshold.