Digital signal processing application in nuclear spectroscopy

Digital signal processing algorithms for nuclear particle spectroscopy are described along with a digital pile-up elimination method applicable to equidistantly sampled detector signals pre-processed by a charge-sensitive preamplifier. The signal processing algorithms provided as recursive one- or multi-step procedures which can be easily programmed using modern computer programming languages. The influence of the number of bits of the sampling analogue-to-digital converter to the final signal-to-noise ratio of the spectrometer considered. Algorithms for a digital shaping-filter amplifier, for a digital pile-up elimination scheme and for ballistic deficit correction were investigated using a high purity germanium detector. The pile-up elimination method was originally developed for fission fragment spectroscopy using a Frisch-grid back-to-back double ionisation chamber and was mainly intended for pile-up elimination in case of high alpha-radioactivity of the fissile target. The developed pile-up elimination method affects only the electronic noise generated by the preamplifier. Therefore, the influence of the pile-up elimination scheme on the final resolution of the spectrometer investigated in terms of the distance between piled-up pulses. The efficiency of developed algorithms compared with other signal processing schemes published in literature

Delayed neutron yield measurement on thermal neutron induced fission of 237Np using cross-correlation technique

The measurement procedure based on the continuous thermal neutron beam modulation with a mechanical chopper was developed for delayed neutron yield measurement of the thermal neutron induced fission of 237Np. The idea of the procedure is similar to that, widely used in modern computer communications for the non-authorized data access prevention. The data is modulated with predefined pattern before transmission to the public network and only recipient that has the modulation pattern is able to demodulate it upon reception. For the thermal neutron induced reaction applications the thermal neutron beam modulation pattern was used to demodulate the measured delayed neutron intensity signals on the detector output, resulting nonzero output only for the detector signals correlated with the beam modulation. The comparison of the method with the conventional measurement procedure was provided and it was demonstrated that the cross-correlation procedure has special features making it superior over the conventional one especially when the measured value is extremely small in comparison with the background. Due to strong sensitivity of measurement procedure on the modulation pattern of the neutron beam one can implement the modulation pattern of specific shape to separate the effect of the thermal part of the beam from the higher energy one in most confident way in the particular experiment. The remarkable property of our method is related to the unique possibility of separation the effects caused exclusively by the thermal neutrons using the neutron TOF measurement available on the IBR-2 pulsed reactor

Comparison of Digital and Analogue Data Acquisition Systems for Nuclear Spectroscopy

In the present investigation the performance of digital data acquisition (DA) and analogue data acquisition (AA) systems are compared in neutron-induced fission experiments. The DA results are practically identical to the AA results in terms of angular-, energy- and mass resolution, and both compare very well with literature data. However, major advantages were found with the digital techniques. DA allows for a very effcient alpha-particle pile-up correction. This is important when considering the accurate measurement of fission-fragment characteristics of highly alpha-active actinide isotopes relevant for the safe operation of generation IV reactors and the successful reduction of long-lived radioactive nuclear waste. In case of a strong alpha-emitter, when applying the alpha-particle pile-up correction, the peak-to-valley ratio of the energy distribution was improved. In addition, DA offers a very exible expanded off-line analysis and reduces the number of electronic-modules drastically, leading to an increased stability against electronic drifts when long measurement times are required.JRC.D.4-Nuclear physic

On the Frisch–Grid signal in ionization chambers

A recent theoretical approach concerning the grid-inefficiency (GI) problem in Twin Frisch–Grid Ionization Chambers was validated experimentally. The experimental verification focused on the induced signal on the anode plate. In this work the investigation was extended by studying the grid signal. The aim was to verify the grid-signal dependency on the grid inefficiency σ. The measurements were made with fission fragments from , using two different grids, with 1 and 2 mm wire distances, leading to the GI values: σ=0.031 and σ=0.083, respectively. The theoretical grid signal was confirmed because the detected grid pulse-height distribution was smaller for the larger σ. By applying the additive GI correction approach, the two grid pulse heights were consistent. In the second part of the work, the corrected grid signal was used to deduce emission angles of the fission fragments. It is inconvenient to treat the grid signal by means of conventional analogue electronics, because of its bipolarity. Therefore, the anode and grid signals were summed to create a unipolar, angle-dependent pulse height. Until now the so-called summing method has been the well-established approach to deduce the angle from the grid signal. However, this operation relies strongly on an accurate and stable calibration between the two summed signals. By application of digital-signal processing, the grid signal's bipolarity is no longer an issue. Hence one can bypass the intermediate summation step of the two different pre-amplifier signals, which leads to higher stability. In this work the grid approach was compared to the summing method in three cases: , and . By using the grid directly, the angular resolution was found equally good in the first case but gave 7% and 20% improvements, respectively, in the latter cases.JRC.D.4-Nuclear physic