Digital signal processing algorithms for nuclear particle spectroscopy are described. The algorithms are presented as recursive procedures, which can easily be programmed using modern computer ...programming languages. The input data flow was formed by particle detector pulses, preprocessed by a charge-sensitive preamplifier and transformed into a sequence of equidistantly sampled signals by a sampling analog-to-digital converter. The pile-up elimination procedure, the influence of the number of bits of the sampling analog-to-digital converter on the energy resolution of the spectrometer, and ballistic deficit correction are also considered. The pile-up elimination method was developed for fission fragment spectroscopy in the case of high α radioactivity of fissile targets (
239
Pu,
241
Am) using a Frisch-grid double ionization chamber. Since the intrinsic energy resolution of a spectrometer based on a double ionization chamber is much worse than that determined by the noise level of the charge-sensitive amplifier, an ultrapure germanium detector was used to provide the highest sensitivity to the errors introduced by measuring procedures. The effect of pile-up elimination procedure on the energy resolution was experimentally investigated at different source intensities. The main characteristics of the developed algorithms are compared with those of other processing procedures published in the literature.
The new experimental setup TANGRA (Tagged Neutrons & Gamma Rays), for the investigation of neutron induced nuclear reactions, e.g. (n,xn’), (n,xn’γ), (n,γ), (n,f), on a number of important isotopes ...for nuclear science and engineering (235,238U, 237Np, 239Pu, 244,245,248Cm) is under construction and being tested at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) in Dubna.
The TANGRA setup consists of: a portable neutron generator ING-27, with a 64-pixel Si charge-particle detector incorporated into its vacuum chamber for registering of α-particles formed in the T(d, n)4He reaction, as a source of 14.1 MeV steady-state neutrons radiation with an intensity of ∼5x107n/s; a combined iron (Fe), borated polyethylene (BPE) and lead (Pb) compact shielding-collimator; a reconfigurable multi-detector (neutron plus gamma ray detecting system); a fast computer with 2 (x16 channels) PCI-E 100 MHz ADC cards for data acquisition and hard disk storage; Linux ROOT data acquisition, visualization and analysis software. The signals from the α-particle detector are used to ‘tag’ the neutrons with the coincident α-particles. Counting the coincidences between the α-particle and the reaction-product detectors in a 20ns time-interval improves the effect/background-ratio by a factor of ∼200 as well as the accuracy in the neutron flux determination, which decreases noticeably the overall experimental data uncertainty.
The anomalous dependence of average prompt fission neutron (PFN) multiplicity on the fission fragment total kinetic energy of
252
Cf(sf) was investigated using digital signal processing (DSP). A twin ...Frisch-grid ionization chamber (TGIC) was used for fission fragment (FF) spectroscopy and PFN was registered with help of fast neutron detector (FND) on liquid scintillator base. The DSP apparatus was build up around the 8-channel fast synchronously sampling waveform digitizers (WFD). It was found that the main limitation of the experimental method, developed in ref. 1 for investigation of the PFN properties in neutron induced fission reaction
235
U(n,f),
239
Pu(n,f) etc is related to the FF energy loses of in the target backing. A modification of the method was suggested to overcome such a limitation.
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.
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.
A twin position-sensitive Frisch grid ionization chamber, intended as a fission fragment detector in experiments to study prompt fission neutron correlations with fission fragment properties, is ...presented. Fission fragment mass and energies are determined by means of the double kinetic energy technique, based on conservation of mass and linear momentum. The position sensitivity is achieved by replacing each anode plate in the standard twin ionization chamber by a wire plane and a strip anode, both readout by means of resistive charge division. This provides information about the fission axis orientation, which is necessary to reconstruct the neutron emission process in the fully accelerated fragment rest-frame. The energy resolution compared to the standard twin ionization chamber is found not to be affected by the modification. The angular resolution of the detector relative to an arbitrarily oriented axis is better than 7° FWHM. Results on prompt fission neutron angular distributions in 235U(n,f) obtained with the detector in combination with an array of neutron scintillation detectors is presented as a proof of principle.
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 efficient
α
‐particle
pile-up correction. This is important when considering the accurate measurement of fission-fragment characteristics of highly
α
‐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
α
‐emitter
, when applying the
α
‐particle
pile-up correction, the peak-to-valley ratio of the energy distribution was significantly improved. In addition, DA offers a very flexible 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.
On the Frisch–Grid signal in ionization chambers Al-Adili, A.; Hambsch, F.-J.; Bencardino, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2012, Letnik:
671
Journal Article
Recenzirano
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 Cf(sf)252, using two different grids, with 1 and 2mm 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: Cf(sf)252, U(n,f)235 and U(n,f)234. 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.
This paper presents a new algorithm for obtaining inter-frame and inter-view (inter-camera) correspondences to solve the problem of tracking an object labeled with infrared markers using a stereo ...pair taken simultaneously in the infrared region. In practice it is often necessary to track an object when it is impossible to have contact with it, for example, the tracking of facial movements using the motion capture technique (Motion Capture, 9, 10) to create realistic animation or the tracking of object movements when interacting with the augmented reality. In such cases contactless object tracking methods are used. In the classic version of this problem, two or more cameras are used to capture the object of interest. In order to restore three-dimensional coordinates of object points, it is necessary to triangulate the received projections of the points. In the case of the visible range, the problem of finding and matching points on the object can be solved using interest point descriptors 2. However, there are situations in which it is impossible to use the visible range data, for example, a uniformly colored or regularly textured object, which makes it senseless to use interest point descriptors. Thus, the use of interest point descriptors significantly limits the scope of application of algorithms because of the imposition of severe restrictions on the class of tracked objects, objects should have uneven texture. In turn, the motion capture method implies the tracking of an object of a predetermined shape, when it is not always possible to establish its shape. In this work, an alternative approach is proposed, i.e., the use of infrared markers and cameras that capture frames in the infrared range which makes the task of finding critical points irrelevant. On the other hand, infrared markers on cameras that operate in the infrared range are indistinguishable from each other. Therefore, there is the problem of finding correspondences which in the case of interest point descriptors is solved by the very nature of the descriptors. In this paper, we describe algorithms that make it possible to restore point correspondences by a sequence of stereo pair images (Fig. 1) and its calibrations. In this case, epipolar constraints and a voting scheme based on the greedy algorithm are used.
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