Pile-up Rejection Circuit Research Articles

Liquid scintillators and composites in fast neutron detection

Helium-3 world crisis requires a development of new methods of neutron detection to replace commonly used 3He proportional counters. One of the option is application of liquid scintillators widely used in detection of fast neutrons, mostly in physics experiments, especially in applications where large volumes are required. Moreover, recently studied 10B loaded liquid scintillators cover detection of neutrons down to thermal energy. The several years' studies of liquid scintillators in our laboratory, brought us a knowledge about their efficiency to neutron detection, gamma sensitivity, etc. We have also tested composite scintillators, which are an alternative to organic single crystals, used in the 70's last century.In the report, we will present the results of the study of several liquid scintillators, also 10B loaded, as well as high flashpoint ones. We also show the neutron detection properties of some samples of composite scintillators. Composites are based on small grains of p-terphenyl or stilbene, introduced into a polymer matrix, which acts as a diffuser. The composite is encapsulated in a housing made of organic glass. P-terphenyl and stilbene are organic scintillators, which were commonly used in the seventies last century. They are characterized by good neutron/gamma discrimination properties. The present studies covers neutron/gamma discrimination by the zero-crossing method, a comparison of detection efficiency of liquid scintillators to 3He detectors and methods to reduce their gamma-ray sensitivity. In conclusion, a detection system, based on several small liquid cells of 2′′ × 2′′, is preferred, with pulse shape discrimination circuit equipped with the pile-up rejection circuit (PUR), as well as lead and tin shielding.

Comprehensive radioassays of samples using the PANDA device

The PANDA (Particles And Non-Destructive Analysis) device is a measuring system developed for non-destructive analysis of samples for safety, security and safeguards. It consists of two complementary measurement positions. The position sensitive alpha–gamma coincidence setup of PANDA has been updated with a pile-up rejection circuit. This article demonstrates, using a 241Am source, that this circuit can be used to identify gamma-ray sum peaks in the spectra. The second measurement position reported here hosts a 10-mm2 windowless silicon drift detector that detects electrons and X-rays with a very good energy resolution. An experimental value of 0.30keV for full width at half maximum was obtained at 17.7keV energy (Np X-rays). Conversion electron spectrometry, for example, provides an independent, complementary means to study actinides whose low energy transitions are often highly converted.

Oxygen depth profiling using the 16O(d,α) 14N nuclear reaction

The excitation function of the 16O(d,α) 14N nuclear reaction has been determined in the deuteron energy range of 0.88–2.28 MeV. Major resonances are observed at deuteron energies of 0.98, 1.31, 1.53, 1.60, 1.73 and 2.22 MeV. The present results show good agreement with those of Haase and Khubeis, however there is a shift of 60 keV in the first resonance compared with the measurements of Amsel. The use of a thin surface barrier detector ( t = 22 μm) and a bias voltage of +20 V coupled with a proper pile-up rejection circuit has allowed the determination of the oxygen depth profiling to a resolution of 16 nm for thick targets. This method is efficient in eliminating interferences from other nuclear reactions such as 16O(d,p) 17O and 12C(d,p) 19C, where emitted protons have severely obscured α-particles from the 16O(d,α) 14N reaction. A 1.08 MeV deuteron beam has been employed to increase the α-yield from the target. The target has been tilted at 70° to enhance depth resolution. This reaction is well suited for the determination of oxygen concentration in oxides of high temperature superconductors.

Digital pulse-shape analyzer based on fast sampling of an integrated charge pulse

A novel configuration for pulse-shape analysis and discrimination has been developed. The current pulse from the detector is sent to a gated integrator and then sampled by a flash analog-to-digital converter(ADC). The sampled data are processed digitally, thus allowing implementation of a near-optimum weighting function and elimination some of the instabilities associated with the gated integrator. The analyzer incorporates pileup rejection circuit that reduces the pileup effects at high counting rates. The system was tested using a liquid scintillator. Figures of merit for neutron-gamma pulse-shape discrimination were found to be: 0.78 for 25 keV (electron equivalent energy) and 3.5 for 500 keV.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Detailed simulation of pile-up effects in single spectra acquisition

A detailed study of pile-up effects in a single acquisition channel has been performed. A computer code of the Monte Carlo type has been written to simulate the acquisition process taking into account both the detailed shape of the input signals to the ADC as well as the characterictics of an auxiliary pile-up rejection circuit. The results of the simulation are used to purge from pile-up effects our experimental data on the energy spectrum of the beta rays from a 35S source.

A new method for quantification of image distortion due to pile-up in scintillation cameras

Characterization of the count-rate performance of scintillation cameras should include not only the specification of count losses. At high count rates, there is also an image distortion due to the mispositioning of pile-up events. In this paper a simple and clinically relevant procedure to quantify this distortion is presented. The images of a square uniform technetium-99m phantom at high and low count rates are used. The fraction of the total counts being correctly positioned is determined as the peripheral count density divided by the total average count density. This ratio, corrected for the camera non-uniformity at low count rates, is called the 'positioning ability'. According to the National Electrical Manufacturers' Association (NEMA), the 'system count rate performance with scatter' should be reported as the measured count rate giving 20% count losses. In this paper it is suggested that this measure be complemented by a measure of the fraction correct positioned events at this count rate. This fraction, the 'high count rate positioning ability', can be easily and accurately measured using our method. The method has been tested on two different scintillation cameras. For one of them the high count rate positioning ability was determined as 91% at a measured count rate of 30,000 s-1 with 20% count losses. For the other camera, the corresponding figures were 88% at 59,000 s-1 and close to 100% at 38,000 s-1, before and after the installation of a new pile-up rejection circuit, respectively.

A pulse shape discriminator with high precision of neutron and gamma ray selection at high counting rate

A pulse shape discriminator based on the zero-crossing principle is described. Due to dc negative feedback loops stabilizing the shaping amplifier and the zero-crossing discriminator, the working of the circuit is not affected by the high counting rate and the temperature variations. The pileup rejection circuit built into the discriminator improves the quality of the n-γ separation at high counting rates. A full γ-ray rejection is obtained for a recoil energy of electrons down to 25 keV. At high counting rates the remaining γ-ray contribution is evidently due to the pileup effect which is equal to about 2% at 4 × 10 5 counts/s.

Microanalysis of fluorine using the 19F(p, α 0) 16O reaction

The 19 F(p, α 0 ) 16 O nuclear reaction seems to be an excellent method for high resolution fluorine depth profiling. Target tilting, a pulse pileup rejection circuit and a high resolution solid state detector were employed. Magnesium fluoride, calcium fluoride and fluorohydrocarbon targets of different thickness were used. The detection of the outcoming alpha particles was done with and without Kapton foils. A depth profile resolution of 10 nm was obtained and 3 nm appears to be feasible.

Measurement of oxygen depth profiles using the 16O(d, α) 14N reaction and a fast pulse pile-up rejection circuit

While the 16O(d, α) nuclear reaction is the best nuclear reaction method for high resolution oxygen depth profiling, its use has been hampered by interfering reactions and electronic pulse pile-up. Employing a Si detector of 22 nm thickness, target tilting and a pulse pile-up rejection circuit with a pulse-pair resolution of 30 ns has made fast routine measurements easy. A depth resolution of 13 nm has been obtained and one of 5 nm appears feasible. Depending on the target composition, a detection sensitivity of down to 0.01 at.% oxygen is realizable.

Rejection of Nal Pulse Pile-Up in Linac Bremsstrahlung Measurements

A pulse pile-up rejection system was developed and used successfully with a NaI gamma spectrometer to measure the bremsstrahlung spectral distribution from a 0.2-radiation-length gold-tungsten target bombarded by high energy electrons from a pulsed electron linear accelerator. The system utilizes a double differentiation technique to reject those scintillation events where more than one gamma ray is detected during a single linac pulse. The pulse pile-up rejection circuit was used effectively over a gamma energy range of 0.25 Mev to 21 Mev and increased data collection speed by about a factor of 20. The performance of the system agrees with theoretical predictions calculated on the basis of Poission statistics. Gamma spectral distributions measured with the system at the EG&G linac are presented to demonstrate utilization of the system.

Gamma Rays from Neutron Capture in Helium-3 and Deuteron Capture in Deuterium

The gamma rays from the ${\mathrm{He}}^{3}(n, \ensuremath{\gamma}){\mathrm{He}}^{4}$ and the $\mathrm{D}(d, \ensuremath{\gamma}){\mathrm{He}}^{4}$ reaction have been observed. The gamma detector, a 3-in.\ifmmode\times\else\texttimes\fi{}4-in. NaI crystal, was surrounded by a plastic scintillator to eliminate the cosmic-ray background. A pileup rejection circuit was used to reduce the background from neutron induced reactions in the NaI. The cross section of the ${\mathrm{He}}^{3}(n, \ensuremath{\gamma}){\mathrm{He}}^{4}$ reaction at 4 MeV is $\ensuremath{\sigma}=5$ \ensuremath{\mu}b/sr at 90\ifmmode^\circ\else\textdegree\fi{}. The intensity ratio, $\frac{I(90\ifmmode^\circ\else\textdegree\fi{}}{I(45\ifmmode^\circ\else\textdegree\fi{})}\ensuremath{\approx}2$, agrees with that expected for electric dipole radiation ($\ensuremath{\Delta}M=0$). The $\mathrm{D}(d, \ensuremath{\gamma}){\mathrm{He}}^{4}$ reaction at 1.35 MeV has a cross section $\ensuremath{\sigma}=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}33}$ ${\mathrm{cm}}^{2}$/sr at 45\ifmmode^\circ\else\textdegree\fi{}.