Frisch-grid Ionization Chamber Research Articles

A method to simulate Twin Frisch-grid ionization chamber response to fission fragments

In this study, the response of a Twin Frisch-grid ionization chamber (TFGIC) to fission fragments (FFs) was investigated using finite element and Monte Carlo methods. The entire process of the fission experiments, including FFs generation, gas ionization, electron drift and collection, and induced charge signal were well reproduced. Through data analysis, pulse height spectra from the anode and grid were transformed into energy and emission-angle information for the FFs. By means of double energy method, the pre-neutron emission fission fragment mass and total kinetic energy (TKE) can be finally determined. Experimental and calculated data of the mass and TKE distribution are shown in good agreement.

Instrumentation for correlated prompt [formula omitted] emission studies in coincidence with fission fragments

Recent theoretical and experimental results have brought renewed interest and focus on the topic of fission fragment angular momentum. Measurements of neutrons and γ rays in coincidence with fission fragments remain the most valuable tool in the exploration of fission physics. To achieve these scientific goals, we have developed a system that combines a state-of-the-art fission fragment detector and n−γ radiation detectors. A new twin Frisch-gridded ionization chamber has been designed and constructed for use with a spontaneous fission source and an array of forty trans-stilbene organic scintillators (FS-3) at Argonne National Laboratory. The new ionization chamber design we present in this work aims at minimizing particle attenuation in the chamber walls, and provides a compact apparatus that can be fit inside existing experimental systems. The ionization chamber is capable of measuring fission fragment masses and kinetic energies, whereas the FS-3 provides neutron and γ-ray multiplicities and spectra. The details of both detector assemblies are presented along with the first experimental results of this setup. Planned event-by-event analysis and future experiments are briefly discussed.

New trapezoid-shaped Frisch-grid ionization chamber for low-energy particle measurements

A new trapezoid-shaped Frisch-grid ionization chamber (TFG-IC) has been built as a part of a varDelta {E}-E telescope system for the detection and identification of charged particles at energies down to a few MeV. To study the effect of the drift electric field uniformity, two types of sealed windows, namely a pair of SSA (split-strip aluminized mylar film) and a pair of DSA (double-sided aluminized mylar film) sealed windows have been investigated. The detector’s performances were studied using a standard ^{241}Am source at different gas pressures, and the total energy-deposit resolution achieved is about 1.1%(FWHM). The varDelta {E}-E telescope, which was composed of TFG-IC and a DSSSD (double-sided silicon strip detector), has been tested using a three-component alpha source and the ^{241}Am source under laboratory conditions. The results show that the energy resolution with the SSA sealed windows which provide uniform drift electric field has a smaller fluctuation than that with the DSA ones; the fluctuations are about 1% and 4% for the former and the latter, respectively. Simulations using the COMSOL software also confirmed the electric-field distortion at the edge of the detector with the DSA windows. A correlation curve between energy resolution and energy deposit of charged particles at various gas pressures and for two gas species is derived for TFG-IC with the SSA sealed windows using the measurement with the ^{241}Am source. Incorporating the above results, we performed Monte Carlo simulations to evaluate the particle-identification capability of the telescope. The results show that the telescope can be extended to the identification of low-energy particles.

Detection of correlated fission fragments with a twin Frisch-grid ionization chamber

Twin Frisch-grid ionization chambers (TFGICs) have been widely used in the measurement of total kinetic energy (TKE), angular distribution, mass, and charge of the correlated fission fragments. To study these correlated fission parameters, we have developed a TFGIC with a digital acquisition system for use at both the Chinese Mianyang research reactor (CMRR) and neutron science facility in the Institute of Nuclear Physics and Chemistry (INPC), as well as the China Spallation Neutron Source (CSNS). The distribution of the electric field was investigated with Garfield toolkit, the results showed that the ratio of the electric field of the collect region to the drift region (Ec /Ed ) must be greater than a critical value Z (1.78). An individual experiment, carried out with a compound alpha source (241Am and 243Am), was used to validate the preliminary performance of this detector. The effects of the electric field on the anode pulse height agreed well with the simulation results. Furthermore, the results also indicated that the energy resolution of (68.40 ± 1.07) keV at 5.39 MeV (243Am) and (69.67 ± 1.09) keV at 5.49 MeV (241Am) could be achieved. An initial in-beam fission experiment of 235U reaction with 14 MeV neutrons was also performed to test the setup, and the results showed that the reconstructed emission angle could achieve a resolution of 0.221 ± 0.002 on the difference of the cosines determined from both halves of TFGIC. The present work primarily reported the development of a TFGIC with a digital acquisition system in INPC.

Study on grid inefficiency for mesh-type Frisch-grid ionization chambers

In this study, the grid inefficiency sigma for a mesh-type Frisch-grid ionization chamber (FGIC) was investigated using the finite element method and Monte Carlo method. A grid inefficiency sigma evaluation model was developed, which can determine the relationship between the physical parameters of the detector and the grid inefficiency with reasonable accuracy. An artificial neural network (ANN) was applied in the investigation of the grid inefficiency factor sigma . The trained ANN was able to describe and predict the grid inefficiency factor sigma with different physical parameters for the mesh-type FGIC. Thus, it can serve as a reference for the development of mesh-type FGICs and correct grid inefficiency sigma measurements.

A Monte Carlo simulation for studying grid inefficiency of Frisch grid ionization chamber

The grid inefficiency (GI) of Frisch grid ionization chambers (FGICs) must be considered in the case of accurate energy measurements. A Monte-Carlo model has been developed based on the Garfield and SRIM toolkits to investigate the GI of FGIC. It could simulate the charge signals from different electrodes without considering the electrical noises and random effects in the experiments. Computations made with the weighting potential and charge signals of FGIC exemplify the possibilities of this model. The GI values obtained with different methods showed the difference among the existing approaches in the literature. In addition, the results of homogeneous deformations of one wire over one grid period showed that deformation in the grid plane caused more distortion on GI than that perpendicular to the grid plane. An individual experiment was also carried out with a compound alpha source (241Am and 243Am) to validate the feasibility of this model. The results showed that the raw pulses and GI values obtained from the simulation agreed well with those measured from the experiment. The present work showed that this Monte-Carlo model could be well applied to investigate such type of detector, which could provide great conveniences for future work to measure the total kinetic energy of the fission fragments.

Characterize the grid inefficiency correction of Frisch grid ionization chamber with Garfield and SRIM

Grid inefficiency (GI) correction is critically important to accurately determine the energy and emission angle of charged particles in Frisch grid ionization chambers (FGIC). Presently, three correction methods have been proposed in the literature. All these three methods rely strongly on the accurate and stable calibration between two different electrical chain gains in experiments. To avoid these challenges, they are firstly investigated with Monte Carlo method by using Garfield and SRIM toolkit. Two types of grid wire (diameter 90 and 180 μm) were simulated to investigate the impacts of GI correction on energy correction, and ten different emission angles were adopted to estimate the effects of these correction methods on the angle reconstruction. The simulation results clearly distinguished the differences among these correction methods in energy determination. The correlation analysis (R = 0.99) among these different correction methods indicated that the impact of either correction approach is small on the determination of emission angle. The present work firstly investigates the effects of GI correction on emission angle with Monte Carlo methods, which is the basis of future work to measure the total kinetic energy and mass distribution of Fission Fragment (FF).

Exploration of grid scheme for Frisch-grid ionization chamber

A new Frisch-grid ionization chamber has been built to explore the appropriate choice of Frisch-grid. Detailed studies of the relationship between grid geometries and detector performance have been performed with an ^{241}Am source. This paper describes and compares the energy resolution of ionization chambers with parallel-wire and mesh grids of different grid parameters. Some specific recommendations for grid selection are provided based on the data currently available. To obtain optimal energy resolution, the operating voltage of the chamber must satisfy the condition of minimum electron collection on the grid with distinct geometries and parameters, respectively. Since there is no established theory applicable to both types of grids, we have devised a careful simulation procedure incorporating the COMSOL and Garfield++ codes to search for the conditions of the minimum electron collection on the grid. The simulation results fit the experimental data well, suggesting that this simulation method successfully predicts the suitable voltage setting when using a mesh grid or parallel wires grid as the shielding electrode.

Development and testing of a Frisch-Grid Ionization Chamber for the measurement of low activity of alpha-particle emitters

Development and testing of a Frisch-Grid Ionization Chamber for the measurement of low activity of alpha-particle emitters

The impacts of the ballistic deficit and electron attachment on the pulse shapes of the Frisch-grid ionization chamber

The pulse shapes of the Frisch-grid ionization chamber (GIC) will be affected by the ballistic deficit and electron attachment. Theoretical derivations and experiments are carried out to clarify the impacts of the two effects on the pulse shapes of the GIC. It is found that the anode amplitude increases with the decrease of the cosine of the emitting angle under the influence of the ballistic deficit, while the anode amplitude decreases with the decrease of the cosine of the emitting angle under the influence of the electron attachment. These opposite variation trends caused by the ballistic deficit and electron attachment could cancel each other out when the attachment probability per unit time equals the inverse of the time constant of the GIC circuit, which improves the energy resolution of the GIC, although the anode amplitude is reduced. The difference of the two variation trends provides a method to judge whether the working gas of the GIC contains electronegative gases.

Research on the electron attachment of oxygen using a Frisch-grid ionization chamber

The electron attachment is studied using a Frisch-grid ionization chamber (GIC) with different number densities of O2 in the working gas and different reduced electric fields. The influence of the electron attachment on the cathode–anode two-dimensional amplitude spectrum of the GIC is measured and evaluated. The method of measuring the attachment probability per unit time using the GIC is established. The quantitative and systematic relationships between the attachment probability per unit time and the number density of O2 and the reduced electric field are obtained from experiments, where the number densities of O2 are from 0 to 2.29 × 1017 cm −3 and the reduced electric fields are from 22 to 577 V/cm/bar. The three-body attachment coefficients of O2 at different mean electron energies (< 1 eV) are measured, which are consistent with those from previous works. For the first time, the three-body attachment coefficients of CO2 at different mean electron energies (<1 eV) are measured. It is found that the three-body attachment coefficients of O2 and CO2 are nearly the same at the same mean electron energy.

Improved method to measure the electron drift velocity using the Frisch-grid ionization chamber

An improved method for processing digital signals of the Frisch-grid ionization chamber to measure the electron drift velocity is proposed, which is based on the analysis of the cathode signal and the differentiated cathode signal. This method allows the real-time measurement eliminating the influence of electron diffusion and it is suitable for working gases with electron loss from the electronegative impurities. The electron drift velocities in gas mixtures of Ar + 9.86% CH4, Ar + 3.45% CO2, (Ar + 3.45% CO2) + x% O2 (x is less than 0.33), (Ar + 3.45% CO2) + y% Air (y is less than 2.09) have been measured, and the results are compared with existing measurements and calculations using MAGBOLTZ-11.4 code. Meanwhile, the influences of the impurities of oxygen and nitrogen on the electron drift velocity are analyzed.

Gating of charge sensitive preamplifiers for the use at pulsed radiation sources

The development of a switch circuit to gate charge sensitive preamplifiers for use at pulsed radiation sources will be presented. This development was used for the 16O(n,α)13C reaction measurement with a Double Frisch Grid Ionization Chamber (DFGIC) at the neutron time-of-flight facility CERN n_TOF in Geneva, Switzerland. Intense instantaneous radiation which is produced in the spallation target of the n_TOF facility (γ-flash) can saturate charge sensitive preamplifiers and prevent signals from being registered in the detection system. The switch circuit made it possible for the first time to perform a measurement with the DFGIC with γ-flash gated off at n_TOF. Nano-second gating of charge sensitive preamplifiers has a wide range of applicability at pulsed radiation sources, where short bursts of radiation must be gated off to avoid saturation, e.g. with HPGe detectors for γ-ray detection. Nano-second gating requires the stray-capacitance of the wideband reflective switch to be compensated to avoid a strong signal during the switch operation. Spectral analysis of the switch circuit shows that additional noise is insignificant.

Prompt fission neutron yields in thermal fission ofU235and spontaneous fission ofCf252

Background: The sharing of excitation energy between the fission fragments is one of the key issues in studying nuclear fission. One way to address this is by studying prompt-fission neutron multiplicities as a function of other fission observables such as the mass, $\overline{\ensuremath{\nu}}\left(A\right)$. These are vital benchmark data for both fission and nuclear deexcitation models, putting constrains on the fragment excitation energy and hence on the competing prompt neutron/$\ensuremath{\gamma}$-ray emission. Despite numerous detailed studies, recent measurements done at JRC-Geel with the SCINTIA array in the epithermal region show surprisingly strong discrepancies to earlier thermal fission data and the Wahl systematics.Purpose: The purpose was to perform measurements of the prompt-fission neutron multiplicity, as a function of fragment mass and total kinetic energy (TKE), in $^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$ and $^{252}\mathrm{Cf}\left(\text{sf}\right)$, to verify and extend the SCINTIA results. Another goal was to validate the analysis methods, and prepare for planned investigations at excitation energies up to 5.5 MeV.Methods: The experiments were conducted at the former 7 MV Van de Graaff facility in JRC-Geel, using a Twin Frisch-Grid Ionization Chamber and two liquid scintillation detectors. A neutron beam with an average energy of 0.5 MeV was produced via the $^{7}\mathrm{Li}$(p,n) reaction. The neutrons were thermalized by a 12 cm thick block of paraffin. Digital data acquisition systems were utilized. Comprehensive simulations were performed to verify the methodology and to investigate the role of the mass and energy resolution on measured $\overline{\ensuremath{\nu}}\left(A\right)$ and $\overline{\ensuremath{\nu}}\left(\text{TKE}\right)$ values. The simulation results also revealed that the $\ensuremath{\partial}\overline{\ensuremath{\nu}}(A)/\ensuremath{\partial}A$ and $\ensuremath{\partial}\overline{\text{TKE}}/\ensuremath{\partial}\overline{\ensuremath{\nu}}$ are affected by the mass and energy resolution. However, the effect is small for the estimated resolutions of this work. Detailed Fluka simulations were performed to calculate the fraction of thermal neutron-induced fission, which was estimated to be about $98%$.Results: The experimental results on $\overline{\ensuremath{\nu}}\left(A\right)$ are in good agreement with earlier data for $^{252}\mathrm{Cf}\left(\text{sf}\right)$. For $^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$, the $\overline{\ensuremath{\nu}}\left(A\right)$ data is very similar to the data obtained with SCINTIA, and therefore we verify these disclosed discrepancies to earlier thermal data and to the Wahl evaluation. The experimental results on $\overline{\ensuremath{\nu}}\left(\text{TKE}\right)$ are also in agreement with the data at epithermal energies. For $^{252}\mathrm{Cf}\left(\text{sf}\right)$ a slope value of $\ensuremath{\partial}\overline{\text{TKE}}/\ensuremath{\partial}\overline{\ensuremath{\nu}}=\left(\ensuremath{-}12.9\ifmmode\pm\else\textpm\fi{}0.2\right)\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/\mathrm{n}$ was obtained. For $^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$ the value is $\left(\ensuremath{-}12.0\ifmmode\pm\else\textpm\fi{}0.1\right)\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/\mathrm{n}$. Finally, the neutron spectrum in the center-of-mass system was derived and plotted as a function of fragment mass.Conclusions: This work clearly proves the lack of accurate correlation between fission fragment and neutron data even in the best-studied reactions. The new results highlight the need of a new evaluation of the prompt-fission multiplicity for $^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$.

Production yields of micro-second isomers populated in 252Cf(SF)

A twin Frisch grid ionization chamber loaded with an ultra-thin 252 Cf sample is used in order to detect spontaneous fission events. The chamber is surrounded by 8 HPGe detectors allowing to perform γ-spectroscopic measurements. We are interested in the decay of isomeric states populated in fission fragments. In this contribution we report on preliminary results on production yields of isomeric states with half-lives ranging from few nanoup to few micro-seconds.

Measurement of the 16O(n, α)13C cross-section using a Double Frisch Grid Ionization Chamber

The 16O(n, α)13C reaction was proposed to be measured at the neutron time-of-flight (n_TOF) facility of CERN. To this purpose, a Double Frisch Grid Ionization Chamber (DFGIC) containing the oxygen atoms as a component in the counting gas coupled with a switch device in order to prevent the charge collection from the so-called γ-flash has been developed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), in Germany. The first 16O(n, α)13C measurement without seeing the charge of the γ-flash at n_TOF has been performed in November 2018. After the electronics did not suffer from the y-flash any more, another huge charge collection was discovered. Due to the high instantaneous flux at the n_TOF facility [1] the amount of that induced charge from neutron induced background reactions was piling up so much that the recognition of 16O(n, α)13C reactions from that background was very difficult. For that reason another 16O(n, α)13C measurement at the time-of-flight facility nELBE at HZDR which has a low instantaneous flux [2], has been performed in April 2019. Both measurements from n_TOF and nELBE will be presented here.

Neutron Multiplicity Correlations with Fission Fragment Mass and Energy from 239Pu(n,f)

There exists experimental evidence for strong fluctuations of the average neutron multiplicity from resonance to resonance in 239Pu(n,f). These fluctuations have been shown to impact nuclear reactor benchmarks by reducing the criticality. The fluctuating neutron multiplicity can be explained as a consequence of the competition between direct fission and the (n,γf) process. However, there is also evidence for fluctuations of the fission fragment mass yields from resonance to resonance. The mass yield fluctuations may also contribute to fluctuations of the neutron multiplicity averaged over all fission fragment masses. In order to model the contribution to the neutron multiplicity fluctuations by the fission fragment mass yield fluctuations new data on the correlations between fission fragment properties and neutron multiplicities are in need. We present experiments carried out to determine prompt neutron multiplicity correlations with fission fragment masses and total kinetic energies in the reaction 239Pu(n,f). The experiment has been performed at the GELINA facility at JRC-Geel. A twin position-sensitive Frisch-grid ionization chamber is used for fission fragment identification via the double kinetic energy technique. An array of scintillation detectors is employed for neutron counting. Correlations between average neutron multiplicities and fission fragment properties have been measured with improved resolution in both mass and TKE, compared to data from the literature.

Performance of a twin position-sensitive Frisch-grid ionization chamber for photofission experiments

A position-sensitive twin Frisch-grid ionization chamber has been constructed for future photofission experiments using nearly monochromatic, linearly polarized gamma-ray beams. By exchanging the anode plates in the standard ionization chamber on both sides by an array of grid- and strip-anodes, which are rotated by 90° relative to each other and read out by means of resistive charge division, a position sensitivity is achieved that allows the azimuthal fragment emission angle and hence the fission axis orientation to be determined. The performance of this gaseous detector has been studied using the well-known 252Cf spontaneous fission process. The fission axis orientation could be determined relative to an arbitrary axis in space with a resolution better than 7° FWHM. Measured pre-neutron mass and total kinetic energy distributions are consistent with literature, which ensures that the mass and energy resolution for fission fragments is not affected by the position-sensitive structure.

Pulse shape analysing system for a gridded ionization chamber

Digital pulse shape analysis (dpsa) has been used with a Frisch-gridded ionization chamber to study the charged particle emission reactions induced by fast neutrons. The structure of Frisch-gridded ionization chamber and his performance were presented in more detail in ref. [1]. Here we describe experimental use of the ionization chamber combined with PXI system in detection of charged particles. The PXI system consisting of a chassis NI PXI-1031, an embedded controller NI PXI-8820 and a high-speed digitizer pixie-4 from XIA [2]. The pixie-4 is a PCI/PXI 4-channel all-digital waveform data-acquisition card featuring on-line pulse-shape analysis. Incoming signals are digitized with 14-bit 75 msps ADCs. Rise-time dpsa has been employed using data as an examples measurements of charged particles originating from reactions on 6Li and 10B nuclei induced by thermalized neutrons from an 241Am-Be source.

Prompt Fission Neutron Investigation in 235U(nth,f) and 252Cf(sf) Reactions

The prompt neutron emission in thermal neutron induced fission of 235U and spontaneous fission of 252Cf was investigated by using digital signal electronics. The goal was to check a new revised data analysis software with fission fragment (FF) kinetic energy corrections after prompt fission neutron (PFN) emission. The revised software was used to reanalyze old data measured in EC-JRC-IRMM, where 252Cf(sf) reaction was investigated. Both measurements were done using similar twin Frisch grid ionization chamber for fission fragment detection with equivalent NE213 fast neutron detector. About 0.5*106 FF with PFN coincidences have been analyzed in both measurements. The fission fragment kinetic energy, mass and angular distribution were investigated along with prompt neutron time of flight and pulse shape analysis using a six channel synchronous waveform digitizer (WFD) with sampling frequency of 250 MHz and 12 bit resolution in the 235U(nth,f) reaction. Similar WFD with sampling frequency of 100 MHz was used for PFN investigation in 252Cf(sf) reaction. These two experiments were considered as a reference for further investigations with a new setup composed of position sensitive ionization chamber to detect FF and an array of 32 liquid scintillators recently constructed in Dubna to detect neutrons.