Gridded Ionization Chamber Research Articles

Cross sections of the Zr91(n,α)Sr88 reaction in the 3.9–5.3 MeV neutron energy region

Cross sections of the $^{91}\mathrm{Zr}(n,\ensuremath{\alpha})^{88}\mathrm{Sr}$ reaction were measured at four incident neutron energies in the range of 3.9 to 5.3 MeV. The experiment was carried out on the Van de Graaff accelerator EG-5 at the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Russia. Fast neutrons were produced via the $^{2}\mathrm{H}(d,n)^{3}\mathrm{He}$ reaction with a deuterium gas target. A twin gridded ionization chamber (GIC) was used as the charged particle detector, in which $^{91}\mathrm{Zr}$ back-to-back samples on a tantalum backing were placed at the common cathode. The relative and absolute neutron fluxes were measured using two $^{238}\mathrm{U}_{3}{\mathrm{O}}_{8}$ samples inside the GIC. Cross-section data obtained in this measurement were compared with those in existing data library and from theoretical calculations using talys code. The present data for the $^{91}\mathrm{Zr}(n,\ensuremath{\alpha})^{88}\mathrm{Sr}$ reaction should be helpful in clarifying the discrepancies in various published nuclear evaluation data. An alpha clustering factor is calculated using the statistical model and knock-on mechanism.

Cross sections of the Ca40(n,α0)37Ar and Ca40(n,α)37Ar reactions in the 8.50–9.50 MeV neutron energy range

Cross sections of the $^{40}\mathrm{Ca}(n,\phantom{\rule{0.16em}{0ex}}{\ensuremath{\alpha}}_{0})^{37}\mathrm{Ar}$ and $^{40}\mathrm{Ca}(n,\phantom{\rule{0.16em}{0ex}}\ensuremath{\alpha})^{37}\mathrm{Ar}$ reactions at five neutron energy points in the $8.50--9.50$ MeV energy region were measured. The monoenergetic neutrons were produced through the $^{2}\mathrm{H}{(d,\phantom{\rule{0.16em}{0ex}}n)}^{3}\mathrm{He}$ reaction based on the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE). A twin gridded ionization chamber (GIC) was used as the charged particle detector. Detailed simulations were performed to determine the nuclear reaction events and detection efficiencies. Present results are compared with existing measurement and evaluation data, which shows that the evaluation data from all libraries are higher than the measurement data in the $8.50--9.50$ MeV region for the $^{40}\mathrm{Ca}(n,\phantom{\rule{0.16em}{0ex}}\ensuremath{\alpha})^{37}\mathrm{Ar}$ reaction. TALYS-1.9 code was used for theoretical calculations. Calculation results using the TALYS-1.9 code with the adjusted parameters are in agreement with the present measurements, which also show that the compound mechanism predominates the $^{40}\mathrm{Ca}(n,\phantom{\rule{0.16em}{0ex}}\ensuremath{\alpha})^{37}\mathrm{Ar}$ reaction in the $8.50--9.50$ MeV region. Both present measured forward/backward ratios and TALYS-1.9 calculations suggest that the direct and preequilibrium mechanisms are non-negligible for the $^{40}\mathrm{Ca}(n,\phantom{\rule{0.16em}{0ex}}\ensuremath{\alpha})^{37}\mathrm{Ar}$ reaction in the $8.50--9.50$ MeV region.

The FFIS spectrometer for determination of fission fragment mass distribution with the energy–velocity method

The FFIS spectrometer (Fission Fragment Identification Spectrometer) for determining independent fission yields has been developed based on the E–v method. By directly measuring the time-of-flight (TOF) and kinetic energy of fission fragments on their flight path, the post-neutron-emission mass yield distributions can be obtained. With the aim of getting the highest possible mass resolution, an axial grid ionization chamber and a TOF measurement system based on microchannel plate (MCP) detectors were designed. The ionization chamber with a silicon nitride entrance window of 100 nm thickness was tested and calibrated with a 252Cf spontaneous fission source. The intrinsic energy resolution for 1.27 MeV/u 63Cu particles is measured to be 450 keV (FWHM). The time resolution was determined with two MCP timing detectors to be 157 ps (FWHM) for 241Am radiation source, implying that the intrinsic time resolution is about 110 ps (FWHM) for a single timing detector. Thermal-neutron-induced fission of 235U was studied at the In-hospital Neutron Irradiator (IHNI). An event-by-event energy loss addback technique was developed based on Geant4 calculation to minimize the correction error. The first results of mass yield distributions from 235U(nth,f) are reported.

Grid ionization chamber based on stainless steel woven wire mesh

The grid electrode of the grid ionization chamber (GIC) is devoted to eliminating the dependence of the anode pulse amplitude on the initial position and orientation of the ionization. The traditional methods of grid production require cumbersome processes and advanced instruments. In this paper, a bonded stainless steel woven wire mesh (SSWWM) grid electrode manufacturing method is proposed. Compared with the traditional grid electrode, the SSWWM grid features the advantages of simple fabrication, low cost, and high mechanical strength. The energy resolutions of the 40-mesh, 60-mesh and 80-mesh SSWWM grids and orthogonal mesh grid realized by the traditional wire winding method were tested using an 241Am source (around 5.486 MeV). The results show that the optimum energy resolution of the SSWWM and orthogonal mesh grids is approximately 47 keV full width at half-maximum (FWHM). The optimal energy resolutions of the 40-mesh and 60-mesh SSWWM grids are comparable, but the initial operating voltages corresponding to the energy resolution plateau are different, mainly because of the effect of the different geometric parameters of the SSWWM grid on the electron transmittance. A simulation program was used to study the electron transmittance of the SSWWM grid. The simulation results are in agreement with the experimental results, indicating that the simulation program can be used as a reference for the selection of the geometric parameters of the SSWWM grid.

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).

Cross-section measurements for the 58,60,61Ni(n, α)55,57,58Fe reactions at 8.50, 9.50 and 10.50 MeV neutron energies * *Supported by the National Natural Science Foundation of China (11775006) and China Nuclear Data Center and the Science and Technology on Nuclear Data Laboratory

Cross sections of the 58,60,61Ni(n, α)55,57,58Fe reactions were measured at 8.50, 9.50 and 10.50 MeV neutron energies based on the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE) with enriched 58Ni, 60Ni, and 61Ni foil samples with backings. A twin gridded ionization chamber (GIC) was used as the charged particle detector, and an EJ-309 liquid scintillator was used to obtain the neutron energy spectra. The relative and absolute neutron fluxes were determined via three highly enriched 238U3O8 samples inside the GIC. The uncertainty of the present data of the 58Ni(n, α)55Fe reaction is smaller than most existing measurements. The present data of 60Ni(n, α)57Fe and 61Ni(n, α)58Fe reactions are the first measurement results above 8 MeV. The present experimental data could be reasonably reproduced by calculations with TALYS-1.9 by adjusting several default values of theoretical model parameters.

Cross sections for the Cl35(n,α)P32 reaction in the 3.3–5.3 MeV neutron energy region

Cross sections for the $^{35}\mathrm{Cl}(n,\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{P}$ reaction were systematically measured at incident neutron energies in the range of 3.3 to 5.3 MeV. The experiment was carried out on the Van de Graaff accelerator EG-5 at the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Russia. Fast neutrons were produced in the reaction $^{2}\mathrm{H}(d,n){\phantom{\rule{0.16em}{0ex}}}^{3}\text{He}$. Alpha particles from the ($n,\ensuremath{\alpha}$) reactions were detected using a gridded ionization chamber (GIC) in which various $^{35}\mathrm{Cl}$ samples (NaCl and ${\text{BaCl}}_{2}$, on a tantalum backing) were placed back to back. The relative and absolute neutron fluxes were measured by two samples of $^{238}\mathrm{U}_{3}\mathrm{O}_{8}$ ($99.999%$) inside the GIC. Data obtained in this measurement were compared with other experimental data of the existing library and theoretical calculations by the talys code. Presented data for the $^{35}\mathrm{Cl}(n,\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{P}$ reaction should help to clarify discrepancies in the various published nuclear data.

Simulation method for measurement of the cross-section of the 14N(n, α)11B reaction using a gridded ionization chamber

Simulation method for measurement of the cross-section of the 14N(n, α)11B reaction using a gridded ionization chamber

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.

Standardization of non-equilibrium 210Pb solutions by LSC and 2πα counting

A procedure for the standardization of 210Pb solutions in radioactive disequilibrium, or incompletely purified from its descendants, has been set up and successfully validated. The method, based on joint measurements of 210Po by alpha-particle spectrometry (2πα counting) with grid ionization chamber and liquid scintillation counting for overall activity estimation, is presented as an alternative to 210Pb measurement by LSC with α/β discrimination.

A simple method for measuring electron drift velocity in gases using grid ionization chamber

A simple method for measuring the electron drift velocity in gases with a given electric field using a grid ionization chamber is proposed and demonstrated. By collimating incident α particles that are perpendicular to the electric field, the drift velocity can be derived easily using the electron drift distance from primary ionization to a grid divided by the time interval between the cathode and anode signal starting times. These experimental settings can avoid additional signal processing of signals and reduce the effect of electron diffusion. Using this method, the measurement of electron drift velocities in 90% Ar + 10% CO2 is presented. Measured results agree well with the simulated values and with existing experimental results.

Scintillation and ionization yields of helium–xenon gas mixture for application in neutron detectors

The scintillation and ionization yields of helium–xenon gas mixture were measured using a gridded ionization chamber with 241Am alpha particles to study the potential of the mixture to be applied in neutron detectors. The ionization yields for various ratios of the mixture gases were obtained with gas pressures of 1.0, 0.657, and 0.100 MPa. The yield data were explained well using the ratio of the number of excited atoms to that of ionized atoms in helium, i.e. The scintillation yield increased with xenon partial pressure and saturated at 10% of the total pressure, while the ionization yield increased up to 1.59 times of the initial value for pure helium at 1% of the total pressure then gradually increased to 1.8 times. The helium gas with added xenon at 10% of its pressure was suggested as a medium of a neutron detector with signal readouts from both scintillation and ionization, since it increases the scintillation yield to more than 1.1 times of pure xenon and increases the ionization yield to more than increases 1.8 times of pure helium.

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.

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.

Fe56,54(n,α)Cr53,51 cross sections in the MeV region

$^{56,54}\mathrm{Fe}(n,\ensuremath{\alpha})^{53,51}\mathrm{Cr}$ cross sections were measured in the neutron energy region of 5--11 MeV using three neutron sources based on accelerators, a twin gridded ionization chamber, and highly enriched $^{56}\mathrm{Fe}$ and $^{54}\mathrm{Fe}$ foil samples. The $^{238}\mathrm{U}(n,f)$ reaction was used to monitor the neutron fluence, and the interferences from the low-energy neutrons were corrected according to the neutron energy spectra obtained through unfolding the pulse height spectra measured by a liquid scintillator. Both the measured cross sections show a ``shoulder'' structure in the 8--11 MeV region which may be caused by the level structure of the residual nuclei. The present paper aims to improve constraint of the $^{56,54}\mathrm{Fe}(n,\ensuremath{\alpha})^{53,51}\mathrm{Cr}$ excitation functions in the MeV region where their neutron energy dependences are significant, while related measurements are nonexistent or scarce and the deviations among existing measurements and evaluations are significant. To obtain more precise excitation functions of the $^{56,54}\mathrm{Fe}(n,\ensuremath{\alpha})^{53,51}\mathrm{Cr}$ reactions, further measurements and improved evaluations are required.

Triton identification in the 6Li(n, t)4He reaction measurement with the grid ionization chamber at CSNS Back-n white neutron source

The measurement of 6Li(n, t)4He differential cross section is the first experiment conducted with the Light-charged Particle Detector Array (LPDA) at the Back-n white neutron source of the China Spallation Neutron Source. The LPDA system consists of three kinds of detectors. One of them is the grid ionization chamber (GIC), which has the capability of particle identification. The particle identification performance of the GIC is presented based on the data collected in this experiment. Signals from the anode and the cathode of the GIC are digitized through the readout electronics and DAQ system. The offline data analysis is performed in two major steps. The first step is the processing of the original signal waveform digitized by the readout electronics. A set of digital filter algorithms including RC-CR filter, band-pass filter and digital CFD are developed and implemented in the original signal processing in order to obtain a high signal-noise ratio and a precise timing resolution. The second step focuses on the identification of triton events. The triton identification efficiency is measured to be 98% using a multivariate analysis algorithm implemented in the TMVA package in ROOT to discriminate the triton events and background events. In general, the performance of the GIC has met the baseline requirement of the experiment measurement.

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.

Particle identification technique using grid ionization chamber at China Spallation Neutron Source

Back-n white neutron source at China Spallation Neutron Source facility requires a detector with charged-particle identification ability for measuring nuclear cross sections. Therefore, a grid ionization chamber (GIC) with an adjustable distance between the cathode and grid was designed and built. Moreover, a corresponding particle identification algorithm is proposed in order to use the signals of the anode (QA) and cathode (QC), or the signal (QA) of the anode and the time difference (Δ t) between the cathode and anode signals, based on the interactive behaviors of charged particles and the GIC's working principle. First, the GIC performance was measured using a 241Am α source for preliminary performance testing, which provided an energy resolution of 5.25%. Its good particle identification performance was demonstrated by identifying 3H and 4He from neutron reactions with 6Li using a 2D QC-QA plot and Δ t-QA plot. Furthermore, 3H and 4He can be completely distinguished from the updated 2D QC-QA plot and Δ t-QA plot, in which 3H with a small incident angle is selected. Finally, it was concluded that our GIC with the proposed particle identification algorithm could identify charged particles effectively for the future measurement of nuclear cross sections.