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

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Abstract

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.

Introduction

The attachment of free electrons on atoms or molecules to form negative ions has been a subject of numerous investigations. The electron attachment is important for the removal of thermal electrons from the upper atmosphere by the process of the attachment-dominated atmospheric dry-air plasmas [1], [2], [3]. Previous researches have revealed that there are two kinds of attachment processes involving electron attachment of oxygen, namely two-body process and three-body process [4], [5], [6].

The electron attachment also plays an important role for the motion of electrons in the electric field within the gas in addition to their drift and diffusion, which is important for the application of gas detectors, such as the Frisch-grid ionization chamber (GIC) and the time projection chamber (TPC) [7], [8], [9], [10]. The GIC is used to study the properties of fission-fragment and the relationship between the prompt neutron and the distribution of fission-fragment [11], [12], [13], [14] in recent years. The measurements of cross sections for neutron induced nuclear reactions emitting charged particles using the GIC are performed by several groups, including those led by V. A. Khryachkov in Obninsk (IPPE) [15], F. Hambsch and G. Giorginis in Geel (IRMM) [11], [12], [13], [14], [16], M. Baba in Japan (Tohoku University) [17], and Yu. M. Gledenov in Dubna (JINR) cooperated with our group [18], [19], [20]. In order to realizes specific goals such as the measurement of long lived alpha-decays and the measurement of the delayed gamma-spectroscopy of fission fragments, improved structures of the GIC are designed [21], [22], [23]. The corrections of the pulse-height defect [24] and the grid inefficiency [25] are also performed to improve the accuracy for the energy measurement of the charged particles. The electron attachment caused by electronegative impurities such as oxygen will make the loss of the pulse height and deteriorate the energy resolution of the GIC [26], [27]. As the airtightness of the gas detectors becomes poor, the air will enter the detectors and the electron attachment from oxygen will occur. Therefore, it is significant to study the influence of the electron attachment on the gas detectors.

In this paper, the effect of electron attachment on the cathode–anode two-dimensional amplitude spectrum of the GIC was measured and evaluated firstly. Then the method of measuring the electron attachment probability per unit time using the GIC was established, and measurements were carried out for the GIC with different number densities of O2 and different reduced electric fields. Finally, the three-body attachment coefficients of O2 and CO2 at different mean electron energies were determined and compared with those from previous measurement.

Section snippets

The experimental setup

The structure of the GIC and the electronics, as well as the data acquisition (DAQ) system are shown in Fig. 1. The waveform digitizer used for data recording is Signatec PDA14, with a sampling frequency of 100 MHz and 14 bit resolution. The coincidence between cathode and anode signals is set as the triggering condition of the DAQ system. The pre-trigger and post-trigger sampling points for cathode and anode signals are set as 2000 and 2096, respectively. The cathode and anode signals were

The influence of the electron attachment on the signal amplitude of the GIC

Fig. 2 shows a schematic diagram of the electrons drifting in the GIC.

The α particles ionize the working gas and produce electron–ion pairs along the particle track. For the electron-sensitive pulse mode GIC, the signals of the cathode and the anode are induced by the drift of the electrons. All electrons are considered to be concentrated at the center of gravity in the ionization track to simplify the analysis, as shown by the red point in Fig. 2. The maximum amplitude of the cathode signal

Measurements of the electron attachment

As indicated in Section 3, the electron attachment will reduce the signal amplitude and deteriorate the energy resolution of the GIC. Therefore, quantitative descriptions and measurements of the electron attachment under different experimental conditions are of great significance.

Attachment probability per unit time, a, is an important parameter to evaluate the effect of the electron attachment. In Section 4.1, the method of measuring a by the GIC is established and the values of a for

Conclusion

The influence of the electron attachment on the cathode–anode two-dimensional amplitude spectrum of the GIC is experimentally measured and evaluated. The method of measuring the attachment probability per unit time, a, is established. The quantitative and systematic relationships between the value of a and the number density of oxygen NO2 and the reduced electric field (E/p)cg are obtained from experiments. a rises monotonically with the increase of NO2 under the same reduced electric field,

CRediT authorship contribution statement

Jie Liu: Conceptualization, Methodology, Writing - original draft, Writing - Original draft preparation. Haoyu Jiang: Writing – review & editing. Zengqi Cui: Writing – review & editing. Yiwei Hu: Writing – review & editing. Haofan Bai: Writing – review & editing. Jinxiang Chen: Writing – review & editing. Guohui Zhang: Supervision, Writing – reviewing & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors would like to thank Dr. Yu. M. Gledenov and Dr. E. Sansarbayar from JINR, Dubna for providing and maintaining the Frisch-grid ionization chamber. They are also grateful to Dr. G. Khuukhenkhuu from Ulaanbaatar University for installing the target. The present work was financially supported by the National Natural Science Foundation of China (Grant Nos. 11775006 and 12075008), Science and Technology on Nuclear Data Laboratory and China Nuclear Data Center .

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