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Gas-Filled Detectors: Ion Chambers
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Radiation interactions in gas can cause excitation and ionization. Excitation is a process in which the energy transferred to a gas atom or molecule is less than the ionization energy. Hence, electrons are elevated to a higher energy level, but are still bound to the nucleus. Energy transferred to electrons greater than their ionization energy causes ionization, so that the electrons and positive ions become separate charge carriers. An electric field applied to the gas volume separates these charge carriers and, in the process, produces an induced current, as described in Chapter 8. The electrons, with a mass more than a thousand times less than that of the positive ions, also have quite different transport properties than heavy ions. Also, negative ions, formed from electron attachment to neutral atoms, have different transport characteristics than positive ions (although similar). Detector and gas properties that affect the charge transport for electrons and ions include mobility, electric field, ionization potential, charge transfer, electron attachment, and recombination. In the following chapter on gas-filled ion chambers, pertinent information on charge transport and ion behavior in gases is presented. Exhaustive studies dedicated to the complexities of electron and ion motion in gases have been published in far more detail than presented here. See, for example, [Loeb 1939, 1960; Huxley and Crompton 1974; Sitar et al. 1993].
General Chemistry
Published in Steven L. Hoenig, Basic Chemical Concepts and Tables, 2019
Ionization energy is the minimum amount of energy needed to remove an electron from a gaseous atom or ion, and is expressed in kJ/mol. The IE increases going across the periodic table due to the fact that the principal energy level (principal quantum number) remains the same while the number of electrons increase, thereby enhancing the electrostatic attraction between the protons in the nucleus and the electrons. Going down the table the IE decreases because the outer electrons are now further from the nucleus and the protons.
Atoms and the Periodic Table of the Elements
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
The ionization energy is the minimal energy needed to remove an electron from the isolated neutral atom in its ground state, leaving the cation in its ground state as well (for instance, we have already seen that the hydrogen-atom ionization energy is 13.6 eV). The ionization energy is always positive, namely, we should provide energy to an atom to ionize it. The “specular” quantity is the electron affinity, which is the energy given off by a neutral atom in its ground state when an electron is inserted, thereby forming an anion in its ground state as well. According to Koopmans’ theorem, the atomic orbitals of the ion are the same as already computed for the neutral atom, so that the Hartree–Fock single-electron energies εj are approximations to the ionization energy and electron affinity.
Theoretical Analysis of Magnetic Pinch Glow Discharge Plasma at Low Pressure
Published in Fusion Science and Technology, 2022
where = average free path of the collision between electron and neutral atom in the absence of magnetic field, which is related to the pressure= corrected mean free path of electron neutral atom collision in magnetic field, which is related to pressure and magnetic field= ionization energy of neutral atom= electric field intensity.
Facile in situ fabrication of a direct Z-scheme BiOCl/bismuth niobate heterojunction and its effective photodegradation of RhB
Published in Journal of Dispersion Science and Technology, 2022
Huining Zhang, Yankui Xiao, Zhongyu Shi, Lihong Tian, Yuling Tang, Xingmao Liu, Yangyi Tian, Yan Lin
To get an insight into the photocatalytic mechanism of BiOCl/Bi3NbO7, the band edges of the photocatalyst were calculated according to the following equation. where ECB and Eg represent the conduction band (CB) edge potential and band gap energy of the photocatalyst, respectively. Ee was the energy of free electrons on the hydrogen scale (∼4.5 eV[55]), and χ was the electronegativity of the semiconductor. Here a, b, and c were the number of atoms in the compound. EIE was the first ionization energy and EEA is electron affinity energy.[42,56,57]
Biomarker characteristics and geological significance of middle and upper Permian source rocks in the southeastern Junggar Basin
Published in Petroleum Science and Technology, 2019
Yongqiang Qu, Huifei Tao, Dongzheng Ma, Tao Wu, Junli Qiu
Source rock powder samples over 80 g were packed with the filter paper and placed in an extractor, in which they are being extracted with sufficient dichloromethane and methanol (9:1 by volume) for 72 hrs. After separation by column chromatography (activated alumina/silica gel = 1/3), the non-polar (saturated hydrocarbons), weakly polar (aromatic hydrocarbons), polar fractions (non-hydrocarbons) and the remaining asphaltenes were flushed with n-hexane, dichloromethane and methanol, respectively. The final extraction mass of each component was recorded in details until constant weights were obtained. Samples are then carefully kept for further instrument tests. The instrument for tests is a gas chromatography-mass spectrometer (Agilent 6890N-GC/5973N-MSD, manufactured by American Agilent Technologies Co., Ltd.). The inlet temperature was 280 °C; the carrier gas, high-purity helium; the carrier gas flowrate, 1.2 mL/min; the carrier gas flow velocity, 40 cm/sec; the chromatographic column, American J&W. HP-5 (30 m × 0.25 mm × 0.25 μm) elastic quartz capillary column; the programed heating process, in which the temperature was raised up from 80 °C to 290 °C at a rate of 4 °C/min and kept constant for 30 min. The mass spectra ion source is an EI source, with the ion source temperature of 230 °C and the quadrupole temperature of 150 °C. The ion source ionization energy equals to 70 eV. The scan model is full-scan and the mass spectrometer and chromatographic spectrometer connection temperature is 280 °C. The mass spectral library is American NIST02L.