Electrons In Liquid Argon Research Articles

Negative ion–molecule reactions in liquid argon following electron capture by N2O

Electrons produced in liquid argon by a short burst of X rays react readily with dissolved N2O with a bimolecular rate constant of 5.8 × 10−10 cm3/s or 3.5 × 1011 M−1 s−1. The addition of H2 or CO to the Ar/N2O solution results in a fast and slower component in the decay of the electron current. We assume that O− ions are formed in the reaction of electrons with N2O and then react with H2 to give[Formula: see text]or with CO to give[Formula: see text]The addition of CH4 does not regenerate electrons since the reaction[Formula: see text]is thought to occur. Reaction 12 is in agreement with the fact that CO2 does not react with electrons in liquid argon.

Production and transport of conduction electrons in a liquid argon ionization chamber

Free electrons produced by α- and β-particles in a liquid argon ionization chamber have been detected. For minimum ionizing particles the collected charge saturates at a field strength of E⪅ 15 kV/cm. 95±4)% of the produced electrons were collected. For strongly ionizing α-particles no saturation was observed up to a field strength of 40 kV/cm, where (25±3)% of the produced electrons were detected. The influence of oxygen and nitrogen, solved in the liquid argon, on the charge collection was studied. A nonlinear relationship between the mean free path length for absorption and the applied electric field indicates the existence of hot electrons in liquid argon. The recombination effect in the ionization column produced by α-particles is enhanced by oxygen and nitrogen impurities in liquid argon.

Drift velocities of electrons, saturation characteristics of ionization and W-values for conversion electrons in liquid argon, liquid argon-gas mixtures and liquid xenon

The drift velocities of electrons, the saturation characteristics of ionization and the W-values for internal conversion electrons emitted from 207Bi in liquid argon, liquid argon-gas (xenon, nitrogen, methane and ethylene) mixtures and liquid xenon have been measured by using gridded ionization chambers. The drift velocity of electrons in xenon or nitrogen-dopes liquid argon shows little increase compared with that in liquid argon, while that in liquid argon-methane or -ethylene mixtures shows a remarkable increase. From each saturation curve, the so-called “recombination coefficient” k is obtained, assuming that the electric field ( E ) dependence of the collected charge ( Q) is represented by Q∝( 1+ k E ) −1 , and the values for liquid rare gases as shown above are tabulated. The W-values in liquid argon-xenon mixture and liquid xenon have been determined by comparing with that in liquid argon. It is shown that admixing liquid argon with a small amount of xenon results in the reduction of the W-value and that the W-value in liquid xenon is much smaller than that in the gas phase. On the basis of these experimental results, the applicability of the liquid rare gases to detector medium is discussed.

Effect of Electric Field Strength on the Free Ion Yields in the X-Radiolysis of Liquids: Influence of Molecular Structure and Temperature

The relative increase in the free ion yield with increasing field strength E, expressed as [Formula: see text] is smaller when the following quantities are larger: (1) dielectric constant, (2) temperature, and (3) separation distance between the geminate ion–electron pairs. The field dependence [Formula: see text] equals 9.7/εT2 cm/V at low E, but at higher fields it is affected by the above three factors and by E itself. Results obtained from the liquids propane (123–233 °K), 2-methylpropane (isobutane, 148–294 °K), 2,2-dimethylpropane (neopentane, 295 °K), argon (87 °K), oxygen (87 °K) and argon–oxygen solutions (87 °K) are presented and analyzed according to a theoretical model. Several types of ion–electron separation (y) distribution functions are tested. Within the framework of the model a power function F(> y) = yminy−x with x < 4 provides a good interpretation of the results when [Formula: see text] a Gaussian distribution function provides the best interpretation of the field effects when [Formula: see text] Either the y distribution has a Gaussian core with a more gently sloping tail, or distributions are more Gaussian-like in liquids in which the electron ranges are greater. The electron range in pure argon (b = 1300 Å) is much smaller than had been expected and is only 2.6 times greater than that in liquid methane (b = 500 Å at 120 °K). Phonon emission by 10–0.01 eV electrons in liquid argon may be relatively efficient and might involve transient states of the type [Formula: see text]

Motion of Electrons in Liquid Argon

The scattering of electrons moving through nonpolar liquids is discussed. The Hartree field of an atom is assumed not to change on passing from gas to liquid. The screening of the long-range polarization potential is given by a self-consistent local field, which is found in terms of the pair correlation function. A microscopic dielectric function follows as a byproduct. The overlap of atomic force fields in the liquid is handled by the use of an effective potential suggested by Cohen. Detailed calculations are made for electrons in liquid argon. The principal result is that the Ramsauer minimum no longer exists in the liquid. The drift velocity in a steady electric field is found from the solution of the Boltzmann equation given by Cohen and Lekner. Agreement between experiment and theory is good.

Drift Velocity and Energy of Electrons in Liquid Argon

Measurements are reported of the energy required for injection of an electron into liquid argon and of the drift velocity of electrons in liquid argon at moderate field strength. It is found that the barrier to electron injection is ---0.33 eV, in moderately good agreement with a theoretical estimate of ---0.45 eV. The observed field dependence of the drift velocity is in good agreement with the recent calculations of Lekner.

Drift velocity of electrons in liquid argon, and the influence of molecular impurities

The drift velocity of electrons has been measured in liquid argon and in liquid argon containing nitrogen, oxygen and hydrogen as impurities. It has been found that with nitrogen and hydrogen in solution the drift velocity increases, but that, because of strong electron attachment, insufficient oxygen could be added to produce an observable effect. The results support the view that the behaviour of electrons in liquid argon can be understood by treatment of the liquid argon as a high pressure gas.

Electron Mobility in Liquid Argon

Experiments of Williams (1957) showed that the drift velocity of electrons in liquid argon to which an electric field F is applied is essentially independent of F. If the electrons remain free then their motion can be described by kinetic theory, from which it appears that electron mobility is proportional to F-I and drift velocity to Fli. This is the dependence reported by Malkin and Schultz (1951), but it is evident that the recent, more exhaustive work of Williams (1957) is correct on this point and therefore that kinetic theory is not applicable to the problem. This theory could in principle be extended to explain a fieldindependent velocity, by supposing a special dependence upon electron energy of the scattering cross section for the collision of electrons with argon atoms, but this is very artificial and unnecessary in view of the alternative explanation suggested here; in any case it leaves further serious objections, which will also be discussed briefly.