Charge distribution about an ionizing electron track in liquid helium

Abstract

The dependence on an applied electric field of the ionization current produced by an energetic electron stopped in liquid helium can be used to determine the spatial distribution of secondary electrons with respect to their geminate partners. An analytic expression relating the current and distribution is derived. The distribution is found to be non-Gaussian with a long tail at larger distances.

Scintillation yield from electronic and nuclear recoils in superfluid $^4$He

“…Signals in superfluid helium include singlet diatomic molecules (excimers), triplet excimers, rotons, phonons, and perhaps quantum turbulence [18][19][20]. Recent experimental measurements of superfluid helium response signals have focused on scintillation as a function of temperature and applied electric field from α and electron sources [21][22][23][24]. In addition to directly measuring these signal channels, predictions of helium response to nuclear and electronic recoils can be constructed from experimental data of He-He and electron-He interaction cross sections [2,3], yielding a full model of the partitioning into various signal channels as a function of recoil energy [5,25,26].…”

Effect of an electric field on liquid helium scintillation produced by fast electrons

“…Since then extensive studies have been carried out to illuminate the behavior of ions and neutrals in this unique substance [3][4][5][6][7][8][9][10][11][12][13]. More recently, there has been renewed interest in studying liquid helium scintillation because of the potential application of LHe as a particle detector and/or a target material in which to conduct nuclear, particle, and astroparticle physics experiments [14][15][16][17][18][19][20][21][22]. These experiments include solar neutrino detection [23][24][25], a search for the permanent electric dipole moment of the neutron [26][27][28], measurement of the free neutron lifetime [29], and detection of light dark matter particles [30][31][32][33].…”

“…On the other hand, a 364 keV electron, such as those from 113 Sn, has a range of ∼7 mm in superfluid helium [38]. With a W value, defined as the average energy loss by the incident particle per ion pair formed, of 43 eV [39], the average separation of ionization events is ∼840 nm, whereas the average separation between the electron bubble and the helium snowball from an electron-ion pair after they thermalized is ∼40 nm [22]. As a result, the thermalized ions from electron tracks are most likely to recombine with their partners, a situation referred to as geminate recombination.…”

“…The length scale of most relevance in this analysis is the so called Onsager radius, R = e 2 /(4π k B T ), which is the separation distance between the two charges where the Coulomb potential is comparable to the thermal energy. In LHe, this radius is larger than 3.7 µm, therefore thermal diffusion can be ignored for moderate or higher fields [22].…”

“…Our group has previously measured the effect of an electric field on LHe scintillation produced by α-particles [21]. We have also reported on the field dependence of the ionization current from electrons in LHe and the resulting determination of the charge thermalization distribution [22]. Guo et al [20] have reported on a measurement of the effect of an electric field on LHe scintillation produced by electrons up to an electric field of 5 kV/cm at a single temperature of 1.5 K. The work presented in this paper significantly expands on both the electric field and temperature ranges.…”