We investigated the emission properties of charge sources based on carbon nanotubes prepared by arc discharge deposition of nanotubes onto a flat copper substrate (Borisenko et al. in Instrum Exp Tech 57(6):755, 2014; Low Temp Phys 41(7):567, 2015). The charge sources were submerged into superfluid helium at temperature T=1.3\documentclass[12pt]{minimal}
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\begin{document}$$T=1.3$$\end{document} K. The collector fixed above the charge source at a distance of 0.3 mm was connected to an electrometer. The current of charges was measured by the electrometer when a high voltage was applied to the charge source. In the originally prepared source, the emission of charges (electrons) on the level of 10-10A\documentclass[12pt]{minimal}
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\begin{document}$$10^{-10}\hbox {A}$$\end{document} is observed at a negative voltage above U=80\documentclass[12pt]{minimal}
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\begin{document}$$U=80$$\end{document} V and increases with increasing voltage. If the source of charge was kept in liquid helium for 15 h, the current–voltage characteristic changed significantly. The current of charges on the same level of 10-10\documentclass[12pt]{minimal}
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\begin{document}$$10^{-10}$$\end{document} A was registered at a voltage of U=150\documentclass[12pt]{minimal}
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\begin{document}$$U=150$$\end{document} V. Extraction of gases from the source placed in a vacuum chamber at room temperature for 48 h leads to the complete recovery of the emission properties. One can assume that the degradation of the emission properties of the sources is associated with the adsorption of helium atoms by carbon nanotubes at low temperatures. We did not observe any degradation of the emission properties of the charge sources in the case of positive charges injection into superfluid helium.
