Attenuation of vacuum ultraviolet light in liquid argon

Abstract

The transmission of liquid argon has been measured, wavelength resolved, for a wavelength interval from 118 to 250 nm. The wavelength dependent attenuation length is presented for pure argon. It is shown that no universal wavelength independent attenuation length can be assigned to liquid argon for its own fluorescence light due to the interplay between the wavelength dependent emission and absorption. A decreasing transmission is observed below 130 nm in both chemically cleaned and distilled liquid argon and assigned to absorption by the analogue of the first argon excimer continuum. For not perfectly cleaned argon a strong influence of impurities on the transmission is observed. Two strong absorption bands at 126.5 and 141.0 nm with approximately 2 and 4 nm width, respectively, are assigned to traces of xenon in argon. A broad absorption region below 180 nm is found for unpurified argon and tentatively attributed to the presence of water in the argon sample.

Ion-beam excitation of liquid argon

“…On the opposite side the cell was closed with an endcap, which served as a Faraday cup flange was cut under an angle of 45 • at its end in such a way that the effective light emitting area seen by the light detector was maximized. The distance the scintillation light had to travel through LAr was minimized to only few millimeters, thereby avoiding absorption effects [26] and effects related to Rayleigh scattering [27]. On the opposite side the cell was closed with a stainless steel endcap, which had an electrically insulated copper plate at its front.…”

“…For a schematic drawing see ref. [26]. This gas system also contained a rare gas purifier (SAES Getters, MonoTorr ® Phase II, PS4-MT3 [28]) which was capable of removing all chemical impurities except other rare gases.…”

“…This correction was carried out analogously to the procedure described in [26]. However, as the correction function was only known down to 118 nm all spectra shown in the following end at this wavelength.…”

“…Also in this experiment the raw data were corrected for the detector response [57], however, no corrections for reflections at the window's surfaces or a diminishing transmission were made. The latter were found to play no important role for wavelengths longer than 250 nm [26]. Background due to stray light, X-rays and dark noise was subtracted; in each case it was thoroughly checked that the parameter settings of the spectrometer and the ion beam did not influence the shape of the spectra.…”

A novel use of light guides and wavelength shifting plates for the detection of scintillation photons in large liquid argon detectors

“…The probability that the photon is Rayleigh scattered along its path is given by P Rayleigh = B exp (−L/λ Rayleigh ), where B is a normalization constant, L is the track length to the intersection, and λ Rayleigh = 1.1 m [18] is the Rayleigh scattering length. There are many different values for λ Rayleigh found in the literature [19][20][21]. The Rayleigh scattering length used here is a recent estimate that falls between the upper and lower values.…”