Measurements of radio propagation in rock salt for the detection of high-energy neutrinos

摘要

We present measurements of the transmission of radio/microwave pulses throughsalt in the Cote Blanche salt mine operated by the North American Salt Companyin St. Mary Parish, Louisiana. These results are from data taken in thesouthwestern region of the 1500 ft. (457 m) deep level of the mine on our thirdand most recent visit to the mine. We transmitted and received a fast,high-power, broadband pulse from within three vertical boreholes that weredrilled to depths of 100 ft. (30 m) and 200 ft. below the 1500 ft. level usingthree different pairs of dipole antennas whose bandwidths span 125 to 900 MHz.By measuring the relative strength of the received pulses between boreholeswith separations of 50 m and 169 m, we deduce the attenuation of the signalattributed to the salt medium. We fit the frequency dependence of theattenuation to a power law and find the best fit field attenuation lengths tobe 93 \pm 7 m at 150 MHz, 63 \pm 3 m at 300 MHz, and 36 \pm 2 m at 800 MHz.This is the most precise measurement of radio attenuation in a natural saltformation to date. We assess the implications of this measurement for a futureneutrino detector in salt.