BEXCO - Room F(201/202/203/204)
[NU108] Results on radio attenuation length recorded in Romanian salt mine
In the specific case of a km3 neutrino detector in a salt mine, cosmic neutrinos are observed indirectly by measuring the radio emission generated by their interaction with the salt. As waves propagate in a non ideal medium before being measured by radio antennas, it is impetuous to have first a good geophysical material description. The attenuation given by radio wave propagation will essentially determine the construction limitations of the detector and also its capabilities. The attenuation of radio waves in salt mines is the first factor that determines: the geometry of a radio detector, the energy threshold of the detector, its resolution and the uncertainties in determining the cosmic neutrino characteristics thus accurate experimental measurements (together with a good theoretical description of the propagation medium) should be performed. First Romanian tests on determining the attenuation length of a radio signal at 400 and 800 MHz on samples from the “Unirea” salt dome in Slanic Prahova, Romania, showed a large deviation from the ideal medium case. The measurement setup consists of: a transmitting and receiving antenna are boreholed in salt, separated by a distance of at least one hundred meters. The transmitted signal’s amplitude is known thus by measuring the propagated signal after a distance d (hundreds of meters) one can evaluate the effect of the propagating medium: it is directly reflected in the attenuation of the signal. A few measurements on distances smaller than 100 m are used to determine the possible presence of faults, to measure the humidity effects, and to determine antennas’ radiation properties. The radio signals are emitted and recorded with the same instrument which facilitates synchronization which in turn allows dispersion measurements. The measurements are carried out using identical pairs of antennas (for emission and reception) which resonate at frequencies of ~200MHz, ~400MHz and 800MHz. We have estimated that the main source of systematic errors for the attenuation length measurements is due to the position of the antenna within the hole, and hole alignment. There is also an uncertainty on the distance between the holes.