U.S Gulf coast salt domes Salt dome demographics: Several hundred known—some are good source of oil Typical ~3-5 km diameters, 5-15 km deep ~200 km3 water equiv. in top 3-5 km for many domes Hockley dome/mine Houston New Orleans

Salt Measurements at WIPP & Hockley Supported through UCLA: DOE ADRP grant (Saltzberg) Results posted at hep-ex, submitted to NIM: WIPP: not so good……. Hockley Mine: very promising!

Results from Hockley Mine rock salt tests All results consistent with >200 meter attenuation lengths Supported by ground-penetrating radar results since early 1970’s Radar pulses sent through ~3 km of salt in some Gulf-coast salt domes

Summary of WIPP/Hockley results Rock salt is perhaps the clearest medium known for EM propagation Usable frequency range from few MHz to ~10 GHz Evaporite beds (WIPP) have problems with impurities, but salt domes appear to be often purified through geologic processes No measureable bi-refringence or depolarization Allows for possibility of polarization tracking May be better than ice in this respect Several other salt domes known to be as good or better than Hockley Avery Island (LA), Weeks Island (LA) Cote Blanche (LA), Grand Saline (TX) Many others expected to be excellent but as yet unmeasured Typical salt volume 50-100 cubic km per salt dome Several hundred known known salt domes in Gulf coast area, probably thousands throughout the world

Properties of materials for UHE Neutrino Detector Air (STP) Ice (H2O) Rock salt (NaCl) Lime stone (CaCO3) Density ρ (g/cm3) 0.0012 0.924 2.22 2.7 Radiation length X0 (cm) 30420 39 10.1 9.0 Refractive index n = 1.000293 1.78 2.43 2.9 Cherenkov　angle (deg) 1.387 55.8 65.7 69.8 Cherenkov threshold energy(keV) …. 107 50 33 Among the materials, rock salt and lime stone have good properties for short radiation length and low Cherenkov threshold energy. Attenuation length in material is proportional to radio wavelength emitted and inverse proportional to tanδ. tanδis the ratio of imaginary and real parts of permittivity which represents the absorption. Recently, the measurements have been done by P. Gorham et al. in situ measurements and by us in the laboratory. Due to our measurements of synthesized rock salt crystal, we get surprisingly large attenuation has been got. It extends over 1km at 1GHz. It is enough for SND if that of natural rock salt is the same. Rock salt: high density, large refractive index and short radiation length From M. Chiba

Measurements of complex permittivity of rock salts and lime stones Cavity perturbation method Absorption depends on the surface condition of the samples, e.g. smoothness, stain etc. 9.4GHz TE107 Q=4000 Size: 23x10x155mm3 1GHz TM010 Q=10000 Size: 230mmf x 30mm The attenuation length is measured as the absorption of radio wave in the cavity. Two types of cavities are employed.

Samples measured around 10GHz Samples for 9.4GHz cavity. Rock salt is fragile, so that it is not easy to make small stick samples ( 1mm x 1mm x 10.2mm ). Lime stone (especially Jura lime stone ) is rigid. The small stick samples are obtained using a milling machine.

Attenuation length Dielectric resonator Compilation of the attenuation lengths. 10MHz and 25GHz are from Hippel 1954. Three data points are in situ Hockley salt mine measurements. The rest are our measurements. Red points are synthesized rock salt data. At 1GHz the attenuation length is over 1km. Pink points are Hockley mine. At 1GHz it is 180m. M.Chiba