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Unique Qualities for Underground Particle Physics Research

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shoparea-s.jpg (19433 bytes) At a depth of 650 m (>2000 mwe shielding), the WIPP underground is surrounded in all directions with a bedded salt deposit containing low levels of primordial radioactivity.  Because of its evaporite deposition and the mining methods used, the mine is extremely dry, seismically inactive and acoustically quiet.

The Experiment Gallery and the Waste Handling/Disposal areas are ventilated with different and separate circuits. Waste handling and disposal operations are conducted many hundreds of meters (through solid halite) distant from the Experiment Gallery. Radiation levels in the Experiment Gallery are not affected by waste handling and isolation in the disposal rooms.

Typical levels of primordial radioactivity measured in bulk samples taken from the existing mine horizon are less than typical hard-rock mines:

Uranium Thorium Potassium (K-40)

30 - 50 ppb

70 - 80 ppb

0.1 - 0.8 ppm

Free neutron flux levels were measured by OSU (Boyd, et. al., Nuclear Instruments and Methods in Physics Research, A 399, 1997, pp 269-274) at 332 +/- 148 neutrons/m2/day.  Thermal and epi-thermal neutron flux levels were measured at 115 +/- 22 neutrons/m2/day.

With such low levels of natural Uranium, and with high constant ventilation, Rn-222 levels in the WIPP underground are dominated by surface air concentrations (Rn-222 < 7 Bq/m3).

For overburdens greater than about 100 mwe, the neutrons from fission and (alpha,n) reactions dominate the thermal and epi-thermal energies. However, the much harder to measure flux of energetic neutrons created by nuclear capture of negative muons in deep inelastic muon-nucleus scattering is chiefly a function of muon flux. At WIPP's depth, we expect a muon flux (this has not been measured yet) of about 2x10-3 /m2/s