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We are exploring the possibility of using mica to set limits on weakly interacting massive particles (WIMPs). Mica is a solid state nuclear track detector capable of recording the keV/amu recoil atoms produced in WIMP-nucleus collisions. One way to apply this idea is to look for fossil tracks in mica as old as 1 billion years. The mica is used as a detector and as a target. To carry out this experiment we select mica which is very old and found very deep underground (to reduce background from muon induced recoils). Then we choose a target atom within the mica, typically Iron or heavier. Given the flux of WIMPs, their interaction cross section with the target nucleus, and a WIMP mass we can calculate the number of recoils produced inside the mica during its lifetime. The damage caused by the recoil is stored and can be revealed by placing the mica in a suitable etchant. The WIMP-recoil etch pits must be separated from a background of etch pits caused by the recoiling daughters of Uranium and Thorium after alpha decay which produce etch pits of comparable size. We believe this is possible using an atomic force microscope to measure the etch pit depths. By limiting the amount of WIMP-recoils we observe we can set limits on the WIMP masses and interaction cross sections. For reasonable values for the age of mica and target concentrations we can hope to set limits which are several orders of magnitude better than current limits. The status of this search will be reported.
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