def getMaterialString(self):
        """
        Returns the MCNXP material string
        """
        matString = 'm10   1001.70c  -0.080538       $Lucite (PMMA / Plexiglass)    rho = 1.19 g/cc\n'
        matString += '      6012.70c  -0.599848    8016.70c       -0.319614                       \n'
        matString += 'm204  7014.70c      -0.755636  $air (US S. Atm at sea level) rho = 0.001225 \n'
        matString += '      8016.70c      -0.231475 18036.70c     -3.9e-005 18038.70c      -8e-006\n'
        matString += '      18040.70c     -0.012842                                               \n'
        matString += 'm5    98252.66c  1  $ Cf-252, rho =15.1 g/cc wiki                           \n'
        matString += 'm406  82204.70c     -0.013781  $Lead,                                       \n'
        matString += '      82206.70c     -0.239557 82207.70c     -0.220743 82208.70c     -0.525919\n'
        matString += 'm456  1001.70c      -0.143716  $Polyethylene - rho = 0.93 g/cc               \n'
        matString += '      6000.70c      -0.856284                                                \n'
        matString += 'm488  14028.70c     -0.009187  $Steel, Stainless 316 rho = 7.92              \n'
        matString += '      14029.70c     -0.000482 14030.70c     -0.000331 24050.70c     -0.007095\n'
        matString += '      24052.70c     -0.142291 24053.70c     -0.016443 24054.70c     -0.004171\n'
        matString += '      25055.70c         -0.02 26054.70c     -0.037326 26056.70c     -0.601748\n'
        matString += '      26057.70c     -0.014024 26058.70c     -0.001903 28058.70c     -0.080873\n'
        matString += '      28060.70c     -0.031984 28061.70c     -0.001408 28062.70c     -0.004546\n'
        matString += '      28064.70c     -0.001189 42092.70c     -0.003554 42094.70c     -0.002264\n'
        matString += '      42095.70c     -0.003937 42096.70c     -0.004169 42097.70c     -0.002412\n'
        matString += '      42098.70c     -0.006157 42100.70c     -0.002507                        \n'
        matString += 'mt3   poly.01t                                                               \n'
        matString += 'mt456 poly.01t                                                               \n'
        matString += 'mt10  poly.01t                                                               \n'
        return matString