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        N H(r) = ce(r-rH) 2/2bH + c2            (7.5)

where bH is the standard deviation of the hydrogen distribution and rH is the position of the maximum hydrogen density. The coefficients cl and c2 are evaluated using the boundary conditions


         NH(r) r=O = NH(O), NH(r) r=rH = NH(rH) (7.6)


where NH (0) and NH(rH) are the minimum and maximum hydrogen density, respectively. From (7.5) and (7.6) the hydrogen coefficients are

     NH(O) - N H (rH)     NH(rH)e-rH/2bH - NH(O)
     C-c2 =2                         2          (7.7)

       r2/2b 2- 1               r /2bH
     e HH                        H1

The average hydrogen density is given by


                   H R NH (r)rdr
                     f rdr
                     0

                       2R2
          2        {-[N (r )e-rH/2bH   N
          2 2   2       1                ( )
   R2 (e-rH/2bH -   2   H
                            2            2
     b-[NH(O) - NH(rH)]erH/2bH - e(RrH) /2b']


                .R - r H      -r H

 + 17   rHbH[erf( -     - erf(-                 (7.8)
                /2 bH         /2 b11