Correlation of two variables correlation coefficient between rows

I have two variables the radius and the mean value of the values inside this radius. The radius gets bigger in a linear way at a fixed step size. The Rows represent the observations e.g.:

radii    value
11      5*10^-4
21      5*10^-4
..      ..

when i use corr / corr2 /coeff

>> corr(radius_bla_rot,field_1_mean_rot_90)

ans =

      0.0930

>> corr2(radius_bla_rot,field_1_mean_rot_90)

ans =

      0.0930

>> corrcoef(radius_bla_rot,field_1_mean_rot_90)

ans =

      1.0000    0.0930
      0.0930    1.0000

I just get one value (0.0930) which tells me that my data has a weak correlation. And now I want to see if there are some radii which correlate and then when the radii get too big there is no more correlation. I have attached the data I am working with right now.