You can not change the width of individual rings.

The only work around is to use multiple series for wider rings. You will of course be restricted to the width being a factor of the default width.

Depending on the required size of the chart you might also be able to use a bubble chart where the x and y point is the same for all points and the size variable changes. The maximum size of a bubble is not very large though.

What information is the thickness of the ring communicating?