I would try the "width" attribute.
Another option would be to use "columnClasses" on the rich:dataTable.
See the developer documentation - it contains almost every relevant information.
Another thing: If you ASK something then don't end your question with "!!" - that does not really look polite.
Oh, and rich:dataTable columnsWidth would work too.
Thank you for your response.
I have found the solution to this problem