$('#ddlBuyer').click(function() {
    $('div#radios input').attr('checked',false);
});
where div#radios encloses all your radio inputs. I'm assuming ddlBuyer is the id of something that gets clicked.
We can't give an answer in regard to #radTopx since we don't know what it is. 
                  carillonator
                   2009-11-30 17:41:34