$.post done callback closure issue

$.post done callback closure issue

function submitSurvey() {
      var reason = $("input:radio[name='reason']:checked");
      var reasonVal = reason.val();
      var reasonHelp = reason.attr('reasonHelp');
      var url = $('#surveyForm').attr('action');
      var posting = $.post( url, {reason: reasonVal});

      posting.done(function(data) {
            alert('You selected: ' + reasonHelp);
      });
}

The alert in posting.done doesnt have access to reasonHelp due to the closure (at least that's what Web Inspector is telling me).

How can I get access to reasonHelp within done (after the posting is done/successful)?