Page get stuck when using AJAX
===

I'm using AJAX for presenting calculation results.
i'm calling for a PHP file that returns the result, and than i present it on the web page.

sometimes the calculation duration is taking a long time, and the page get stuck until the AJAX call has returned with the answer.

is there a way for using ajax, and still get the ability to perform other actions on the web page, and don't have to wait until the AJAX call has returned.

I'm using this AJAX call function( a standard function as i know).

    function GetCalculation(str)
    {
    var result ;
    if (window.XMLHttpRequest)
      {// code for IE7+, Firefox, Chrome, Opera, Safari
      xmlhttp=new XMLHttpRequest();
      }
    else
      {// code for IE6, IE5
      xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
      }
    xmlhttp.onreadystatechange=function()
      {
      if (xmlhttp.readyState==4 && xmlhttp.status==200)
        {        
    		result = xmlhttp.responseText ;        		
        }
      }
      
    xmlhttp.open("GET","GetRouts.php?q="+str,false);
    xmlhttp.send();
    result = xmlhttp.responseText ;
    return result;
    }

Thank you,
Guy