Is there a way to determine the Facebook Page or Application in a HTTP referral

I run Facebook advertisements, and when the users show up, their HTTP referer [sic] is something akin to:

http://www.facebook.com/ajax/emu/end.php?eid=

Where the 7-bit encoded string =~ [A-Za-z0-9_-]+

What is the format of that string开发者_开发百科? It's not base64. And can I extract from that data the page or app that my advertisement was displayed on that the user clicked on my ad?