ASP.Net c# Which radio button in a given GroupName is selected?

I have 30 individual RadioButtons. I can not use a RadioButtonList. There are 3 groups of buttons. Each group has a unique GroupName. Everything works properly in the web browser. How can i tell on a post back which button is selected within each of the given GroupsNames?

EDIT: the function i used

private string getRadioValue(ControlCollection clts, string groupName)
{
    string ret = "";
    foreach (Control ctl in clts)
    {
        if (ctl.Controls.Count != 0)
        {
            if (ret == "")
                ret = getRadioValue(ctl.Controls, groupName);
        }

        if (ctl.ToString() == "System.Web.UI.WebControls.RadioButton")
        {
            RadioButton rb = (RadioButton)ctl;
            if (rb.GroupName == groupName && rb.Checked == true)
                ret = rb.Attributes["Value"];
        }
    }
    return ret;
}