check only one checkbox at a time

<script type="text/javascript">
function CheckBoxCheck(rb) {
            debugger;
            var gv = document.getElementById("<%=GridView1.ClientID%>");
            var chk = gv.getElementsByTagName("input"); ;
            var row = rb.parentNode.parentNode;
            for (var i = 0; i < chk.length; i++) {
                if (chk[i].type == "checkbox") {
                    if (chk[i].checked && chk[i] != rb) {
                        chk[i].checked = false;
                        break;
                    }
                }
            }
        }

<asp:GridView ID="GridView1" runat="server"> 
<columns>
 <asp:TemplateField HeaderText="check">
<edititemtemplate>
<asp:CheckBox ID="CheckBox1" runat="server" />
</edititemtemplate>
  <itemtemplate>
<asp:CheckBox ID="CheckBox1" runat="server" OnCheckedChanged="CheckBoxCheck(this);" />
</itemtemplate>

</columns>