Radio Button in Repeater

Question

Hi

 I want by default Radio Button should be ticked. I am using below code but it is not worling. If i Uncheck nithing happens

<asp:Repeater ID="rptData" runat="server" OnItemDataBound="rptParticipant_ItemDataBound"> 
<ItemTemplate> 
<tr> <td>
<asp:Literal ID="ltrlNum" Text="<%# Convert.ToString(Container.ItemIndex + 1) %>" runat="server"></asp:Literal></td> 
<td > <asp:Literal ID="ltrlNomineeName" runat="server" Text='<%# Eval("Name") %>'></asp:Literal> </td> 
<td > <asp:Literal ID="ltrlDesignation" runat="server" Text='<%# Eval("Designation") %>'></asp:Literal> </td> 
<td > <asp:Literal ID="ltrlPhoneNo" runat="server" Text='<%# Eval("PhoneNo") %>'></asp:Literal> </td> 
<td > <asp:Literal ID="ltrlEmail" runat="server" Text='<%# Eval("Email") %>'></asp:Literal> </td> 
<td class="text-center"> 
<div class="btn-group btn-group-toggle" data-toggle="buttons"> 
<asp:RadioButton ID="rb1" runat="server" class="form-check-input-styled" AutoPostBack="true" OnCheckedChanged="rbtnSelectEmp_OnCheckedChanged" /> </div> </td> 
</tr> 
</ItemTemplate> 
</asp:Repeater>

protected void rbtnSelectEmp_OnCheckedChanged(object sender, EventArgs e)
{
    foreach (RepeaterItem item in rptData.Items)
    {
        RadioButton rbtn = (RadioButton)item.FindControl("rb1");
        rbtn.Checked = false;
    }
    ((RadioButton)sender).Checked = true;
}

Thanks