oracleconnection.close() dont close the connection in my session browser

Question

 I make run of test connection, I expect to see clear session browser, but at the end of the program, I see more then 6 sessions in my session browser
This is the code:
private void testConnection()
{
string connectionString = "data source=(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=10.206.2.16)(PORT=1521))(CONNECT_DATA =(SERVER = DEDICATED)(SERVICE_NAME = DEVCALC)));user id=nava_am;password=amrani08;Min Pool Size=10; Connection Lifetime=120;";
OracleConnection oraConn = new OracleConnection(connectionString);
        try
        {
            oraConn.Open();
        }
        catch (Exception e)
        {
        }

        finally
        {
            oraConn.Dispose();    //or without this function
            oraConn.Close();
        }
}
plz, help me!!