You have this kind of options. You can go for the

Code:
Path.GetTempFileName()
Creates a uniquely named, zero-byte temporary file on disk and returns the full path of that file.

Code:
System.Guid.NewGuid
to get a unique GUID

Or You can use the current time(with seconds) with that RadioButton to create unique id

Code:
System.DateTime.Now.ToString("ddMMyyyhhmmss")