To identify peaks with transition energies from a decay you need a relation between the channels of your spectrum and their corresponding energies (calibration). To calibrate a spectrum, you need to identify two peaks in the spectrum or a calibration from a calibration spectrum. The energies of these positions can be determined from a calibration spectrum. If you know two channels and their corresponding energies, you can define the calibration with the command:
tv calibration position enter chn energy chn energy
If you have a calibration in a file you can load it. To load a calibration you can either use the hotkey E to load the default calibration file *.cal or you switch to the text-mode and enter the full command:
tv calibration position read calfile
You can abbreviate this command with:
tv c p r calfile