Gain Matching

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To easily gain-match, you can use the TGainMatch class. A separate TGainMatch is created for each channel. You can create a TGainMatch by invoking:

TGainMatch *myGain = new TGainMatch; 

You can specifically set the channel of the TGainMatch using

myGain->SetChannel(channel_number);

Coarse Gains

To effectively gainmatch automatically, we need to make sure the gains for each channel are set roughly to the correct value. If this isn't already the case, you can use the CoarseMatch method of TGainMatch. This method works best on sources with two very strong transitions such as 60Co. To gain match a specific channel, use:

   myGain->CoarseMatch(histogram,channel_number,low_energy,high_energy);

where histogram is the TH1* to gain match, channel_number is used if you want to gain match a specific channel, low_energy is the lowest energy peak to gain match, and high_energy is the highest energy peak to gain match. low_energy and high_energy are defaulted to the 60Co values.

Once the gain-matching is complete, the energy coefficients can be written to the TChannel,

myGain->WriteToChannel();

and the TChannels can all be written to a cal file using the normal TChannel::WriteCalFile("name_of_cal.cal")

The way coarsematching works is by searching out the two largest peaks, and calling that the low and high energy peaks. This is why this works best for 60Co. These peaks are found, fit, and a gain and offset is calculated. As these peaks are very close together, this is just to roughly determine the calibration parameters as almost every energy will be an extrapolation from these two close points. Once the data is coarse matched, the gains can be more finely gainmatched.

Using CalManager

You can add TGainMatch instances to a TCalManager. This can be done using:

myCalManager->AddToManager(myGain);

If the channel has not been set for the TGainMatch, you can also call

myCalManager->AddToManager(myGain,channel_number);

To automate the gain-matching and filling of a cal manager, you can use the static function:

TGainMatch::CoarseMatchAll(myCalManager,charge_chan_mat, low_energy, high_energy);

where energy_chan_mat is the TH2* of Charge vs. ChannelNumber, low_energy is the lowest energy peak in the gain match, and high_energy is the highest energy peak in the gain match. low_energy and high_energy are defaulted to the 60Co peaks (see above). Once the TGainMatch::CoarseMatchAll is finished, myCalManager will be filled with the gains of every channel fit. It should be noted that the cal manager is filled with a deep copy of the TGainMatch and not a reference to it. TCalManager explains how to access the various TGainMatches contained it. Finally, to write these gain coefficients to the Channels, use

myCalManager->WriteToChannel();

This calls the WriteToChannel() function for each TGainMatch contained in the TCalManager.

Fine Gain Matching

Fine gain matching is what we normally think of gain matching as. The fine gain matching class will accept two charge histograms, a test channel, two peak energies, and attempt to calibrate these spectra accordingly. The way this works is first by attempting to match up the test channel (something reasonably calibrated) with the current channel to determine if there were any large gain jumps. Once this is done, the newly roughly matched energy spectrum is used to determine roughly were the gamma rays should be in the charge spectrum. The peaks are found in the charge spectrum, fit, and a new "fine matched" set of energy coefficients are created.

To fine gain match using one source, use:

   myGain->FineMatch(energy_histogram, test_histogram, charge_histogram, low_energy, high_energy);

To fine gain match all of the channels, you can use the FineMatchAll function. It works just like the FineMatch function, except a TH2* is passed instead of a TH1*, and a TCalManager is required. You must pass the hit-pattern vs. charge as the TH2*. For example,

TGainMatch::FineMatchAll(myCalManager, hp_vs_charge, hp_vs_energy, test_histogram, low_energy, high_energy);

To write the fine gains to the channel, you do it the same as with course gains.

myGain->WriteToChannel();

Or with a TCalManager full of gains

myCalManager->WriteToChannel();

Manual Gain Matching

You can also calculate gains manually. One you have fit two peaks in the charge spectrum, you can use:

myGainMatch->CalculateGain(centroid_1, centroid_2, energy_1, energy_2);

A print out of the p0 offset and p1 gain will be created for that channel. This can be copied into your calibration file.