Cut 2D-histogram

I am currently trying to analyze the energy loss of electrons in an active target gas. When I drew a 2D histogram with the ∆E/∆s versus ∑∆s (i.e. energy loss per step divided by the length of the step, versus the accumulated depth of the electron) I get the following histogram:

2d_histo.pdf (303.4 KB)

I don’t understand where this accumulation of points is coming from (it seems pretty unrealistic). Besides, the histogram seems to end sharply just above it. I do not know what is causing these effects

ROOT Version: 6.22/07
Platform: MacOS
Compiler: Not Provided

By “accumulation of points” I meant the thick horizontal bar located around 60 keV/mm

Hi Javier,

true, both effects (the excess at 60 keV/mm and the cut-off at 75 keV/mm) look unrealistic. I’d suggest to check the code that produces your histogram.

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Hi yus, here is a piece of the code:

    string str;
    while(getline(*file, str))

        *file >> stepNumber >> Edep >> stepLength;


    TCanvas *c2 = new TCanvas("c2", "Bragg canvas");
    Int_t bragg_bins = 1000; // bins of histogram
    TH2F *bragg_hist = new TH2F("bragg_hist", Form("%s, %.2f MeV, %.0f K, %.0f mbar, %.0f V/cm", string(gas).c_str(), initial_energy, temperature, pressure, electric_field), bragg_bins, 0, 1400, bragg_bins, 0, 200);
    Double_t depth = 0; // accumulated depth
    Double_t stoppingPower;
    for(Int_t i=0; i<Edepvec.size(); i++)
        if (stepNumbervec[i] != 1)
            // stick to the same electron? -> add the step length to the total range
            depth += stepLengthvec[i];
            stoppingPower = Edepvec[i]*1000/stepLengthvec[i];
            bragg_hist->Fill(depth, stoppingPower);
            // another electron? -> filling the last step of the previous one and clear depth
            depth = 0;
    //bragg_hist->Rebin2D(4, 4);

I didn’t upload it originally because it seemed pretty straightforward to me… The code reads a .txt file with the step number of the electron trajectory, the energy lost in that step and the length of the step, for example:
1 0.000125801 0.325053
2 0.0325084 74.1814
3 0.052952 120.936
4 0.0850733 226.414
5 0.0120996 31.1658
(where the second column is in MeV, and the third is in mm).
If you spot any problem please let me know. Otherwise I guess I will have to start looking at the Geant4 simulation that generates the file.

Thanks in advance

How large is this text file of yours? Can you post it here or maybe share it via your favorite file-sharing service like Dropbox/Google Drive/Mega etc.?

It is quite large actually. This is the link to the file uploaded to google drive:

I must say, however, that when I ran the simulation for protons, just to see if I recovered the Bragg peak, I got this histogram for 3 MeV protons:

And none of the effects I observed with the electrons histogram appeared.

Yes, I reproduced the plot. There is probably something wrong with the way your text file was generated.

1 Like

Yes, that is what I am looking at right now. Guess I’ll have to post a topic in a Geant4 forum :laughing:. Thank you anyway for the help!