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Doppler Reconstruction for Gamma Spectroscopy: Tracking the First Interaction of a Gamma Ray

This study explores the best method for finding the coordinates of the first interaction of a gamma ray in gamma spectroscopy using Doppler reconstruction and tracking techniques. Experimental and simulation results are compared to determine the most accurate approach.

markchambers
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Doppler Reconstruction for Gamma Spectroscopy: Tracking the First Interaction of a Gamma Ray

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  1. Benchmarking Tracking by Doppler Reconstruction Dirk Weisshaar, NSCL @ Or: What’s the best way finding the coordinates of the first interaction of a gamma ray?

  2. Gamma spectroscopy with fast beam Ge γ rays of 28Si at v/c = 0.38 in GRETINA 36Ar θ v/c ≈ 0.4 S800 28Si ϴ [rad] in GRETINA energy [keV] (laboratory frame) • (Obvious) requirements for a spectrometer: • Doppler-shift correction •  Spatial resolution • Lorentz Boost •  Detection efficiency at forward angle • …and GRETINA is a perfect match beam

  3. Key question for Doppler reconstruction What are the coordinates of the first interaction of the gamma ray? In the past (and for the lazy folks): Use the Main Interaction, which is the interaction point with the highest energy deposition. In the days of tracking: Determine the track of the gamma ray and therefore the first interaction in the track. How I track: Go through all possible tracks/permutation of the interaction points reported in a crystal. Findtrack with smallest figure-of-merit FoM with angle θen computed from energies and Compton formula and θvec computed from coordinates.

  4. Some experimental results Doppler-reconstructed spectrausing MAIN INTERACTION (black) or TRACKED 1st INTERACTION (magenta) 275keV 1779keV

  5. 1779keV, tracked and main interaction Mpt: main interaction point Trkpt: tracked first interaction point For events withMpt ≠ Trkpt using FIRST TRACKED INTERACTION using MAIN INTERACTION

  6. 1779keV, tracked and main interaction Mpt ≠ TrkptMpt used Mpt = Trkpt Mpt ≠ TrkptTrkpt used

  7. diffFoM A FoMMpt can be found as the smallest FoM for all possible tracks with the Main Interaction pointfixed as first interaction point. With FoMTrk being the FoM result from the tracking we define: diffFoM = FoMMpt – FoMTrk (always ≥ 0) Mpt used Trkpt used using MAIN INTERACTION using FIRST TRACKED INTERACTION diffFoM diffFoM

  8. Resolution and diffFoM 0 < diffFoM < 0.2 0.2 – 1.0 1.0 – 2.0 2.0 – 4.0 > 4.0 Trkpt used Mpt used Mpt Trkpt For small values of diffFoM and for large values: Use Main Interaction Point!

  9. Do we learn anything from the FoM value? 0 < diffFoM < 0.2 0.2 – 1.0 1.0 – 2.0 2.0 – 4.0 > 4.0 Trkpt used Mpt FoMTrk FoMTrk FoMTrk FoMTrk FoMTrk FoMTrk FoMTrk FoMTrk FoMTrk FoMTrk Trkpt

  10. A new hope ….(still 1779keV) Consider those events for which number of hit segments equals number of interaction points,i.e. events for which GRETINA decomposition put only ONE interaction per segment. Mpt used #Pts = #Seg Trkpt used#Pts = #Seg using MAIN INTERACTION FIRST TRACKED INTERACTION diffFoM diffFoM

  11. The case where Tracking beats Mpt Mpt used #Pts = #Seg Trkpt used#Pts = #Seg For events where GRETINAdecomp put ONE interactionper segment AND for diffFoM in ‘mid-range’, thetracked 1st interaction leadsto a better result for the Doppler reconstruction. diffFoM diffFoM diffFOM in [0.1:1] Main interactionbetter diffFOM in [1:3] Tracked interactionbetter diffFOM in [3:10] Main interactionbetter

  12. diffFoM/FoM I couldn’t find any helpful meaning of the absolute value of the FoM for the Doppler correction.But how about diffFoM/FoM, as ‘relative improvement from Mpt to Trkpt’? Trkpt used#Pts = #Seg Mpt used #Pts = #Seg diffFoM/FoM diffFoM/FoM Trkpt used#Pts = #SegdiffFoM [1:3] Mpt used #Pts = #Seg diffFoM [1:3] diffFoM/FoM diffFoM/FoM

  13. What does the simulation say? SIMULATION ucgretina, 1779keV, 6mm packing, NO SMEARING W=#pts W=#segs W=1 main interaction Large diffFoMMpt better Tracked 1st interaction 17keV Mpt≠TrkptMpt used Mpt≠Trkpt Trkpt used Tracked 1st main interaction

  14. Conclusion As of now, for performing the Doppler-shift correction the use of the Main Interaction Pointas first interaction point leads to better peak shapes and resolution then using theTracked First Interaction Pointfrom a state-of-the-art tracking algorithm purely based on the Compton-energy formula. Furthermore: Fast beam data with GRETINA is an excellent way to investigate position resolution andthe ability of tracking algorithms to identify the first interaction point of a gamma-ray track.Fast beam data shown is available to everyone interested in it.Also the raw data (traces), allowing to do ‘decomp’ again (other fit, other basis, …)

  15. Discussion Many more slides

  16. n Reconstructed 1779keV, diffFoM with different weights W=#pts W=#segs W=1 main interaction Tracked 1st interaction

  17. Reconstructed 1779keV, gated on events with (Num interaction == Num Segments) W=#pts W=#segs W=1 Mpt Trkpt Main≠TrackedMain used Main≠Tracked Tracked used Tracked 1st

  18. n Experimental spectra: Black: all events, main interaction used (100%, FWHM 15.1keV, ~84000cts) Magenta: main interaction = tracked interaction (50%, FWHM 14.4keV, ~42000cts) Red: main = tracked, #interaction=#segments (11%, FWHM 13.3keV) Normalized bytotal countsin [1500:2000] Normalized by peak amp Log scale Normalized by peak amp Linear scale Not normalized

  19. n Comparison simulation with ‘realistic’ position resolution. Black: simulated, ALL event and main interaction used Red: simulated, as black, but position smearing of sigma=1.8mm usedBlue: In-beam data, events with #interaction=#hit segment, tracked=main interaction.

  20. n 19Ne, beta .3870 3.3%, 272keV NNDC: 275.1 21Ne, beta .3566 2.1%, 349.5keV NNDC: 350.7

  21. n 23Na, beta .3580 1.3%, 627.7keV NNDC: 627.5 23Na, beta .3586 1.5%, 439.7keV NNDC: 440.0

  22. n 30P, beta .3671 1.6%, 705.0keV NNDC: 708.7 26Al, beta .3716 1.1%, 829.3keV NNDC: 829.3

  23. n 26Al, beta .3730 1.1%, 1011.2keV NNDC: 1011.7 24Mg, beta .3714 0.9%, 1368.7keV NNDC: 1368.6

  24. n 28Si, beta .3722 0.9%, 1779.1keV NNDC:1779.0 24Mg, beta .3740 0.8%, 2755.1keV NNDC: 2754.0

  25. n 28Si, beta .3746 0.9%, 2839.5keV NNDC:2838.3 28Si, beta .3763 0.9%, 5107.9keV Nndc:5107.6

  26. n 16O, beta .375 1.6%, 6116keV NNDC: 6129

  27. Decomp (Mpt) vs segment based

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