High granularity to reduce the effect of the “prompt flash” radiation Polarization sensitivity Imaging capabilities for background suppression DESPEC (DEcay SPECtrocsopy) γ-ray tracking cluster Stanislav Tashenov GSI, Darmstadt Pulse Shape Analysis to improve the position resolution Tracking of the γ-rays back to the origin

Stack of 3 planar 2D stripe Ge detectors 68mm 2 x 68mm 2 x 20mm 2 + 2mm guard ring 6mm gap between crystals 8x8 segmentation 1 – 3 mm 3D position resolution with PSA Energy resolution: 0.2% Detector Module

time energy Current RISING cluster : 128 Cd Tasks: Improve the correlation between the implantation and the decay for long-lived isomers Identify gamma events from the background sources Suppress the Compton background Increase the absolute efficiency by reconstructing the initial energy from the Compton escape events Motivation: background suppression

Identification of the photopeak events and the escape events Reconstruction of the initial energy from the escape events Rejection of the events from background sources Tracking algorithm features

Construction of the “Figure of Merit” for all possible interactions sequences for the case of the photopeak and the escape event Selecting the case witch maximizes the Figure of Merit Tracking principle

Figure of Merit for the photopeak event

Figure of Merit for the escape event initial energy estimation Energy estimation: Weighted average:

Figure of Merit for the escape event

Results: photopeak events Compton escape suppression without BGO shields. This effect is impossible to achieve without tracking!

Increase of the Peak / Total Significant increase of the Peak/Total ratio (~90%) with respect to the non-segmented detectors without use of BGO shields Tracking efficiency doesn’t include single hit interactions, pair production, bremsstrahlung etc. MGT code: EnergyEffic.P/T [MeV] no increase in P/T

Efficiency gain with respect to non-segmented detectors Energy MeV Tracking Efficiency (escape) Tracking Efficiency (total) Results: escape events Energy Resolution: FWHM: ~1.5% Lorencian Profile

Optimization - resolution/efficiency

Background suppression via Imaging

“Ideal” (100% efficient) tracking assumed Background suppressed spectrum

Trade-off between background suppression factor and statistics left in spectrum Background suppression by a factor of 10 possible while keeping ≈ % of events! (1 mm position resolution)

Outlook Tracking after PSA (together with A. Kaplanov, KTH Stockholm) Tracking in realistic experimental situation in presence of Bremsstrahlung photons (together with P. Detistov, Sofia) Tracking for Multiplicity > 1

End

Germanium shell (AGATA) R inn = 15 cm R out = 24 cm E Tracking P/T (keV) efficincy Resolution = 3 mm Closest distance = 5 mm

Dependance of the background suppression factor on the position resolution

Optimization with respect to the Figure of Merit “triangle”

Simulation with the background radiation: Cleaning of the Compton component of the background “Software” anti-Compton shield → no BGO required

Background suppression via Imaging ħωħω E

DESPEC γ- tracking array Open symbols: results of MGT tracking code Filled symbols: results of the new algorithm S. Tashenov GSI Significant increase of the Peak/Total ratio (~90%) with respect to the non-segmented detectors without use of BGO shields

DESPEC γ- tracking array S. Tashenov GSI Energy MeV Tracking Efficiency (escape) Tracking Efficiency (total) Energy Resolution: FWHM: ~1.5% Lorencian Profile Significant increase of the photopeak efficiency (by 50%) with respect to the non-segmented detectors due to the reconstruction of the energy from the Compton escape events

DESPEC γ- tracking array S. Tashenov GSI Suppression of the background by factor of 10 while keeping 90% of statistics Compromising statistics it is possible to achieve the factor of 100