Crosstalk Analysis of ATC2 and impurity measurements

Transcription

1 Crosstalk Analysis of ATC2 and impurity measurements Institute for nuclear physics University of Cologne March 29 B. Birkenbach, B. Bruyneel, J. Eberth, H.Hess, D. Lersch, G. Pascovici, P. Reiter, A. Wiens,

2 Crosstalk Crosstalk correction is needed for AGATA Crosstalk is present in any segmented detector* Creates energy shifts proportional to fold* Can be corrected* No crosstalk between detectors in ATC1** Is there crosstalk between detectors in ATC2? * Crosstalk properties of 36-fold segmented hexagonal HPGe detectors; B. Bruyneel, et al.; Nuclear Instrument and Methods in Physics A; 29 ** Technical design report on AGATA detectors: detectors, crystals and cryostat performance

3 Crosstalk and XIA Pixie16 ATC2 measurements with XIA s Pixie16 modules - 6 Co and 137 Cs - 15 of 111 Channels - 7 Pixie16 Modules - 1 MHz, 12 bit - 5GB Listmode 6 Co ΔE [kev] with XIA ΔE [kev] with analog Not final version of ATC2 Red Core (A, ) Green Core (B, 1) Blue Core (C, 2)

4 Crosstalk-analysis Without Crosstalk E core E seg1 E seg2. E segn meas = E seg1 E seg2. E segn true With Crosstalk E core E seg1 E seg2. E segn meas = 1 + δ δ δ n 1 δ δ 1n δ δ 2n δ n1 δ n E seg1 E seg2. E segn true

5 Estimation of the matrix elements Sort one fold events Estimate slope parameter for all combinations (~ 11 )

6 Matrix for Correction Matrix Elements Energy dependence of xtalk-effects on ATC x1e Data Segment δ δ δ n 1 δ δ 1n δ δ 2n δ n1 δ n Hit Segment -2.

7 Motivation - Impurity measurements Why measure the impurity concentration? Detector Simulations need input: Lattice orientation (fixed by Canberra) Mobility parameters (expected as constant) Crosstalk parameters proportional?? derivative! Space charge distribution Best is a fast direct measurement independent of other crystal properties

8 CV-Analysis Capacitance Voltage (CV) Measurements* *First proposed in 1942 (W. Schottky; 1942; Z. Phys.; 118:539) Principle work flow of a 3d CV-Analysis Measure capacitance for different Voltage Reconstruct surfaces of depleted regions Reconstruct space charge distribution from set of surfaces 1 2 3

9 Capacity measurements using the pulser 16 - Measure the shift of the pulser-peak of each segment depending on the applied voltage. - Normalise this to one value (4 Volts) given by Canberra Capacity [pf] A1 A2 A3 A4 A5 A6 C Applied Voltage [V]!!

10 Measure the capacity for different Voltages V Capacity [pf] V 5 V... A1 B1 C1 D1 E1 F1 A2 B2 C2 D2 E2 F2 A3 B3 C3 D3 E3 F3 A4 B4 C4 D4 E4 F4 A5 B5 C5 D5 E5 F5 A6 B6 C6 D6 E6 F6 Segments 4 V

11 Differences between data from Canberra and measured data 5 Theoretical Values for 1V without coupling Capacitor with 1 nf coupling Capacitor cm pf 6 pf 4 capacity [pf] cm -3 3 pf 75 pf Canberra XIA Le Croy A3 - Core bias [V]

12 Take own absolute data Use a Wien-bridge to measure capacities and resistivity R 1 R 2 use a cryostat without U electronics R 3 R x HV C x C 3 U ω detector

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14 Summary and outlook Summary No crosstalk between detectors in ATC2 First steps in impurity measurements are made Capacity measurements work in principle, some differences with data provided by Canberra First Simulations are made and look promising Outlook Do our own absolute measurements with a bridge Further development analysis

15 Thank you Thank you!

16 The capacity data given by the manufacturer The data given was taken by the manufacturer before segmentation and before encapsulation! For the CV-analysis precise values are needed for each segment.

17 Space charge distribution in AGATA-Detectors A crystal of AGATA is made of N-type Germanium with an impurity concentration of.4 to cm -3.

18 Problems with the given data Just more data 6 5 capacity [pf] 4 3 B3 Canberra LeCroy XIA bias [V]

19 Resistivity measurements Three-dimensional electrical impedance tomography apply sinusoidal currents through electrode to a volume and measure the resulting voltages on the electrodes Compute the internal resistivity based on this boundary data Pictures and methods by the Inverse Problem Group, University of Kuopio, Finland

20 data core:1 hit core: x1e Data Segment Hit Segment

21 data core: hit core: x1e Data Segment Hit Segment -2.

22 data core: hit core: x1e Data Segment Hit Segment

23 data core: hit core: x1e Data Segment Hit Segment -1.8

24 data core:1 hit core: x1e Data Segment Hit Segment -1.8

25 data core:1 hit core: x1e Data Segment Hit Segment -.6

26 data core:2 hit core: x1e Data Segment Hit Segment -.6

27 data core:2 hit core: x1e Data Segment Hit Segment

28 data core:2 hit core: x1e Data Segment Hit Segment -2.

29 Capacity anomaly Core to segment capacity (symmetric crystal) Capacity [pf] Measured in S1, total = 46.7pF S2 46.pF S3 46.9pF Calculation: total = 37.4pF -Not a calculation error (est.< 3%) -Not a volume effect (calc.192g) Seg1 Seg2 Seg3 Seg4 Seg5 Seg6 Lithium contact ~ 2.5mm?!?

30 1) Depletion layer boundary estimation " Reconstruction is not unique: Φ(R,θ)=1 " 2D example with coaxial geometry: S 1 Given = 6 capacities C 1 C 6 All solutions for field Φ(r,θ): Φ(r,θ)= Smoothest solution: limit to 6 lowest moments Gauss theoreme -> linear system -> defines C,A 1,A 2,A 3,B 1,B 2 Solution given by Φ(r,θ)=!

31 2) Space charge reconstruction Idea is based on charge neutrality: (e.g. Knoll 3 rd ed. Pag. 373): e.n D -- ρ(x) N D.a = N A.b In 3D, using weightingfields Φ i (x): -a x b -- -e.n A = = Parametrization of ρ(x), e.g. assume V 1 V2 linear system : Q = M α Q