rkr detector system -...

1. The detector arrangement

2. The lifetime system

3. Digital Doppler measurement

4. AMOC

RKR

Martin-Luther-Universität Halle

The detector system of the EPOS systemThe detector system of the EPOS system

• 3 experiments: lifetime spectroscopy (16 BaF2 detectors); Doppler coincidence (2 Gedetectors), and AMOC (1 Ge and 1 BaF2 detector)

Detector systemDetector system

• digital detection system:

- lifetime: almost nothing to adjust; time scale exactly the same for all detectors; easy realization of coincidence

- Doppler: better energy resolution and pile-up rejection expected; easy coincidence setup

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MC-simulated spectrum:lifetimes: 0.15 ns 2 ns 140 nsIntensity: 5 % 10 % 85 %

Cou

nts

Time (ps)

Repetition time: C E G I

Simulation parametersStatistics: 107

FWHM: 0,2 nsBackground: 0,04%Channel width: 0,1 ns

Beam repetition time for lifetime spectroscopy Beam repetition time for lifetime spectroscopy


• trep=77 ns repetition time is standard operation mode at ELBE

• is used for FEL’s

• is perfect for lifetimes τ < 7 ns, i.e. most materials

• for nano-porous materials: trep too short

• slow mode with trep > 500 ns necessary

• real advantage of electron LINAC

• primary time structure can be adopted with low loss of overall intensity • thumb rule: τmax = 0.1 trep

Lifetime systemLifetime system


• lifetime will be measured with direct digitizing of anode pulses

• external coincidence system is required to avoid useless digitizing (not shown)

one of eight parallel lifetime channels

Lifetime systemLifetime system


• problem with mixing into one channel: delay cable must be elongated for slow mode

• several choices for the detector tubes: XP2020, HH3378-50, R7400U-096, and also the MCP-PMT’s(previous talk)

Selection of PMT

Philips

Type XP2020QHead-on

H3378-50Head-on

R7400U-096Metal package

R3809U-57MCP-PMT

photocath.diameter (mm)

BA51.0

BA51.0

Cs-Te11.0

Cs-Te11.0

voltage (V)gain

rise time (ns)transit time (ns)TTS (ps)

1.4 0.7 0.78 0.1528 16 5.4 0.55~250 370 ~100 25

windowrange (nm)peak λ (nm)quant. eff.

fused silica fused silica fused silica160-650 160-650 160-320420 420 2400.25 0.24 0.113000 3000 800 -30003×107 2.5×106 5×104 2×105

cost (EUR)

MgF2115-320

2300.11

1000 3650 700 15000

EPOS-02 (J. Cizek)

XP 2020XP 2020


Sweep of two anode signals

Digital lifetime spectrometer

• XP 2020 too slow for a positron pulse of σt< 100 ps (TTS ≈ 250 ps)

recorded with 2 GS/s

• successfully used e.g. at Tokyo University by H. Saito

• obtained resolution of 110 ps in coincidence setup (only ≈ 50 counts/s)

• not very stable in long-term use

• two tubes available in Halle

• in May 2004 we’ll get 2 Photek MCP-PMTs for testing -> we will compare all detectors for final decision


Hamamatsu H3378Hamamatsu H3378--5050

photo taken at Tokyo University


Anode spectrum of Hamamatsu R7400UAnode spectrum of Hamamatsu R7400U--0909

• a faster digitizer is required (>= 4 GS/s)

• however: very small window (only 10 mm opening)

• Anode pulse of ultra fast Hamamatsu R4700U-09 as measured with 2 GS/s digitizer

• spectral sensitivity fits best for BaF2: sensitivity for slow component (310 nm) reduced by 0.10 compared to fast one (220 nm)

recorded with 2 GS/s

R 7400U-09

Cs-Te + silica photocathode

EPOS-02 (J. Cizek)

slowfast

• geometrical problem when arranging 16 detectors in a ring


PhotekPhotek PMT 325PMT 325

• expected pulse height of single-stage PMT´s: ≈1 mV

• however: expected lifetime > 10 a of continuous operation

• amplification necessary (40…60 dB)

• easily done for fT > 5 GHz

• amplifiers also necessary to decouple the anode pulses when mixed together to one coincidence channel

• otherwise the anode pulses are intermixed and the coincidence circuit cannot work


Amplifiers necessaryAmplifiers necessary

• sample rate can be smaller 50…100 MHz

• resolution should be 14 bit (16384 channels)

• when 511 keV is at 80% of maximum energy -> 39 eV/ch

• only one such digitizer available: Compuscope 14100 (GaGe)

• is PCI-Card with dual input (single input: 100 MS/s and dual input: 50 MS/s)

• one card with additional memory is available in Halle (27 k€)


Digital Doppler measurementDigital Doppler measurement

• single channel Doppler and coincidence mode easy to realize by software

• hope: better energy resolution, higher throughput

• better time resolution expected

• more accurate detection of pile-up pulses -> lower background at E > 511 keV

• which is only reason for high momentum background in a 511 keV system


Doppler coincidence easy to realizeDoppler coincidence easy to realize

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recorded with 50 MS/s and 12 bit resolution

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• when additional disturbance of signal -> pulse will be ignored

• example additional RF of about 1 MHz overlayed

• only pulses with certain shape can be selected


LineLine--shape discrimination possibleshape discrimination possible

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Channel B Channel A

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recorded with 50 MS/s and 12 bit resolution

• combination of lifetime and Doppler spectroscopy

• test needed -> can both cards operated in the same PC

• external coincidence required


AMOCAMOC

• Digital detector for the whole EPOS possible

• Main advantages:

- hardly anything to adjust

- extreme stability

- easy remote control

- time scale for all detectors exactly known and equal within 10-5

- line-shape discrimination of pulses possible

• drawback: pulse rate of a single detector limited by online software processing of pulses to about 5x104 s-1


ConclusionsConclusions

Thank you for your attention!

This presentation can be found as pdf-file on our Websites:http://positron.physik.uni-halle.de

http://positronannihilation.net

contact: [email protected]

rkr detector system -...

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