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DEAR SDD --> SIDDHARTA Si licon D rift D etector for H adronic A tom R esearch and T iming A pplications Carlo Fiorini (Politecnico di Milano) Development of a soft X-ray detection apparatus, based on Silicon Drift Detectors (SDD), with high energy resolution

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slide1

DEAR SDD --> SIDDHARTA

Silicon Drift Detector for Hadronic Atom Research and Timing Applications

Carlo Fiorini

(Politecnico di Milano)

Development of a soft X-ray detection apparatus,

based on Silicon Drift Detectors (SDD),

with high energy resolution

and high background reduction

for application in exotic atoms researches

slide3

Exotic

atom

e.m. position

of K line

(keV)

(eV)

(eV)

Required precision

 (eV)

 (eV)

hydrogen

6.46

 160

 200

~ 5

~ 10

deuterium

7.81

 500

 800

~ 25

~ 100

Experimental requirements

slide5

The classical PIN diode detector

The anode capacitance is proportional to the detector active area

slide6

The Semiconductor Drift Detector

The electrons are collected by the small anode,

characterised by a low output capacitance.

Anode

Advantages:very high energy resolution at fast shaping times, due to the small anode capacitance, independent of the active area of the detector

slide7

The Silicon Drift Detector with on-chip JFET

  • JFET integrated on the detector
  • capacitive ‘matching’: Cgate = Cdetector
  • minimization of the parasitic capacitances
  • reduction of the microphonic noise
  • simple solution for the connection detector-electronics in monolithic arrays
  • of several units
slide8

The integrated JFET

Detector produced at the MPI Halbleiterlabor, Munich, Germany

slide10

Silicon Drift Detector performances

Quantum efficiency of a 300 mm thick SDD

55Fe spectrum measured with a SDD

(5 mm2) at –10°C with 0.5 ms shaping time

slide11

Silicon Drift Detector Droplet or SD3

T=-30°C a τsh=1µs

Canode= 50 fF

(vs. 100fF conventional SDD)

slide13

SDD PIN Si(Li) 150 K 5.9 keV line

800

700

PIN Tsh=20us

600

500

FWHM (eV)

400

300

Si(Li) Tsh=20us

200

SDD Tsh=1us

100

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

A (cm-2)

Spectroscopic resolution: detector comparison - 1

slide14

Spectroscopic resolution: detector comparison - 2

FWHMmeas of monoenergetic emission line 5.9 keV

1cm2detector at 150 K

SDD FWHM=140eVtshap =1ms

Si(Li) FWHM=180eVtshap =15ms

PIN diode FWHM=750eVtshap =20ms

CCD FWHM=140eVtframe=1s

slide15

Measure of the line shift – ideal case *

The case: kaonic hydrogen, 200 cm2 detection systemFor 6000 events (~50 pb-1 )

Estimated peak position 6.3 keV, line width about 245 eV, peak shift about 160 eVDetection system based on SDDs

* No background contribution considered

slide17

IK

IA

hn

hn

t

IA

tdr max

t

Timing with the anode signal

slide18

Timing resolution with SDD

A=0.1cm2 Tdrift = 70ns

A=0.5cm2Tdrift =350ns

A= 1cm2Tdrift =700ns

With:

r= 2kW/cm

H = 450mm

slide19

Kaontrigger

Concidencewindows

tdr max

Detectedpulses

Consideredpulses

Kaon trigger

X-ray pulse

Background pulse

Triggered acquisition

slide20

Background reduction with triggered acquisition

r =number of detected kaons per detected X-ray = 103Br=background rate = 103 events/s

Tw=sinchronization window

Tw = r xt drift max = 103x 1 ms = 1ms

B = Brx Tw = 103 s-1x 10-3 s = 1

S/B = 1/1

slide21

Signal/Background with CCD

·Actual value of the S/B ratio measured with DEAR atDANEusing CCDsS/B  1/100 in kaonic hydrogen

expected:

S/B  1/500 in kaonic deuterium

slide22

IK

IA

hn

hn

t

IK

t

IA

tdr max

t

Timing with the prompt signal from the backplane

Estimated time resolution: about 300 ns

slide24

Monolithic array of Silicon Drift Detectors

Pixel area = 5 mm2

Total array area = 95 mm2

slide25

Pb plate

Ti foil

Zr foil

X-ray lines

BTF e+/e - beam

S1

S2

scintillators

Pb shielding

e+, e –g

shower

SDD X-ray detector

(4 chips prototype)

DEAR test setup (SDD) at the BTF

slide26

Operations:

The first stage of the project of the new detector deals with the characterization of the SDD performances.

The characterization concerns the finalization of trigger efficiency and energy resolution, as a function of background environment and time window. This information will fix also the dimension of the single cell. These measurements are planned to be performed with a prototype device. The answers coming from these tests will be used for the construction of the final detector array and associated electronics with optimal characteristics.

slide27

Beam conditions at BTF:

Energy: varying between 50 ÷ 750 MeV

Intensity: varying between 1÷ 103e+/e- s-1 (preference is for positrons)

tbunch :  10 ns; bunch frequency: 1 ÷ 49 Hz

Gate window 0.1 – 1 ms

BTF run period required:

2-4 weeks in the period June 2003 - October 2003

slide28

The detector: 1 cm2 SDD prototype

Front-side: field strips, JFET

Back-side: entrance window

  • 65 rings, 1 cm2 area
  • 280mm high-resistivity + 12mm epi-layer

detector presently under test at Politecnico di Milano

slide29

Preliminary measurements

Leakage current ~ 3 nA @ room T

Voltage divider threshold voltage

~ -50V for 8 rings ( 65 rings bias

should be feasible with ~ - 400V)