roma jan.2006 whim and mission opportunities wide field monitor prospect for use of silicon and...

Roma Jan.2006 WHIM and mission opportunities

Wide Field Monitor

Prospect for use of Silicon and scintillator detectors

Based on work made at:

IASF - INAF Sezione di Bologna

IASF - INAF Sezione di Milano

IASF - INAF Sezione di Roma

ENEA FIS Bologna

Politecnico di Milano, Dpt. Elettronica e Inf.

Università di Pavia, Dpt. Ing. Elettronica

PNSensor GmbH München


Wide Field Monitor

What may be requested to it?

Primarily:Sensitivity (to transient events)

FOV coverage

Angular resolution

Extended energy range

Eventually:Energy resolution

Time resolution

Coded mask system

coupled to a

“position sensitive”

detector plane


Building blocks for the detector plane

Why scintillators ?

א Many materials available with various characteristic of

density, velocity, light output.א May be shaped in many forms and sizeא Consolidated technologyא New appealing materials with improved spectroscopic New appealing materials with improved spectroscopic

capabilitiescapabilities

Can directly compete in performances with solid state detector


array with CsI(Tl) elements

0.03 x 0.03 x 2cm in size

Volume: 2 10-4 cm3

AGILE MiniCalorimeter detector elements

CsI(Tl) 1.5 x 2.3 x 37.5 cm in size

Volume: 1.3 102 cm3


Building blocks for the detector plane

Why Silicon Photodetectors?

High QE (90%) for visible lightك Si technology allows many device design focussed on lowك

noise level (SDC-PD), or speed (avalanche or PIN PD) Can be used as detector for visible photon or directly for lowك

energy X-rays ,Naturally suited for ‘array architectures’ (small, ligth, ruggedك

etc..)


The Silicon Drift Chamber

The collecting anode capacitance is very small (> 0.1 pF) and

independent from the device area

very low noise readout


SDC as direct X detector

Range: > .6 30 keV

active area 10 mm2

Si thickness 300 mm

JFET embedded

E threshold 0.6 keV

E resolution @ 20°C 5% FWHM @5.9 keV(0.5 sec sh. time) 0.9% FWHM @ 60 keV

Noise (ENC) 45 e- rms @ 20°C

241Am

55Fe


SDC coupled to a scintillator

Range: 15 1000 keV

crystal CsI(Tl)

light yield 25 - 38 e-/keV

E threshold < 16 keV

efficiency 80% @ 200 keV(1 cm crystal) 25% @ 1 MeV

energy resolution 4.8% FWHM @ 662 keVat room temperature 137Cs


Prototype SDC-PD: as they look like

studies on

Bonding on ceramic support

Passivation SDC

Materials for optical coupling

SDC area ~10 mm2

Top view

Bottom view

1.2 cm


One unique detector for extended energy range

X-ray interacts in Si delivering a fast charge pulse : (< 10 ns)

-ray pass throug Si and interact in CsI(Tl) delivering a slow pulse: (few s)

The identification of the interaction type will be done with a Pulse Shape Discrimination (PSD) technique

Main Characteristics:

– Low energy threshold (~2 keV)

– Extended energy range (related to crystal thickness)

– Excellent energy resolution

M. Marisaldi, IEEE Trans. NS Vol 51, No 4, 2004, p. 1916

Si CsI(Tl)

X

Direct detection in Si

Scintillationlight detection

SDD scintillator


Fast vs slow component

Am-241

• In the plane fast-slow channel the two operation modes (X,) are well defined in two row with different r = Channelfast / Channelslow

In Si: r = 0.92 In CsI: r = 0.54


Pulse Shape Discrimination (PSD)

CsISi

rM

Factor of merito M100% PSD possible when M >

1.5

• 100% PSD for E>3.6 keV in Si and E>35 keV in CsI• PSD still possibile per E>1.5 keV in Si and E>16 keV in CsI• lower noise and greater light yield –––> lower PSD limit

6.7 - 17 keV in Si

70 - 180 keV in CsI


PSD limit vs Temperature

25 °C: 4.5 keV in Si, 46 keV in CsI

M=1.5

10 °C: 2.0 keV in Si, 18 keV in CsI0 °C: 1.7 keV in Si, 15 keV in CsI

-20 °C: 1.0 keV in Si, 7 keV in CsI


How much to cool?

Threshold in CsI

•cooling at 10 °C is enough to fill the efficiency gap between Silicon and the crystal


Mixed interactions

With PSD it is possible to discriminate mixed interactions in Si and CsI

Mixed events can be rejected,or corrected

60 keV in CsI + I KL and Cs KL X-rays in Si: r~0.87

26 keV in Si:r=0.92


Wide field monitor design

Coded mask instrument

Example of a monitor that can be realised with already available components:

• pixel size d=3.6 mm

• detector size D=400 mm

• mask size M=800 mm

• mask-destector focal length l=1 m

• fully coded FOV = 43.6°• FWHM = 77.3° (1.4 sr)

• angolar resolution = 18’• point source localisation = 3.5’ at 5• number of pixels: 12000.


Gamma flash sensitivity

Integral flux for 3 different GRB (, , Ep spectral parameters, Band D. et al., 1993, ApJ 413, 281).

Solid : =-1, =-2.

Dashed: =-0.5, =-2.

Dot-dashed: =-1, =-3.

Faintest detectable burst (1-1000 keV), from Band, D., (2003) ApJ 588, 945

Trigger range 20 - 1000 keVTrigger range 1.5 - 40 keV

SDC/scintillator detectors cover, in an unique instrument an energy band over 3 order of magnitude.

The spectroscopic capabilities of SDC allow a continuing monitoring of a detected burst during the pointing of the narrow field instruments.


Further scientific revenues from a Wide Field Monitor with an extended energy range

Transient studies: A monitor working on an extended Energy range can be

used to study strong absorbed sources like that one found by INTEGRAL.

Monitoring of known sources: If the monitor FOV is large enough it can be

possible the monitoring of the timing and spectral variability of known sources

GRB studies: A wide energy band can be a benefit on the studies of GRB

Cosmic Background: Like SAX-PDS a monitor with good sensitivity can be

used for CB studies


Technical challenge: number of pixel

• X and with exploding number of channels

• PICsIT-INTEGRAL (2002): 4.096 chTRACKER AGILE (2006): 46.000 chGLAST even more

• Read-out electronic chain using very large integration techniques with:

Whole analogue chain suitable for spectroscopy

Many embedded logical function to ‘harmonize’ the behaviour of different detector in an unique array

Low power consumption, miniaturisation, Latch-up e SEU immunity

• Use of Application Specific Integrated Circuits (ASIC) with mixed analogue-digital technology is mandatory.


HERITAGE: ICARUS ASIC

16 channels each one with:charge-preamp, shaping amplifierdiscriminator peak & hold Multiplexer command logicpower: 8 mW/chnoise: 950 e- rms

For PIN PD e CsI(Tl)

256 chip on PICsIT-INTEGRAL

ASIC for SDC

ICARUS footprint

16 channe/ASIC:I/F to SDD shaping amplifierdiscriminator peak & hold Multiplexer command logicpower: 8 mW/chnoise: 60 e- rms

For SDC:2 possibilities:8 ch for X-ray detection8 ch for CsI(Tl)

RUA ASIC

1 prototype built

each channel with:I/F to detector shaping amplifierdiscriminator peak & hold ADC I/F

Noise with SDC: > 50 e- rms

Can be used for many different detectors

ASIC for electronic read-out


RUA prototype

RUA layout

Chip Area 13.7 mm2

Channel Area 3.3 mm2

Digital output 10 bits

# of programmable reg. 47

Programmable parametersAmp. gain 1, 2, 5, 10

Peaking time 0.5, 1, 3, 6 µs

Pole-zero correction 0.1, 0.2, 0.5, 1, 2 ms

Polarity + / -

Fine gain 1 ÷ 2 with 10-bit

Threshold 1.5 V ÷ 1.7 V with 8-bit

Rise time protection 1, 2, 5, 8, 10 µs


RUA Shaper programmability

Variuos peaking time programmable with RUA


Possible improvement: new materials

New Lanthanum composites recently available

LaBr3(Ce) LaCl3(Ce) CsI(Tl)

Density g/cm3 5.29 3.79 4.51

Decay time ns 26 28 600 - 3400

Light yield ph/keV 63 49 50

Light yield vs NaI(Tl) % 130 70-90 45

Wavelength of max em nm 350 380 560

Hygroscopic yes yes no

Res.FWHM @661 keV % 2.8 3.8 8(with PMT)


New materials: can be used with SDC?

Yes if a wavelength shifter is used between crystal and PD

Estimated Energy resolution FWHM @ 661 keV vs efficiency of light collection

in the SDC (noise SDC considered 50 e- rms)

PSD for use of both Si and crystal at the same time may be still possible: need To Be Investigated

(%) Res @ 661 keV

50 1.7

30 2.3

10 4.6

roma jan.2006 whim and mission opportunities wide field monitor prospect for use of silicon and...

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