Charged particles detectors Arrays (1)

Basic concepts of particle detection:scintillators & semiconductors

Light charged particles (p, α, e) Arrays:DIAMANT, ISIS, EUCLIDES, MiniOrange

Large Arrays: CHIMERA, INDRA(MULTICS, RingCOUNTER (Garfield))

Heavy fragments detection: RFD (recoil filter detector), Saphir

Charged Particles identifications

the slow component (τ ~ ms)due to delayed phosporescence

(from triplet state) is larger for particles with large dE/dx

energy levelsab

sorp

tion

fluo

resc

ence

phos

phor

esce

nce

singlet triplet

prompt fluorescence(from singlet state):

~ few ns

light yield

S = scintillator efficiencykB = fitting constant

stilbeneC14H12

Organic scintillators

Inorganic Scintillators: CsI(Tl), BaF2, …

α particleEα=95 MeV

τf = 800 nsτs = 4000 ns

−+

−=

ss

s

ff

f ththtL

ττττexpexp)(

Light output:

Sum of two exponential functions: fast & slow components

1. τs independent of particle nature

2. R = hs/(hf+hs) increases with decreasingionisation density

3. τf increases with decreasing ionisation density

it is possible to identify different particles

CsI(Tl)

Lfast

L slow

N.B. CsI have been used at first for particle studies:- less fragile than NaI- good particle discrimination

Optimization of particle discrimination:

- ballistic deficit effect:amplitude degradation at the output of pulse shaping circuit, due tofinite shaping time constant

[N.B. the preamplifier rise-time correspondsto the charge collection time ⇒ full charge collection is obtained only with

∞ shaping time constant]

particle-type information is carried by preamplifier rise-time constant⇒ ballistic deficit B depends on type of particle

Qtfull chargecollection

Qppartial charge

collection

B = 1 – F = 1 – Qp/Qt

Very good method for particle discrimination withCsI(Tl) + PIN photodiode detectors

instead of PM tube: usefull in compact geometry

PIN diodesemiconductor Device(photodiode)

CsI(Tl) + PIN photodiode detectors15×15×3 mm3

pulse generatorsimulted α and p signals measured signals

ballisticdeficit

Figure of merit

quality of particleidentification

yx

yxxy ww

PPM

+

−=

particleseparationdown toM ~ 0.6

separation energy thresholdEα ~ 4 MeVEp ~ 2.5 MeV

J. Gal et al., NIMA366(1995)120

- zero-crossing method:the zero-crossing point of a bipolar signaldepends on the pulse-shapeof the original unipolar signal (input rise time)

1. different particlesgive differentunipolar signals(different rise time)

particle-type information is carried by the preamplifier rise-time constant

⇒ zero-crossing depends on type of particle

2. bipolar signalwith zero-crossing dependingon input rise time

CR-RC-CRdouble differentiating circuit

the time interval measured by TAC is proportional to the decay-timeof the detector pulse

Also used for particle discrimination with CsI(Tl) + PIN photodiode detectors

DIAMANT: EUROBALL ancillary84 CsI(Tl) with PIN diode detectors4π geometryinner radius R = 32mm to 49mm

4π array

Advantages:- high efficiency: εproton ≈ 70%, εα ≈ 50%- low energy threshold: 2 MeV for p, 4 MeV for α

Limitation:- large dead time (long decay time of light pulse τ ~ 1000 ns)

⇒ limitation in count rate- large absorption & scattering of γ’s

⇒ limitation in resolving power of Ge arrayOperating mode: DIAMANT alone: particle-xn channelsDIAMANT + Ge : particle-xn + xn channels

α p

p α timeenergy

target

Particle identification:- ballistic deficit;- zero-crossover;- mixed method.

light charged particledetector array

Charged Particles identifications bySolid State Detectors (Si, …)

- smaller dead time (τ ~100-200 ns, compare to 1000 ns for CsI)- good energy resolution (~ 10-20 keV)- limited γ-absorption- possibility of large solid angle coverage (~ 4π)- large sizes, up to 20 cm2

Detection method:1. ∆E energy loss

2. E-∆E telecopes

3. Pulse Shape Analysis

Si detectors are preferred to Ge:- simplicity of operation (room temperature, …)- lower γ-absorption (ZSi=14, ZGe = 32, ρSi = 2.33 g/cm3 ρGe = 5.32 g/cm3, …)- …

- Si detectors, ∆E method 28Si i (@95 MeV) + 58Np and α dE/dx spectra

p αEmZ

dxdE 2

∝

- usefull to discriminate betweenfew types of particles: p, α

- detailed simulation studies ofdE/dx in Si for various particles

⇒ different dE/dx for different particles

Si detectorn-type2 segments170 µm

overlapping dstribution

Si-Ball: NORDBALL ancillary17 ∆E Si detectorsn-type, pentagon shape

- thickness 170 µm

- shielding with absorber foilsto optimize p and α penetration(optimum thickness: MonteCarlo simulation)

- 4π geometry: Ω ~ 90% 4π- Inner radius R = 5 cm- Housing sphere radius R = 10 cm

Multiplicity identifier

energy

p αp

α

register unit

particleidentifier spectrum

target

γ-spectra particle gated

2pα

4p

3p

2p

as a consequence of theoverlapping energy distributionsof p and α

T. Kuronyanagi et al., NIMA316(1992)289

3pα

analysis of contaminantshows

12 % α interpreted as p0.9 % p interpreted as α

22

mZEEmZE

dxdE

=×∝×

t ~ 100-200 µm t ~ 1000 µm

26.5 MeV/A

T = E + ∆E

∆E

- Si detectors, ∆E-E method

Very usefull method to separate ions up to A = 25-30

ISIS/EUCLIDES: GASP/EUROBALL ancillary40 E-∆E Si n-type telescopes130 µm + 1000 µm- capacitance C = 850 pF, 130 pF- shielding with Al foil (~10-20 µm) to reduce radiation damage from scattered beam ions(optimum thickness: MonteCarlo simulation)

4π geometry: Ω∆E ~ 72% 4π, ΩE ~ 65% 4πInner radius R = 6.7 cm

γ-spectra particle gated⇒ increased selectivity Ge array

∆E

E

ISIS32S(@140 MeV) + 40Ca

Operating mode: Stand-alone+ InnerBall+ Innerball + Hector+ Neutron-Wall+ Recoil Filter Detectorefficiency: εproton ≈ 50%, εα ≈ 40%

-Si detectors, PSA method

zero-crossover method

p α

p

α

heavy-ions

Tim

e ZCO

[ns]Energy [MeV] Energy [MeV]

TimeZCO [ns]

S

N

E=8-8.2 MeV

E=156-158 MeV

Light particles

Heavy particles

proton

C peak

Si-Ball Berlin(EUROBALL ancillary)

162 Si (p+-n-n+ structure) - thicknes ~ 500 µm- Active area ~ 750 mm2

G. Pausch et al., NIMA365(1995)176

Dedicated Arrays: CHIMERAMultifragmentation, transition liquid-gasHeavy Ion Reactions 10 MeV/A – 1 GeV/AE*~ 250-350 MeV, 4 ≤ T ≤ 8 MeV

- large number of particles- several Z and A- wide dinamic energy range

Caloric curve of the nucleus Caloric curve of the water

Multifragmentation: T≈5 MeV, E*≈4-5/A MeV

Vaporization: T>6 MeV, E*>10/A MeVJ. Pochodzalla et al., Phys. Rev. Lett. 75(1995)1040

CHIMERA(GANIL, LNS, GSI(?))

1m

1°

30°

TARGET

176°

Beam

688detectors 504

detectors

unique device for:- granularity (1192 mod.) - low energy threshold (∼250 keV/A for H.I.)- efficiency (~ 95% )

good event reconstructioneven with high multiplicity

1192 ∆E-E Si-CsI(Tl) telescopes

Si thickness ~ 300 µmCsI(Tl) thickness ~ 10 cm

9 rings in forward directionsphere Inner radius R = 40 cm

Large scattering chamber

SiCsI(Tl)

(Pd)18x18mm2

300µm

10cm

Si-CsI(Tl) telescope

∆E-E, E-TOF, PSD in CsI(Tl)

∆E-TOF M,E∆E-E Z,E (dΕ/dx ∝ AZ2/E)

C

Z =50Sn

Si-∆

E (h

igh

gain)

Si-∆

E (lo

wga

in)

CsI-Fast CsI-Fast

A=16

Si-∆

ETOF

p

t

d

4He

6He

3He

Li

H.I.PSDCsI(Tl)

Identification method

100 nsHF Cyclotron

HF Start

TOFSiCsI(Tl)

(Pd)18x18mm2

300µm

10cm

Fast

Slow

light particles

low energy threshold + high energy resolution

3 stages telescope

MULTICS48 modules

∆E I

C[M

eV]

∆E I

C+Si

[MeV

]

∆ESi [MeV]

∆ECsI [MeV]

Other Dedicated Arrays for charged particles:MULTICS (+MEDEA, LNS), Ring Counter (+GARFIELD, LNL)Heavy Ion Reactions at intermediate energy10 MeV/A – 100 MeV/A