diamant, isis, euclides, miniorange chimera,...
TRANSCRIPT
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