Hybrid Detector Array

(2001-2003)

The RIKEN-ATOMKI hybrid arrayGábor Kalinka (ATOMKI, Debrecen)

3rd Japan-Hungary Joint Seminaron Physics in Modern Science and Technology

Progress in Science and Technology with Particle and Photon BeamsOctober 8-12, 2007, Debrecen – Szeged – Budapest

A typical experimental setup as dreamt of and actually realized at RIKEN RIBF beamline

Gamma

Particle

The RIKEN-ATOMKI gamma-ray/charged particle hybrid array (2001-2003)

Gamma ray detectors Charged particle detectorsRole of the detector • Transition probabilities• Excitation energies• Level scheme

Requirements• High efficiency• High energy resolution• High granularity

Detector of choice• NaI(Tl) + PMT• 160 detector units

Made by: RIKEN

Detector Array for Low Intensity

radiation = DALI

•Reaction channel selection

•Stop ~110 MeV/nucleon particles•Good particle identification•High energy resolution•High granularity•Compact geometry

•CsI(Tl) + Si pin photodiode•312 detector units

ATOMKI (1998, 2001-2003 )

General purpose Riken-AtomkiCsI Array = GRACIA

Preceding reference work: the DIAMANT-II.,III.,IV. 4π low-energy charged particle detector system for large γ-spectrometers

scintillator : 14 x 14 x 3 mm3 CsI(Tl) for ~ 30 MeV/ amu particlesphotodiode : 10 x 10 mm2 Silicon pin

100 elements at highest granularityelectronics: highly integrated, dedicated VXI-D standard

Excellent energy- and particle-resolution (almost 2 times better than that of

Microball at Gammasphere)

EUROBALL, (France, Italy)EXOGAM (Ganil, France) AFRODITE (iThemba, South Africa)

Collaboration with •CENBG, Bordeaux; •MSI, Stockholm; •INFN, Napoli

Intrinsic particle resolving capability of CsI(Tl) scintillation detectors (low energy region < 80 MeV) based on ionization density dependent risetime with

dedicated electronics using combined ballistic deficit + zero crossing method

Particle Energy (arb. unit)

PROTONS

EUROBALL + DIAMANT with VXICommissioning Experiment; April 2000

170Er + 30Si (165 MeV)

DEUTERONS

ALPHAS

Pulses from PIN-diodes

Par

tic

le T

ype

Ris

e/d

ecay

ti

me

Ion

mass (io

nizatio

n

den

sity)

Ultimate limit

Simplified statistical considerations for nuclear radiation detectors

E

Ncreat FNcreatcreat

creatcoll NN 1creatcoll N

1355.2355.22

22 F

ENN

FWHM

coll

collcreat

Tot

Tot

“Signal particles” : • e-h pairs / semiconductor• photons / scintillation• quasiparticles/superconductive• phonons / thermal

detectorsThe mean energy to create one signal particle : ε

Creation

Collection

Total

Quasi-Poissonian0 ≤ F ≤ 1 : Fano factor

Binomial0 ≤ η ≤ 1 : coll. eff.

Quasi-Gaussian

Detector ε F η FWHM/<N> @ 1 MeV

Si 3.6 eV 0.1 0.98 0.14 % (1.4 keV)

CsI(Tl) 18 eV 1 0.5 2.2 % (22 keV)

The key factor on performance is the collection efficiency, it should be maximized !

Photodetector

Crystal

Light reflector

Light exit cones

2ΘC

How can the light collection efficiency be improved ?

crystalextc nn /)sin(

pdcrystalglue nnn

Total internal reflection critical angle:

Optimal crystal to photodetector optical coupling:

nCsI=1.8

Reflecting back the escaped light

scattering

High quality outer reflector

16x16x55 mm3

Very high reflectivity interference mirror film based on alternating anisotropic polimer layers from 3M company (GBO optics)

CsI(Tl)emission

“ These films can yield optical results that aredifficult or impossible to achieve with conven-tional multilayer optical designs.”

VM2000 visible range mirror foil

The evolution of the spectral performance vs light collection efficiency

Light collection efficiency

αγ

Pulse height amplitude

A finished detector

The energy resolution capability of the GRACIA CsI(Tl)+Si pin photodiode detector system is just a little bit inferior to that of DIAMANT !

4 4.5 5 5.5 6 6.5 7 7.50

10

20

30

40

50

60

70

80

Relative FWHM energy resolution [%]N

umbe

r of d

etec

tors

GRACIA detectors @ 1.3 MeV gamma

γ-performance statisticsof the whole array

@ 1.3 MeV

γ α

Amplitude and resolution statistics (uniformity) of the elements of the GRACIA detector system measured with 5.5 MeV alpha particles from 241Am

FWHM=4.4 %

Signal amplitude

Energy resolution

ηLight ≈ 70 %

Particle identification at low (<20 MeV, ATOMKI) and high (<100 MeV, RIKEN) energies

H1, H2, H3 He3, He4

γ in Si

<20 Mev / DIAMANT electronics <100 MeV / standard electronics p-d separation > 2 MeV p-α separation > 5 MeV

γ

DALI and GRACIA at RIKEN Heavy Ion Nuclear Physics Lab.