RIKEN-ATOMKI Hybrid Detector Array (2001-2003)

1. Hybrid Detector Array (2001-2003) The RIKEN-ATOMKI hybrid arrayGábor Kalinka (ATOMKI, Debrecen)3rd Japan-Hungary Joint Seminaron Physics in Modern Science and TechnologyProgress in Science and Technology with Particle and Photon BeamsOctober 8-12, 2007, Debrecen – Szeged – Budapest Gamma Particle A typical experimental setup as dreamt of and actually realized at RIKEN RIBF beamline

2. Gamma ray detectorsCharged particle detectors Role 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 The RIKEN-ATOMKI gamma-ray/charged particle hybrid array (2001-2003) • 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-Atomki • CsIArray = GRACIA

3. Preceding reference work: the DIAMANT-II.,III.,IV. 4πlow-energycharged particle detector system for large γ-spectrometers scintillator : 14 x 14 x 3 mm3 CsI(Tl) for ~ 30 MeV/ amu particles photodiode : 10 x 10 mm2 Silicon pin 100 elements at highest granularity electronics: highly integrated, dedicated VXI-D standard • Collaboration with • CENBG, Bordeaux; • MSI, Stockholm; • INFN, Napoli EUROBALL, (France, Italy) EXOGAM (Ganil, France) AFRODITE (iThemba, South Africa) Excellent energy- and particle-resolution (almost 2 times better than that of Microball at Gammasphere)

4. 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 Rise/decay time Ion mass (ionization density) Ultimate limit

5. Simplified statistical considerations for nuclear radiation detectors • “Signal particles” : • e-h pairs / semiconductor • photons / scintillation • quasiparticles/superconductive • phonons / thermal The mean energy to create one signal particle : ε detectors Quasi-Poissonian 0 ≤ F ≤ 1 : Fano factor Binomial 0 ≤ η ≤ 1 : coll. eff. Quasi-Gaussian Creation Collection Total The key factor on performance is the collection efficiency, it should be maximized !

6. Light reflector Light exit cones Crystal 2ΘC Photodetector How can the light collection efficiency be improved ? 16x16x55 mm3 nCsI=1.8 Total internal reflection critical angle: scattering Optimal crystal to photodetector optical coupling: High quality outer reflector Reflecting back the escaped light

7. “ These films can yield optical results that are difficult or impossible to achieve with conven- tional multilayer optical designs.” CsI(Tl) emission Very high reflectivity interference mirror film based on alternating anisotropic polimer layers from 3M company (GBO optics) VM2000 visible range mirror foil

8. γ α Pulse height amplitude Light collection efficiency A finished detector The evolution of the spectral performance vs light collection efficiency

9. The energy resolution capability of the GRACIA CsI(Tl)+Si pin photodiode detector system is just a little bit inferior to that of DIAMANT ! γα γ-performance statistics of the whole array @ 1.3 MeV

10. Amplitude and resolution statistics (uniformity) of the elements of the GRACIA detector system measured with 5.5 MeV alpha particles from 241Am Signal amplitude FWHM=4.4 % Energy resolution ηLight≈ 70 %

11. Particle identification at low (<20 MeV, ATOMKI) and high (<100 MeV, RIKEN) energies <20 Mev / DIAMANT electronics <100 MeV / standard electronics p-d separation > 2 MeV p-αseparation > 5 MeV γ in Si γ H1, H2, H3 He3, He4

12. DALI and GRACIA at RIKEN Heavy Ion Nuclear Physics Lab.