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

2. The RIKEN-ATOMKI gamma-ray/charged particle hybrid array (2001-2003) Gamma ray detectors Charged 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 D etector A rray for L ow I ntensity 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 ) G eneral purpose R iken- A tomki C s I A rray = GRACIA

3. Preceding reference work: the DIAMANT-II.,III.,IV. 4 π low-energy charged particle detector system for large γ- spectrometers scintillator : 14 x 14 x 3 mm 3 CsI(Tl) for ~ 30 MeV/ amu particles photodiode : 10 x 10 mm 2 Silicon pin 100 elements at highest granularity electronics: 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

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 detectors The mean energy to create one signal particle : ε Creation Collection Total Quasi-Poissonian 0 ≤ F ≤ 1 : Fano factor Binomial 0 ≤ η ≤ 1 : coll. eff. Quasi-Gaussian Detector ε F η FWHM/ @ 1 MeV Si3.6 eV0.10.980.14 % (1.4 keV) CsI(Tl)18 eV10.52.2 % (22 keV) The key factor on performance is the collection efficiency, it should be maximized !

6. Photodetector Crystal Light reflector Light exit cones 2ΘC2ΘC How can the light collection efficiency be improved ? Total internal reflection critical angle: Optimal crystal to photodetector optical coupling: n CsI =1.8 Reflecting back the escaped light scattering High quality outer reflector 16x16x55 mm 3

7. 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 are difficult or impossible to achieve with conven- tional multilayer optical designs.” VM2000 visible range mirror foil

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

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 ! γ-performance statistics of the whole array @ 1.3 MeV γαγα

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

11. Particle identification at low (<20 MeV, ATOMKI) and high (<100 MeV, RIKEN) energies H 1, H 2, H 3 He 3, He 4 γ in Si <20 Mev / DIAMANT electronics<100 MeV / standard electronics p-d separation > 2 MeVp- α separation > 5 MeV γ

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