HYDE HYbrid DEtectors for neutrons LNL Trento -TIFPA Cosenza – Gruppo Collegato Frascati FBK CSN5 – Roma – 9 aprile 2015

Outline Prologue: ORIONE+TREDI = HYDE. Red emitting polysiloxane scintillators. Pulse shape discrimination polysiloxane scintillators. 3D sensor for coupling with polysiloxanes and first tests. Response to fast and thermal neutrons in 3D with converters. Planar sensor tests and new system design.

 Development of polysiloxane based organic scintillators doped with fluorescent dyes for the energy-scintillation conversion and with o- carborane for the sensitization to thermal neutrons.ORIONE ORganic scIntillators fOr NEutrons

Stable on a wide range of temperatures (-100 °C up to 250 °C) vs. commercial PVT (Tg at 90 °C) and it can be handled without crazing. Polysiloxane Scintillators High radiation hardness with respect to commercial plastic scintillators (unaffected up to 40 KGy). PVT PSS A. Quaranta, S. Carturan, et al., Mater. Chem. Phys., 137 (2013) 951.

Sample  yield (% EJ-212) (% EJ-212)  yield (% EJ-212) (% EJ-212)  yield  yield (% EJ-254) (% EJ-254)  yield (% EJ-254) no B 65 ± ± B 4% 44 ± ± ± ± 16 B 6% 40 ± ± ± ± 15 B 8% 37 ± ± ± ± 11 Polysiloxane Scintillators Light yield comparable with commercial plastic scintillators. B 4% B 6% B 8% LY (%EJ-254) 72 ± ± ± 22 Eff./EJ ± ± ± ± ± 0.2 High solubility of carborane and higher efficiency with respect boron doped commercial systems.

Single column 3D diodes: Low depletion voltages and leakage currents Excellent electrical yield Radiation hardness up to ~1e15cm -2 (~20:1) - Null-field lines! Bulk Guard ring 10x10 holes matrixTREDI

beam position signal induced on the central strip 50ns 0 very fast component + long tail due to hole diffusion [G. Kramberger et al, 8 th RD50 Workshop, 2006] Ballistic deficit effects at short peaking times (20 ns) [S. Kuehn et al., 2007 IEEE – NSS] After 1e15 n/cm 2 TCT laser test at JSI Ljubljana CCE test with  source at the University of Freiburg Before irradiationTREDI

HYDE (Main Goals) Si p-type P diffused (n + ) Nitride Oxide p-stop Substrate contact Scintillator Feedthrough (n + ) Al contact Signal Fast n p Th n  Li 10 B Filling of 3D structures with PSS for the simultaneous detection of light (directly with the 3D structure or by means of an external photodetector) and of reaction products with the 3D detector.

HYDE (Planned Steps) Production of red polysiloxane scintillators suitable for red enhanced silicon photodetectors. Production and filling of large 3D structures for allowing suitable detection volumes. Pulse shape discrimination tests on polysiloxane scintillators. Assembling of the obtained systems for the realization of the hybrid detector.

2,5-Diphenyloxazole (PPO) for the energy transfer from the network. Lumogen Violet (LV): ET from PPO for wavelength shifting from UV to blue. Lumogen Red (LR): ET from LV for WS in the red. Red Emitting Polysiloxanes

Optimization of non-radiative ET rate from PPO to LV. Test with different concentrations of LR. Evidence for both radiative and non-radiative short range ET. Red Emitting Polysiloxanes

Scintillation yield test on APD with higher sensitivity in the red. 17% yield increase with alpha particles (0.01% LV). 34% yield increase with gamma rays (0.01% LV). Scintillation Yield Measurements APD 34% 17%

Pulse Shape Discrimination PSD is given by delayed fluorescence rising from the combination of close excited triplet states. In liquids triplets interacts through diffusion. In plastics homogenously distributed dyes are too far. High dye concentrations may supply the needed distance between dye molecules. PSA in BC501

Time (ns) neutrons γ rays Time (ns) 1% PPO 8% neutrons γ rays 8% PPO Time (ns) EJ212 Fast (30 ns) vs slow (500 ns) integration time interval γ n n γ 8% PPO 1% PPO slow PSD in PSPS fast neutrons γ rays PSD in PS Scintillators PSD in PS scintillators has been demonstrated even with low concentrations of primary dye (PPO).

PS Liquid Scintillators EJ309 PDPDM20 PMDM50 PMDM60 PPTMTS TPTMTSPPM100 Polsiloxane liquid resins were studied for the production of non- toxic liquid scintillators.

OligomersDiphenyl-dimethyl Phenylmethyl 67% PSLS PS Liquid Scintillators Very good light yield as compared with the commercial non-toxic EJ-309. Very good pulse shape discrimination between neutrons and gammas.

Single Type Column inspired design. n + 3D electrodes (diffused) and p + planar ohmic regions on the back. p-spray isolation. 200x200x200 µm 3 cavities. All metal contacts on one side thanks to narrow poly-Si columns for easy filling of the wells. 3D First Slot

Very good depletion already at few Volts: depletion voltage between 5 and 10 V and nearly complete depletion at 50 V. Simulations and Electrical Tests Breakdown voltage between 50 and 60 V. Leakage currents of few tens of nA.

Resins were poured on the 3D sensor and kept in low vacuum for releasing the air trapped in the wells. Cross-linking of phenyl substituted polysiloxane resins inside the cavity at 60 °C overnight. Very good adhesion to Si walls. Filling Tests

Isochronous Cyclotron – Rez (CZ) n/s in the range 4 – 12 MeV. Polysiloxane as “hydrogen provider” for fast neutrons. Promising response (10 V and 4  s of shaping time). Tests with Fast Neutrons Not filled Filled

Tests with Thermal Neutrons LVR-15 research nuclear reactor – Rez (CZ). Collimated beam 1.5×10 7 n/(s×cm 2 ). Polysiloxane with 30% wt. of 10 B metal Powder. 6 LiF powder. B LiF No

Collected charge spectra obtained from 241 Am α particles impinging the 3D sensor from the pillar side at 20 and 40 V. At 40 V the low energy peak enlightens an inhomogenous electric field distribution. Spectra scan (wavelength 850 nm) from the sensor back side at 20 and 45 V. At 40 the signal from Si pillar is highly reduced due to the low charge collection efficiency at low shaping times (4  s). Functional Characterization HoleHole Pillar Pillar 40 V 20 V

Charge Collection Simulations Charge collection dynamics, accounting for the mutual influence between cavities, was studied with TCAD simulations. Four different hit positions for a particles were considered from the pillar side. The fast component of output currents of the two electrodes compensate each other in Pos2. For this reason the main contribution to the collected charge comes from the slow component.

3D sensor schematic cross- section (not to scale), with values of the main geometrical parameters with all the contacts are on the front side. Planar System Tests Test on a planar diode with a converter coating were performed in order to validate the GEANT4 simulations for the device optimization. Planar sensor with guard ring and sputtered converter on the top

Optical microscopy images of sputtered converter on planar sensors Thin Film Deposition 500 nm 10 B 500 nm 10 B 4 C 1000 nm 10 B 4 C Thin film of enriched boron compounds were deposited by means of RF sputterng. Layers with the lower thickness were also deposited on a 3D sensor but a test on the thickness and conformity of the layer was not possible.

Spectra obtained with different samples with a collimated flux of thermal neutrons of about 1x10 6 n/(cm 2 s) for 1h on planar sensors. V bias = 200 V and shaping time of 500 ns Enriched boron coating exhibits higher efficiency. Simulated efficiencies: 1.0% for 500 nm B 4 C, 1.8% for 1000 nm B 4 C and 1.3% for B. The simulation resembles quite well the spectrum shape. Thermal Neutrons on Planar Sensor Experimental spectrum after background subtraction GEANT4 simulation

Spectra obtained with different samples with a collimated flux of thermal neutrons of about 1x10 6 n/(cm 2 s) for 20 min. on 3D sensors. V bias = 10 V and shaping time of 4  s. LiF filled sensor exhibits higher efficiency. The simulation resembles quite well the spectrum shape of the LiF filled detector. The other systems cannot be simulated due to the inaccuracy on the coating on the lateral sides of the wells. Thermal Neutrons on Coated 3D Sensor

New Detector Design New detectors for thermal neutrons were designed in order to better exploit the hole walls in the detection of the reaction products. Lateral doping was avoided in order to minimize the dead layer for the impinging reaction products. Uniform electric field through the whole wafer. The sensor should combine the properties of a planar structure with the efficiency of a 3D system. Design submission 2 nd November Batch under fabrication at FBK, due by April 2015.

Conclusions (good news) Red polysiloxane scintillators have been produced for improving the responsivity of red enhanced photodetectors. Pulse shape discrimination capability has been demonstrated for polysiloxane based scintillators. Polysiloxanes can be coupled to silicon based detectors. A response to fast neutrons has been obtained with polysiloxane rubber as a hydrogen provider. 3D systems filled with suitable thermal neutron converters give a good response to thermal neutrons.

Conclusions (bad news and wip)  The efficiency of large 3D systems designed for polysiloxanes is quite poor.  The efficiency to fast neutrons is very poor due to the small volumes involved in the detection.  Thermal neutron detection through 3D systems can be attained only with highly concentrated converters, rather than with polysiloxanes.  Improved 3D systems for the detection of thermal neutrons through converter filling have been designed.  Hybrid detectors can be still realized by coupling a polysiloxane scintillating system for fast neutrons (thanks to its easy coupling with slicon) with a 3D filled detector for thermal neutrons.

A. Quaranta, S. Carturan, A. Campagnaro, M. Dalla Palma, M. Giarola, N. Daldosso, G. Maggioni, G. Mariotto, “Highly fluorescent xerogels with entrapped carbon dots for organic scintillators”, Thin Solid Films, Vol. 553, no., 2014, pp M. Dalla Palma, A. Quaranta, T. Marchi, G. Collazuol, S. Carturan, M. Cinausero, M. Degerlier, F. Gramegna, “Red Emitting Phenyl-Polysiloxane Based Scintillators for Neutron Detection”, IEEE Transactions on Nuclear Science, Vol. 61, no. 4, 2014, pp M. Dalla Palma, S.M. Carturan, M. Degerlier, T. Marchi, M. Cinausero, F. Gramegna, A. Quaranta, “Non-toxic liquid scintillators with high light output based on phenyl-substituted siloxanes”, in publication Optical Materials. R. Mendicino, M. Boscardin, S. Carturand, M. Cinausero, G. Collazuole, G.-F. Dalla Betta, M. Dalla Palma, F. Gramegna, T. Marchi, E. Perillo, M. Povoli, A. Quaranta, S. Ronchin, N. Zorzi, “Novel 3D silicon sensors for neutron detection”, JINST 9 C R. Mendicino, M. Boscardin, S. Carturan, G.-F. Dalla Betta, M. Dalla Palma, G. Maggioni, A. Quaranta, S. Ronchin, “Characterization of 3D and planar Si diodes with different neutron converter materials”, in publication Nuclear Instruments and Methods A.Publications