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Recent developments in LaBr 3 detectors for high energy gamma-rays

Recent developments in LaBr 3 detectors for high energy gamma-rays. F. Camera University of Milano – INFN sez. of Milano. LaBr 3 Scintillators. FWHM 540 ps. L.Y.  63 ph/keV Decay Time  16 ns l  380 nm N  1.9 r = 5.3 g/cm 3 RL (661 keV) 1.9 cm.

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Recent developments in LaBr 3 detectors for high energy gamma-rays

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  1. Recent developments in LaBr3 detectors for high energy gamma-rays F. Camera University of Milano – INFN sez. of Milano

  2. LaBr3 Scintillators FWHM 540 ps L.Y.  63 ph/keV Decay Time  16 ns l 380 nm N  1.9 r = 5.3 g/cm3 RL (661 keV) 1.9 cm High Interest in the Scientific Community (Base Science, Medical Imaging, Space Research) In 2007 more than 40 papers on LaBr3 / LaCl3 detectors published in IEEE and NIM

  3. Activities in Milano • Linearity, energy and time resolution tests • Different PM tested at different voltages • Tests with and without the use of a preamplifier • Test with APD and HPD planned in future • Response with high energy gamma rays • PuC source - 6.13 MeV g-rays • AmBe+Ni source - 8.98 MeV g-rays • p (20 MeV) + C  15.1 MeV - Catania February 2008 - • Natural radioactivity measurement • Single and coincident measurements • Particle Identification Measurements • Particle identifications tests on LaBr3 and LaCl3 • Digitalization and PSA tests • Signals acquired with 100 MHz – 2 GHz ADC • PSA algorithms tested for time, energy and PID • Gamma Imaging with Segmented PMT • PSF experimental Measurement • ISR Calculation and measurement • GEANT simulations + Light tracking • SHIDRA Light tracking code for Medical PET • Voltage Stabilization • Temperature Effects • Voltage Divider Design • F.Camera et al. CR – IEEE - 2007 • R. Nicolini et al. NIM A582(2007)554 • F.C.L.Crespi et al. – IEEE - 2008 • S.Brambilla et al. CR – IEEE – 2007 • S. Riboldi et al. CR – IEEE – 2007 • S. Brambilla et al. – IEEE 2008

  4. High energy g-rays measurements with LaBr3 • LaBr3 Gain Stability and Linearity • Critical especially for Eg > 5 MeV • Measurements of mono-energetic high energy g-rays • Doppler Broadening – Imaging • PMT – VD and other photo-sensors • Digital Electronics • How a LaBr3 Array can complete/compete with an HPGe array

  5. The tube must be used at low voltage • Not optimal performances of Tubes • Bad timing • New special designed voltage divider • (Milano INFN Electronic workshop). • The VD takes energy signal at 6° dinode • and pre-amplify it. Time signal is taken from • anode (on tests). Test at LNS – 12C(p,p’)12C Beam time February 2008 LaBr3 Gain Stability and Linearity • The light yield in of LaBr3 crystal is too high for standard PMT tubes • Linearity • Temperature drift • Voltage drift • These effects are ‘new’ for scintillator physics. LaBr3 crystals, because of light output) are the only with resolution below 3% at 661 keV • The light yield in of LaBr3 crystal is too high for standard PMT tubes • Linearity • Temperature drift • Voltage drift • These effects are ‘new’ for scintillator physics. LaBr3 crystals, because of light output) are the only with resolution below 3% at 661 keV. Energy resolution: 19 keV at 662 kev Time resolution: 230 ps (intrinsic)

  6. LaBr3 Gain Stability and Linearity • The scintillation properties of LaBr3 do not show a dependence on temperature • … but the PMT do • Linearity • Temperature drift • Voltage drift Energy resolution: 19 keV at 662 kev Time resolution: 230 ps (intrinsic) • Temperature effects can deteriorate resolution • The Dependence is Linear, gain drift • approximately - 0.5 % for degrees • If temperature is monitored the drift can be • corrected (only a small hysteresis) is present • There is a initial period of temperature • stabilization which is not possible to correct

  7. LaBr3 Gain Stability and Linearity • PMT gain is very sensitive to voltage. Excellent energy resolution requires voltage stabilization • Linearity • Temperature drift • Voltage drift Energy resolution: 19 keV at 662 kev Time resolution: 230 ps (intrinsic) • The HV unit should provide voltage with a • stability below 0.01 % • Not all HV units commonly used for • scintillators can provide such stability • Event by Event measurement of HV ?

  8. Measurements of mono-energetic high energy g-rays 12C(p,p’)12C* LNS Catania Measurement in Catania 12C(p,p’)12C* Am-Be-Ni PuC Measurements in Milano Am-Be-Ni Joint Proposal ESA-MILANO-LNS for beam time in 2009 Energy Resolution

  9. New Technology on PMTs • There are two new type PMT tubes on market • Photonics – Clarity Class • Hamamatsu SBA-UBA class • In this tubes the quantum efficiency is up to 45% Photonics - Clarity Hamamatsu - SBA Breakthrough in PMT development Tests using these two kind of tubes are now running in Milano

  10. Doppler Correction – Imaging • Large Crystals give large efficiency for high energy g-rays (16% at 10 MeV) • .. but • they substand a large solid angle • this will affect energy resolution LaBr3 4’x 8’ placed at 20 cm from target 1 MeV g-rays source v/c = 0.1 Is it possible to localize the interaction Points ?

  11. Projected charge Scintillation light flash on photocathode i Charge distribution sampling by anode array Doppler Correction – Imaging • Segmented Phototubes • 6mm x 6mm segments • Medical Imaging Techniques

  12. Doppler Correction – Imaging • The PSF function at 140 keV has been measured for a 1’ x 1’ LaBr3 * PSF Segments • The PSF function at 140 keV will be measured for a 3’ x 3’ LaBr3 • Full Simulations are now running to extract the ISR • GEANT + SCIDRA (g-rays interactions + light transport)** • The higher the energy of g-rays the better will be the localization *Thanks to R.Pani and M.Cinti - INFN and Policlinico of Rome ** Thanks to C.Fiorini from Milano Politecnico

  13. Digital Electronics • The prototype of the VME digital board has been built and tested in a Kmax environment • 2 channels for time • 1 channel for energy • The performance for BaF2 and • LaBr3 detectors are as expected • Energy Resolution • Time Resolutions • Fast vs Slow Rejection (for BaF2) • New (final) version of a 4 channel board digital board for BaF2 and LaBr3 scintillators will be built in 2009.

  14. Digital Electronics Time Resolution Energy Resolution • General performances for time resolution using the digital board and an analogue card with a 14 bits 100 MHz ADC • Using Pulser  125 ps • Using two signals from one LaBr3 crystal  550 ps (Thr. = 150 keV HV = 450 V) • Using two BaF2 crystals  600 ps (Thr. = 150 keV )

  15. A LaBr3 array for g spectroscopy can complete an • HPGe Array in several physics cases • Very high background • Few g transitions • Extremely rare events • High energy g-rays • ‘Low’ Budget • Simple experimental setup 4’ x 8’ LaBr3 Array at 20 cm 4’ x 10’ LaBr3 at IEEE-2007

  16. A LaBr3 array for g-spectroscopy can complete an • HPGe Array in several physics cases • Efficiency  Higher in LaBr3 array • Crystals are much larger and much cheaper • Time resolution  much better in LaBr3 array • 500 ps vs 10 ns time resolution • TOF measurements isolate ‘ 10 cm source ‘ vs ‘ 3 m source’ • Maintenance • No cooling • No vacuum • No FET • Energy Resolution HPGe detectors are 10 times better • 25 keV vs 2 keV • Doppler Broadening • in HPGe it is possible to perform Gamma ray Tracking • Gamma Imaging in large LaBr3 ? • Spatial Resolution will be much worse than in HPGe

  17. Thank you

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