Crystal R&D Activity in Korea

1. Crystal R&D Activity in Korea B.G. Cheon (Hanyang), H.J.Kim (KNU), E. Won (KU), S.S. Myoung S.K. Kim(SNU), Y.J. Kwon (Yonsei)

2. Introduction & Background • We, Korean group reviewed possible options for the endcap ECL from the scratch. • The goal is to see if there are alternatives to pure CsI crystal option we have. • Parameters we looked at in particular : - light yield (energy resolution) - decay time (pileup, occupancy) - radiation hardness - beam background suppression - budget and other fabrication issues

3. Compilation of X-tals a. at peak of emission; b. up/low row: slow/fast component; c. measured with bi-alkali PMT

4. Pure CsI crystals • Decay time ~30 ns which is 40 times faster than CsI(Tl). Solves pileup problem. • Light yield is ~5% CsI(Tl) and peak emission is 320 nm (UV region) • Radiation hardness may be OK (need to checked carefully) up to 1035 • Readout by APD or P.P. • No change to geometry of calorimeter • Cost is ~$4/cc • Currently under R&D by sBELLE group

5. LSO (or LYSO), GSO, LuAG:Pr • Decay time with 40 ns. Solves pileup problem. • Smaller radiation length and Moller radius makes shorter and finer segmentation possible. • Radiation hard to 100MRad • Light output is half of CsI(Tl), and peak emission is 420 nm • Use PD, APD or P.P. for photosensor • LYSO has slightly more light output than LSO, and may be easier to obtain commercially • GSO has similar characteristics but has large thermal neutron cross section • LuAG:Pr is also good candidate except the cost • Currently the cost is ~$30/cc!! • Italian Endcap ECL default option

6. PbWO4 (PWO) • Decay time with 10& 30 ns. Solves pileup problem. • Smaller radiation length and Moller radius makes shorter and finer segmentation possible. • Radiation hard to 10MRad • Light output is 0.1-0.6% CsI(Tl) • Cooling to -25 degree with PMT shows reasonable performance • Peak emission is 420 nm • Use APD or P.P. for photosensor • CMS, PANDA is using • Currently the cost is ~$3/cc

7. Optimization of the PbWO4 and increase of the light output 3x3 matrix 20x20x200mm3 PM-readout 4x lighter if cooled down Response to high energy photons @MAMI, Mainz • Optimization of the PbWO4 (collaboration RINP, Minsk and the manufacturer BTCP at Bogoroditsk, Russia) • reduction of defects (oxygen vacancies) • reduced concentration of La-, Y-Doping • better selection of raw material • optimization of production technology +80% at room T° Development of the PWO-II : Light yield increased Calor2008

8. BSO (Bi3Si4O12) • Main decay time is 100 ns. • Smaller radiation length and Moller radius makes shorter and finer segmentation possible. • Radiation hard to 1-10 MRad • Light output is 3-4% of CsI(Tl), and peak emission is 480 nm • Use APD or P.P. for photosensor • BSO:Ce shows stronger radiation hardness • Beamtest results shows reasonable resolution • Cost will be cheaper than BGO (No Ge) and growing is easier (Cubic structure, low melting) • Need to produced in large quantity (~$3/cc?) => BSO option seems OK, if 100 ns decay time is OK

9. Results and Discussion for existing X-tals • Pure CsI is baseline option, however it may be problem with higher luminesity (>1035) • L(Y)SO, PbWO4 and BSO are reasonable option. • BSOseems the most reasonable next candidate considering all characteristics if it can be produced large quantity. If we can cool down to -25 degree, PWO is the best candidate since it is being produced large quantity. BSO and PWO costs ~3$/cc & can be used with 20cm length with finer segmentation. • Detail study and comparison of different candidates coupled with photo sensor are necessary to select the best performance one.

10. SNU Used CsI(Tl) Pure CsI An alternative idea APD or PP Fast Slow • Logic (and probably advantages) • Radiation damage only to front ~10 cm of crystals  need to be checked • High energy signals  enough signal in CsI(Tl) crystals ->do not lose resolution • Fast/Slow  another handle for shower correction by knowing shower shape • Fast trigger signal using fast signal  blind to beam background • Much cheaper Endcap ECL upgrade : 11 M USD (8.2M for crystals) Crystal costs ¼ of full crystal  2 M  total <5 M should be OK

11. SNU Phoswich definition • A phoswich('phosphor sandwich') is a combination of scintillators with dissimilar pulse shape characteristics optically coupled to each other and to a common PMT. Pulse shape analysis distinguishes the signals from the two scintillators, identifying in which scintillator the event occurred. Idea: re-use (possibly) un-damaged rear part of endcap CsI(Tl) crystals Pure CsI CsI(Tl) Etot = E1*a + E2*b a,b : calibration factor E2=0 : 1st crystal interaction E1=0 : 2nd crystal interaction Both : Etot can be calculated

12. SNU Phoswich R&D Crystal Gean4 Simulation • CsI 8cm*8cm*30cm -15cm +15cm 10cm CsI(Tl) Pure CsI Gamma: 100 MeV 200 MeV 400 MeV 500 MeV 1 GeV Note the difference in the emission spectrum of two X-tals E_dep_pure ->N_photon according to Intensity ->Apply transmission curve Some transmit to csi(Tl)->fast signal Other + E_dep_Tl slow signal

13. SNU E5/Etot E10/Etot E10/Etot E10/Etot One Crystal E10/Etot>0.5 >0.7 10MeV: 83% 82% 100MeV: 86% 73% 1GeV: 51% 13%

14. SNU Phoswich R&D Crystal Gean4 Simulation - Resolution E(pure) vs. E(CsI(Tl)) 200 MeV 100 MeV 500 MeV 1 GeV σ /E 5 cm E=a*E(Tl )+ b*E(pure) fit to each energy distribution E 30cm*30cm*30cm Energy resolution is 2% at 1 GeV

15. KNU Phoswich R&D Crystal source test Small size Crystal R&D • Two Belle type of crystals were received from KEK and cut into test samples (1x1x1cm3) for this study. They are polished and wrapped with Teflon sheet. • Maxium 40 keV x-ray energy is used for luminescence test • 2” bi-alkali high gain PMT is used for 662 keV gamma and 5.5 MeV alpha-ray test. Configuration • 1x1x1cm3 cubic CsI • 1x1x1cm3 cubic CsI:Tl • 1x1x2cm3 CsI+CsI:Tl (from 1 &2)

16. KNU Phoswich R&D Crystal Configuration X-ray X-ray emission emission Pure CsI X-ray X-ray emission CsI(Tl) emission Am241, Cs137 a g a g Pulse height Decay time Pulse height Decay time Pulse height Decay time a Q: Doesemission of CsI de-excite CsI:Tl ?

17. KNU X-ray luminescence device at KNU and source test

18. KNU Measured x-ray luminescence 310 nm 490 nm ?? 550 nm Pure CsI CsI(Tl) Strange enhancement !!! 490 nm 550 nm Pure to Tl Tl to pure Because of the mystery above, we cannot draw any conclusions

19. KNU Pulse height/decay time comparison Cs137 (gamma) Am-241 (alpha) Pure CsI Pure to Tl Am-241 (alpha) Am-241 (alpha)

20. HYU Test setup for cosmic rays Power Supply(HV) -1500V Amplifier FADC 400MHz Linux PC PMT (High gain Xp2206) ULS Notice Korea Fedora core 6 CsI (Tl) 20cm CsI (pure) 10cm T.Y.Kim HYU Physics Hybrid signal shape measurement@ sbelle Korea Meeting Page 20

21. HYU Cosmic ray - Data • CsI (pure) CsI (Tl) CsI (pure) T.Y.Kim HYU Physics Hybrid signal shape measurement@ sbelle Korea Meeting Page 21

22. HYU Cosmic ray - Data • CsI (Tl) CsI (Tl) CsI (pure) T.Y.Kim HYU Physics Hybrid signal shape measurement@ sbelle Korea Meeting Page 22

23. Summary on phowich • Phoswich option may reduce the budget significantly (5 cm pure CsI costs < 5M US $). • Geant4 simulation (very preliminary) shows the energy resolution is ~ 2% at 1 GeV. • E = a*E(pure) + b*E(CsI(Tl)) seems to make everything complicated. • Phoswich x-ray luminescence shows a strange behavior (need to understand, calibration issue?). • Phoswich fast and slow components are 50:50 % in the signal. • More R&D is needed to understand situation better.

24. Summary on this talk • Pure CsI is a default option • We are looking at - LSO : expensive but others look fine - BSO : decay time 100ns, no mass production - PbWO4 : operation at -25 oC is desired as feasible alternative options • Phoswich[CsI:CsI(Tl)] has been studied. • We would like to continue R&D efforts to reduce number of options, if not one option