Transcript Document
CsI Veto Detector Performance Study He Dao DMRC. Tsinghua University For KIMS Collaboration ULE WIMP Experiment • WIMP search • Ultra-Low Energy wimp experiment – HPGe detector – Expected threshold 100 eV – Correspond WIMP mass limit: ~1GeV System Structure CsI detector structure • Three parts of crystal – Cylinder top with a slope – Tube side – Cylinder bottom – Optical gel connection • Cooler hole • Low background PMT • Al Shell only for safety HV Selection • Daq: CAMAC; Source Cs-137 ; Output: signal amplitude • -1300V selected • A reference if HV changed Incidence position dependency • Influence factors: – Big dimension causes serious photon absorption – Conjunction section reflection – Cooler hole – Only one PMT used • • • Daq: MAC Source: Cs-137 Test consideration: height and angular dependency Source position dependency Height (cm): 1.5, 7, 13, 22, 28 Angle (degree): 180 Height (cm): 5 (near the hole) Angle (degree): 0, 90, 150, 180 Height dependency • • • Peak position – The nearer incident position from PMT, the larger amplitude of output signal – About 70% response while source near the bottom relating to the top position Peak resolution – Round 16%, best situation when source in middle height, top and bottom worse. Main reason: Big size causes photon absorption; pieces section reflection Angular dependency • • Peak position – No obvious difference Resolution – The cable hole causes serious resolution difference, 90 degree’s response is best. That maybe because the cooler hole is void while I did this test. Fortunately, as a veto detector, the resolution is not very important. Oscilloscope Calibration (Crystal top) for internal background measurement HV: -1200V Source information: Calibration Result: • E(keV) = ( channel - p0 ) / p1 E(keV) channal error 662 5.94170e+03 3.93589e+00 Param Value Error 1173 1.05634e+04 1.16126e+01 p0 3.30050e+01 1.23173e+01 1332 1.19898e+04 1.17900e+01 p1 9.03272e+00 1.53536e-02 Internal background • • • • Only CsI crystal top 15cmPb, 5cm Cu Daq: Oscilloscope 10 days Peak Pos (channel) Energy (keV) 2308 259 3273 366 5947 621 8384 932 13175 1462 23547 2611 Possible source : Decay chain, internal source, and Radon. More accurate measurement by HPGe detector running in Y2L. Photon collection efficiency comparison 662 keV gamma HV (minus volt) Oscilloscope scale (mV/div) Peak position (channel) Resolution (%) crystal top 1200 100 5942 9 All crystal (source near the top) 1300 50 5884 16 According to HV selection result, if high voltage is set at 1300V the signal amplitude should be about 705/463 to that of 1200V, considering the scale change, the photon collection efficiency of CsI crystal top is 705/463 * 100/50 * 5942/5884 ~= 3 times to that of whole detector! Summary • Working Voltage: – Wide range , -1300V selected • Incidence position dependency – Obvious height dependency, weakest situation 70% signal amplitude compared to strongest – Not serious angular dependency • Internal background – Decay chain, internal source, and Radon. – More accurate measurement running now by HPGe detector in Y2L • Photon collection comparison – Only top 3 times better than whole detector Plan • Pulse Shape Discrimination • More accurate internal background content and activity • MC simulation Thank you!