Si-detector macroscopic damage parameters during irradiation from measurements of dark current evolution of with fluence Craig Buttar, University of Sheffield collaborators P Booth, I Dawson, PJ Dervan, C Grigson, RS Harper, R Nicholson, University of Sheffield Maurice Glaser, CERN, Alick Macpherson, PSI/CERN
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Si-detector macroscopic damage parameters during irradiation from measurements of dark current evolution of with fluence Craig Buttar, University of Sheffield.
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Si-detector macroscopic damage parameters during irradiation from measurements of dark current
evolution of with fluence
Craig Buttar, University of Sheffieldcollaborators
P Booth, I Dawson, PJ Dervan, C Grigson, RS Harper, R Nicholson, University of Sheffield
Maurice Glaser, CERN, Alick Macpherson, PSI/CERN
Craig Buttar NSS 2002 2
Outline
• Radiation damage in Si
• ATLAS SCT PS irradiation facility
• Current evolution with fluence
• Results from proton irradiation
• Pion irradiation at PSI
• Results from pion irradiation
• Summary of results-comparison to NIEL
Craig Buttar NSS 2002 3
Radiation effects
• Irradiation by heavy particles: s, ps,… results in displacement of atoms from their lattice sites.– Linear increase in leakage current with fluence: I=D
• Change in effective doping due to donor removal and acceptor creation– type inversion np at ~1013-1014neqcm-2
– Change in depletion voltage, primarily due to effN
At the Large Hadron Collider
•Expect levels ~1.4x1014(1MeV)neqcm-2 in regions closest to interactions-central tacking region of ATLAS and CMS
• Detector irradiation programme at CERN PS
Craig Buttar NSS 2002 4
PS Irradiation setup
30m
Temperatureand currentmonitoring
-7oC Dry N2
Atmosphere
Controlledenvironnmentbox
Proton Beam
Moving Stage
CirculatingChiller Coolant
PC
IEEE 488
RS 232
Detectors
IntelligentMotionController
Ethernet toSMTP server
• Irradiate detectors with voltage applied at ~-70C
• Monitor temperature and current during the irradiation between beam spills
• Small beam spot requires scanning of detectors
• Monitor fluence and uniformity of irradiation
• Measure fluence by activating Al foils
– measure 24Na peak at 1369keV, T1/2=16hrs
– Calibrate counter from secondary emission counter
• A model for current evolution with fluence based on bulk current has been used to analyse detectors currents during irradiations with protons and pions
• The model appears to work well but there are deviations from the expected power laws
• Values of and have been extracted from the data and are larger than other results, but care required when comparing.
• Ratio of alpha agrees with relative NIEL-but need to reduce errors from fluence on pion measurements.
Craig Buttar NSS 2002 15
More work
• Improve model, why are there deviations from the power law ?
• Investigate effect of annealing
• Make measurements at other sites with a range of particle and energies