Kugler, A.

Kushpil, S.

Kushpil, V.

Mikhaylov, V.

Svoboda, O.

Tlusty, P.

GSI Repository

Radiation hardness of the PSD APDs for the CBM experiment∗V. Kushpil1, A. Kugler1, S. Kushpil1, V. Mikhaylov†1,2, O. Svoboda1, and P. Tlusty11NPI of ASCR, ˇRezˇ, Czech Republic; 2CTU, Prague, Czech RepublicThe projectile Spectator Detector (PSD) of the CBM ex-periment is designed to register forward spectator nucleonsand fragments emitted in nucleus-nucleus collisions at verylow polar angles. It will be used to determine the collisioncentrality and the reaction plane orientation.The PSD is a fully compensating modular lead-scintillator calorimeter. The Avalanche Photo-Diodes(APD) are used to read out the scintillation light viawavelength shifting fibers. An important characteristic ofthe APD is its radiation hardness to a neutron fluxes of1013 n/cm2 which corresponds to two months of CBM ex-periment operation.Two different APD samples, Ketek PM3375 and ZecotekMAPD-3N, were irradiated at the NPI ˇRezˇ Cyclotron Facil-ity by quasi-monoenergetic secondary neutron beam withenergy of 35 MeV. A sample of Zecotek APD was irradi-ated with a dose of 3.4±0.2 1012 n/cm2, while two samplesof Ketek APDs were irradiated with 2.5± 0.2 1012 n/cm2.Doses were measured with a special PIN diode calibratedwith a dose equivalent to 1 MeV neutron [1]. The operationtemperature during the tests was kept at 22± 0.5◦ C.The APD characteristics were measured before and afterthe irradiation. The Capacitance-Voltage (C-V), Current-Voltage (I-V), and Capacitance-Frequency (C-F) charac-teristics were studied using dedicated testing setup at NPIˇRezˇ [2,3]. After irradiation, the C-V technique showed sig-nificant decrease of hysteresis and fast but not completeself-annealing. The I-V curve revealed about 1000 timesincrease of dark current after irradiation. The C-F studyshowed significant increase of short-living traps in Silicon.The test results suggest an increase of internal APD noise,especially of the high frequency, which dependents on theamount of short-living traps in the APD volume.Figures 1 (2) show the results of the Ketek (Zecotek)APD tests with LED and cosmic muons. Both APDs havea maximum signal (noise) amplitude of about 0.3 − 0.4 V(0.05 V) which corresponds to 20− 30 ph.e (3 ph.e). Afterirradiation both APDs are unable to resolve single photonsdue to high noise levels. This is not critical for the PSDperformance since there are at least 15 ph.e. produced inone PSD module already by a cosmic muon. The signaland noise peaks for irradiated Ketek APD are very closewhich makes it very difficult to separate signal from noise.On a contrary, signal and noise peaks for Zecotek APDs are∗Work supported by the European Community FP7 – Capaci-ties, contract HadronPhysics3 n◦283286, LG12007 of the MECR andM100481202 of the ASCR grants, by project MSMT LG14004 of Co-operation Program between JINR and NPI in 2013-2014.† mikhaylov@ujf.cas.czFigure 1: Test results with LED and cosmic muons ofKetek APD before (upper) and after (lower) irradiation.Figure 2: Test results with LED and cosmic muons of Ze-cotek APD before (upper) and after (lower) irradiation.well separated from each other, what allows reliable signalfrom noise separation even after irradiation.References[1] V. Kushpil, S. Kushpil and Z. Huna, EPJ Web of Conferences24 (2012) 07008.[2] V. Kushpil, V. Mikhaylov, S. Kushpil, P. Tlusty, O. Svoboda,A. Kugler, doi:10.1016/j.nima.2014.11.071[3] V. Kushpil, S. Kushpil, JINST 7 (2012) C01084.GSI SCIENTIFIC REPORT 2014 MU-NQM-CBM-01DOI:10.15120/GR-2015-1-MU-NQM-CBM-01 37

Radiation hardness of the PSD APDs for the CBM experiment

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Radiation hardness of the PSD APDs for the CBM experiment

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