Reduced γ-γ time walk to below 50 ps using the multiplexed-start and multiplexed-stop fast-timing technique with LaBr₃(Ce) detectors

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• 作者：J.-M. Ré ; gis^a ; ^{regis@ikp.uni-koeln.de" class="auth_mail" title="E-mail the corresponding author} ; N. Saed-Samii^a ; ^{nima@ikp.uni-koeln.de" class="auth_mail" title="E-mail the corresponding author} ; M. Rudigier^a ; ^b ; S. Ansari^a ; M. Dannhoff^a ; A. Esmaylzadeh^a ; C. Fransen^a ; R.-B. Gerst^a ; J. Jolie^a ; V. Karayonchev^a ; C. Mü ; ller-Gatermann^a ; S. Stegemann^a
• 关键词：Lifetime measurements ; The GCD method ; Time walk ; LaBr3(Ce) scintillators
• 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• 出版年：2016
• 出版时间：1 July 2016
• 年：2016
• 卷：823
• 期：Complete
• 页码：72-82
• 全文大小：830 K

文摘

The electronic γ–γ fast-timing technique using arrays consisting of many LaBr₃(Ce) detectors is a powerful method to determine lifetimes of nuclear excited states with a lower limit of about 5 ps. This method requires the determination of the energy-dependent time walk of the zero time which is represented by the centroid of a prompt γ–γ time distribution. The full-energy peak versus full-energy peak prompt response difference which represents the linearly combined mean γ–γ time walk of a fast-timing array consisting of 8 LaBr₃(Ce) detectors was measured using a standard ¹⁵²Eu γ-ray source for the energy region of 40–1408 keV. The data were acquired using a “multiplexed-start and multiplexed-stop” analogue electronics circuitry and analysed by employing the generalized centroid difference method. Concerning the cylindrical 1.5 in.×1.5 in. LaBr₃(Ce) crystals which are coupled to the Hamamatsu R9779 photomultiplier tubes, the best fast-timing array time resolution of 202(3) ps is obtained for the two prompt γ lines of ⁶⁰Co by using the leading-edge timing principle. When using the zero-crossover timing principle the time resolution is degraded by up to 30%, dependent on the energy and the shaping delay time of the constant fraction discriminator model Ortec 935. The smallest γ–γ time walk to below 50 ps is obtained by using a shaping delay time of about 17 ns and an optimum “time-walk adjustment” needed for detector output pulses with amplitudes smaller than 400 mV.