https://indico.ihep.ac.cn//event/9242/

Yuhang introduced that LGAD were designed for particle physics experiments, medical and timing applications.He further added that to study the radiation hardness of LGAD, several sets of diodes were irradiated with reactor neutrons, 192MeV pions and 800MeV protons to the same equivalent fluences and it was found that the gain decreases with irradiation, which was attributed to effective acceptor removal in the multiplication layer. Xin Asked why is the time ranging in nano-seconds instead of pico-seconds on page:3(b) plot in x-axis. Yuzhen replied that this could be the reason because the LGAD taken in this paper is thick and it takes time to reach the current(basically charge) carriers from cathode to anode ring.

Later in his slides Yuhang replied the answers asked by the group members by email: Suyu: Ques: In Figure 4 (a) & (b), I think the turning point from steeply rising to moderately rising locates on 100V. Why do they say “300 V is required to raise the electric field”? Speaker’s Thoughts(Answer): When the bias voltage is around 300V, the gain will not change much when the detector is affected by a small amount of irradiation or other factors. But if we use 100V, gain fluctuations will be very large.

Yuzhen: Ques: In Figure 4 (c) and (d), the indicated stages of signal are different between W7 and W8, especially the 1.)drift of electrons, why? Answer: There is an upper limit to the current generated by the electron drift in the non-multiplier region when U is certain. Because of the high gain of W8, the voltage in the non-multiplier region is relatively low, and the current rises slowly, the current is easy to reach the upper limit.

Amit Pathak: Ques: In the section: 3.2 Irradiated Samples, The dependence of charge collection on fluence is shown in figure 6. Samples from both wafers were irradiated with neutrons. Selected samples from W8 were irradiated with 800 MeV protons and those from W7 with 192 MeV pions. In the Picture Description: 6, They have irradiated W7 wafer with neutron(Picture 6a) and pions(Picture 6b)(Energy 192 MeV) but in the case of W8 wafer with neutron(Picture 6c) and protons(Picture 6d)(Energy 800 Mev). Why are there two different energy scale to compare the dependence of charge collection on fluence? Answer: Pointed about this question that The fluences of particles were scaled to 1 MeV neutron equivalent fluences by using hardness factor: 0.92 for reactor neutron(>100keV) and 1.14 for 192MeV pions and 0.71 for 800MeV protons.

Shi Xin: Ques: On page 7, it says about the reason for gain degradation: “The reason must therefore be related to the decrease of the multiplication gain rather than trapping of the drifting charge”. How to draw this. Conclusion? Answer: The relative decrease of measured charge is much more pronounced for LGAD than for standard devices (see figure 7 of the paper). The difference between LGAD and Fz-p is the multiplication gain.

Ryuta: Q: About Fig.11, what is the meaning of Vmr ? Especially, why the curves start to rise up from certain values (=Vmr) ? and the degreasing of Vmr toward 0V might indicate what ? Answer: Vmr is depletion voltage of p+ layer. The value of Vmr is is determined by doping concentration in p+ layer. When Vmr toward 0V, the gain is 0, and there is no multiplier layer.

Author also compared the results of measured induced currents after back illuminium in the LGAD irradiated to phi{eq}=2*10^14cm^-2 from W7 and W8.

Summary was the gain of the devices decreased fast and almost vanished at irradiation of 10^15cm^-2. The decrease of the gain after irradiation was attributedto removal of acceptors in the p+ layer. The removal was faster for charged hadrons. The leakage current increased due to linear increase of generation current with fluence, but was moderated by the decrease of multiplication.

Special topic60:

The Author presented the basic idea of his learning for python programming language. She has started with basic grammar of python with List and Dictionary and later with continue and break statements Later she explained the functions in python by explaining with suitable examples how to define a function and how to import tools. She also explained how to read a file and write a file in python language. Python is very efficient and powerful programming language among all the langauges and it was a very introductory topic for all of us.

Amit Pathak introduced the next JC98 paper with psi(2S) decaying into 4-leptons and J/psi.