Chapter 3 Extra-galactic Gamma-Ray Sources

Extra-galactic gamma-ray sources, such as gamma-ray bursts, active galactic nuclei, starburst galaxies, are interesting and important targets for LHAASO observations. In this chapter, the prospects of detecting these sources with LHAASO and their physical implications are studied. The upgrade plan for the Water Cherenkov Detector Array (WCDA), which aims to enhance the detectability of relatively lower energy photons, is also presented. In addition, a study on constraining the extragalactic background light with LHAASO observation of blazars is presented.

Muon identification in a compact single-layered water Cherenkov detector and gamma/hadron discrimination using machine learning techniques

The muon tagging is an essential tool to distinguish between gamma and hadron-induced showers in wide field-of-view gamma-ray observatories. In this work, it is shown that an efficient muon tagging (and counting) can be achieved using a water Cherenkov detector with a reduced water volume and 4 PMTs, provided that the PMT signal spatial and time patterns are interpreted by an analysis based on machine learning (ML). The developed analysis has been tested for different shower and array configurations. The output of the ML analysis, the probability of having a muon in the WCD station, has been used to notably discriminate between gamma and hadron induced showers with $$S/ \sqrt{B} \sim 4$$ S / B ∼ 4 for shower with energies $$E_0 \sim 1\,$$ E 0 ∼ 1 TeV. Finally, for proton-induced showers, an estimator of the number of muons was built by means of the sum of the probabilities of having a muon in the stations. Resolutions about $$20\%$$ 20 % and a negligible bias are obtained for vertical showers with $$N_{\mu } > 10$$ N μ > 10 .

A prototype anti-scatter detector for megavoltage X-ray imaging

In this work, a prototype anti-scatter detector based on Cherenkov radiation is developed by using glass rods. Scattering lends deleterious effects to the megavoltage x-ray portal imaging and anti-scatter detector can effectively reduce these effects. A 10 cm long glass rod with 1 mm in diameter is used as a Cherenkov detector prototype and it is studied for its response to x-ray scattering from, e.g., machine head and patient. It is subjected to 6 MV x-ray beam generated by linear accelerator (LINAC) with different field sizes (from 3 X 3 to 20 X 20 cm2) at different air gaps such as 10, 30 and 46 cm. The Cherenkov signal created by the detector is transmitted through optical fiber to photomultiplier tube (PMT) and measured by electrometer. The patient scattering is studied by placing a solid water phantom at isocenter. The response of single pixel Cherenkov detector is compared with the conventional ionization chamber detector. It has been observed that glass rod based Cherenkov detector is less sensitive to scatter radiation than ion-chamber for air gap of 10 cm. The Cherenkov signal created by glass rod is quite weak for larger air gaps and the uncertainties are quite high. Moreover, the coupling between Cherenkov detector and optical fiber is quite crucial for transmitting the Cherenkov signal from glass rod into optical fiber.

A prototype anti-scatter detector for megavoltage X-ray imaging

In this work, a prototype anti-scatter detector based on Cherenkov radiation is developed by using glass rods. Scattering lends deleterious effects to the megavoltage x-ray portal imaging and anti-scatter detector can effectively reduce these effects. A 10 cm long glass rod with 1 mm in diameter is used as a Cherenkov detector prototype and it is studied for its response to x-ray scattering from, e.g., machine head and patient. It is subjected to 6 MV x-ray beam generated by linear accelerator (LINAC) with different field sizes (from 3 X 3 to 20 X 20 cm2) at different air gaps such as 10, 30 and 46 cm. The Cherenkov signal created by the detector is transmitted through optical fiber to photomultiplier tube (PMT) and measured by electrometer. The patient scattering is studied by placing a solid water phantom at isocenter. The response of single pixel Cherenkov detector is compared with the conventional ionization chamber detector. It has been observed that glass rod based Cherenkov detector is less sensitive to scatter radiation than ion-chamber for air gap of 10 cm. The Cherenkov signal created by glass rod is quite weak for larger air gaps and the uncertainties are quite high. Moreover, the coupling between Cherenkov detector and optical fiber is quite crucial for transmitting the Cherenkov signal from glass rod into optical fiber.