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Cosmic-ray muon imaging is a kind of nondestructive detection technology which can be used to detect unknown objects in geological exploration, civil engineering and nuclear safety. Transmission imaging and scattering tomography schemes are studied. The transmission scheme uses a multilayer detector to measure the direction of a cosmic-ray muon passing through an object. The scattering scheme involves placing two detectors upstream and downstream of the object to record the incident and exit directions of the muon passing through the object. The effect of the detector resolution on the imaging clarity of transmission imaging was studied. The applicable scenarios of the two schemes were analyzed. The results by calculating show that in the transmission imaging of a hundred-meter object, a spatial resolution of 2.5 m can be achieved, and Cu and Fe can be discriminated with a density difference of 1.1 g/cm3. Scattering tomography is mainly suitable for meter-level objects, which can detect 0.2 m chamber and distinguish 0.05 m heavy metal blocks in rock.

During the research phase of acrylic panel for the Jiangmen Underground Neutrino Observatory (JUNO) central detector (CD), the darkroom transmittance measurement system (DTMS) was designed and built, and a massive amount of measurements were carried out to help determine the composition and processing techniques of the acrylic panel. The mass production of acrylic panels was started after the pilot production. The requirement of transmittance measurement put forward new demands on operation, and a new measurement system was considered to support removable and non-destructive measurement on site. After the accomplishment of design, development and verification were completed, the laser measurement system came into use in the acrylic workshop of Taixing Donchamp Acrylic Ltd, and the transmittance results of acrylic spherical panels met the requirement of JUNO. The optical design, tooling design, data processing interface and uncertainty analyses of the laser measurement system are discussed in detail, and the measured transmittance results are also introduced in this article.

The Central Detector (CD) of the Jiangmen Underground Neutrino Observatory (JUNO) uses 20,000 tons of liquid scintillator as target mass, and the design value of energy resolution of neutrino is 3% at 1 meV. Acrylic transmittance is an important parameter for CD in order to maximize the detection of scintillating photons. The composition and processing techniques of acrylic can surely affect its transmittance. How the composition, thermoforming temperature, heat preservation time and surface treatment process of acrylic affect its transmittance was measured and analyzed. According to these studies, JUNO determined its special acrylic composition and processing techniques: no components of plasticizer or anti-UV in the composition, decreasing the time span and temperature during the demolding of flat panel, and adopting suitable thermoforming temperature of spherical panel. Finally, the preproduction of spherical acrylic panels meets the JUNO requirement confirming a transmittance in ultrapure water greater than 96% at the wavelength of 420 nm.

The limitation of the traditional bias neutralization method is proved, and a new neutralization method is proposed to measure the secondary electron yield of insulating materials. While measuring the secondary electron yield of an insulating sample using the bias neutralization method, the region of an insulating sample irradiated by an electron beam may not be neutralized, because electrons enforced by the bias are not returned to the proper location. The above-mentioned phenomenon is verified by a simulation. To achieve proper neutralization, we propose a method of moving the electron beam to irradiate the metal sample stage without applying a bias voltage, which generates many low-energy electrons around the insulating sample. Those electrons are automatically attracted to the positively charged region of the insulating sample surface and rejected if enough electrons accumulated on the surface. The limitation of neutralization of bias voltage was verified by simulation, and the new neutralization method was proved to be effective through experiments.

The Jiangmen Underground Neutrino Observatory (JUNO) has 20 kilo-ton liquid scintillator as target mass contained by a huge acrylic sphere to carry out the research on neutrino physics. Acrylic transmittance is considered as an important optical performance of the JUNO Central Detector as it has a direct relationship to the number of photons detected by the JUNO Central Detector and further affects the energy resolution of JUNO. The transmittance requirement of acrylic spherical panel for the JUNO Central Detector is exceeding 96% at the wavelength of 420 nm in ultrapure water and a specific measurement system was built and studied in Institute of High Energy Physics for this purpose, as the existing equipment cannot perform the sample test in the liquid and support the long sample length of 120 mm. After improving the technology of thermoforming, the transmittances of the acrylic spherical panels meet the requirement of JUNO, which guarantees the batch production of acrylic panels on time. The design of the measurement system, the constitution of hardware, the development of control and data acquisition software are introduced, and the measurement uncertainty of the system and the transmittance results of the acrylic samples from the spherical panel are discussed in this article.

A compact T0 detector with high time resolution is developed. The T0 detector is based on a multi-anode MCP-PMT coupled with two fused quartzes. The characteristics of this MCP-PMT are studied by a fast laser pulse in laboratory firstly. Cosmic ray test has been carried out to study T0 detector’s signal features and time resolution. The T0 detector’s time resolution is less than 40 ps for the cosmic ray events. It can be applicable in cosmic ray test, beam test, collider experiment and detector developments.

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy, precisely measure oscillation parameters and study solar neutrinos, supernova neutrinos and geo-neutrinos, etc. The central detector (CD) of JUNO has 20,000 tons liquid scintillator as target mass, which contains inside a huge acrylic sphere with inner diameter of 35.4 m, supported by a stainless steel structure. The whole structure of CD will be installed inside a cylindrical water pool, and the acrylic sphere will be submerged in the center of water pool. The operating temperature of CD is designed to be 21 °C as long as over 20 years, which is determined by the mechanical requirement of the structure and physics consideration. For this operating temperature, a special cooling system will be used to maintain the temperature inside the water pool. The main structure of CD is composed of acrylic and stainless steel, and they have much different thermal expansion coefficients, strengths and life times. Change in temperature may affect the safety of CD. As part of reliability analysis, the effect of cooling system failure on the CD is considered, and finite element method is used in our thermal calculation. In this article, the temperature fields before and after cooling system failure are calculated and analyzed, and the temperatures of different locations of water pool after cooling system failure are compared and discussed in detail.