The Performance Test Of Water Cherenkov Detector And Test Of Air Shower Core Array Detector

Experiments found that the all-particle energy spectrum of Cosmic Ray (CR) with energy above 10¹¹eV follows a power law with negative index in the form of E^-γ .At～3×10¹⁵eV, the energy spectrum changes to be steeper. This structure is called knee. Since this obvious bend of the energy spectrum indicates changes of the composition, origin, acceleration and propagation mechanism of the primary CR particles, which have special significance, the origin of knee has drawn much attention since it was discovered by MSU in 1958.Water Cherenkov calorimenter is a kind of new detector with the advantages of good performance and low price. The detector was used to receive cherenkov light and get rid of hadron background form gamma-ray signals above 100TeV by measuring the intensity ofμgenerated in the extensive air showers. Firstly, we studied the performance of PMT(Photomultiplier Tube) by measuring dark current, absolute gain, relative gain and so on. Then, we measured the single particle spectrum under the conditions of empty water tank, tank full of tap water and tank full of purified water, respectively. The attenuation length of Cherenkov photons in purified water, and the relationship between counting rate of detector and zenith of incidence cosmic rays were also measured. Then, we made another column-shape water Cherenkov detector measured the intensities of cosmic ray background at Lasa, Yangbajing and Namuco using local water and purified water as medium. The relationship between counting rate of detector and discriminator's threshold under conditions of water barrel with different amount and quality of water, and the detective efficiency of detector to cosmic rays with different zenith angle were also measured.For detecting primary Comic-Ray (proton, helium, iron nucleus) energy spectra at knee, the ASγCollaboration plans to set core array detectors in the centre of ASγarray in Yangbajing .The core array detector is a kind of new fiber plastic scintillated detector for detecting charged particle. It will take place of the old air light guide scintillators in the center of EAS. The photons come to PMT's Light Cathode by the fibres in the plastic scintillators. Core array detector mainly detects high energy electromagnetic components in the showers. The weight nucleus components can be distinguished and the ratio of them can be got by Monte Carlo simulation. The upper surface of core array detector was divided into 80 little panes. The uniformity of the detector have been studied by putting the radiative element Sr⁹⁰ into these panes one by one and the result shows that it is appropriate with our request.