A wide range of astronomical evidence implies the existence of Dark Matter, but as yet the nature of this major component of the Universe is completely unknown. A leading candidate explanation is ...that Dark Matter is composed of Weakly Interacting Massive Particles (WIMPs) formed in the early universe and gravitationally clustered together with the standard baryonic matter. Such WIMPs could in principle be detected through their collisions with ordinary nuclei in a sensitive target, producing observable low-energy (<100 keV) nuclear recoils. The predicted collision rates are very low and require ultra-low background detectors with large (0.1 { 10 tons) target masses, located in deep underground sites to reduce the background produced by neutrons from cosmic ray muons 1{4.
Borexino is a solar neutrino experiment designed to observe the 0.86
MeV
Be
7
neutrinos emitted in the pp cycle of the sun. Neutrinos will be detected by their elastic scattering on electrons in 100
...ton of liquid scintillator. The neutrino event rate in the scintillator is expected to be low (
∼
0.35
events per day per ton), and the signals will be at energies below 1.5
MeV, where background from natural radioactivity is prominent. Scintillation light produced by the recoil electrons is observed by an array of 2240 photomultiplier tubes. Because of the intrinsic radioactive contaminants in these PMTs, the liquid scintillator is shielded from them by a thick barrier of buffer fluid. A spherical vessel made of thin nylon film contains the scintillator, separating it from the surrounding buffer. The buffer region itself is divided into two concentric shells by a second nylon vessel in order to prevent inward diffusion of radon atoms. The radioactive background requirements for Borexino are challenging to meet, especially for the scintillator and these nylon vessels. Besides meeting requirements for low radioactivity, the nylon vessels must also satisfy requirements for mechanical, optical, and chemical properties. The present paper describes the research and development, construction, and installation of the nylon vessels for the Borexino experiment.
As part of the DarkSide program of direct dark matter searches using two-phase argon TPCs, a prototype detector with an active volume containing 10kg of liquid argon, DarkSide-10, was built and ...operated underground in the Gran Sasso National Laboratory in Italy. A critically important parameter for such devices is the scintillation light yield, as photon statistics limits the rejection of electron-recoil backgrounds by pulse shape discrimination. We have measured the light yield of DarkSide-10 using the readily-identifiable full-absorption peaks from gamma ray sources combined with single-photoelectron calibrations using low-occupancy laser pulses. For gamma lines of energies in the range 122–1275keV, we get light yields averaging 8.887±0.003(stat)±0.444(sys) p.e./keVee. With additional purification, the light yield measured at 511keV increased to 9.142±0.006(stat) p.e./keVee.
The liquid handling systems for the Borexino solar neutrino detector Alimonti, G.; Avanzini, M.B.; Back, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2009, Volume:
609, Issue:
1
Journal Article
Peer reviewed
The successful deployment of the Borexino solar neutrino detector required assorted physical and chemical operations to produce exceptional pure fluids and fill multiple detector zones. The ...composition and flow rates of high purity gases and liquids had to be precisely controlled to maintain liquid levels and pressures. The system was required to meet exceptional requirements for cleanliness and leak-tightness. A large scale modular system connecting fluid receiving, purification and fluid delivery processes was developed for Borexino. At the core is a flow control system that delivers scintillator components to plants for purification, and then fills the Borexino detector volumes with ultrahigh purity buffer or ultrahigh purity scintillator. The liquid handling system maintains precise control over the liquid levels and differential pressures between the different volumes of the detectors that are separated by flexible nylon vessels. The preparation, commissioning and operation of the system for filling the Borexino detector with scintillator is described.
DarkSide-50 is a two phase argon TPC for direct dark matter detection which is installed at the Gran Sasso underground laboratory, Italy. DarkSide-50 has a 50-kg active volume and will make use of ...underground argon low in 39Ar. The TPC is installed inside an active neutron veto made with boron-loaded high radiopurity liquid scintillator. The neutron veto is installed inside a 1000 m3 water Cherenkov muon veto. The DarkSide-50 TPC and cryostat are assembled in two radon-free clean rooms to reduce radioactive contaminants. The overall design aims for a background free exposure after selection cuts are applied. The expected sensitivity for WIMP-nucleon cross section is of the order of 10−45cm2 for WIMP masses around 100GeV/c2. The commissioning and performance of the detector are described. Details of the low-radioactivity underground argon and other unique features of the projects are reported.
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