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 ...tons 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.
Ultra-cold neutrons (UCN), neutrons with energies low enough to be confined by the Fermi potential in material bottles, are playing an increasing role in measurements of fundamental properties of the ...neutron. The ability to manipulate UCN with material guides and bottles, magnetic fields, and gravity can lead to experiments with lower systematic errors than have been obtained in experiments with cold neutron beams. The UCN densities provided by existing reactor sources limit these experiments. The promise of much higher densities from solid deuterium sources has led to proposed facilities coupled to both reactor and spallation neutron sources. In this paper we report on the performance of a prototype spallation neutron-driven solid deuterium source. This source produced bottled UCN densities of 145 +/-7 UCN/cm3, about three times greater than the largest bottled UCN densities previously reported. These results indicate that a production UCN source with substantially higher densities should be possible.
A method is described for fabricating photonic crystal slabs, using a combination of laser interference lithography for generating a regular periodic structure (the crystal lattice), and focused ion ...beam-assisted deposition for defining defects in this lattice, which may act as waveguides or resonators. As an example, results will be shown of a photonic crystal slab with a line defect in silicon nitride.
In the UCNτ experiment, ultracold neutrons (UCN) are confined by magnetic fields and the Earth’s gravitational field. Field-trapping mitigates the problem of UCN loss on material surfaces, which ...caused the largest correction in prior neutron experiments using material bottles. However, the neutron dynamics in field traps differ qualitatively from those in material bottles. In the latter case, neutrons bounce off material surfaces with significant diffusivity and the population quickly reaches a static spatial distribution with a density gradient induced by the gravitational potential. In contrast, the field-confined UCN—whose dynamics can be described by Hamiltonian mechanics—do not exhibit the stochastic behaviors typical of an ideal gas model as observed in material bottles. In this report, we will describe our efforts to simulate UCN trapping in the UCNτ magneto-gravitational trap. We compare the simulation output to the experimental results to determine the parameters of the neutron detector and the input neutron distribution. The tuned model is then used to understand the phase space evolution of neutrons observed in the UCNτ experiment. We will discuss the implications of chaotic dynamics on controlling the systematic effects, such as spectral cleaning and microphonic heating, for a successful UCN lifetime experiment to reach a 0.01% level of precision.
We report the measurement of the
8B solar neutrinos interaction rate with the Borexino detector. The extremly high radio-purity reached in the Borexino scintillator, combined with the efficient ...software rejection of cosmogenic background, allows to investigate the recoiled electron spectrum, induced by
8B solar neutrinos, down to the unprecedented energy threshold of 2.8 MeV.
The rate of
8B solar neutrino interaction as measured through their scattering on the target electrons is
0.26
±
0.04
stat
±
0.02
syst
c/d/100 tons. This corresponds to an equivalent electron neutrino flux of
(
2.65
±
0.44
stat
±
0.18
syst
)
×
10
6
cm
−
2
s
−
1
, as derived from the elastic scattering only, in good agreement with existing measurements and predictions.
Current Status of the BOREXINO experiment Galbiati, Cristiano; Balata, M.; de Bari, A. ...
Nuclear physics. Section B, Proceedings supplement,
2005, Letnik:
143
Journal Article
The status of the BOREXINO experiment is presented. The physics potential of the experiment is reviewed.
The crucial issue of the direct determination of the
7
Be solar neutrino flux will be addressed by the Borexino experiment, a real time, massive calorimetric liquid scintillation detector to be ...installed at the Gran Sasso Laboratory. The challenge of the extremely low radioactive level allowed in the scintillator for the feasibility of the measurement required the precise and sensitive evaluation of its radiopurity with a dedicated 5 tons prototype, the Counting Test Facility. The main experimental features of the CTF and its unprecedented results in the area of the low activity measurements are described in this paper, together with their implications in the design of the full scale experiment.
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