170 research outputs found
Methods for precise photoelectron counting with photomultipliers
Abstract A series of measurements has been performed on a THORN EMI 9351 phototube in order to investigate its response to a low light intensity. Precise procedures to determine the intensity of the incident photon flux have been developed and compared. The data show that the various approaches give consistent and reliable results, thus allowing the precise calibration of the device for applications of photon counting
An online radon monitor for low-background detector assembly facilities
Backgrounds from long-lived radon decay products are often problematic for low-energy neutrino and rare-event experiments. These isotopes, specifically , , and , easily plate out onto surfaces exposed to radon-loaded air. The alpha emitter is particularly dangerous for detectors searching for weakly-interacting dark matter particles. Neutrons produced via (\upalpha , n) reactions in detector materials are, in some cases, a residual background that can limit the sensitivity of the experiment. An effective solution is to reduce the activity in the air in contact with detector components during fabrication, assembly, commissioning, and operation. We present the design, construction, calibration procedures and performance of an electrostatic radon detector made to monitor two radon-suppressed clean rooms built for the DARKSIDE-50 experiment. A dedicated data acquisition system immune to harsh operating conditions of the radon monitor is also described. A record detection limit for specific activity in air achieved by the device is (STP). The radon concentration of different air samples collected from the two DARKSIDE-50 clean rooms measured with the electrostatic detector is presented
Solar neutrino detection in a large volume double-phase liquid argon experiment
Precision measurements of solar neutrinos emitted by specific nuclear
reaction chains in the Sun are of great interest for developing an improved
understanding of star formation and evolution. Given the expected neutrino
fluxes and known detection reactions, such measurements require detectors
capable of collecting neutrino-electron scattering data in exposures on the
order of 1 ktonne yr, with good energy resolution and extremely low background.
Two-phase liquid argon time projection chambers (LAr TPCs) are under
development for direct Dark Matter WIMP searches, which possess very large
sensitive mass, high scintillation light yield, good energy resolution, and
good spatial resolution in all three cartesian directions. While enabling Dark
Matter searches with sensitivity extending to the "neutrino floor" (given by
the rate of nuclear recoil events from solar neutrino coherent scattering),
such detectors could also enable precision measurements of solar neutrino
fluxes using the neutrino-electron elastic scattering events. Modeling results
are presented for the cosmogenic and radiogenic backgrounds affecting solar
neutrino detection in a 300 tonne (100 tonne fiducial) LAr TPC operating at
LNGS depth (3,800 meters of water equivalent). The results show that such a
detector could measure the CNO neutrino rate with ~15% precision, and
significantly improve the precision of the 7Be and pep neutrino rates compared
to the currently available results from the Borexino organic liquid
scintillator detector.Comment: 21 pages, 7 figures, 6 table
The Nylon Scintillator Containment Vessels for the Borexino Solar Neutrino Experiment
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
A Study of the Residual 39Ar Content in Argon from Underground Sources
The discovery of argon from underground sources with significantly less 39Ar
than atmospheric argon was an important step in the development of
direct-detection dark matter experiments using argon as the active target. We
report on the design and operation of a low background detector with a single
phase liquid argon target that was built to study the 39Ar content of the
underground argon. Underground argon from the Kinder Morgan CO2 plant in
Cortez, Colorado was determined to have less than 0.65% of the 39Ar activity in
atmospheric argon.Comment: 21 pages, 10 figure
The Borexino detector at the Laboratori Nazionali del Gran Sasso
Borexino, a large volume detector for low energy neutrino spectroscopy, is
currently running underground at the Laboratori Nazionali del Gran Sasso,
Italy. The main goal of the experiment is the real-time measurement of sub MeV
solar neutrinos, and particularly of the mono energetic (862 keV) Be7 electron
capture neutrinos, via neutrino-electron scattering in an ultra-pure liquid
scintillator. This paper is mostly devoted to the description of the detector
structure, the photomultipliers, the electronics, and the trigger and
calibration systems. The real performance of the detector, which always meets,
and sometimes exceeds, design expectations, is also shown. Some important
aspects of the Borexino project, i.e. the fluid handling plants, the
purification techniques and the filling procedures, are not covered in this
paper and are, or will be, published elsewhere (see Introduction and
Bibliography).Comment: 37 pages, 43 figures, to be submitted to NI
Results from the first use of low radioactivity argon in a dark matter search
Liquid argon is a bright scintillator with potent particle identification
properties, making it an attractive target for direct-detection dark matter
searches. The DarkSide-50 dark matter search here reports the first WIMP search
results obtained using a target of low-radioactivity argon. DarkSide-50 is a
dark matter detector, using two-phase liquid argon time projection chamber,
located at the Laboratori Nazionali del Gran Sasso. The underground argon is
shown to contain Ar-39 at a level reduced by a factor (1.4 +- 0.2) x 10^3
relative to atmospheric argon. We report a background-free null result from
(2616 +- 43) kg d of data, accumulated over 70.9 live-days. When combined with
our previous search using an atmospheric argon, the 90 % C.L. upper limit on
the WIMP-nucleon spin-independent cross section based on zero events found in
the WIMP search regions, is 2.0 x 10^-44 cm^2 (8.6 x 10^-44 cm^2, 8.0 x 10^-43
cm^2) for a WIMP mass of 100 GeV/c^2 (1 TeV/c^2 , 10 TeV/c^2).Comment: Accepted by Phys. Rev.
Novel regulatory therapies for prevention of Graft-versus-host disease
Graft-versus-host disease is one of the major transplant-related complications in allogeneic hematopoietic stem cell transplantation. Continued efforts have been made to prevent the occurrence of severe graft-versus-host disease by eliminating or suppressing donor-derived effector T cells. Conventional immunosuppression does not adequately prevent graft-versus-host disease, especially in mismatched transplants. Unfortunately, elimination of donor-derived T cells impairs stem cell engraftment, and delays immunologic reconstitution, rendering the recipient susceptible to post-transplant infections and disease relapse, with potentially lethal consequences. In this review, we discuss the role of dynamic immune regulation in controlling graft-versus-host disease, and how cell-based therapies are being developed using regulatory T cells and other tolerogenic cells for the prevention and treatment of graft-versus-host disease. In addition, advances in the design of cytoreductive conditioning regimens to selectively target graft-versus-host disease-inducing donor-derived T cells that have improved the safety of allogeneic stem cell transplantation are reviewed. Finally, we discuss advances in our understanding of the tolerogenic facilitating cell population, a phenotypically and functionally distinct population of bone marrow-derived cells which promote hematopoietic stem cell engraftment while reducing the risk of graft-versus-host disease
The SOX experiment in the neutrino physics
SOX (Short distance neutrino Oscillations with BoreXino) is a new experiment that takes place at the Laboratori Nazionali del Gran Sasso (LNGS) and it exploits the Borexino detector to study the neutrino oscillations at short distance. In different phases, by using two artificial sources Cr-51 and Ce-144-Pr-144, neutrino and antineutrino fluxes of measured intensity will be detected by Borexino in order to observe possible neutrino oscillations in the sterile state. In this paper an overview of the experiment is given and one of the two calorimeters that will be used to measure the source activity is described. At the end the expected sensitivity to determine the neutrino sterile mass is shown
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