58 research outputs found
Measurement of the ionization response of amorphous selenium with 122keV rays
We performed a measurement of the ionization response of 200 m-thick
amorphous selenium (aSe) layers under drift electric fields of up to 50
V/m. The aSe target was exposed to ionizing radiation from a Co
radioactive source and the ionization pulses were recorded with high
resolution. Using the spectral line from the photoabsorption of 122keV
rays, we measure the charge yield in aSe and the line width as a function of
drift electric field. From a detailed microphysics simulation of charge
generation and recombination in aSe, we conclude that the strong dependence of
recombination on the ionization track density provides the dominant
contribution to the energy resolution in aSe. These results provide valuable
input to estimate the sensitivity of a proposed next-generation search for the
neutrinoless decay of Se that aims to employ imaging
sensors with an active layer of aSe.Comment: 16 pages, 11 figures. Prepared for submission to JINS
Pulse shape study of the fast scintillation light emitted from xenon-doped liquid argon using silicon photomultipliers
Xenon-doped liquid argon has been proposed as a good alternative to pure
liquid argon in scintillation detectors. In this study, we report on the
measurement of the time profile of scintillation light emitted from xenon-doped
liquid argon with molar concentrations up to 1600 ppm. A compact setup has been
developed for this study, with silicon photomultiplier (SiPM) as the
photosensor and and as scintillation
sources. An effective model based on the de-excitation processes has been
developed to describe the data. The results show that xenon-doped liquid argon
is a good fast scintillator and can be used in lieu of tetraphenyl butadiene
(TPB) in a way that preserves its capability for particle identification via
pulse shape discrimination (PSD)
Development of a very low-noise cryogenic pre-amplifier for large-area SiPM devices
Silicon Photomultipliers (SiPMs) are an excellent candidate for the
development of large-area light sensors. Large SiPM-based detectors require
low-noise pre-amplifiers to maximize the signal coupling between the sensor and
the readout electronics. This article reports on the development of a low-noise
transimpedance amplifier sensitive to single-photon signals at cryogenic
temperature. The amplifier is used to readout a 1 cm SiPM with a signal
to noise ratio in excess of 40
Cryogenic Characterization of FBK HD Near-UV Sensitive SiPMs
We report on the characterization of near-ultraviolet high density silicon
photomultiplier (\SiPM) developed at Fondazione Bruno Kessler (\FBK) at
cryogenic temperature. A dedicated setup was built to measure the primary dark
noise and correlated noise of the \SiPMs\ between 40 and 300~K. Moreover, an
analysis program and data acquisition system were developed to allow the
precise characterization of these parameters, some of which can vary up to 7
orders of magnitude between room temperature and 40~K. We demonstrate that it
is possible to operate the \FBK\ near-ultraviolet high density \SiPMs\ at
temperatures lower than 100~K with a dark rate below 0.01 cps/mm and total
correlated noise probability below 35\% at an over-voltage of 6~V. These
results are relevant for the development of future cryogenic particle detectors
using \SiPMs\ as photosensors
Cosmogenic 11C production and sensitivity of organic scintillator detectors to pep and CNO neutrinos
Several possible background sources determine the detectability of pep and
CNO solar neutrinos in organic liquid scintillator detectors. Among such
sources, the cosmogenic 11C nuclide plays a central role. 11C is produced
underground in reactions induced by the residual cosmic muon flux. Experimental
data available for the effective cross section for 11C by muons indicate that
11C will be the dominant source of background for the observation of pep and
CNO neutrinos. 11C decays are expected to total a rate 2.5 (20) times higher
than the combined rate of pep and CNO neutrinos in Borexino (KamLAND) in the
energy window preferred for the pep measurement, between 0.8 and 1.3 MeV.
This study examines the production mechanism of 11C by muon-induced showers
in organic liquid scintillators with a novel approach: for the first time, we
perform a detailed ab initio calculation of the production of a cosmogenic
nuclide, 11C, taking into consideration all relevant production channels.
Results of the calculation are compared with the effective cross sections
measured by target experiments in muon beams.
This paper also discusses a technique for reduction of background from 11C in
organic liquid scintillator detectors, which allows to identify on a one-by-one
basis and remove from the data set a large fraction of 11C decays. The
background reduction technique hinges on an idea proposed by Martin Deutsch,
who suggested that a neutron must be ejected in every interaction producing a
11C nuclide from 12C. 11C events are tagged by a three-fold coincidence with
the parent muon track and the subsequent neutron capture on protons.Comment: 11 pages, 6 figures; added one section detailing comparison with
previous estimates; added reference
Measurement of Scintillation and Ionization Yield and Scintillation Pulse Shape from Nuclear Recoils in Liquid Argon
We have measured the scintillation and ionization yield of recoiling nuclei
in liquid argon as a function of applied electric field by exposing a
dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy
pulsed narrow band neutron beam produced at the Notre Dame Institute for
Structure and Nuclear Astrophysics. Liquid scintillation counters were arranged
to detect and identify neutrons scattered in the TPC and to select the energy
of the recoiling nuclei. We report measurements of the scintillation yields for
nuclear recoils with energies from 10.3 to 57.3 keV and for median applied
electric fields from 0 to 970 V/cm. For the ionization yields, we report
measurements from 16.9 to 57.3 keV and for electric fields from 96.4 to 486
V/cm. We also report the observation of an anticorrelation between
scintillation and ionization from nuclear recoils, which is similar to the
anticorrelation between scintillation and ionization from electron recoils.
Assuming that the energy loss partitions into excitons and ion pairs from
Kr internal conversion electrons is comparable to that from Bi
conversion electrons, we obtained the numbers of excitons () and ion
pairs () and their ratio () produced by nuclear recoils from
16.9 to 57.3 keV. Motivated by arguments suggesting direction sensitivity in
LAr-TPC signals due to columnar recombination, a comparison of the light and
charge yield of recoils parallel and perpendicular to the applied electric
field is presented for the first time.Comment: v2 to reflect published versio
Final results of Borexino Phase-I on low energy solar neutrino spectroscopy
Borexino has been running since May 2007 at the LNGS with the primary goal of
detecting solar neutrinos. The detector, a large, unsegmented liquid
scintillator calorimeter characterized by unprecedented low levels of intrinsic
radioactivity, is optimized for the study of the lower energy part of the
spectrum. During the Phase-I (2007-2010) Borexino first detected and then
precisely measured the flux of the 7Be solar neutrinos, ruled out any
significant day-night asymmetry of their interaction rate, made the first
direct observation of the pep neutrinos, and set the tightest upper limit on
the flux of CNO neutrinos. In this paper we discuss the signal signature and
provide a comprehensive description of the backgrounds, quantify their event
rates, describe the methods for their identification, selection or subtraction,
and describe data analysis. Key features are an extensive in situ calibration
program using radioactive sources, the detailed modeling of the detector
response, the ability to define an innermost fiducial volume with extremely low
background via software cuts, and the excellent pulse-shape discrimination
capability of the scintillator that allows particle identification. We report a
measurement of the annual modulation of the 7 Be neutrino interaction rate. The
period, the amplitude, and the phase of the observed modulation are consistent
with the solar origin of these events, and the absence of their annual
modulation is rejected with higher than 99% C.L. The physics implications of
phase-I results in the context of the neutrino oscillation physics and solar
models are presented
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Spectroscopy of geo-neutrinos from 2056 days of Borexino data
We report an improved geo-neutrino measurement with Borexino from 2056 days
of data taking. The present exposure is
protonyr. Assuming a chondritic Th/U mass ratio of 3.9, we obtain geo-neutrino events. The null
observation of geo-neutrinos with Borexino alone has a probability of (5.9). A geo-neutrino signal from the mantle is
obtained at 98\% C.L. The radiogenic heat production for U and Th from the
present best-fit result is restricted to the range 23-36 TW, taking into
account the uncertainty on the distribution of heat producing elements inside
the Earth.Comment: 4 pages, 4 figure
Measurement of neutrino flux from the primary proton--proton fusion process in the Sun with Borexino detector
Neutrino produced in a chain of nuclear reactions in the Sun starting from
the fusion of two protons, for the first time has been detected in a real-time
detector in spectrometric mode. The unique properties of the Borexino detector
provided an oppurtunity to disentangle pp-neutrino spectrum from the background
components. A comparison of the total neutrino flux from the Sun with Solar
luminosity in photons provides a test of the stability of the Sun on the
10 years time scale, and sets a strong limit on the power production in
the unknown energy sources in the Sun of no more than 4\% of the total energy
production at 90\% C.L.Comment: 15 pages, 2 tables, 3 figure
WARP: a double phase Argon programme for Dark Matter detection
WARP (Wimp ARgon Programme) is a double phase Argon detector for Dark Matter detection under construction at Laboratori Nazionali del Gran Sasso. We present recent results obtained operating deep underground a prototype detector with sensitive mass 2.3 litres. 1. WARP: a double phase argon detector for Dark Matter detection. A double phase Argon detector offers unique sensitivity for the search of dark matter in the form of WIMPs: such detector has the highest discrimination of background events in favour of potential WIMP interactions, which are expected to produce low energy Ar recoils with typical energies of a few tens keV. The basic concept of the detector is the measurement of both the scintillation and the ionization produced by particle interactions inside a liquid argon sensitive volume. Two simultaneous criteria can be applied to select Ar recoils eventually produced by WIMPs: i) Prompt scintillation versus ionization. The prompt scintillation light produced by a particle interacting in the liquid argon phase is detected by PMs. The ionization electrons are extracted from the liquid into the gas and accelerated by an appropriate electric field to produce a proportional (high gain), secondary light pulse seen by the same PMs. The pulse ratio S2/S1 of secondary light S2 (from drift time-delayed ionization) over prompt scintillation light S1 is strongly dependent from columnar recombination of the ionising tracks: therefore nuclear recoils produce typical signals with pulse ratio S2/S1 about 60 times lower than electrons. ii) Pulse shape discrimination of primary scintillation: the primary light is emitted with two components with very large difference in decay times (fast 7 ns, and slow 1.8 μs). The relative amount of the slow component strongly depends from the interacting particle, being around 0.7 for electrons and. 0.1 for heavy charged paricles. The WARP liquid argon detector under construction has a sensitive volume of 100 liters. The goal scintillation yield is of the order of 1 collected photoelectron per keV and the detection threshold for the WIMPs 30 keV. A detailed description of the 100 liters detector can be find in reference [1]. 1 INFN and Dept. of Physics University of Pavia: P. Benetti, E. Calligarich, M. Cambiaghi, C. De Vecchi, R. Dolfini, L. Grandi, A. Menegolli, C. Montanari, M. Prata, A. Rappoldi, G.L. Raselli, M. Roncadelli, M. Rossella, C. Rubbia (Spokesperson), C. Vignoli. INFN and Dept. of Physics University of Napoli "Federico II": F. Carbonara, A.G. Cocco, G. Fiorillo, G. Mangano, R. Santorelli. INFN Laboratori Nazionali del Gran Sasso and University of L'Aquila: F. Cavanna, N. Ferrari, O. Palamara,. L. Pandola. Princeton University, Physics Department: F. Calaprice, C. Galbiati, Y. Zhao. Institute of Nuclear Physics, Krakow : A. Szelc. Figure 1. Energy spectrum observed with the WARP 2.3 liters prototype in the LNGS underground laboratory inside a 10 cm thick Pb shielding. The overlapped red histogram is the expected (montecarlo-simulated) background by interactions of environmental gamma rays. The residual events below 650 keV are produced by Ar and Kr contaminations inside the liquid Argon. Figure 2. Residual energy spectrum after subtraction of the estimated background from environmental gamma rays. The residual spectrum (upper blue curve) is perfectly fitted by the sum of the beta spectra of Ar (green curve, end-point 565 keV, rate 1.1 Bq/litre) and Kr (red curve, end-point 687 keV, rate 0.5 Bq/litre). The vertical scale is expressed in counts/sec/keV. 2. The WARP 2.3 liters prototype detector In order to perfect the detection method, a 2.3 liters prototype detector is in operation at Laboratori Nazionali del Gran Sasso since February 2005. The detector has been equipped, in subsequent phases, with 2'' and 3'' PMs made of low background materials for an onsite detailed study of the backgrounds. The structure is a down-scaled version of the 100 liters detector, with field-shaping electrodes and gas to liquid extraction and acceleration grids. The chamber is filled with ultra-purified argon in order to allow for long drift times of free electrons. Purity is maintained stable by means of continuous argon recirculation. 2.1.1. Study of the β and γ detector backgrounds. The overall background of the 2.3 litres prototype installed underground inside a 10 cm thick Pb shielding has been carefully measured and identified. The total trigger rate above a threshold of 30 keV is about 5 Hz. From a detailed study of the energy spectrum shape (Figure 1) it is shown that about 2 Hz are produced by gamma ray interactions from radioactivity of materials surrounding the sensitive volume; the remaining 3 Hz are produced by the β decays of Kr and Ar dissolved in the liquid argon. In particular, the specific activity of Ar was found to be 1.1 ± 0.4 Bq/litre of liquid Argon, in very good agreement with ref. [2]. We notice that no particular care in the selection of materials was adopted, since in this test phase the background itself helps in the identification of the rejection power. Most of the backgrounds will be strongly reduced in the 100 litres setup. Figure 3. R-like events recorded with the 2.3 liters chamber during 13.4 days of live time in june 2005. The plot shows the primary signal energy (in keV) along the drift time, expressed in μs. The fiducial volume is defined by drift times between 10 and 35 microseconds. Figure 4. Energy distribution of R-like events inside the cathode (upper plot), and inside the fiducial volume (lower plot). The red histogram in the lower plot is the result of a simulation of the expected signal from environmental neutrons in the underground area. 2.1.2. Analysis of Recoil-like events. Data recorded during 13.4 days of live time in a run done in june 2005 have been analyzed looking for recoil-like events by applying the two selection criteria described in section 1. About 6.5 millions events have been processed. The spatial and energy distribution of the 580 selected R-like events (see Figure 3) suggests the following origin for the signals: i) R-like events in the cathode region are mostly induced by decays of Rn daughters. Rn is introduced in the chamber during the filling together with the Ar: being electrically neutral it is uniformly distributed inside the chamber. Daughter nuclei, produced into an ionized state, are drifted to the cathode by the electric field, where they stick. Subsequent decays may end up: (a) with the heavy ion entering the cathode and the α or β travelling in the LAr; (b) with the heavy ion travelling in the LAr and producing the observed R-like signal. The two peaks observed in the energy spectrum (Figure 4, upper plot) are coherently explained by the nuclear recoils from α decays Po Pb (ER=110 keV) and Po Bi (ER=144 keV), assuming a light yield of 0.7 photoelectrons/keV. ii) R-like events inside the fiducial volume are induced by environmental neutrons. Both the event rate and the shape of the energy spectrum (Figure 4, lower plot) are compatible with the expected interactions induced by environmental neutrons inside the underground area (represented by the red histogram). The WARP 2.3 liters chamber in operation at LNGS proofs that the double discrimination technique is effective for separation of recoil events. The first results of the 2.3 liters test (with no neutron shielding) show that the observed background is understood, and that recoil-like signals are compatible with the expected neutron background in the underground area. References [1] WARP proposal, available online at http://warp.pv.infn.it/proposal.pdf [2] H.H. Loosli and H. Oeschger, Earth and Plan. Sci. Lett. 7 (1969) 6
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