8,513 research outputs found
A vestige low metallicity gas shell surrounding the radio galaxy 0943-242 at z=2.92
Observations are presented showing the doublet CIV 1550 absorption lines
superimposed on the CIV emission in the radio galaxy 0943-242. Within the
errors, the redshift of the absorption system that has a column density of
N_CIV = 10^{14.5 +- 0.1} cm-2 coincides with that of the deep Ly-alpha
absorption trough observed by Rottgering et al. (1995). The gas seen in
absorption has a resolved spatial extent of at least 13 kpc (the size of the
extended emission line region). We first model the absorption and emission gas
as co-spatial components with the same metallicity and degree of excitation.
Using the information provided by the emission and absorption line ratios of
CIV and Ly-alpha, we find that the observed quantities are incompatible with
photoionization or collisional ionization of cloudlets with uniform properties.
We therefore reject the possibility that the absorption and emission phases are
co-spatial and favour the explanation that the absorption gas has low
metallicity and is located further away from the host galaxy (than the emission
line gas). The estimated low metallicity for the absorption gas in 0943-242 (Z
\~ 1% solar) and its proposed location -outer halo outside the radio cocoon-
suggest that its existence preceeds the observed AGN phase and is a vestige of
the initial starburst at the onset of formation of the parent galaxy.Comment: 11 pages,5 figures, A&A accepte
Status of the ANAIS Dark Matter Project at the Canfranc Underground Laboratory
The ANAIS experiment aims at the confirmation of the DAMA/LIBRA signal. A
detailed analysis of two NaI(Tl) crystals of 12.5 kg each grown by Alpha
Spectra will be shown: effective threshold at 1 keVee is at reach thanks to
outstanding light collection and robust PMT noise filtering protocols and the
measured background is well understood down to 3 keVee, having quantified K, U
and Th content and cosmogenic activation in the crystals. A new detector was
installed in Canfranc in March 2015 together with the two previous modules and
preliminary characterization results will be presented. Finally, the status and
expected sensitivity of the full experiment with 112 kg will be reviewed.Comment: Contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs,
Zaragoza, June 22 to 26, 201
Light yield determination in large sodium iodide detectors applied in the search for dark matter
Application of NaI(Tl) detectors in the search for galactic dark matter
particles through their elastic scattering off the target nuclei is well
motivated because of the long standing DAMA/LIBRA highly significant positive
result on annual modulation, still requiring confirmation. For such a goal, it
is mandatory to reach very low threshold in energy (at or below the keV level),
very low radioactive background (at a few counts/keV/kg/day), and high
detection mass (at or above the 100 kg scale). One of the most relevant
technical issues is the optimization of the crystal intrinsic scintillation
light yield and the efficiency of the light collecting system for large mass
crystals. In the frame of the ANAIS (Annual modulation with NaI Scintillators)
dark matter search project large NaI(Tl) crystals from different providers
coupled to two photomultiplier tubes (PMTs) have been tested at the Canfranc
Underground Laboratory. In this paper we present the estimates of the NaI(Tl)
scintillation light collected using full-absorption peaks at very low energy
from external and internal sources emitting gammas/electrons, and
single-photoelectron events populations selected by using very low energy
pulses tails. Outstanding scintillation light collection at the level of
15~photoelectrons/keV can be reported for the final design and provider chosen
for ANAIS detectors. Taking into account the Quantum Efficiency of the PMT
units used, the intrinsic scintillation light yield in these NaI(Tl) crystals
is above 40~photoelectrons/keV for energy depositions in the range from 3 up to
25~keV. This very high light output of ANAIS crystals allows triggering below
1~keV, which is very important in order to increase the sensitivity in the
direct detection of dark matter
Analysis of backgrounds for the ANAIS-112 dark matter experiment
The ANAIS (Annual modulation with NaI(Tl) Scintillators) experiment aims at
the confirmation or refutation of theDAMA/LIBRA positive annual modulation
signal in the low energy detection rate, using the same target and technique,
at the Canfranc Underground Laboratory (LSC) in Spain. ANAIS-112, consisting of
nine 12.5 kg NaI(Tl) modules produced by Alpha Spectra Inc. in a 3x3matrix
configuration, is taking data smoothly in "dark matter search" mode since
August, 2017, after a commissioning phase and operation of the first detectors
during the last years in various setups. A large effort has been carried out
withinANAIS to characterize the background of sodium iodide detectors, before
unblinding the data and performing the first annual modulation analysis. Here,
the background models developed for all the nine ANAIS-112 detectors are
presented. Measured spectra from threshold to high energy in different
conditions are well described by the models based on quantified activities
independently estimated following several approaches. In the region from 1 to 6
keVee the measured, efficiency corrected background level is 3.58+-0.02 keV-1
kg-1 day-1; NaI crystal bulk contamination is the dominant background source
being 210Pb, 40K, 22Na and 3H contributions the most relevant ones. This
background level, added to the achieved 1 keVee analysis threshold (thanks to
the outstanding light collection and robust filtering procedures developed),
allow ANAIS-112 to be sensitive to the modulation amplitude measured by
DAMA/LIBRA, and able to explore at three sigma level in 5 years the WIMP
parameter region singled out by this experiment.Comment: Final version for publicatio
Production and relevance of cosmogenic radionuclides in NaI(Tl) crystals
The cosmogenic production of long-lived radioactive isotopes in materials is
an hazard for experiments demanding ultra-low background conditions. Although
NaI(Tl) scintillators have been used in this context for a long time, very few
activation data were available. We present results from two 12.5 kg NaI(Tl)
detectors, developed within the ANAIS project and installed at the Canfranc
Underground Laboratory. The prompt data taking starting made possible a
reliable quantification of production of some I, Te and Na isotopes with
half-lives larger than ten days. Initial activities underground were measured
and then production rates at sea level were estimated following the history of
detectors; a comparison of these rates with calculations using typical cosmic
neutron flux at sea level and a selected description of excitation functions
was also carried out. After including the contribution from the identified
cosmogenic products in the detector background model, we found that the
presence of 3H in the crystal bulk would help to fit much better our background
model and experimental data. We have analyzed the cosmogenic production of 3H
in NaI, and although precise quantification has not been attempted, we can
conclude that it could imply a very relevant contribution to the total
background below 15 keV in NaI detectors.Comment: Proceedings of the Low Radioactivity Techniques 2015 workshop, March
2015, Seattle (US
Background analysis and status of the ANAIS dark matter project
ANAIS (Annual modulation with NaI Scintillators) is a project aiming to set
up at the new facilities of the Canfranc Underground Laboratory (LSC), a large
scale NaI(Tl) experiment in order to explore the DAMA/LIBRA annual modulation
positive result using the same target and technique. Two 12.5 kg each NaI(Tl)
crystals provided by Alpha Spectra took data at the LSC in the ANAIS-25 set-up.
The comparison of the background model for the ANAIS-25 prototypes with the
experimental results is presented. ANAIS crystal radiopurity goals have been
achieved for Th-232 and U-238 chains, but a Pb-210 contamination
out-of-equilibrium was identified, whose origin has been studied. The high
light collection efficiency obtained with these prototypes allows to anticipate
an energy threshold of the order of 1 keVee. A new detector, with improved
performances, was received in March 2015 and very preliminary results are
shown.Comment: 6 pages, 7 figure
Background model of NaI(Tl) detectors for the ANAIS Dark Matter Project
A thorough understanding of the background sources is mandatory in any
experiment searching for rare events. The ANAIS (Annual Modulation with NaI(Tl)
Scintillators) experiment aims at the confirmation of the DAMA/LIBRA signal at
the Canfranc Underground Laboratory (LSC). Two NaI(Tl) crystals of 12.5 kg each
produced by Alpha Spectra have been taking data since December 2012. The
complete background model of these detectors and more precisely in the region
of interest will be described. Preliminary background analysis of a new 12.5 kg
crystal received at Canfranc in March 2015 will be presented too. Finally, the
power of anticoincidence rejection in the region of interest has been analyzed
in a 4x 5 12.5 kg detector matrix.Comment: Contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs,
Zaragoza, June 22 to 26, 201
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