207 research outputs found
Irradiation-induced Ag nanocluster nucleation in silicate glasses: analogy with photography
The synthesis of Ag nanoclusters in sodalime silicate glasses and silica was
studied by optical absorption (OA) and electron spin resonance (ESR)
experiments under both low (gamma-ray) and high (MeV ion) deposited energy
density irradiation conditions. Both types of irradiation create electrons and
holes whose density and thermal evolution - notably via their interaction with
defects - are shown to determine the clustering and growth rates of Ag
nanocrystals. We thus establish the influence of redox interactions of defects
and silver (poly)ions. The mechanisms are similar to the latent image formation
in photography: irradiation-induced photoelectrons are trapped within the glass
matrix, notably on dissolved noble metal ions and defects, which are thus
neutralized (reverse oxidation reactions are also shown to exist). Annealing
promotes metal atom diffusion, which in turn leads to cluster nuclei formation.
The cluster density depends not only on the irradiation fluence, but also - and
primarily - on the density of deposited energy and the redox properties of the
glass. Ion irradiation (i.e., large deposited energy density) is far more
effective in cluster formation, despite its lower neutralization efficiency
(from Ag+ to Ag0) as compared to gamma photon irradiation.Comment: 48 pages, 18 figures, revised version publ. in Phys. Rev. B, pdf fil
DANSSino: a pilot version of the DANSS neutrino detector
DANSSino is a reduced pilot version of a solid-state detector of reactor
antineutrinos (to be created within the DANSS project and installed under the
industrial 3 GW(th) reactor of the Kalinin Nuclear Power Plant -- KNPP).
Numerous tests performed at a distance of 11 m from the reactor core
demonstrate operability of the chosen design and reveal the main sources of the
background. In spite of its small size (20x20x100 ccm), the pilot detector
turned out to be quite sensitive to reactor antineutrinos, detecting about 70
IBD events per day with the signal-to-background ratio about unity.Comment: 16 pages, 11 figures, 3 tables. arXiv admin note: substantial text
overlap with arXiv:1304.369
Search for sterile neutrinos at the DANSS experiment
DANSS is a highly segmented 1~m plastic scintillator detector. Its 2500
one meter long scintillator strips have a Gd-loaded reflective cover. The DANSS
detector is placed under an industrial 3.1~ reactor of the
Kalinin Nuclear Power Plant 350~km NW from Moscow. The distance to the core is
varied on-line from 10.7~m to 12.7~m. The reactor building provides about 50~m
water-equivalent shielding against the cosmic background. DANSS detects almost
5000 per day at the closest position with the cosmic
background less than 3. The inverse beta decay process is used to detect
. Sterile neutrinos are searched for assuming the model
(3 active and 1 sterile ). The exclusion area in the plane is obtained using a ratio of positron energy
spectra collected at different distances. Therefore results do not depend on
the shape and normalization of the reactor spectrum, as well
as on the detector efficiency. Results are based on 966 thousand antineutrino
events collected at 3 distances from the reactor core. The excluded area covers
a wide range of the sterile neutrino parameters up to
in the most sensitive region.Comment: 10 pages, 13 figures, version accepted for publicatio
Characterization of 30 Ge enriched Broad Energy Ge detectors for GERDA Phase II
The GERmanium Detector Array (GERDA) is a low background experiment located
at the Laboratori Nazionali del Gran Sasso in Italy, which searches for
neutrinoless double beta decay of Ge into Se+2e. GERDA has
been conceived in two phases. Phase II, which started in December 2015,
features several novelties including 30 new Ge detectors. These were
manufactured according to the Broad Energy Germanium (BEGe) detector design
that has a better background discrimination capability and energy resolution
compared to formerly widely-used types. Prior to their installation, the new
BEGe detectors were mounted in vacuum cryostats and characterized in detail in
the HADES underground laboratory in Belgium. This paper describes the
properties and the overall performance of these detectors during operation in
vacuum. The characterization campaign provided not only direct input for GERDA
Phase II data collection and analyses, but also allowed to study detector
phenomena, detector correlations as well as to test the strength of pulse shape
simulation codes.Comment: 29 pages, 18 figure
Background free search for neutrinoless double beta decay with GERDA Phase II
The Standard Model of particle physics cannot explain the dominance of matter
over anti-matter in our Universe. In many model extensions this is a very
natural consequence of neutrinos being their own anti-particles (Majorana
particles) which implies that a lepton number violating radioactive decay named
neutrinoless double beta () decay should exist. The detection
of this extremely rare hypothetical process requires utmost suppression of any
kind of backgrounds.
The GERDA collaboration searches for decay of Ge
(^{76}\rm{Ge} \rightarrow\,^{76}\rm{Se} + 2e^-) by operating bare detectors
made from germanium with enriched Ge fraction in liquid argon. Here, we
report on first data of GERDA Phase II. A background level of
cts/(keVkgyr) has been achieved which is the world-best if
weighted by the narrow energy-signal region of germanium detectors. Combining
Phase I and II data we find no signal and deduce a new lower limit for the
half-life of yr at 90 % C.L. Our sensitivity of
yr is competitive with the one of experiments with
significantly larger isotope mass.
GERDA is the first experiment that will be background-free
up to its design exposure. This progress relies on a novel active veto system,
the superior germanium detector energy resolution and the improved background
recognition of our new detectors. The unique discovery potential of an
essentially background-free search for decay motivates a
larger germanium experiment with higher sensitivity.Comment: 14 pages, 9 figures, 1 table; ; data, figures and images available at
http://www.mpi-hd.mpg/gerda/publi
The background in the neutrinoless double beta decay experiment GERDA
The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground
laboratory (LNGS) of INFN is searching for neutrinoless double beta decay of
76Ge. The signature of the signal is a monoenergetic peak at 2039 keV, the
Q-value of the decay, Q_bb. To avoid bias in the signal search, the present
analysis does not consider all those events, that fall in a 40 keV wide region
centered around Q_bb. The main parameters needed for the neutrinoless double
beta decay analysis are described. A background model was developed to describe
the observed energy spectrum. The model contains several contributions, that
are expected on the basis of material screening or that are established by the
observation of characteristic structures in the energy spectrum. The model
predicts a flat energy spectrum for the blinding window around Q_bb with a
background index ranging from 17.6 to 23.8*10^{-3} counts/(keV kg yr). A part
of the data not considered before has been used to test if the predictions of
the background model are consistent. The observed number of events in this
energy region is consistent with the background model. The background at Q-bb
is dominated by close sources, mainly due to 42K, 214Bi, 228Th, 60Co and alpha
emitting isotopes from the 226Ra decay chain. The individual fractions depend
on the assumed locations of the contaminants. It is shown, that after removal
of the known gamma peaks, the energy spectrum can be fitted in an energy range
of 200 kev around Q_bb with a constant background. This gives a background
index consistent with the full model and uncertainties of the same size
- …