747 research outputs found
Investigation of decay in Nd and Nd to the excited states of daughter nuclei
Double beta decay of Nd and Nd to the excited states of
daughter nuclei have been studied using a 400 cm low-background HPGe
detector and an external source consisting of 3046 g of natural NdO
powder. The half-life for the two-neutrino double beta decay of Nd to
the excited 0 state in Sm is measured to be
y.
For other transitions to the 2, 2, 2, and
0 levels in Sm, limits are obtained at the level of y. In the case of Nd only limits for the transitions to the 2, 0, and 2 excited states in
Sm were obtained and are at the level of \sim (4-8)\cdot 10^{20}$ y.Comment: 13 pages, 6 figure
Search for EC and ECEC processes in Sn
Limits on EC (here EC denotes electron capture) and ECEC processes
in Sn have been obtained using a 380 cm HPGe detector and an
external source consisting of 53.355 g enriched tin (94.32% of Sn). A
limit with 90% C.L. on the Sn half-life of y for
the ECEC(0) transition to the excited state in Cd (1871.0
keV) has been established. This transition is discussed in the context of a
possible enhancement of the decay rate by several orders of magnitude given
that the ECEC process is nearly degenerate with an excited state in the
daughter nuclide. Prospects for investigating such a process in future
experiments are discussed. The limits on other EC and ECEC processes
in Sn were obtained on the level of y at the
90% C.L.Comment: 14 pages, 4 figure
Phase stability, ordering tendencies, and magnetism in single-phase fcc Au-Fe nanoalloys
Bulk Au-Fe alloys separate into Au-based fcc and Fe-based bcc phases, but
L1 and L1 orderings were reported in single-phase Au-Fe nanoparticles.
Motivated by these observations, we study the structural and ordering
energetics in this alloy by combining density functional theory (DFT)
calculations with effective Hamiltonian techniques: a cluster expansion with
structural filters, and the configuration-dependent lattice deformation model.
The phase separation tendency in Au-Fe persists even if the fcc-bcc
decomposition is suppressed. The relative stability of disordered bcc and fcc
phases observed in nanoparticles is reproduced, but the fully ordered L1
AuFe, L1 AuFe, and L1 AuFe structures are unstable in DFT.
However, a tendency to form concentration waves at the corresponding [001]
ordering vector is revealed in nearly-random alloys in a certain range of
concentrations. This incipient ordering requires enrichment by Fe relative to
the equiatomic composition, which may occur in the core of a nanoparticle due
to the segregation of Au to the surface. Effects of magnetism on the chemical
ordering are also discussed.Comment: 23 pages, 11 figure
First test of an enriched CdWO scintillating bolometer for neutrinoless double-beta-decay searches
For the first time, a cadmium tungstate crystal scintillator enriched in
Cd has been succesfully tested as a scintillating bolometer. The
measurement was performed above ground at a temperature of 18 mK. The crystal
mass was 34.5 g and the enrichment level ~82 %. Despite a substantial pile-up
effect due to above-ground operation, the detector demonstrated a high energy
resolution (2-7 keV FWHM in 0.2-2.6 MeV energy range), a powerful
particle identification capability and a high level of internal radiopurity.
These results prove that cadmium tungstate is an extremely promising detector
material for a next-generation neutrinoless double-beta decay bolometric
experiment, like that proposed in the CUPID project (CUORE Upgrade with
Particle IDentification)
Searches for neutrinoless double beta decay
Neutrinoless double beta decay is a lepton number violating process whose
observation would also establish that neutrinos are their own anti-particles.
There are many experimental efforts with a variety of techniques. Some (EXO,
Kamland-Zen, GERDA phase I and CANDLES) started take data in 2011 and EXO has
reported the first measurement of the half life for the double beta decay with
two neutrinos of Xe. The sensitivities of the different proposals are
reviewed.Comment: 8 pages, prepared for TAUP 201
Double beta decay: present status
The present status of double beta decay experiments (including the search for
, EC and ECEC processes) are reviewed. The results of
the most sensitive experiments are discussed. Average and recommended half-life
values for two-neutrino double beta decay are presented. Conservative upper
limits on effective Majorana neutrino mass and the coupling constant of the
Majoron to the neutrino are established as eV and , respectively. Proposals for future double beta decay
experiments with a sensitivity for the at the level of (0.01-0.1)
eV are considered.Comment: 33 pages included 7 figures and 14 tables; an extended version of the
invited talk at 13th Lomonosov Conference of Elementary Particle Physics,
23-29 August, 2007, Moscow, Russi
Improvement of radiopurity level of enriched CdWO and ZnWO crystal scintillators by recrystallization
As low as possible radioactive contamination of a detector plays a crucial
role to improve sensitivity of a double beta decay experiment. The radioactive
contamination of a sample of CdWO crystal scintillator by thorium
was reduced by a factor , down to the level 0.01 mBq/kg
(Th), by exploiting the recrystallization procedure. The total alpha
activity of uranium and thorium daughters was reduced by a factor ,
down to 1.6 mBq/kg. No change in the specific activity (the total
activity and Th) was observed in a sample of ZnWO crystal produced
by recrystallization after removing mm surface layer of the
crystal.Comment: 14 pages, 5 figures and 2 table
Searches for neutrinoless double beta decay
Neutrinoless double beta decay is a lepton number violating process whose
observation would also establish that neutrinos are their own anti-particles.
There are many experimental efforts with a variety of techniques. Some (EXO,
Kamland-Zen, GERDA phase I and CANDLES) started take data in 2011 and EXO has
reported the first measurement of the half life for the double beta decay with
two neutrinos of Xe. The sensitivities of the different proposals are
reviewed.Comment: 8 pages, prepared for TAUP 201
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