1,280 research outputs found
Beta asymmetry parameter in the decay of 114In
The beta asymmetry parameter A for the pure Gamow-Teller decay of 114In is
reported. The low temperature nuclear orientation method was combined with a
GEANT4 based simulation code allowing for the first time to address in detail
the effects of scattering and of the magnetic field. The result, A = -0.994 +/-
0.010stat +/- 0.010syst, constitutes the most accurate value for the asymmetry
parameter of a nuclear beta transition to date. The value is in agreement with
the Standard Model prediction of A = -1 and provides new limits on tensor type
charged weak currents.Comment: 11 pages, 2 figures; additional information was added on systematic
effects, the magnetic field map and the calculation of the Qcos(theta) value
Performance of Geant4 in simulating semiconductor particle detector response in the energy range below 1 MeV
Geant4 simulations play a crucial role in the analysis and interpretation of
experiments providing low energy precision tests of the Standard Model. This
paper focuses on the accuracy of the description of the electron processes in
the energy range between 100 and 1000 keV. The effect of the different
simulation parameters and multiple scattering models on the backscattering
coefficients is investigated. Simulations of the response of HPGe and
passivated implanted planar Si detectors to \beta{} particles are compared to
experimental results. An overall good agreement is found between Geant4
simulations and experimental data
Seasonal and site-specific variation in vapour and aerosol phase PAHs over Flanders (Belgium) and their relation with anthropogenic activities
Peer reviewe
Measurement of the -asymmetry parameter of Cu in search for tensor type currents in the weak interaction
Precision measurements at low energy search for physics beyond the Standard
Model in a way complementary to searches for new particles at colliders. In the
weak sector the most general decay Hamiltonian contains, besides vector
and axial-vector terms, also scalar, tensor and pseudoscalar terms. Current
limits on the scalar and tensor coupling constants from neutron and nuclear
decay are on the level of several percent.
The goal of this paper is extracting new information on tensor coupling
constants by measuring the -asymmetry parameter in the pure Gamow-Teller
decay of Cu, thereby testing the V-A structure of the weak interaction.
An iron sample foil into which the radioactive nuclei were implanted was cooled
down to milliKelvin temperatures in a He-He dilution refrigerator. An
external magnetic field of 0.1 T, in combination with the internal hyperfine
magnetic field, oriented the nuclei. The anisotropic radiation was
observed with planar high purity germanium detectors operating at a temperature
of about 10\,K. An on-line measurement of the asymmetry of Cu
was performed as well for normalization purposes. Systematic effects were
investigated using Geant4 simulations.
The experimental value, = 0.587(14), is in agreement with the
Standard Model value of 0.5991(2) and is interpreted in terms of physics beyond
the Standard Model. The limits obtained on possible tensor type charged
currents in the weak interaction hamiltonian are -0.045
0.159 (90\% C.L.). The obtained limits are comparable to limits from other
correlation measurements in nuclear decay and contribute to further
constraining tensor coupling constants
Confirmation of Parity Violation in the Gamma Decay of
This paper reports measurements using the technique of On Line Nuclear
Orientation (OLNO) which reexamine the gamma decay of isomeric Hf and specifically the 501 keV 8 -- 6
transition. The irregular admixture of E2 to M2/E3 multipolarity in this
transition, deduced from the forward-backward asymmetry of its angular
distribution, has for decades stood as the prime evidence for parity mixing in
nuclear states. The experiment, based on ion implantation of the newly
developed mass-separated Hf beam at ISOLDE, CERN into an
iron foil maintained at millikelvin temperatures, produces higher degrees of
polarization than were achieved in previous studies of this system. The value
found for the E2/M2 mixing ratio, = -0.0324(16)(17), is in close
agreement with the previous published average value = - 0.030(2), in
full confirmation of the presence of the irregular E2 admixture in the 501 keV
transition. The temperature dependence of the forward-backward asymmetry has
been measured over a more extended range of nuclear polarization than
previously possible, giving further evidence for parity mixing of the 8 and 8 levels and the deduced E2/M2 mixing ratio.Comment: 28 pages, 9 figures, accepted for publication in Physical Review
The half-life of Fr in Si and Au at 4K and at mK temperatures
The half-life of the decaying nucleus Fr was determined in
different environments, i.e. embedded in Si at 4 K, and embedded in Au at 4 K
and about 20 mK. No differences in half-life for these different conditions
were observed within 0.1%. Furthermore, we quote a new value for the absolute
half-life of Fr of t = 286.1(10) s, which is of comparable
precision to the most precise value available in literature
Disease, invasions and conservation : no evidence of squirrelpox virus in grey squirrels introduced to Italy
Native red squirrels Sciurus vulgaris in Great Britain and Ireland are threatened by alien grey squirrels S. carolinensis through exploitation competition and spillover of squirrelpox virus (SQPV). By accelerating the replacement of red squirrels by the invader, SQPV represents a fundamental factor to consider when planning management and conservation strategies. In mainland Europe, grey squirrels introduced to Italy threaten the survival of the whole continental red squirrel population, but no extensive surveys for SQPV presence have been carried out in the region. We therefore investigated SQPV infection in north Italian grey squirrel populations through a combination of serological and molecular methods. Firstly, we analysed sera from 285 individuals through an enzyme\u2010linked immunosorbent assay (ELISA) to detect antibodies against SQPV. Secondly, a PCR designed to amplify a segment of the G8R SQPV gene was carried out on DNA extracted from swabs and skin tissue samples from a second set of 66 grey squirrels. ELISA tests identified four reactors (1.4%), but the subsequent PCR survey did not detect any SQPV DNA. Based on the low prevalence observed and on PCR results, we believe that the four suspected positives were the result of an ELISA cross\u2010reaction following exposure to another pox virus. Considering sample size and performances of the two methods, confidence of freedom from SQPV resulted above 99.9%. However, because of the severe impact of SQPV on red squirrels, we recommend the implementation of a passive surveillance plan for the early detection of an SQPV emergence in continental Europe
Invading parasites: spillover of an alien nematode reduces survival in a native species
It is widely assumed that spillover of alien parasites to native host species severely impacts na\uefve populations, ultimately conferring a competitive advantage to invading hosts that introduced them. Despite such host-switching events occurring in biological invasions, studies demonstrating the impact of alien macroparasites on native animal hosts are surprisingly few. In Europe, native red squirrels (Sciurus vulgaris) are replaced by introduced North American grey squirrels (S. carolinensis) mainly through resource competition, and, only in the United Kingdom and Ireland, by competition mediated by a viral disease. In Italy such disease is absent, but spillover of an introduced North American nematode (Strongyloides robustus) from grey to red squirrels is known to occur. Here, we used long-term (9 years) capture-mark-recapture and parasitological data of red squirrels in areas co-inhabited by grey squirrels in Northern Italy to investigate the impact of this alien helminth on na\uefve native squirrels\u2019 body mass, local survival, and reproduction of females. We found no negative effect of the alien parasite on body mass or reproductive success, but intensity of infection by S. robustus reduced survival of both male and female squirrels. Significantly, survival of squirrels co-infected by their native nematode, Trypanoxyuris sciuri, was less affected by S. robustus, suggesting a protective effect of the native helminth against the new infection. Hence, we demonstrate that alien S. robustus spillover adds to the detrimental effects of resource competition and stress induced by grey squirrels, further reducing the fitness of the native species in the presence of the invasive competitor
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