161 research outputs found
Systematic grid-wise radon concentration measurements and first radon map in Cyprus
A systematic study of the indoor airborne radon concentration in the central
part of the Nicosia district was conducted, using high-sensitivity active radon
portable detectors of the type "RADIM3A". From a total of 108 measurements in
54 grids of 1 km^2 area each, the overall mean value is 20.6 \pm 13.2 Bq m^-3
(A.M.\pm S.D.). That is almost twice less than the corresponding average
worldwide value. The radon concentration levels in drinking water were also
measured in 24 sites of the residential district, using the high-sensitivity
radon detector of the type "RADIM3W". The mean value obtained from these
measurements is 243.8 \pm 224.8 mBq L^-1, which is relatively low compared to
the corresponding internationally accepted level. The associated annual
effective dose rates to each measurement were also calculated and compared to
the corresponding worldwide values. From the geographical coordinates of the
measuring sites and the corresponding radon concentration values, the digital
radon map of the central part of the Nicosia district was constructed for the
first time, by means of the ArcMap software package.Comment: 21 pages including 2 tables and 8 figure
Gamow peak in thermonuclear reactions at high temperatures
The Gamow peak represents one of the most important concepts in the study of thermonuclear reactions in stars. It is widely used in order to determine, at a given plasma temperature, the effective stellar energy region in which most charged-particle induced nuclear reactions occur. It is of importance in the design of nuclear astrophysics measurements, including those involving radioactive ion beams, and for the determination of stellar reaction rates. We demonstrate that the Gamow peak concept breaks down under certain conditions if a nuclear reaction proceeds through narrow resonances at elevated temperatures. It is shown that an effective stellar energy window does indeed exist in which most thermonuclear reactions take place at a given temperature, but that this energy window can differ significantly from the commonly used Gamow peak. We expect that these findings are especially important for thermonuclear reactions in the advanced burning stages of massive stars and in explosive stellar environments
Inclusive pion and eta production in p+Nb collisions at 3.5 GeV beam energy
Data on inclusive pion and eta production measured with the dielectron
spectrometer HADES in the reaction p+93Nb at a kinetic beam energy of 3.5 GeV
are presented. Our results, obtained with the photon conversion method,
supplement the rather sparse information on neutral meson production in
proton-nucleus reactions existing for this bombarding energy regime. The
reconstructed e+e-e+e- transverse-momentum and rapidity distributions are
confronted with transport model calculations, which account fairly well for
both pi0 and eta production.Comment: 12 pages, 9 figures, submitted to Physical Review
Searching a Dark Photon with HADES
We present a search for the e+e- decay of a hypothetical dark photon, also
names U vector boson, in inclusive dielectron spectra measured by HADES in the
p (3.5 GeV) + p, Nb reactions, as well as the Ar (1.756 GeV/u) + KCl reaction.
An upper limit on the kinetic mixing parameter squared epsilon^{2} at 90% CL
has been obtained for the mass range M(U) = 0.02 - 0.55 GeV/c2 and is compared
with the present world data set. For masses 0.03 - 0.1 GeV/c^2, the limit has
been lowered with respect to previous results, allowing now to exclude a large
part of the parameter region favoured by the muon g-2 anomaly. Furthermore, an
improved upper limit on the branching ratio of 2.3 * 10^{-6} has been set on
the helicity-suppressed direct decay of the eta meson, eta-> e+e-, at 90% CL
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