3,384 research outputs found
ATLAS Monitored Drift Tube Chambers in E = 11 MeV Neutron Background
The influence of fast neutrons on the occupancy and the single tube
resolution of ATLAS muon drift detectors was investigated by exposing a chamber
built out of 3 layers of 3 short standard drift tubes to neutron flux-densities
of up to 16 kHz/cm2 at a neutron energy of E=11 MeV. Pulse shape capable NE213
scintillaton detectors and a calibrated BF3 neutron detector provided
monitoring of the neutron flux-density and energy. The sensitivity of the drift
chamber to the neutrons was measured to be 4*10-4 by comparing data sets with
and without neutron background. For the investigation of tracks of cosmic muons
two silicon-strip detectors above and underneath the chamber allow to compare
measured drift-radii with reference tracks. Alternatively, the single tube
resolution was determined using the triple-sum method. The comparison between
data with and without neutron irradiation shows only a marginal effect on the
resolution and little influence on the muon track reconstruction.Comment: 4 pages, 11 figures, conferenc
Role of cross-shell excitations in the reaction 54Fe(d_pol,p)55Fe
The reaction 54Fe(d_pol,p)55Fe was studied at the Munich Q3D spectrograph
with a 14 MeV polarized deuteron beam. Excitation energies, angular
distributions and analyzing powers were measured for 39 states up to 4.5 MeV
excitation energy. Spin and parity assignments were made and spectroscopic
factors deduced by comparison to DWBA calculations. The results were compared
to predictions by large scale shell model calculations in the full pf-shell and
it was found that reasonable agreement for energies and spectroscopic factors
below 2.5 MeV could only be obtained if up to 6 particles were allowed to be
excited from the f_7/2 orbital into p_3/2, f_5/2, and p_1/2 orbitals across the
N=28 gap. For levels above 2.5 MeV the experimental strength distribution was
found to be significantly more fragmented than predicted by the shell model
calculations.Comment: 9 pages, 12 figures, 3 tables, submitted to European Physical Journal
Development of Muon Drift-Tube Detectors for High-Luminosity Upgrades of the Large Hadron Collider
The muon detectors of the experiments at the Large Hadron Collider (LHC) have
to cope with unprecedentedly high neutron and gamma ray background rates. In
the forward regions of the muon spectrometer of the ATLAS detector, for
instance, counting rates of 1.7 kHz/square cm are reached at the LHC design
luminosity. For high-luminosity upgrades of the LHC, up to 10 times higher
background rates are expected which require replacement of the muon chambers in
the critical detector regions. Tests at the CERN Gamma Irradiation Facility
showed that drift-tube detectors with 15 mm diameter aluminum tubes operated
with Ar:CO2 (93:7) gas at 3 bar and a maximum drift time of about 200 ns
provide efficient and high-resolution muon tracking up to the highest expected
rates. For 15 mm tube diameter, space charge effects deteriorating the spatial
resolution at high rates are strongly suppressed. The sense wires have to be
positioned in the chamber with an accuracy of better than 50 ?micons in order
to achieve the desired spatial resolution of a chamber of 50 ?microns up to the
highest rates. We report about the design, construction and test of prototype
detectors which fulfill these requirements
Q-Value for the Fermi Beta-Decay of 46V
By comparing the Q-values for the 46Ti(3He,t)46V and 47Ti(3He,t)47}V
reactions to the isobaric analog states the Q-value for the superallowed
Fermi-decay of 46V has been determined as Q_{EC}(46V)=(7052.11+/-0.27) keV. The
result is compatible with the values from two recent direct mass measurements
but is at variance with the previously most precise reaction Q-value. As
additional input quantity we have determined the neutron separation energy
S_n(47Ti)=(8880.51+/-0.25) keV
0+ states and collective bands in 228Th studied by the (p,t) reaction
The excitation spectra in the deformed nucleus 228Th have been studied by
means of the (p,t)-reaction, using the Q3D spectrograph facility at the Munich
Tandem accelerator. The angular distributions of tritons were measured for
about 110 excitations seen in the triton spectra up to 2.5 MeV. Firm 0+
assignments are made for 17 excited states by comparison of experimental
angular distributions with the calculated ones using the CHUCK3 code.
Assignments up to spin 6+ are made for other states. Sequences of states are
selected which can be treated as rotational bands and as multiplets of
excitations. Moments of inertia have been derived from these sequences, whose
values may be considered as evidence of the two-phonon nature of most 0+
excitations. Experimental data are compared with interacting boson model and
quasiparticle-phonon model calculations and with experimental data for 229Pa.Comment: 21 pages, 14 figure
New supersymmetric quartet of nuclei in the A=190 mass region
We present evidence for a new supersymmetric quartet in the A=190 region of
the nuclear mass table. New experimental information on transfer and neutron
capture reactions to the odd-odd nucleaus 194 Ir strongly suggests the
existence of a new supersymmetric quartet, consisting of the 192,193 Os and
193,194 Ir nuclei. We make explicit predictions for the odd-neutron nucleus 193
Os, and suggest that its spectroscopic properties be measured in dedicated
experiments.Comment: 5 pages, 4 figures, updated figures and revised text, Physical Review
C, Rapid Communication, in pres
Spectroscopy of Ne for the thermonuclear O()Ne and F()O reaction rates
Uncertainties in the thermonuclear rates of the
O()Ne and F()O reactions
affect model predictions of light curves from type I X-ray bursts and the
amount of the observable radioisotope F produced in classical novae,
respectively. To address these uncertainties, we have studied the nuclear
structure of Ne over MeV and MeV using
the F(He,t)Ne reaction. We find the values of the
4.14 and 4.20 MeV levels to be consistent with and
respectively, in contrast to previous assumptions. We confirm the recently
observed triplet of states around 6.4 MeV, and find evidence that the state at
6.29 MeV, just below the proton threshold, is either broad or a doublet. Our
data also suggest that predicted but yet unobserved levels may exist near the
6.86 MeV state. Higher resolution experiments are urgently needed to further
clarify the structure of Ne around the proton threshold before a
reliable F()O rate for nova models can be determined.Comment: 5 pages, 3 figures, Phys. Rev. C (in press
Possible experimental signature of octupole correlations in the 0 states of the actinides
= 0 states have been investigated in the actinide nucleus
Pu up to an excitation energy of 3 MeV with a high-resolution (p,t)
experiment at = 24 MeV. To test the recently proposed = 0
double-octupole structure, the phenomenological approach of the
spdf-interacting boson model has been chosen. In addition, the total 0
strength distribution and the strength fragmentation have been compared
to the model predictions as well as to the previously studied (p,t) reactions
in the actinides. The results suggest that the structure of the 0 states
in the actinides might be more complex than the usually discussed pairing
isomers. Instead, the octupole degree of freedom might contribute
significantly. The signature of two close-lying 0 states below the
2-quasiparticle energy is presented as a possible manifestation of strong
octupole correlations in the structure of the 0 states in the actinides.Comment: 6 pages, 5 figures, published in Phys. Rev. C 88, 041303(R) (2013
New supersymmetric quartet of nuclei in the A=190 mass region
We present evidence for a new supersymmetric quartet in the A=190 region of
the nuclear mass table. New experimental information on transfer and neutron
capture reactions to the odd-odd nucleaus 194 Ir strongly suggests the
existence of a new supersymmetric quartet, consisting of the 192,193 Os and
193,194 Ir nuclei. We make explicit predictions for the odd-neutron nucleus 193
Os, and suggest that its spectroscopic properties be measured in dedicated
experiments.Comment: 5 pages, 4 figures, updated figures and revised text, Physical Review
C, Rapid Communication, in pres
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