45 research outputs found
An Optical Readout TPC (O-TPC) for Studies in Nuclear Astrophysics With Gamma-Ray Beams at HIgS
We report on the construction, tests, calibrations and commissioning of an
Optical Readout Time Projection Chamber (O-TPC) detector operating with a
CO2(80%) + N2(20%) gas mixture at 100 and 150 Torr. It was designed to measure
the cross sections of several key nuclear reactions involved in stellar
evolution. In particular, a study of the rate of formation of oxygen and carbon
during the process of helium burning will be performed by exposing the chamber
gas to intense nearly mono-energetic gamma-ray beams at the High Intensity
Gamma Source (HIgS) facility. The O-TPC has a sensitive target-drift volume of
30x30x21 cm^3. Ionization electrons drift towards a double parallel grid
avalanche multiplier, yielding charge multiplication and light emission.
Avalanche induced photons from N2 emission are collected, intensified and
recorded with a Charge Coupled Device (CCD) camera, providing two-dimensional
track images. The event's time projection (third coordinate) and the deposited
energy are recorded by photomultipliers and by the TPC charge-signal,
respectively. A dedicated VME-based data acquisition system and associated data
analysis tools were developed to record and analyze these data. The O-TPC has
been tested and calibrated with 3.183 MeV alpha-particles emitted by a 148Gd
source placed within its volume with a measured energy resolution of 3.0%.
Tracks of alpha and 12C particles from the dissociation of 16O and of three
alpha-particles from the dissociation of 12C have been measured during initial
in-beam test experiments performed at the HIgS facility at Duke University. The
full detection system and its performance are described and the results of the
preliminary in-beam test experiments are reported.Comment: Supported by the Richard F. Goodman Yale-Weizmann Exchange Program,
ACWIS, NY, and USDOE grant Numbers: DE-FG02-94ER40870 and DE-FG02-97ER4103
Unambiguous Identification of the Second 2+ State in 12C and the Structure of the Hoyle State
The second 2+ state of 12C, predicted over fifty years ago as an excitation
of the Hoyle state, has been unambiguously identified using the 12C(g,a_0)8Be
reaction. The alpha particles produced by the photodisintegration of 12C were
detected using an Optical Time Projection Chamber (O-TPC). Data were collected
at beam energies between 9.1 and 10.7 MeV using the intense nearly
mono-energetic gamma-ray beams at the HIgS facility. The measured angular
distributions determine the cross section and the E1-E2 relative phases as a
function of energy leading to an unambiguous identification of the second 2+
state in 12C at 10.03(11) MeV, with a total width of 800(130) keV and a ground
state gamma-decay width of 60(10) meV; B(E2: 2+ ---> gs) = 0.73(13) e2fm4 [or
0.45(8) W.u.]. The Hoyle state and its rotational 2+ state that are more
extended than the ground state of 12C presents a challenge and constraints for
models attempting to reveal the nature of three alpha particle states in 12C.
Specifically it challenges the ab-initio Lattice Effective Field Theory (L-EFT)
calculations that predict similar r.m.s. radii for the ground state and the
Hoyle state.Comment: Accepted for Publication in the Physical Review Lette
Barrier and internal wave contributions to the quantum probability density and flux in light heavy-ion elastic scattering
We investigate the properties of the optical model wave function for light
heavy-ion systems where absorption is incomplete, such as Ca
and O around 30 MeV incident energy. Strong focusing effects
are predicted to occur well inside the nucleus, where the probability density
can reach values much higher than that of the incident wave. This focusing is
shown to be correlated with the presence at back angles of a strong enhancement
in the elastic cross section, the so-called ALAS (anomalous large angle
scattering) phenomenon; this is substantiated by calculations of the quantum
probability flux and of classical trajectories. To clarify this mechanism, we
decompose the scattering wave function and the associated probability flux into
their barrier and internal wave contributions within a fully quantal
calculation. Finally, a calculation of the divergence of the quantum flux shows
that when absorption is incomplete, the focal region gives a sizeable
contribution to nonelastic processes.Comment: 16 pages, 15 figures. RevTeX file. To appear in Phys. Rev. C. The
figures are only available via anonynous FTP on
ftp://umhsp02.umh.ac.be/pub/ftp_pnt/figscat
High intensity neutrino oscillation facilities in Europe
The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Fréjus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of μ+ and μ− beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular He6 and Ne18, also stored in a ring. The far detector is also the MEMPHYS detector in the Fréjus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. However, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive
Optical-model Description of Alpha+o-16 Elastic-scattering and Alpha-cluster Structure in Ne-20
O16(,) elastic scattering angular distributions have been measured for incident energies 39.3, 49.5, and 69.5 MeV. These data, and previous measurements at 32.2, 104, and 146 MeV, have been subjected to a global optical model analysis. The deduced global potential has two energy-dependent parameters which are found to vary smoothly with energy and it is uniquely determined by the data. Backward angular distributions measured between 40 and 54 MeV are also presented and shown to be nicely reproduced by the model. The sensitivity of the cross sections to the various regions of the real potential has been investigated as a function of energy using the notch test technique. The low energy behavior of the differential cross sections can be understood in terms of the semiclassical decomposition of Brink and Takigawa. A natural extrapolation of the global potential below 30 MeV is shown to reproduce the wide bump observed in the experimental excitation functions around 20 MeV. This bump is shown to be due to an l=8 shape resonance and is interpreted as the J=8+ member of the K=04+ rotational band of Ne20, in contradiction with the current attribution. Other bound and quasibound states supported by the potential are discussed in the light of orthogonality condition model-type arguments and shown to be consistent with the well-known K=01+ and 0- bands, and with the first three states of the K=04+ band of Ne20. NUCLEAR REACTIONS O16(,), measured (), E=39.3, 49.5, 69.5 MeV; global optical model analysis, E=32-146 MeV; semiclassical decomposition of the scattering amplitude; investigation of the compatibility of the potential description with existing low energy data and comparison with cluster models. © 1983 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Measurement of resonance widths in 20Na using the 19Ne + p elastic scattering
info:eu-repo/semantics/publishe
Test results and conditioning procedure of a limited streamer-tube calorimeter.
The CHARM II Collaboration has built a massive, fine-grained calorimeter for the study of the elastic scattering upsilon // mu e **(** minus **) yields upsilon // mu e **(** minus **). A short description of the detector will be followed by the presentation of some results obtained by exposing 40 of the 441 planes of the calorimeter to a beam of electrons and pions. Comments will be given about the conditioning procedure followed for the 154,560 limited streamer tubes which compose the active part of the calorimeter.SCOPUS: ar.jinfo:eu-repo/semantics/publishe