114 research outputs found
Digital pulse-shape discrimination of fast neutrons and gamma rays
Discrimination of the detection of fast neutrons and gamma rays in a liquid
scintillator detector has been investigated using digital pulse-processing
techniques. An experimental setup with a 252Cf source, a BC-501 liquid
scintillator detector, and a BaF2 detector was used to collect waveforms with a
100 Ms/s, 14 bit sampling ADC. Three identical ADC's were combined to increase
the sampling frequency to 300 Ms/s. Four different digital pulse-shape analysis
algorithms were developed and compared to each other and to data obtained with
an analogue neutron-gamma discrimination unit. Two of the digital algorithms
were based on the charge comparison method, while the analogue unit and the
other two digital algorithms were based on the zero-crossover method. Two
different figure-of-merit parameters, which quantify the neutron-gamma
discrimination properties, were evaluated for all four digital algorithms and
for the analogue data set. All of the digital algorithms gave similar or better
figure-of-merit values than what was obtained with the analogue setup. A
detailed study of the discrimination properties as a function of sampling
frequency and bit resolution of the ADC was performed. It was shown that a
sampling ADC with a bit resolution of 12 bits and a sampling frequency of 100
Ms/s is adequate for achieving an optimal neutron-gamma discrimination for
pulses having a dynamic range for deposited neutron energies of 0.3-12 MeV. An
investigation of the influence of the sampling frequency on the time resolution
was made. A FWHM of 1.7 ns was obtained at 100 Ms/s.Comment: 26 pages, 14 figures, submitted to Nuclear Instruments and Methods in
Physics Research
LNCS
We present two algorithmic approaches for synthesizing linear hybrid automata from experimental data. Unlike previous approaches, our algorithms work without a template and generate an automaton with nondeterministic guards and invariants, and with an arbitrary number and topology of modes. They thus construct a succinct model from the data and provide formal guarantees. In particular, (1) the generated automaton can reproduce the data up to a specified tolerance and (2) the automaton is tight, given the first guarantee. Our first approach encodes the synthesis problem as a logical formula in the theory of linear arithmetic, which can then be solved by an SMT solver. This approach minimizes the number of modes in the resulting model but is only feasible for limited data sets. To address scalability, we propose a second approach that does not enforce to find a minimal model. The algorithm constructs an initial automaton and then iteratively extends the automaton based on processing new data. Therefore the algorithm is well-suited for online and synthesis-in-the-loop applications. The core of the algorithm is a membership query that checks whether, within the specified tolerance, a given data set can result from the execution of a given automaton. We solve this membership problem for linear hybrid automata by repeated reachability computations. We demonstrate the effectiveness of the algorithm on synthetic data sets and on cardiac-cell measurements
Transition rates and nuclear structure changes in mirror nuclei 47Cr and 47V
Lifetime measurements in the mirror nuclei 47Cr and 47V were performed by
means of the Doppler-shift attenuation method using the multidetector array
EUROBALL, in conjunction with the ancillary detectors ISIS and the Neutron
Wall. The determined transition strengths in the yrast cascades are well
described by full pf shell model calculations.Comment: Latex2e, 11 pages, 3 figure
Very high rotational frequencies and band termination in 73Br
Rotational bands in 73Br have been investigated up to spins of 65/2 using the
EUROBALL III spectrometer. One of the negative-parity bands displays the
highest rotational frequency 1.85 MeV reported to date in nuclei with mass
number greater than 25. At high frequencies, the experimental dynamic moment of
inertia for all bands decrease to very low values, indicating a loss of
collectivity. The bands are described in the configuration-dependent cranked
Nilsson-Strutinsky model. The calculations indicate that one of the
negative-parity bands is observed up to its terminating single-particle state
at spin 63/2. This result establishes the first band termination case in the A
= 70 mass region.Comment: 6 pages, 6 figures, submitted to Phys. Rev. C as a Rapid
Communicatio
Collective and broken pair states of 65,67Ga
Excited states of 65Ga and 67Ga nuclei were populated through the 12C(58Ni,αp) and 12C(58Ni,3p) reactions, respectively, and investigated by in-beam γ-ray spectroscopic methods. The NORDBALL array equipped with a charged particle ball and 11 neutron detectors was used to detect the evaporated particles and γ rays. The level schemes of 65,67Ga were constructed on the basis of γγ-coincidence relations up to 8.6 and 10 MeV excitation energy, and Iπ=27/2 and 33/2+ spin and parity, respectively. The structure of 65,67Ga nuclei was described in the interacting boson-fermion plus broken pair model, including quasiproton, quasiproton-two-quasineutron, and three-quasiproton fermion configurations in the boson-fermion basis states. Most of the states were assigned to quasiparticle + phonon and three quasiparticle configurations on the basis of their electromagnetic decay properties
REX-ISOLDE: post-accelerated radioactive BEAMS at CERN-ISOLDE
The ISOLDE RIB-facility at CERN has today been producing a vast range of radioactive beams since more than 30 years. The low-energy beams of ISOLDE will be complemented by a post-accelerator, REX-ISOLDE, currently being assembled. In order to convert the pseudo-DC, singly-charged beam from the ISOLDE mass separators into a cooled and bunched beam at higher charge states a novel scheme of trapping, cooling and charge-state breeding has been devised, using a linear Penning trap and an Electron Beam Ion Source (EBIS). This allows for subsequent acceleration by a short, cost-effective LINAC consisting of an RFQ, an IH-structure and three seven-gap resonators, reaching 0.8 - 2.2 MeV/u. The installation of REX-ISOLDE is well underway and the first post-accelerated radioactive beams are expected to be obtained during late 2000
ContextD: an algorithm to identify contextual properties of medical terms in a Dutch clinical corpus
Conceptual design of the early implementation of the NEutron Detector Array (NEDA) with AGATA
The NEutron Detector Array (NEDA) project aims at the construction of a new high-efficiency compact neutron detector array to be coupled with large (Formula presented.) -ray arrays such as AGATA. The application of NEDA ranges from its use as selective neutron multiplicity filter for fusion-evaporation reaction to a large solid angle neutron tagging device. In the present work, possible configurations for the NEDA coupled with the Neutron Wall for the early implementation with AGATA has been simulated, using Monte Carlo techniques, in order to evaluate their performance figures. The goal of this early NEDA implementation is to improve, with respect to previous instruments, efficiency and capability to select multiplicity for fusion-evaporation reaction channels in which 1, 2 or 3 neutrons are emitted. Each NEDA detector unit has the shape of a regular hexagonal prism with a volume of about 3.23l and it is filled with the EJ301 liquid scintillator, that presents good neutron- (Formula presented.) discrimination properties. The simulations have been performed using a fusion-evaporation event generator that has been validated with a set of experimental data obtained in the 58Ni + 56Fe reaction measured with the Neutron Wall detector array
Evidence for a spin-aligned neutron-proton paired phase from the level structure of Pd
The general phenomenon of shell structure in atomic nuclei has been
understood since the pioneering work of Goeppert-Mayer, Haxel, Jensen and
Suess.They realized that the experimental evidence for nuclear magic numbers
could be explained by introducing a strong spin-orbit interaction in the
nuclear shell model potential. However, our detailed knowledge of nuclear
forces and the mechanisms governing the structure of nuclei, in particular far
from stability, is still incomplete. In nuclei with equal neutron and proton
numbers (), the unique nature of the atomic nucleus as an object
composed of two distinct types of fermions can be expressed as enhanced
correlations arising between neutrons and protons occupying orbitals with the
same quantum numbers. Such correlations have been predicted to favor a new type
of nuclear superfluidity; isoscalar neutron-proton pairing, in addition to
normal isovector pairing (see Fig. 1). Despite many experimental efforts these
predictions have not been confirmed. Here, we report on the first observation
of excited states in nucleus Pd. Gamma rays emitted
following the Ni(Ar,2)Pd fusion-evaporation reaction
were identified using a combination of state-of-the-art high-resolution
{\gamma}-ray, charged-particle and neutron detector systems. Our results reveal
evidence for a spin-aligned, isoscalar neutron-proton coupling scheme,
different from the previous prediction. We suggest that this coupling scheme
replaces normal superfluidity (characterized by seniority coupling) in the
ground and low-lying excited states of the heaviest N = Z nuclei. The strong
isoscalar neutron- proton correlations in these nuclei are predicted to
have a considerable impact on their level structures, and to influence the
dynamics of the stellar rapid proton capture nucleosynthesis process.Comment: 13 pages, 3 figure
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