95 research outputs found
Thermodynamics of highly interacting blend PCHMA/dPS by TOF-SANS
We investigate the thermodynamics of a highly interacting blend of poly(cyclohexyl methacrylate)/deuterated poly(styrene) (PCHMA/dPS) with small-angle neutron scattering (SANS). This system is experimentally challenging due to the proximity of the blend phase boundary (>200 °C) and degradation temperatures. To achieve the large wavenumber q-range and flux required for kinetic experiments, we employ a SANS diffractometer in time-of-flight (TOF) mode at a reactor source and ancillary microscopy, calorimetry, and thermal gravimetric analysis. Isothermal SANS data are well described by random-phase approximation (RPA), yielding the second derivative of the free energy of mixing (Gâł), the effective interaction (ÏÌ
) parameter, and extrapolated spinodal temperatures. Instead of the CahnâHilliardâCook (CHC) framework, temperature (T)-jump experiments within the one-phase region are found to be well described by the RPA at all temperatures away from the glass transition temperature, providing effectively near-equilibrium results. We employ CHC theory to estimate the blend mobility and Gâł(T) conditions where such an approximation holds. TOF-SANS is then used to precisely resolve Gâł(T) and ÏÌ
(T) during T-jumps in intervals of a few seconds and overall timescales of a few minutes. PCHMA/dPS emerges as a highly interacting partially miscible blend, with a steep dependence of Gâł(T) [mol/cm3] = â0.00228 + 1.1821/T [K], which we benchmark against previously reported highly interacting lower critical solution temperature (LCST) polymer blends
B(E1) Strengths from Coulomb Excitation of 11Be
The (E1;) strength for Be has been extracted from
intermediate energy Coulomb excitation measurements, over a range of beam
energies using a new reaction model, the extended continuum discretized coupled
channels (XCDCC) method. In addition, a measurement of the excitation cross
section for Be+Pb at 38.6 MeV/nucleon is reported. The (E1)
strength of 0.105(12) efm derived from this measurement is consistent
with those made previously at 60 and 64 MeV/nucleon, i n contrast to an
anomalously low result obtained at 43 MeV/nucleon. By coupling a
multi-configuration description of the projectile structure with realistic
reaction theory, the XCDCC model provides for the first time a fully quantum
mechanical description of Coulomb excitation. The XCDCC calculations reveal
that the excitation process involves significant contributions from nuclear,
continuum, and higher-order effects. An analysis of the present and two earlier
intermediate energy measurements yields a combined B(E1) strength of 0.105(7)
efm. This value is in good agreement with the value deduced
independently from the lifetime of the state in Be, and has a
comparable p recision.Comment: 5 pages, 2 figures, accepted for publication in Phys. Lett.
Single-Proton Removal Reaction Study of 16B
The low-lying level structure of the unbound system B has been
investigated via single-proton removal from a 35 MeV/nucleon C beam. The
coincident detection of the beam velocity B fragment and neutron allowed
the relative energy of the in-flight decay of B to be reconstructed. The
resulting spectrum exhibited a narrow peak some 85 keV above threshold. It is
argued that this feature corresponds to a very narrow (100 keV)
resonance, or an unresolved multiplet, with a dominant + configuration which decays by d-wave neutron
emission.Comment: 16 pages, 5 figures, 1 table, submitted to Phys. Lett.
Helium Clustering in Neutron-Rich Be Isotopes
Measurements of the helium-cluster breakup and neutron removal cross sections
for neutron-rich Be isotopes A=10-12,14 are presented. These have been studied
in the 30 to 42 MeV/u energy range where reaction measurements are proposed to
be sensitive to the cluster content of the ground-state wave-function. These
measurements provide a comprehensive survey of the decay processes of the Be
isotopes by which the valence neutrons are removed revealing the underlying
alpha-alpha core-cluster structure. The measurements indicate that clustering
in the Be isotopes remains important up to the drip-line nucleus 14^Be and that
the dominant helium-cluster structure in the neutron-rich Be isotopes
corresponds to alpha-Xn-alpha.Comment: 5 pages, 2 tables and 3 figure
One-neutron removal reactions on neutron-rich psd-shell nuclei
A systematic study of high energy, one-neutron removal reactions on 23
neutron-rich, psd--shell nuclei (Z=5-9, A=12-25) has been carried out. The
longitudinal momentum distributions of the core fragments and corresponding
single-neutron removal cross sections are reported for reactions on a carbon
target. Extended Glauber model calculations, weighted by the spectroscopic
factors obtained from shell model calculations, are compared to the
experimental results. Conclusions are drawn regarding the use of such reactions
as a spectroscopic tool and spin-parity assignments are proposed for 15B, 17C,
19-21N, 21,23O, 23-25F. The nature of the weakly bound systems 14B and 15,17C
is discussed.Comment: 11 pages + 2 figure
Cluster structure of 13C probed via the 7Li(9Be,13C*->9Be+alpha) reaction
A study of the 7Li(9Be,4He9Be)3H reaction at E{beam}=70 MeV has been
performed using resonant particle spectroscopy techniques and provides a
measurement of alpha-decaying states in 13C. Excited states are observed at
12.0, 13.4, 14.1, 14.6, 15.2, 16.8, 17.9, 18.7, 21.3 and 23.9 MeV. This study
provides the first measurement of the three highest energy states. Angular
distribution measurements have been performed and have been employed to
indicate the transferred angular momentum for the populated states. These data
are compared with recent speculations of the presence of chain-like structures
in 13C.Comment: accepted for publication in Nuclear Physics
Single-neutron transfer from 11Be gs via the (p,d) reaction with a radioactive beam
The 11Be(p,d)10Be reaction has been performed in inverse kinematics with a
radioactive 11Be beam of E/A = 35.3 MeV. Angular distributions for the 0+
ground state, the 2+, 3.37 MeV state and the multiplet of states around 6 MeV
in 10Be were measured at angles up to 16 deg CM by detecting the 10Be in a
dispersion-matched spectrometer and the coincident deuterons in a silicon
array. Distorted wave and coupled-channels calculations have been performed to
investigate the amount of 2+ core excitation in 11Be gs. The use of "realistic"
11Be wave functions is emphasised and bound state form factors have been
obtained by solving the particle-vibration coupling equations. This calculation
gives a dominant 2s component in the 11Be gs wave function with a 16% [2+ x 1d]
core excitation admixture. Cross sections calculated with these form factors
are in good agreement with the present data. The Separation Energy prescription
for the bound state wave function also gives satisfactory fits to the data, but
leads to a significantly larger [2 x 1d] component in 11Be gs.Comment: 39 pages, 12 figures. Accepted for publication in Nuclear Physics A.
Added minor corrections made in proof to pages 26 and 3
On the variation of fatigue-crack-opening load with measurement location
The work presented here evaluates the vlidity of using the load at the point of linearity on the displacement-load curve, as suggested by Elber, as an experimental measure of the crack-tip-opening load. Displacement-load behavior was investigated for a fatigue-cracked modified compact specimen of a nickel-base superally. Displacements were determined at the notch mouth using a standard clip-on gage, along the crack surface using a laser-interferometric displacement gage and, in the plastic zone ahead of the crack, using an optical-interferometry technique. Acoustic-emission monitoring was employed as a means to detect potential crack extension during measurement-load cycles and to detect physical-crack closure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43930/1/11340_2006_Article_BF02324983.pd
alpha-decay of excited states in 11C and 11B
Studies of the 16O(9Be,alpha7Be)14C and 7Li(9Be,alpha7Li)5He reactions at
E{beam}=70 MeV have been performed using resonant particle spectroscopy
techniques. The 11C excited states decaying into alpha+7Be(gs) are observed at
8.65, 9.85, 10.7 and 12.1 MeV as well as possible states at 12.6 and 13.4 MeV.
This result is the first observation of alpha-decay for excited states above 9
MeV. The alpha+7Li(gs) decay of 11B excited states at 9.2, 10.3, 10.55, 11.2,
(11.4), 11.8, 12.5,(13.0), 13.1, (14.0), 14.35, (17.4) and (18.6) MeV is
observed. The decay processes are used to indicate the possible three-centre
2alpha+3He(3H) cluster structure of observed states. Two rotational bands
corresponding to very deformed structures are suggested for the positive-parity
states. Excitations of some observed T=1/2 resonances coincide with the
energies of T=3/2 states which are the isobaric analogs of the lowest 11Be
states. Some of these states may have mixed isospin.Comment: accepted for publication in Nuclear Physics
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