Search

The particle size distribution of particles in liquid-based suspensions and emulsions is an important parameter in a wide variety of industrial applications. Many particle-sizing methods require the transmission of light through a sample of the system, and therefore these particulate systems must be severely diluted. Many systems are unstable on dilution and therefore have to be measured at high volume concentration. Sound waves interact with both the suspending medium and the dispersed phase and are able to propagate through concentrated systems. The development of new ultrasonic transducer technology together with advances in digital signal processing has opened the way for a powerful new analysis termed acoustic attenuation spectroscopy. The technique consists of propagating ultrasonic waves of a range of frequencies through the particulate system and accurately measuring the attenuation at each frequency. This attenuation spectrum can be converted to a particle size distribution and a measure of the concentration of the dispersed phase. It offers the particle technologist the means to monitor and control particle formation and reduction processes.

New data for the elastic and inelastic scattering of 24.4 MeV protons from 6, 7Li are presented and a summary of all the available data for the elastic, inelastic, and charge exchange scattering of 24–50 MeV protons from these same targets is given. The cross-section data for Ep ≅25 and 50 MeV are examined theoretically within the framework of the microscopic folding model and the distorted-wave approximation. Standard p-shell wave functions, supplemented by renormalization factors deduced from electromagnetic and β-decay data, are used to describe the target nuclei in these calculations. Results obtained using a phenomenological 1 fm range Yukawa interaction illustrate the information on proton-neutron differences contained in the data for quadrupole transitions in 7Li and differences in the energy dependence of the spin-flip and non-spin-flip isovector central components of the effective interaction contained in the data for the (p, n) reaction on this same target. Results obtained with the more realistic G-matrix interaction of Bertsch et al. give a reasonable description of the overall features of the experimental data after 20–60 % reductions in the strengths of its varous components are made. The calculations fail to provide a consistent picture of the energy dependence of the optical potential and the quadrupole transition potentials. Some difficulties are also encountered in describing the cross sections for scattering to the 0+, T = 1 level in the mass-6 systems.

Doubly differential cross sections for the production of ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ near the velocity of the incident beam for pion laboratory angles from 0 to 20 degrees are presented. Beams of $^{20}\mathrm{Ne}$ with $\frac{E}{A}=280, 380, \mathrm{and} 480$ MeV and $^{40}\mathrm{Ar}$ with $\frac{E}{A}=535$ MeV incident on C, NaF, KCl, Cu, and U targets were used. A sharp peak in the ${\ensuremath{\pi}}^{\ensuremath{-}}$ spectrum and a depression in the ${\ensuremath{\pi}}^{+}$ spectrum is observed at 0\ifmmode^\circ\else\textdegree\fi{} near the incident projectile velocity. The effect is explained in terms of Coulomb interactions between pions and fragments of the incident beam. Least squares fits to the data using the Coulomb correction formulas of Gyulassy and Kauffmann and an effective projectile fragment charge are made. The relationship between these data and previously measured projectile fragmentation data is discussed and a simple parametrization of projectile mass, target mass, and beam energy dependence of the differential cross sections is given.NUCLEAR REACTIONS C, NaF, Cu, U $(^{20}\mathrm{Ne},{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})X$, $\frac{E}{A}=280\ensuremath{-}480$ MeV; C, KCl $(^{40}\mathrm{Ar},{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})X$, $\frac{E}{A}=535$ MeV; measured $\ensuremath{\sigma}({E}_{\ensuremath{\pi}},{\ensuremath{\theta}}_{\ensuremath{\pi}})$, ${\ensuremath{\theta}}_{\ensuremath{\pi}}=0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}20\ifmmode^\circ\else\textdegree\fi{}$, $\ensuremath{\pi}$ velocity near beam velocity; deduced projectile fragment charges, Coulomb effects.

From the scattering of 35 MeV protons from 206 Pb accurate excitation energies and angular distributions have been determined for the strongly excited collective states. These states are compared to corresponding states in 207,208 Pb. A possible explanation of the anomaly in the 5 - strength is given in terms of the core wave functions.

Core excitations up to E/sub x/ = 4 MeV in /sup 63/Cu have been studied by the reactions /sup 63/Cu(p,p')/sup 63/Cu and /sup 65/Cu(p,t)/sup 63/Cu at 40 MeV proton energy. The transferred angular momentum L has been determined for each transition on the basis of the angular distribution shape. A quartet-plus-doublet pattern is consistently observed for the groups of states corresponding to the 2/sup +//sub 1/, 3/sup -//sub 1/, and 4/sup +//sub 1/ states of the core nucleus /sup 62/Ni. This implies the existence of doublets arising from the coupling of collective states of the core with the 2p/sub 1/2/ proton orbital, in addition to the quartets from the coupling with the 2p/sub 3/2/ proton orbital considered in the conventional weak-coupling excited-core model. It is pointed out that the existence of a weak-coupling situation cannot be proved only on the basis of transfer-reaction data, and in this regard the importance of a comparative study of the inelastic-scattering and transfer-reaction data is emphasized.

Measurements of light charged particle spectra from 20 Ne + Au at 100 and 156 MeV/nucleon are compared with results for similar systems at 9, 13, 19, 43, 241, 393, and 800 MeV/nucleon. Spectra at each energy are fitted with a moving source model to extract the temperatures, cross sections and source velocities for protons and light nuclei in the intermediate rapidity region. The 4 He/p production ratio decreases drastically with incident energy, whereas the d/p and t/p ratios are almost constant.

Inelastic scattering of 71 MeV 3He particles from 16O shows an enhancement and structure of the continuum consistent with the assumption of a giant quadrupole resonance. Completely microscopic model calculations indicate that the excitation of 1−(T= 1) and 0+(T=0) states may account for only about 10 % of the total cross sections of the excitation region 17–27 MeV.

This paper describes an arrangement for introducing feedback into a charged particle magnetic analysis system for nuclear reaction studies. In initial tests of the system, a resolution of 5 keV has been obtained in (p,p′) studies at 30 MeV with 70% of the cyclotron internal beam on target. This corresponds to a resolving power p/Δp of 12000. Essential features of the system, in addition to the feedback, are a careful definition of the cyclotron source by means of internal slits and the use of dispersion matching to cancel the effect of coherent on-target energy spread.

The reaction 208 Pb(d, p) 209 Pb has been studied in the region below the Coulomb barrier in order to investigate the accuracy with which spectroscopic factors can be obtained from this process. Both distorted wave and analytic calculations are discussed. The dependence of the spectroscopic factors on the geometry of the bound-state well leads to a value of 6.06 fm for the root-mean-square radius of the nuclear potential. This is rather larger than the value obtained from electron scattering measurements.

The inelastic scattering of 17.5-MeV protons from a number of nuclei in the $2s\ensuremath{-}1d$ shell has been studied using lithium-drifted silicon detectors. Results for the even-$A$ nuclei ${\mathrm{O}}^{16}$, ${\mathrm{Mg}}^{24}$, ${\mathrm{Mg}}^{26}$, ${\mathrm{Si}}^{28}$, and ${\mathrm{S}}^{32}$ are presented here. Angular distributions are obtained for up to twenty levels in each nucleus. While some of the angular distributions having the same $l$ value are similar, there were a number of cases where angular distributions to states in the same nucleus with the same spin and parity have very different angular distributions. The differential cross sections for the most strongly excited levels are compared with a distorted-wave Born-approximation calculation using collective form factors. Reasonable fits to the differential cross sections were obtained for the $l=2$ transitions to the first excited states of ${\mathrm{Mg}}^{24}$, ${\mathrm{Si}}^{28}$, and ${\mathrm{S}}^{32}$ and for the $l=3$ transitions to the lowest-lying ${3}^{\ensuremath{-}}$ states of ${\mathrm{O}}^{16}$, ${\mathrm{Mg}}^{24}$, ${\mathrm{Si}}^{28}$, and ${\mathrm{S}}^{32}$. A previously unreported level in ${\mathrm{S}}^{32}$ at 6.76 MeV was observed.

The photoneutron yield curve of natural lithium has been determined for incident bremsstrahlung energies up to 18.5 MeV. This yield curve shows no gross structure in the region of 17 MeV as indicated in some previous measurements. The resulting cross section indicates the presence of three high energy levels in 7 Li at 13.6 MeV, 15.3 MeV and 16.5 MeV. Additional measurements using a neutron detection system with a response deliberately designed to be sensitive to slow neutrons were made simultaneously with the above yield curve determination. This “slow neutron” yield curve suggests that the discrepancies amongst the earlier results may be due to the different responses of the various neutron detection systems used. An outline of a possible test to verify this suggestion is given.

Angular distributions for the reactions 6Li(d, p)7Li (ground state and 0.48 MeV level), 9Be(d, p)10Be (ground state and 3.37 MeV level), 10B(d, p)11B (ground state, 2.12, 4.44 and 5.02 MeV levels) and the elastic scattering of deuterons on 6Li and 9Be have been measured for bombarding energies between 4.5 and 6.0 MeV. Absolute cross sections have been obtained for the9Be+d data. An analysis of the data has been made using the optical-model and the distorted-wave and Hauser-Feshbach theories.

The proton proton bremsstrahlung cross section was measured at an incident proton energy of 10.5 MeV. The upper limit of 1.3 μb/sr2 helps to distinguish between the various calculations at this energy.

The differential cross section for the inelastic scattering of protons leading to the ( J π = 0 + , T = 1) state of 6 Li at 3.56 MeV has been measured at E p = 24.4 MeV. A real spin-isospin dependent interaction with a Yukawa shape, a strength of 12.7 MeV and a range of 1.0 fm fits the data well at small angles.

Doubly differential cross sections for producing ..pi../sup +/ and ..pi../sup -/ were measured for several target-projectile combinations. They were /sup 40/Ar+C, Ca, and U at 1050A MeV and /sup 20/Ne+Be and NaF at 655A MeV. The ..pi../sup -//..pi../sup +/ ratios are smaller than those expected from several Coulomb effect calculations. The Ne+NaF..--> pi../sup -/ data exhibit a peak at 90/sup 0/ in the center of mass and p/sub ..pi../ = 0.4m/sub ..pi../c.

A low pressure multiwire proportional counter, a Bragg curve counter, and an array of CaF2/plastic scintillator telescopes have been developed in a geometry suitable for close packing into a 4π detector designed to study nucleus-nucleus reactions at 100–200 MeV/nucleon. The multiwire counter is hexagonal in shape and gives X−Y position information using resistive charge division from nichrome-coated stretched polypropylene foils. The Bragg curve counter is a hexagonal pyramid with the charge taken from a Frisch gridded anode. A field shaping grid gives the Bragg curve counter a radial field. The scintillator telescopes are shaped as truncated triangular pyramids such that when stacked together they form a truncated hexagonal pyramid. The light signal of the CaF2-plastic combination is read with one phototube using a phoswich technique to separate the ΔE signal from the E signal. The entire system has been tested so far for particles with 1 ≦ Z ≦ 18 and gives good position, charge, and time resolution.

Observations down to 2° in the 48Ca(p,p′) reaction at 201 MeV reveal 0+→1+ strength with certainly only at the previously known excitation of 10.22 MeV. Compared to DWBA calculations, the strength of this state is only ∼ 30%.

In a series of seventeen nuclei ranging from 51V to 14Ce, broad resonance structures are observed at energies between 8 and 10 MeV, nearly mass independent. These resonances have very forward peaked angular distributions which imply that they are populated by an angular momentum transfer of zero. This together with the observed excitation energies suggests an M1 character for these resonances. In 51V, 58Ni, 60Ni, 62Ni, a sharp peak located at an excitation energy above the threshold for neutron emission is interpreted as a part of the T0 + 1 component of the M1 resonance. Cross sections are given for all the M1 resonances. For 58Ni, 90Zr, 92Mo, 120Sn and 140Ce, an “attenuation” factor for the cross sections is extracted in a DWIA calculation assuming simple shell-model structures for these resonances.