Cross sections for neutron induced alpha production in carbon were measured at seventeen energies between 18 and 22 MeV, using a deuterated anthracene crystal as both target and detector. Pulse shape discrimination was employed to separate the alphas and elastically scattered deuterons from the other reaction products. Published (n,d) elastic scattering data were used as a standard to obtain the alpha production cross sections. Comparison with available measurements shows good agreement

Includes abstract. / Includes bibliographical references. / The iThemba LABS neutron beam facility is currently being used for various applications of fast neutron studies, such as measurements of fission cross sections, the biological effectiveness of high-energy neutrons, calibration of detectors used for dose monitoring in space and aircrafts, and the development of neutron dose monitors. Neutron beams with energies up to 200 MeV are produced at iThemba LABS by irradiating thin targets of 7Li and 9Be with protons from the separated-sector cyclotron. The neutrons are collimated to produce a beam with a diameter of about 50 mm at a flight path of 7.7 m from the target. The collimator geometry is designed to maximize the central part of the beam resulting in a beam with a uniform intensity throughout its diameter and a small penumbra. Secondary neutrons produced from the interactions of the primary charged particles with structural parts e.g. beampipes, shielding wall, target holder, etc. have been observed in the measured neutron fluence spectra. The Monte Carlo radiation transport code FLUKA were used to study the effects of secondary neutrons on the neutron fluence spectra. Results obtained from the calculations were compared with those obtained experimentally.

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The neutral pion radiative width has been measured to 8.411 eV ± 1.8% + 1.13% - 1.70% (lifetime = 7.826 ± 0.14 + 0.088 - 0.133 x 10-17 s) utilizing the Primakoff effect and roughly 4.9 to 5.5 GeV photons at the Thomas Jefferson National Accelerator Facility in Newport News, VA. The Hall B Photon Tagger, the Hall B Pair Spectrometer, a state of the art Hybrid Calorimeter enabled precision incident photon energy measurement, photon flux measurement, and neutral pion identification, respectively. With these and other hardware and software tools, elastic neutral pion yields were extracted from the data. A well developed and understood simulation calculated geometric and software cut efficiency curves. The simulation also provided photo-pion production response functions to fit the experimental cross sections and extract the Primakoff cross section and thus the neutral pion radiative width and lifetime. Future work includes improving understanding of the nuclear incoherent process and any other background sources of elastic neutral pions in this data.

The threshold electrodisintegration of the deuteron has been measured at momentum transfers of $Q\sp2$ = 8.7, 20.3, 31.3, 35.5, and 41.7 fm$\sp{-2},$ for electron beam energies of 347, 574, 750, 813, and 903 MeV at the MIT-Bates Linear Accelerator Center in April and May of 1990. The high momentum resolution of the ELSSY spectrometer ($\sim$10$\sp{-4}$ in $\Delta p/p$) and the relatively short usable liquid deuterium target length of 3.65 cm allowed a fairly good energy resolution ($\sim$2 MeV) to be achieved. This in turn made possible a reliable separation between the elastic scattering and inelastic scattering to the threshold for break-up of the deuteron at 2.23 MeV, and enabled a measurement of a threshold cross section averaged over an excitation energy of $E\sb{np}$ = 0-3 MeV. This cross section at high momentum transfer provides one of the best examples of the meson exchange currents associated with the short range N-N force. Various theoretical predictions show that the participation of the $\Delta$ resonance is also significant. However, the predictions are generally quite sensitive to the form factor of $\pi$NN vertices, since a complete dynamic theory for the internal structures of hadrons is still not available. At high momentum transfer relativistic effects are anticipated to be quite significant. In order that the threshold electrodisintegration of the deuteron can serve as a good example for the study of the short range N-N interaction, a full relativistic calculation may be required.

Deuteron electrodisintegration cross sections near 180$\sp\circ$ have been measured in the break-up threshold region for the squared four-momentum transfer $Q\sp2$ range 1.21 to 2.77 (GeV/c)$\sp2$. These measurements constitute part of Experiment NE4, performed at the Standford Linear Accelerator Center during the years 1985 and 1986. The data have relatively coarse energy resolution, 12 to 20 MeV in relative neutron-proton energy $E\sb{np}$, and predictions are examined using two methods: Various non-relativistic predictions are folded with Monte-Carlo determined resolution functions, and a model-dependent resolution-unfolding procedure was employed, yielding results averaged over $E\sb{np}$ from 0 to 10 MeV. Systematic errors arose predominantly from a $\pm$0.25% uncertainty in the scattered electron energy $E\sp1$. These results are compared with theoretical predictions averaged over similar ranges of $E\sb{np}$. The comparisons indicate that meson exchange currents (MEC) have a strong influence on the measured cross section up to $E\sb{np}$ = 20 MeV. However, the calculations have great sensitivity to the choice of form factor for the meson-nucleon coupling. Evidence for a possible change in slope of the cross section has been obtained for the first time. This feature is predicted to arise from interference effects between the IA, $\pi$ and $\rho$ exchange, $\Delta$ resonance interactions, and, perhaps, a quark exchange effect. No existing model lies in complete agreement with the data over the entire measured range of $Q\sp2$. The inelastic structure functions $W\sb1$($E\sb{np}$, $Q\sp2$), and $W\sb2$($E\sb{np}$, $Q\sp2$) are obtained from the present results and previous forward angle data. The deduced ratios, $W\sb1$/$W\sb2$ $\approx$ 1 for $E\sb{np}$ $>$ 50 MeV, but decrease as $E\sb{np}$ $\to$ 0, in accord with earlier results at lower $Q\sp2$. All non-relativistic predictions are in agreement above $E\sb{np}$ = 50 MeV, indicating that the IA interaction dominates in this region. In contrast, no prediction is in good agreement at small $E\sb{np}$. The present results expose the inadequacies of non-relativistic treatments of MEC, and should stimulate the development of relativistic theories employing nucleons with MEC, and more formally sound quark-inspired models.

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