This thesis describes measurements of the pion induced pion production reaction π⁺d → π⁺π⁻p p performed with a 280 MeV incident π⁺ beam at TRIUMF. The data are compared with an improved version of the Oset and Vicente-Vacas theoretical model [12]. The goal of the experiment and of the analysis was to provide a larger body of data for the free reaction and to test the validity of theoretical models. In the process, the ability to determine the values of the coupling constants C, f∆ , gN*∆π within such a model framework would be explored. The knowledge of the precise value of these coupling constants would constrain N* decay branching ratios and other pion induced reaction mechanisms like Double Charge Exchange. A previous experiment [23] had indicated that the pion induced pion production on deuterium is essentially a quasifree process with the reaction occurring on the neutron leaving the proton merely a spectator. The main difference with respect to the free reaction is the effect of Fermi motion of the neutron. Although we were interested in studying the free reaction (π⁻p → π⁺π⁻n), we chose a deuterium target so that the experiment could be run with a π⁺beam, since the π⁻ beam flux is about 6 times lower than the flux of the positive pion beam at 280 MeV, the energy at which our experiment was performed. Such a flux would have required a much longer running time for the experiment in order to achieve the same statistical accuracy. The quasifree nature of the process was also confirmed in our experiment. This experiment involved a coincidence measurement of the quasifree process and as such provided four-fold differential cross section spectra of the reaction thus allowing for a microscopic comparison between data and theoretical models. In the theoretical description we incorporated additional amplitudes for the N* → N(ππ)p-wave diagrams required to describe the reaction cross section at Tπ = 280 MeV. We also added the Fermi motion of the nucleon to the model to account for the deuterium environment. The 'free' parameters of the model are the largely unknown coupling constants listed above. We fixed C to be -2.08 by requiring the energy dependence of the model to be that of the measurement of [22] and compared the energy and angular distributions of the model to our data for several values of the f∆ and gN*∆π coupling constants ranging between 0 and 2 (where the units are 4/5 fNNπ) and between 1.08 and 1.53 respectively. We found reasonable sensitivity of the model to the f∆ variation, but only limited sensitivity to the value of the gN*∆π coupling constant. Overall we achieved a very good agreement between data and the theoretical predictions for f∆ values smaller than 0.5 and gN*∆π values closer to its lower limit. Improved statistical accuracy of the data would however be needed to better constrain the values of the coupling constants. On the basis of our results we feel that this model is a useful tool for planning future experiments and that a more extensive (π, 2π) experimental program, where differential cross sections are measured for differing isospin channels, would provide a further, more stringent test on the model allowing for a more precise determination of the coupling constants. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

The coherent nuclear ¼0 photoproduction reaction is sensitive to the nuclear matter form factor i.e. the distribution of matter within the nucleus. Accurate measurements of the nuclear matter distribution as charaterised by the r.m.s. radius are important for applications to nuclear theories, neutron stars, atomic parity non-conservation and heavy ion collisions. This thesis presents the results from a new experiment to measure coherent ¼0 photoproduction on 208Pb, 40Ca, 16O and 12C. The ultimate goal of the research programme is to make a high precision measurement of the nature of the neutron skin of 208Pb. The first major step in this direction is to achieve an accurate data set of coherent pion photoproduction which is presented in this thesis. The experiment was performed in the A2 hall of the MAMI electron accelerator facility at the InstitÄut fur Kernphysik, Mainz, Germany. An 883 MeV beam of electrons was directed on to a 10¹m nickel radiator producing a Bremsstrahlung photon beam which was then 'tagged' with a resolution of 2 MeV using the Glasgow Photon Tagging Spectrometer. The photon beam was incident on one of the 4 experimental targets inducing the reaction A(°,¼0)A. The neutral ¼0s were then detected via their two photon decay in the newly installed 4¼ Crystal Ball and TAPS detector systems. The results from all four targets are presented as differential and total cross sections covering the energy range E°=(135-300) MeV and covering the full 180± of the pion polar angle. Comparisons have been made with previous data and with the latest theoretical calculations of Dreschel et. al. which employ detailed pion optical potentials in describing the pion-nucleus final state interaction. It is concluded that the 208Pb cross sections show good agreement with the calculations indicating that the pion-nucleus FSI distortions are well accounted for by the model. A pleasing reduction in statistical and systematic uncertainties from previous measurements is also observed. While the 208Pb cross sections are finalised it is suggested that the 12C and 16O data would benefit from a further analysis utilising the coincident detection of nuclear decay photons to isolate incoherent events and allow a more detailed comparison with theory. A first comparison of the theoretical model with the new high quality data gives first indications of a neutron skin on 208Pb. A future scheme for the full detailed extraction of the matter distribution from the new data set is also suggested.

No description available.

Thesis (Ph. D. in Physics)--University of California, Berkeley, Sept. 1955. / Includes bibliographical references (p. 71-73). 68

Tübingen, University, Diss., 2004.

Universiẗat, Diss., 2004--München.

The aim of this research project was to investigate ways of improving the accuracy of dosimetric measurements in pion radiotherapy. Interest in this area was stimulated by the results of recent experimental work which revealed that materials from which dosimeters in pion radiotherapy are routinely constructed are not tissue equivalent for pi-. Two means of achieving the stated objective were identified: 1. To produce materials which are tissue equivalent for pions, to use in the construction of phantoms and dosimeters. 2. To evaluate correction factors necessary to convert dose recorded under non-tissue equivalent conditions to that for tissue. An attempt was made to produce muscle and bone equivalent phantom materials. The extent to which the materials produced could be considered tissue equivalent was judged by comparing experimentally determined carbon to oxygen (C:O) and nitrogen to oxygen (N:O) pion atomic capture ratios with those for the corresponding tissue type. Negative pion atomic capture ratios were also evaluated for sets of simple organic compounds to aid further development of the theoretical models necessary to determine correction factors.

An experimental investigation of the absorption reaction ⁴He(π⁺,ppp) has been undertaken on the M11 beamline at the TRIUMF cyclotron. Positive pions at an average kinetic energy of 165 MeV were directed onto a cylindrical liquid 4He target and the outgoing protons were measured by a combination of two time-of-flight arrays and two plastic scintillator telescopes. A description of the apparatus, experimental technique and calibration is presented. Results from triple proton coincidences at a single orientation of three of the detectors are discussed. Their angular settings with respect to the pion beam were 40°, 136° and —55°. Comparisons are made with Monte-Carlo simulations of three and four body phase spaces. Identification of a quasi-free three nucleon absorption mode is made for the first time at this energy. An integrated cross-section for this process is determined (σQ₃N = 4.4 ± 0.6mb). The quantitative agreement between these results and those of another recent experiment¹ indicate that a small fraction(≈10%) of the coincidences could be due to a two step absorption mechanism. ¹Backenstoss et al. Phys. Rev. Lett 61:923(1988) / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.