Student Number : 0000713F - PhD thesis - School of Physics - Faculty of Science / The Doppler shift and the Doppler broadening of prompt gamma emissions were measured for some residues formed in the interaction of 33 A MeV 12C ions with a 63Cu target using the AFRODITE detector array at Faure, Cape Town. This is a potentially new technique to carry out nuclear interaction studies. Coincident gamma rays emitted by the residues are used in their identification. Detection at angles other than 90◦ with respect to the beam axis gives the magnitude of the mean Doppler shifts and the average linear momentum transfer. The Doppler broadening of the detected gamma lines at 90 ◦ with respect to the beam axis could give the residue recoil angular distribution. The precise shapes of the Doppler shifted and broadened gamma lines for each of the residues extracted, reveals the distribution, in magnitude and angle, of the momentum transferred in the interaction process. In addition, characteristic gamma energy transitions of each residue populated carry additional information on angular momentum (spin) transfer, production cross-section and nuclear excitation states. The measured residues show a unique distribution of momentum ranging from single nucleon transfer to complete damping of the projectile momentum. The measured observables are consistent with the existing data from other techniques, making the new technique viable option for studying nuclear interaction kinematics. A comparison of the experimental measurements with the predictions of the model developed in Milano 1 and GEANT4 calculations shows that the model developed in Milano model give a much better agreement compared to the GEANT4 calculations, attributed to the assumption of projectile break-up and re-emission process of some of the fragments during the first step of the nuclear interaction process.

<p>Reaction cross sections were measured for protons at 65.5 MeV, for deuterons at 37.8, 65.5, 97.4 MeV, for ³He at 96.4, 137.8, 167.3 MeV, and for ⁴He at 69.6, 117.2, 163.9 and 192.4 MeV. Targets were ⁹Be, ¹²C, ¹⁶O, ²⁸Si, ^40,48Ca, ^58,60Ni, ^{112,116,118,120,124}Sn and ²⁰⁸Pb. ⁴⁸Ca and ¹¹⁸Sn targets were used only for some of the measurements. Rest of the targets have been measured for all energies and projectiles but ⁴He at 69.6 MeV where reaction cross sections were measured for ⁹Be, ¹²C, ¹⁶O, ²⁸Si, ⁴⁰Ca targets. A modification of a standard attenuation technique was used. Details of the experimental design are presented.</p><p>Experimental uncertainties were 2-3% for p, 3% for d and 3-10% for ^3,4He. </p><p>A strong forward peaking of the reaction products was observed for ^3,4He. Therefore the standard reaction cross section measurement technique was not applicable for these projectiles. The forward peaking is also responsible for the increase of experimental uncertainties for these projectiles. The forward peaking of the reaction products is not known for other projectiles and has also not been observed with ^3,4He at different - both higher and lower - energies. Possible explanations for this phenomenon are discussed.</p><p>Optical model calculations of the reaction cross sections are in good agreement with the measured values.</p><p>The measurements were performed with beams from the Gustav Werner cyclotron at the The Svedberg Laboratory, Uppsala.</p>

<p>Fission is the most important nuclear reaction for society at large today due to its use in energy production. However, this has raised the problem of how to treat the long-lived radioactive waste from nuclear reactors. A radical solution would be to change the composition of the waste into stable or short-lived nuclides, which could be done through nuclear transmutation. Such a concept requires accelerator-driven systems to be designed, where those for transmutation are reactor hybrids. This thesis is a contribution to the knowledge base for developing transmutation systems, specifically with respect to the computational modeling of the underlying nuclear reactions, induced by the incident and secondary particles. Intermediate energy fission cross sections are one important type of such data. Moreover, they are essential for understanding the fission process itself and related nuclear interactions. </p><p>The experimental part of this work was performed at the neutron beam facility of the The Svedberg Laboratory in Uppsala. Fission cross sections of ²³⁸U, ²⁰⁹Bi, ^natPb, ²⁰⁸Pb, ¹⁹⁷Au, ^natW, and ¹⁸¹Ta were measured for neutrons in the range <i>E</i>_n = 30-160 MeV using thin-film breakdown counters for the fission fragment detection. A model was developed for the determination of the efficiency of such detectors. </p><p>A compilation of existing data on proton-induced fission cross sections for nuclei from ¹⁶⁵Ho to ²³⁹Pu was performed. The results, which constitute the main body of information in this field, were added to the worldwide EXFOR database. The dependences of the cross sections on incident energy and target nucleus were studied, which resulted in systematics that make it possible to give estimates for unmeasured nuclides. </p><p>Nucleon-induced fission cross sections were calculated using an extended version of the cascade exciton model. A comparison with the systematics and the experimental data obtained in the present work revealed significant discrepancies. A modification of the model was made that significantly improved the predictions. </p>

Fission is the most important nuclear reaction for society at large today due to its use in energy production. However, this has raised the problem of how to treat the long-lived radioactive waste from nuclear reactors. A radical solution would be to change the composition of the waste into stable or short-lived nuclides, which could be done through nuclear transmutation. Such a concept requires accelerator-driven systems to be designed, where those for transmutation are reactor hybrids. This thesis is a contribution to the knowledge base for developing transmutation systems, specifically with respect to the computational modeling of the underlying nuclear reactions, induced by the incident and secondary particles. Intermediate energy fission cross sections are one important type of such data. Moreover, they are essential for understanding the fission process itself and related nuclear interactions. The experimental part of this work was performed at the neutron beam facility of the The Svedberg Laboratory in Uppsala. Fission cross sections of 238U, 209Bi, natPb, 208Pb, 197Au, natW, and 181Ta were measured for neutrons in the range En = 30-160 MeV using thin-film breakdown counters for the fission fragment detection. A model was developed for the determination of the efficiency of such detectors. A compilation of existing data on proton-induced fission cross sections for nuclei from 165Ho to 239Pu was performed. The results, which constitute the main body of information in this field, were added to the worldwide EXFOR database. The dependences of the cross sections on incident energy and target nucleus were studied, which resulted in systematics that make it possible to give estimates for unmeasured nuclides. Nucleon-induced fission cross sections were calculated using an extended version of the cascade exciton model. A comparison with the systematics and the experimental data obtained in the present work revealed significant discrepancies. A modification of the model was made that significantly improved the predictions.

Reaction cross sections were measured for protons at 65.5 MeV, for deuterons at 37.8, 65.5, 97.4 MeV, for 3He at 96.4, 137.8, 167.3 MeV, and for 4He at 69.6, 117.2, 163.9 and 192.4 MeV. Targets were 9Be, 12C, 16O, 28Si, 40,48Ca, 58,60Ni, 112,116,118,120,124Sn and 208Pb. 48Ca and 118Sn targets were used only for some of the measurements. Rest of the targets have been measured for all energies and projectiles but 4He at 69.6 MeV where reaction cross sections were measured for 9Be, 12C, 16O, 28Si, 40Ca targets. A modification of a standard attenuation technique was used. Details of the experimental design are presented. Experimental uncertainties were 2-3% for p, 3% for d and 3-10% for 3,4He. A strong forward peaking of the reaction products was observed for 3,4He. Therefore the standard reaction cross section measurement technique was not applicable for these projectiles. The forward peaking is also responsible for the increase of experimental uncertainties for these projectiles. The forward peaking of the reaction products is not known for other projectiles and has also not been observed with 3,4He at different - both higher and lower - energies. Possible explanations for this phenomenon are discussed. Optical model calculations of the reaction cross sections are in good agreement with the measured values. The measurements were performed with beams from the Gustav Werner cyclotron at the The Svedberg Laboratory, Uppsala.

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