Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis--University of California, Berkeley, 1959. / "Physics and Mathematics" -t.p. Includes bibliographical references (p. 63-64).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The radionuclide 75Se (T1/2= 119.8 days) decays to the stable isotope 75As by 100 % electron capture. Applications of this radioisotope include its use as a radiotracer in agricultural investigations and as a potential irradiation source in high-activity brachytherapy. The application of this isotope as a radiotracer in clinical studies has been limited due to a lack of availability of carrier-free 75Se. In this study the excitation functions for the production of carrier-free 75Se, other selenium radioisotopes and radiocontaminants produced via natBr(p,x) nuclear reactions were measured by the use of the stacked foil technique. Three separate stacks were assembled from aluminium and copper monitor foils and potassium bromide tablets. The latter were prepared by pressing KBr salt into tablets with a thickness of 200 mg/cm2 and a diameter of 20 mm, which are sandwiched between thin Al foils. The monitor foils, with a diameter of 19 mm, were punched from foil sheets. The stacks were irradiated at proton beam energies of 100.9 MeV, 66.8 MeV and 40.4 MeV respectively at the National Accelerator Centre cyclotron facility. After bombardment the KBr tablets were sealed in plastic bags to prevent the loss of any krypton isotopes produced. The gamma-ray spectra of the induced radioactivity in each of the target foils were recorded by means of a Ge-detector coupled with a SILENA 16-k multichannel analyser. The measured excitation functions for the above-mentioned isotopes are presented. Where applicable the cross-section values are compared with previously published values, while the others are presented as new data. Theoretical calculations by means of the computer code ALICE (IPPE) were also done for comparison. / AFRIKAANSE OPSOMMING: Die radionuklied 75Se (T1/2= 119.8 dae) verval deur 100 % elektronvangs na die stabiele isotoop 75As. Toepassings vir hierdie radioisotoop sluit in sy gebruik as 'n radiospoormiddel in landbou-ondersoeke en as 'n potensiële stralingsbron in hoë aktiwiteit bragiterapie. Die aanwending van hierdie isotoop as 'n radiospoorder in kliniese studies word egter beperk deur die gebrek aan beskikbaarheid van draer-vry 75Se. In hierdie studie is die opwekkingskrommes vir die produksie van draer-vry 75Se, ander selenium radioistope en radiokontaminante bepaal deur die natBr(p,x) kernreaksies te meet met behulp van die foelie-stapel metode. Drie verskillende stapels, bestaande uit aluminium- en koper-monitor foelies en kalium-bromied tablette, is saamgestel. Laasgenoemde is voorberei deur KBr sout saam te pers tot tablette met 'n dikte van 200 mg/cm2 en 'n deursnit van 20 mm en wat omsluit is met dun Al-foelies. Die monitor-foelies, met 'n deursnit van 19 mm, is gepons uit foelieplate. Die stapels is bestraal met protonbundels met energieë van onderskeidelik 100.9 MeV, 66.8 MeV en 40.4 MeV by die Nasionale Versneller Sentrum, Faure, se siklotron-fasiliteit. Na bombardering is die KBr tablette verseël in plastieksakkies om verliese van enige vervaardigde kripton isotope te verhoed. Die gamma-straal spektra van die geinduseeerde radioaktiwiteit in elke teiken is opgeneem met behulp van 'n Ge-detektor wat gekoppel was aan 'n SILENA 16-k multikanaal-analiseerder. Bogenoemde isotope se gemete opwekkingskrommes word aangebied. Waar van toepassing word die kansvlakwaardes vergelyk met vorige gepubliseerde waardes terwyl ander aangebied word as die eerste data bekend. 'n Vergelyking met die teoreties berekende kansvlakwaardes van die rekenaar kode ALICE (IPPE) word ook gedoen.

A delayed-coincidence spectrometer system was used to measure nuclear lifetimes in the picosecond region by the centroid-shift method. Timing signals were derived from two plastic scintillators; each plastic scintillator was located within a specially constructed NaI(Tl) detector. Each NaI(Tl) detector was used to detect the gamma ray which Compton scattered from an associated plastic scintillator. Energy identification was achieved by summing the signals from the plastic and the NaI(Tl) detectors to give full energy gamma-ray photopeaks. To test the effectiveness of the system, the half-lives of the first excited state of 134Ba and the first and second excited states of 144Nd were measured. The half life of the first excited state of 134Ba was measured as 4.4 - 1.3 psec; this result is in agreement with a previously reported value of 5.0 t 1.5 psec. The half-life for the first excited state of 144Nd was determined to be 1.5 ± 1.0 psec while the half-life for the second excited. state of 144Nd was determined to be 5.1 ± 0.5 psec. The half-life value for the second excited state of 144Nd is in disagreement with previously reported values of 21 ± 2 psec and 100 ± 30 psec which were also determined by delayed-coincidence methods. Although the result of 1.5 ± 1.0 psec for the first excited state lifetime differed from a previous result of 3.4 * 0.1 psec obtained by Coulomb excitation, this difference was due to the inability of the present spectrometer system to resolve the 618- and 696-keV gamma rays of 144Nd. It is concluded that a lower lifetime limit measurable with the system described in this study is about one picosecond, provided that the gamma rays can be resolved in the sum energy spectrum of the plastic and NaI(T1) detectors.Ball State UniversityMuncie, IN 47306

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