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Kernfisiese metings om 'n kilocurie 60Co-bron
Thesis(Ph.D.)--Stellenbosch University, 1972.
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| Language: | af_ZA |
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Stellenbosch : Stellenbosch University
2012
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| _version_ | 1867614133272182786 |
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| access_status_str | Open Access |
| author | Visser, Christiaan Jacobus |
| author2 | Mouton, W. L. |
| author_browse | Mouton, W. L. Visser, Christiaan Jacobus |
| author_facet | Mouton, W. L. Visser, Christiaan Jacobus |
| author_sort | Visser, Christiaan Jacobus |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis(Ph.D.)--Stellenbosch University, 1972. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/54330 |
| institution | Stellenbosch University (South Africa) |
| language | af_ZA |
| last_indexed | 2026-06-10T12:47:10.728Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2012 |
| publishDateRange | 2012 |
| publishDateSort | 2012 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/54330 Kernfisiese metings om 'n kilocurie 60Co-bron Visser, Christiaan Jacobus Mouton, W. L. Stellenbosch University. Faculty of Science. Dept. of Physics. Nuclear reactions Dissertations -- Physics UCTD Thesis(Ph.D.)--Stellenbosch University, 1972. ENGLISH ABSTRACT: (Formulas did not scan well. See theses abstract in the PDF document p. 90) The major part of the thesis is devoted to a study of the energy spectrum of a 5000 Ci 60co source of finite dimensions. Measurements of the exposure dose distribution at various distances from the source have also-been performed. The determination of mean lifetimes of nuclear states utilizing nuclear resonance fluorescence techniques and the 60co source is also included. This parameter is an important one in the calculation of the shape and intensity of the emitted 60co spectrum. In chapter 1 a general discussion and motivation for the project is followed by a brief introduction to ionization chamber dosimetry, nuclear resonance fluorescence and elastic scattering of gamma radiation from atoms. The dose distribution, as measured with a Baldwin Farmer dosimeter in roentgen units, is discussed in chapter 2. The irradiation enclosure, the source (which is encapsulated in stainless steel) and the measurements are described. Measurements of the dose distribution were performed (i)on and above a flat circular table with the source on the axis of thetable at different heights above the table surface and (ii) in the space surrounding the source, hoisted to its maximum height, with an empty irradiation chamber. Regression coefficients for the linear relationships (log· as a function of log r) obtained from the measurements are given for various source dosimeter configurations. Standard measurements of the exposure dose at a horizontal distance, 60 cITT froITT the source in its highest position, gives value of approximately 121 less than the value specified by the manufacturers This is mainly due-to the attenuation caused by the stainless steel capsule surrounding the source. Finally an illustration of a practical application of the dose distribution measurements is given. An unique method for the determination of the continuum of energy degraded photons emitted by the source, is discussed in chapter 3. This continuum is mainly due to Compton scattering in the source itself and the capsule surrounding it. The nuclear resonance fluorescence effect is used to measure the intensity and shape of the spectrum for the energy region 0,478 to 1,265 MeV. Resonant scatterers containing the nuclides 7Li, 63cu, 65cu, 27Al, 45sc, 59co, 35c1 and 31P were used and the resonantly scattered radiation was detected by a 20" cm3 Ge(Li) detector. The experimental set up, procedure followed and calculations are discussed in detail. The results are summarized in Table 3.2 and Figure 3:4 An average value of 108 photons per electronvolt per second is obtained for the energy region 0,478 to 1,265 MeV. (Approximately 40% of the total curie-content.) In chapter 4 the determination of the intensity of theprimary 1,17 and 1,33 MeV photons emitted by the source, is discussed. Elastic scattering (mainly Rayleigh and Thomson) from copper, arsenic, cobalt, zinc, phosphorous, aluminium and hexachloro-ethane were observed to provide average values of (a) (b,94 ± 0,13) x 1014 photons of energy 1,17 MeV per second and (b) (1,01 ± 0,12) x 10 14 photons of energy 1,33 MeV per second. This amounts to 62% of the total curie-content. The relevant formulae as well as the calculation of differential cross sections for elastic scattering for low Z (Z ~ 33) atoms are also discussed. The results obtained are compared with those of chapters 2 and 3. Three methods for the determination of mean lifetimes T of nuclear energy levels are discussed in chapter 5. The methods, which involve the observation of nuclear resonance fluorescene are the following: I • (1) The selfabsorption technique, where the incident spectrum N(iEr), detection efficiency and angular distribution of the scattered radiation need not to be known. (2) Determination of the incident spectrum making use of elastic scattering from lead (the angular distribution must be known, but not the detection efficiency). ( 3) Observation of nuclear resonance fluorescence in the direct beam, from the source, making use of the determined shape of the energy spectrum of the radiation from the source. (This method relies on accurate knowledge of the detection efficiency of the spectrometer and angular distributions as well as lifetimes and spins of the levels used to determine the continuum.) The second and third methods are new in the sense that N{E~) is obtained in a unique manner. The results are summarized in the following table: (Due to two possible (N(El')~h) and N(Er)~ 1 )) for the continuum of the third method, 2·values are given for T for.each energy level.) Energy T Method Nuclide (MeV·) (xl0-12 s) (1) 64zn 0,99 1,9 ± 1,2 (2) 64zn 0,99 2,0 ± 0,3 66zn 1,'04 2,3 ± 1,0 68zn 1,08 l,0 ± 0,3 (3) 64zn 0' ,99 1,7 ± 0,7 (a) 2,9 ± 1,2 (b) 66zn .1,04 1,8 ± 0,8 (a) 3,0 :!" 1,3 (b) 68zn 1,08 1,8 :!" 1,6 (a) 2,9 ± 2,5 (b) 75As 0,865 1,2 ± 0,3 (a) 1,8 :!" 0,4 (b) 1,075 o' 24 +- O, 03 (a) · 0,39 ± 0,06(b) (a): N(E j(l) r V An assessment of the three methods is also given. Doctoral 2012-08-27T11:36:29Z 2012-08-27T11:36:29Z 1972-03 Thesis http://hdl.handle.net/10019.1/54330 af_ZA Stellenbosch University 124 pages : illustrations. application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Nuclear reactions Dissertations -- Physics UCTD Visser, Christiaan Jacobus Kernfisiese metings om 'n kilocurie 60Co-bron |
| title | Kernfisiese metings om 'n kilocurie 60Co-bron |
| title_full | Kernfisiese metings om 'n kilocurie 60Co-bron |
| title_fullStr | Kernfisiese metings om 'n kilocurie 60Co-bron |
| title_full_unstemmed | Kernfisiese metings om 'n kilocurie 60Co-bron |
| title_short | Kernfisiese metings om 'n kilocurie 60Co-bron |
| title_sort | kernfisiese metings om n kilocurie 60co bron |
| topic | Nuclear reactions Dissertations -- Physics UCTD |
| url | http://hdl.handle.net/10019.1/54330 |
| work_keys_str_mv | AT visserchristiaanjacobus kernfisiesemetingsomnkilocurie60cobron |