Modifications to the University of British Columbia Van de Graaff Generator have provided for the production of beams of singly-charged alpha particles. Alterations have been made to the ion source, analysing magnet, and reverse electron beam energy stabilizing system. Well-focussed beams of 10 to 15 microamps resolved of singly-charged alpha particles were available, at energies up to above 1.2 Mev.
The nuclear reaction Li⁷ (∝,γ)f) B¹¹ was studied by bombarding targets of lithium metal evaporated onto copper backings. The gamma rays from the decay of states of B¹¹ were observed with NaI (Tl) scintillation counters and associated electronic equipment, including a 30 channel Marconi Pulse Amplitude Analyser.
In the range of alpha particle energies available, three resonances were known for the capture of alphas by Li⁷ , forming states of B¹¹ at 9.28, 9.19 and 8.92 Mev. The decay of these states included cascades through lower excited states, in particular one at 4.46 Mev.
The widths of these resonances were measured respectively as 8, 1 and <1 kev, in laboratory co-ordinates. The second of these values is significantly lower than previously reported. Measurements were also made of the yields of gamma radiation, and the angular distributions of certain gamma rays from each resonance. Experimental results and calculations have been compared with appropriate theoretical values to obtain information on the angular momenta and parity of certain of the B¹¹ states. The zero spin of the incoming alpha particles puts a useful limitation on the input channel spin.
Assignments suggested by the data were as follows. For the 4.46 Mev state, 5/2⁻ ; for the 9.28 Mev state, 5/2⁺. Data for the 9.19 Mev state cannot distinguish between 3/2⁻~and 5/2⁻ , while for the 8.92 Mev state, the angular momentum would be restricted to 3/2 or 5/2 if the state was formed by the capture of p-wave alphas, but the parity was not determined.
These results indicate that the states of B¹¹ are certainly more complex than the simple single-particle picture proposed by Jones and Wilkinson (1952), which is inadequate to describe the present results. Further investigation is invited. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/40612 |
| Date | January 1957 |
| Creators | Phillips, Gilbert James |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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