Influence of reaction channel on the isomeric cross-section ratio
Summary The influence of reaction channel on the isomeric cross-section ratio was investigated by analysing the experimental data on the reactions 52Cr(p, n)52m,gMn, 52Cr(3He, t)52m,gMn, 54Fe(d, α)52m,gMn, 54Fe(n, t)52m,gMn and 54Fe(3He, α p)52m,gMn over the incident particle energy range extending up to 35 MeV. The influence is most pronounced when the channels differ widely, for example (p, n) and (3He, t) processes, i.e. when the reaction mechanisms are different. The nuclear model calculational code EMPIRE-II described the isomeric cross-section ratio rather well in the case of a simple nucleon emission reaction, but not when complex reaction channels were involved.
Isomeric cross-section ratio for the formation of 58Com,g in neutron, proton, deuteron, and alpha-particle induced reactions in the energy region up to 25 MeV.
Excitation functions were determined for {sup 58}Fe({ital p},{ital n}){sup 58}Co{sup {ital m}}, {sup nat}Fe({ital d},{ital xn}){sup 58}Co{sup {ital m}}, {sup 55}Mn({alpha},{ital n}){sup 58}Co{sup {ital m}}, and {sup 59}Co({ital n},2{ital n}){sup 58}Co{sup {ital m}} reactions from the respective thresholds to 14.12 MeV in work with protons, 12.97 MeV with deuterons, 13 MeV with neutrons, and 25.52 MeV with alpha particles. The radioactivity of the activation product {sup 58}Co{sup {ital m}}({ital T}{sub 1/2}=9.15 h) was determined by high resolution {gamma}-ray and x-ray spectrometry. Using the present {sigma}{sub {ital m}} results and the ({sigma}{sub {ital m}}+{sigma}{sub {ital g}}) data reported earlier, the isomeric cross-section ratio {sigma}{sub {ital m}}/({sigma}{sub {ital m}}+{sigma}{sub {ital g}}) was determined for each reaction. Statistical model calculations taking into account the precompound effects were performed for the above-mentioned four reactions as well as for the {sup 58}Ni({ital n},{ital p}){sup 58}Co{sup {ital m},{ital g}} process. A consistent set of model parameters was used. The isomeric cross-section ratio for the pair {sup 58}Co{sup {ital m},{ital g}} strongly depends on the level scheme and branching ratios of the known levels of {sup 58}Co. Different reactions produced different angular momentum distributions of the compound nucleus, resulting in different isomeric cross-section ratio at the samemore » excitation of the compound nucleus. The ratio was found to be relatively high for target nuclei with high spin values. {copyright} {ital 1996 The American Physical Society.}« less
Fieldwork in geography teaching: A critical review of the literature and approaches
Abstract Virtually all lecturers in geography recognise the importance of fieldwork as a vital mode of teaching in the subject. This paper draws on material produced as part of a HEFCE review of teaching and learning in the field and assesses the implications of recent changes in higher education for field studies in geography. The literature on the development of, and recent changes in, fieldwork practice is reviewed and assumptions about appropriate forms of teaching and assessment are challenged. The need for carefully integrated preparation of project‐orientated fieldwork is stressed and the importance of debriefing and feedback after field visits is emphasised. Various suggestions for guidelines on good practice are presented. Finally, a range of future issues and problems in fieldwork is identified and discussed.