- Interaction between Nucleus and Electromagnetic Field -

 

Throughout this seminar, students are supposed to acquire deeper insight and interdisciplinary vision by performing experiments on nuclear electromagnetic moments and hyperfine interaction in nuclear levels. This seminar consists of two parts: theory and experiment. In the theory part, students will study basic nuclear structure and interaction between nucleus and electromagnetic field. In the experimental part, students study experimetal techniques required to detect gamma rays and to analyse them. This seminar is performed at Yoshida campus (Kyoto) and main experiment is done at Institute for Integrated Radiation and Nuclear Science (Kumatori, Osaka).

Two experiments, PAC and Mössbauer spectroscopy, are concerned. Students will study both methods and select either as a main experiment.

Institute for Integrated Radiation and Nuclear Science, Kyoto Univ. (Kumatori, Osaka)

PAC(Perturbed Angular Correlation) is known as a useful technique applicable to measure the electromagnetic moments of intermediate states with relatively long lifetime(typically ~100 ns). In this technique, the precession of nuclei in an intermediate state under a well defined electromagnetic field is observed through the angular correlation of gamma-gamma cascade accompanied by this intermediate state as a function of time.

In this experiment course, the magnetic moment of 245 keV state of ¹¹¹Cd(I^π=5/2⁺, T_1/2=85 ns) is measured and the nuclear structure is discussed in comparison with the single particle model.

There are some nuclides with the energy levels of the order of keV (ex. 14.4 keV for the first excited state of ⁵⁷Fe), which can be resonantly excited using a gamma ray source of the same level. This phenomenon is called Mössbauer effect that is realized when the gamma ray is emitted and absorbed without recoil. Since the nuclear energy levels are affected by surrounding electronic states, known as hyperfine interaction, precise observation of the energy spectrum allows us to obtain the information of nuclear parameter and/or local electronic state around the nucleus. In this seminar, using a material with well-known electronic states, the nuclear magnetic moments of excited and ground state of ⁵⁷Fe are evaluated.

To observe the energy spectrum of the nuclear level, the energy of gamma ray is shifted by Doppler effect using a source vibrated mechanically with a transducer.

A typical Mössbauer experimental setup.