Laboratory of Nuclear Spectroscopy
The Laboratory of Nuclear Spectroscopy was part of the former Department of Nuclear Spectroscopy. The Department of Nuclear Spectroscopy was founded in 1972 by Prof. Zh. Zhelev (1923-1988), one of the pioneers in the high resolution alpha-spectroscopy. Since that time the activity of the Department was concentrated in the field of nuclear physics. It covered many topics connected with nuclear structure physics and applications. The basic experimental equipment included two beta- spectrometers , mass-separator, ion-implantator etc. Major part of the fundamental research was performed in close collaboration with the Joint Institute for Nuclear Research in Dubna. The properties of transitional nuclei (Sm, Eu, La etc.) have been experimentally investigated. Gamma-spectroscopy methods have been applied to study the performance of fuel elements in the Nuclear Power Plant Kosludui. Diverse nuclear equipment has been also developed.
In 1989 the former Department was transformed to Department of Nuclear Physics and Astrophysics. The head of the Department was Acad. W. Andrejtscheff (1941-2001), who will be remembered for his pioneering investigations on short-lived isomers. His main interests was devoted to the structure of low-lying excited states in atomic nuclei. In collaboration of FZ-Rossendorf he developed a method for precise life-time measurements. He had also experience in studying the properties of low-lying E1 transitions in atomic nuclei. Based on the scientific contacts of Acad. W. Andrejtscheff the main part of the research in the field of nuclear physics have been performed in close collaboration with scientific teams of large research centers as the ILL-Grenoble, the Universities of Cologne and Stuttgart. The main results at that time were the improvement of the method for life-time measurements and the correlation between beta- and gamma- deformation in atomic nuclei. Acad. W. Andrejtscheff has proposed new systematic of low-lying E1 transitions where the importance of core polarization effects was first established. This new interpretation was done within the quasiparticle-phonon model.
Another field of activity in 90-ties was connected with the development of the quasiparticle-phonon model. The model has been established in the second half of 70-ties in Dubna. The team of Laboratory of Nuclear Spectroscopy has enlarged the phonon basis of the model including three phonon components and the continuum effects. It permitted to predict the properties of the low-lying 1- states and to study the process of nucleon emission of highly excited states.
The staff of the Department of Nuclear Physics and Astrophysics has taken the main part of the organization of the International School of Nuclear Physics, Neutron Physics and Nuclear Energy. The school was founded in 1973 by Prof. Zh. Zhelev to stimulate the activity of the nuclear science community. In 90-ties because of the supervision of Acad. W. Andrejtscheff the status of the school was changed and today the stile of the school is more close to the study conference than to the school. In 2003 will be held the XV edition of the school.
In 2002 the Department of Nuclear Physics and Astrophysics was reorganized. Today, the activity connected with nuclear physics is associated to the Direction of Nuclear Physics of the Institute. This Direction consists of 4 Laboratories. The largest one is Laboratory of Nuclear Spectroscopy. The research topics of the Laboratory cover wide field of investigation including nuclear theory, experimental nuclear physics and applications.
The main results of theory are connected with the developing of qusiparticle-phonon model. Recently, the properties of low-lying isovector mode have been calculated. It gives opportunity for microscopic description of so called mixed-symmetry states in atomic nuclei. The properties of highly excited pygmy resonance are calculated. The theoretical results are done in collaboration with the research groups of Universities of Naples and Giessen , IPN-Orsay, BLTP-Dubna.
In the experimental field, the nuclei around mass number A=100 have been studied, with interest focused on new phenomena like high-K isomers, magnetic rotation etc. Recent experimental investigations include the study of gamma-scattering and gamma-absorption processes in medium and heavy nuclei, thus revealing the structure of low-lying states. A new direction of experimental study will be concentrated on the process of photo-fission. The experimental results are obtained in collaboration with FZ-Rossendorf and University of Stuttgart.
The new field of activity of the Laboratory includes the investigation of radioactive contaminated terrain and soils. Radiological investigation has been done in the Buhovo region. The study includes: geodetic work, gamma-dose mapping, measuring of radon exhalation and radon concentration. The total investigated area is around 3.6 x 106 m2 . The evaluation and the interpretation of the data are in progress. The radiological measurements and analysis also are done within the project “Engineering Works for Closing of Uranium Mines in Eleshnisa and Dospat”.
|Orlin Bogomilov Jordanov||Assistant Professor, Ph.D.|
|Galina Lazarova Asova||Assistant Professor, Ph.D.||5561|
|Nikolay Vasilev Gutev||Physicist, Ph.D.|
Development and refinement of nuclear models
The microscopic model of atomic nuclei – quasiparticle-phonon model (QPM) – was developed in collaboration with Bogoliubov Laboratory of Theoretical Physics (Dubna). Within the model new type of electromagnetic transitions – “boson” forbidden transitions – were studied. It is shown that the transitions dominate in the decay of low-lying 1- excited states and also are the important signature of mixed-symmetry states. The members of Laboratory of Nuclear Spectroscopy did the systematic of the low-lying E1 transitions.
- The influence of the GDR on the low-energy E1 transitions in spherical nuclei.
- Microscopic structure of low-lying positive patity states in nuclei near shell closure.
- New evidance for the E1 core polarization in spherical nuclei.
- Boson forbidden low-energy E1 transitions in spherical nuclei.
Gamma-spectroscopy of selected nuclei
Complete gamma-spectroscopy investigations on selected nuclei are performed, including mesurements of high-resolution single gamma-spectra, gamma-gamma coincidences, excitation functions, gamma-gamma angular distributions, lifetimes etc., as well as, interpretation of the experimental results in the framework of contemporary nuclear models.
- Collective vibrational bands built on two-quasiparticle exitations in Te isotopes.
- Level stucture and transition probabilities in 140Ce.
- Neutron core exitations in the N=50 nucleus 89Y.
Investigation on the structure of the even-even, odd and odd-odd transitional nuclei
A unified treatment of the even-even, odd, and odd-odd transitional nuclei is undertaken in which the physical states of the odd nuclei are used as a basis building blocks (see fig.1) - 1. The model is conceived using an evidence derived from a specific experimental systematic and is based on particle - anharmonic core coupling calculations of the wave functions of the correspondent odd nuclei (see for instance - 3.)
- R.V.Jolos, M.M.Michailova, Comptes rendus de l’Acad.bulg. des Sciences, v.49 (1996) p.33.
- M.M.Michailova, JINR Report, E6-88-578, Dubna (1988)
- M.M.Michailova, Comptes rendus de l’Acad.bulg. des Sciences, v.52(1999) p.23.
High-resolution gamma-spectroscopy for environmental protection
An essential part of the Laboratory activities in the last years was connected with scientific support of the remedial measures undertaken in Bulgaria after the closing of the uranium industry. Thereby the methods of the high-resolution gamma-ray spectroscopy were widely applied. Solving the specific problems in Bulgaria a fruitful cooperation with IAF-Radioökologie Dresden has been established. In the frame of these activities detailed radiological investigations have been performed some years ago in the Buhovo region. A PHARE Project "Engineering works for closing of the uranium mines at Eleshnitsa and Dospat" (see Picture) is going on. An expert team of the Laboratory is responsible for the radiological measurements performed in the frame of the Radiation Protection Program executed during the implementation of the project. In addition to these activities the Laboratory started several systematical investigations in the field of the environmental radioactivity. Some of them are performing in cooperation with the Physics Department of the Plovdiv University.