Department of Physics

In-beam spectroscopy

Home page of the JYFL Gamma Group

Nuclear shapes and excitations

Personnel

Rauno Julin, professor, the group leader
Sakari Juutinen, senior research assistant
Peter Jones, senior researcher
Paul Greenlees, academy researcher
Päivi Nieminen, post-doctoral researcher
Markus Nyman, PhD student
Panu Rahkila, PhD student
Juha Sorri, PhD student
Steffen Ketelhut, PhD student
Pauli Peura, PhD student

Introduction

Nuclei present us with one of Nature's most intricate examples of the interplay between single-particle motion, collectivity and pairing in a quantum many-body system. This interplay is seen as a rich tapestry of coexisting nuclear shapes and other exotic excitations. Nuclear gamma-ray and electron-spectroscopic methods used in conjunction with heavy ion beams form the backbone for experimental studies of these stuctures. The in-beam spectroscopy group has been at the forefront in the development of the recoil-decay tagging (RDT) technique for studies of exotic and heavy nuclei. These studies invlove the coupling of arrays of germanium or silicon detectors to the gas-filled recoil separator RITU. In 1994, the co-operation between British physicists and the JYFL in-beam group led to an important agreement about the use of the British TESSA gamma-ray detector array and the SACRED electron spectrometer, associated electronics and data-acquisition system at JYFL. This foreign investment was vital for a quick start of the high-quality in-beam spectroscopy research at the JYFL accelerator laboratory. This led to the coupling of the DORIS array of TESSA detectors to RITU for the first RDT studies at JYFL. The success of these studies led to the construction of the joint-European JUROSPHERE array, which was used in several campaigns from 1996-2001. Building upon these successes, the group (in collaboration with the University of Liverpool) extended the RDT technique using the SACRED electron spectrometer at the target position of RITU. In 2003, following the break-up of the EUROBALL spectrometer, the JUROGAM array of germanium detectors was constructed. The array consists of 43 detectors from EUROBALL and the UK-France loan pool. Combined with RITU it is one of the most powerful systems in the world for gamma-ray spectroscopy of exotic nuclei. Further foreign investment came in 2002 with the addition to the RITU focal plane of the U.K. GREAT spectrometer and novel Total Data Readout (TDR) data acquisition system, again improving the spectroscopic power of the combined system.

Highlights

As can be seen from the figure below, the work of the JYFL in-beam spectroscopy group is focussed on the study of exotic nuclei close to the proton dripline and on the structure of heavy (transfermium) elements. All the results discussed below have been obtained at JYFL in collaboration with a large number of institutes.

Heavy Elements

Recent highlights in the spectroscopy of heavy elements have been the observation of rotational bands in the odd-mass nuclei 251Md, 253No and 255Lr - the latter being the heaviest nucleus ever to be studied in-beam. These experiments were performed using the JUROGAM array of germanium detectors. Also of note from this region was the study of 254No using the SACRED electron spectrometer, revealing the presence of high-K bands.

Light Pb Region

Studies of shape coexistence effects in the light Pb and Po region has been one of the cornerstones of the in-beam spectroscopy group programme. A large number of experiments have been carried out using various germanium arrays coupled to RITU, with production cross sections at the 200nb level well within the spectroscopic limit. Recent highlights have been the first observation of excited states in 182Pb and non-yrast states in 186Pb. A study of 190Po revealed evidence for the onset of prolate deformation in the Po isotopes. The addition of the Cologne plunger device to JUROGAM and RITU has enabled lifetime measurements to be made in very neutron-deficient nuclei for the first time. The so-called RDDS technique has so far been employed in studies of 186,188Pb and 194Po, yielding further insight into the mixing and coexistence of different shapes in these nuclei.

Proton-Emitting Nuclei

The group is also active in the study of proton-emitting nuclei. To date, experiments have been performed to investigate the properties of 171Au, 146Tm, 161Re and 166,167Ir. Further studies of this type are planned for the near future.


Publications: 


Future Plans

Following the recent successes with the JUROGAM array and the SACRED electron spectrometer, the group (in collaboration with a number of U.K. institutes) intends to combine the two spectrometers to form a device with the working title "SAGE". The device will beunique, and capable of simultaneous measurements of gamma-rays and conversion electrons emitted in the decay of heavy exotic nuclei. In order to further lower the limits for spectroscopy, a collaborative effort is underway to instrument the target position germanium or silicon detectors with digital electronics. This will allow the use of higher counting rates and thus higher beam intensities, effectively reducing the cross section limit attainable within a given measurement time. The group is also involved in the development of instrumentation for the next generation radioactive beam facilities FAIR and EURISOL, and also participates in the AGATA project to develop an "Advanced Gamma-Ray Tracking Array".