Keynote Speech by Prof. Andrei Andreyev

Date:16-07-2013   |   【Print】 【close

Speaker Prof. Andrei Andreyev  University of York, UK  Japan Atomic Energy Agency

Topic 1: Shape coexistence in the lead region studied by in-source laser spectroscopy at RILIS-ISOLDE

Time: 4 p.m. July 18th

Venue: Meeting room, on 6th floor,Technology building, IMP


The competition between spherical and deformed nuclear shapes at low energy gives rise to shape coexistence in the region of the neutron-deficient lead isotopes with Z~82 and N~104 [1]. In order to determine to which extent the ground and/or isomeric states of those and neighboring nuclides are affected by this phenomenon, an extended campaign of investigation of changes in the mean-square charge radii is on-going at ISOLDE. By combining the highsensitivity of the in-source laser spectroscopy technique, ISOLDE mass separation and Windmill alpha-decay spectroscopy setup [2], it has been possible to study long isotopic chains of lead [3] and polonium [4], down to N=100 and N=107, respectively, and, recently, thallium isotopic chain down to N=98 [5], see Figure.

In this contribution, we will first present the basics of the resonance laser specttroscopy as applied in shape coexistence studies. This will be followedby the discusson of systematics of charge radii in thallium isotopes [5] together with the first preliminary results of the 2012 campaign at ISOLDE to study long chains of the astatine and lightest gold isotopes [6]. In the gold and astatine cases, next to Faraday cup and Windmill measurements, also the Multi-Reflection Time-of-Flight (MR-ToF) mass separation technique [7] involving the ISOLTRAP collaboration was used.

Figure. Charge radii for Pt-At isotopes. For the sake of clarity the data for different elements are shifted relative to each other by a vertical off-set. Tl data for the light isotopes are from ISOLDE  [5] and Gatchina. Preliminary data for gold and astatine chains are from [6].

[1] K.Heyde and J. Wood. Rev. Mod. Physics 83, 1467 (2011)

[2] A.N. Andreyev et al,, Phys. Rev. Lett. 105, 252502,(2010)

[3] H. De Witte et al., Phys. Rev. Lett. 98, 112502 (2007)

[4] T.E. Cocolios et al., Phys. Rev. Lett. 106, 052503 (2011)

[5] A.N. Andreyev, A. Barzakh et al., IS511 experiment at ISOLDE (2012)

[6] A.N. Andreyev, V. Fedosseev, P. Van Duppenet al., IS534 experiment at ISOLDE (2012)

[7] R. N. Wolf et al.,Nucl. Instr. and Meth. A 686, 82-90 (2012)

Topic 2: Beta-delayed fission: from neutron-deficient to neutron-rich nuclei

Time: 4 p.m. July 19th

Venue:Meeting room, on 6th floor,Technology building, IMP


In the last decade, through technological, experimental and theoretical advances, the situation in experimental low-energy fission studies has changed dramatically. With the use of advanced production and detection techniques,much more detailed fission information can be obtained for traditional regions of fission research and, very importantly,new regions of nuclei have become accessible for fission studies.

The talk will,first of all, give a review of recent low-energy fission experiments in very proton-rich nuclei in the lead region.Results of experiments at ISOLDE(CERN) on the very exotic process of beta-delayed fission (bDF) of the neutron-deficient isotopes178,180Tl [1], 194,196At and 200,202Fr will be presented. The studies of Tl and Atisotopeswere facilitated by the use of the highly-selective Resonance Ionization Laser Ion Source of ISOLDE [2]. As a result of these experiments, a new type and a region of asymmetric fission was established, which includes isotopes 178,180Hg (N/Z=1.22-1.25), in addition to the previously known broad area of asymmetric fission in the heavy actinides with N/Z~1.55-1.6. The much more intense beams of the future ISOL-based facilities will allow in-depth studies of these and neighbouring bDF isotopes. Some examples of complementary experiments to study beta-delayed fission at the velocity filter SHIP (GSI, Darmstadt) will be given.

The talk will also address the prospects of detailed bDF studies in the neutron-rich isotopes, which will become possible with the new generation of ISOL-based facilities and approaches using the multi-nucleon transfer reactions. As some examples, possible bDF studies of very neutron-rich isotopes of Fr, Ac and Pa will be presented.

The recent complementary fusion-fission experiments in the lead region, performed by our collaboration at the tandem of Japan Atomic Energy Agency (JAEA) will also be reviewed.

[1]   A.Andreyev et al., “New type of asymmetric fission in proton-rich nuclei”, Phys. Rev. Lett. 105, 252502 (2010)

[2]   S. Rothe et al., “Measurement of the first ionization potential of astatine by laser ionization

Spectroscopy”, Nature Communications (2013).