Speaker
Mr
Yusuke Kaneya
(Graduate School of Science and Engineering, Ibaraki University / Japan Atomic Energy Agency)
Description
The first ionization potential (IP) directly reflects a valence electronic configuration influenced by relativistic effects which are significantly noticeable for heavy elements. Information on IP of heavy elements, therefore, gives us a better understanding of relativistic effects. IPs of heavy actinides with atomic number Z > 100, however, have not been measured by conventional techniques, such as resonance ionization mass spectrometry (RIMS), because these elements are only available in non-weighable quantities down to the one-atom-at-a-time scale. This condition forces us to call for a different experimental approach.
Here, we have focused on a surface ionization process. Since the surface ionization process takes place between an atom and a metal surface, this method is applicable to one-atom-at-a-time scale experiments. In fact, we ionized and mass-separated short-lived isotopes using the surface ionization method installed in the JAEA-ISOL system [1]. Further improvement of the surface ionization type ion-source has been recently applied to measure the IP of lawrencium (Lr, Z = 103). 27-s 256Lr produced in the 249Cf + 11B reaction was successfully ionized [2]. The IP measurement of Lr is now under way.
In this work, we measured ionization efficiencies of various short-lived lanthanides and evaluated their IPs, as a test experiment for measurement of IPs of heavy actinides.
Short-lived lanthanides, 143mSm, 143Eu, 148mTb, 154Ho, 157Er, and 165Yb, were produced by the irradiation of a 67.9- MeV 11B4+ beam delivered from the JAEA tandem accelerator on 136Ce / 141Pr / 159Tb and 142Nd / 147Sm / natEu targets. Short-lived 168Lu was also produced in the reaction of 162Dy with a 11B4+ beam. Nuclear reaction products recoiling from the targets were transported to the ion-source of the JAEA-ISOL set up by a He/CdI2 gas-jet transport system. The products were ionized in the ion-source, accelerated with 30 kV, mass-separated, and collected on an aluminized Mylar tape. The amounts of the collected ions were determined by gamma-ray measurement with a HP-Ge detector. To calculate ionization efficiencies, the amounts of the transported products were also determined by direct collection using a separate catcher system.
IPs of various short-lived lanthanides are evaluated based on the following Saha-Langmuir equation:
α= n_i/n_0 =exp((φ-IP)/kT) ,
where n_i and n_0 indicate the number of ions and that of atoms on a metal surface, respectively. T, k, and φ are the absolute temperature of the metal surface, the Boltzmann constant, and the work function of the specific metal surface, respectively. The experimental ionization efficiency β is expressed by using the α as follows:
β= n_i/(n_0+n_i )= α/(α+1) .
Obtained IP values of short-lived lanthanides with tracer scale atoms were compared with literature values measured with macro-scale amounts of these elements.
[1] S. Ichikawa, et al., Nucl. Instr. and Meth. A 374, 330 (1996).
[2] T. K. Sato, et al., Rev. Sci. Instrum. 84, 023304 (2013).
Primary author
Mr
Yusuke Kaneya
(Graduate School of Science and Engineering, Ibaraki University / Japan Atomic Energy Agency)
Co-authors
Dr
Asai Masato
(Japan Atomic Energy Agency)
Dr
Ichikawa Shinichi
(Nishina Center for Accelerator Based Science, RIKEN)
Dr
Miyashita Sunao
(Graduate school of Science, Hiroshima University)
Dr
Nagame Yuichiro
(Japan Atomic Energy Agency)
Dr
Ooe Kazuhiro
(Institute of Science and Technology, Niigata University)
Dr
Osa Akihiko
(Japan Atomic Energy Agency)
Dr
Sato Nozomi
(Japan Atomic Energy Agency)
Dr
Schädel Matthias
(Japan Atomic Energy Agency)
Dr
Stora Thierry
(ISOLDE, CERN)
Dr
Tetsuya Sato
(Japan Atomic Energy Agency)
Dr
Toyoshima Atsushi
(Japan Atomic Energy Agency)
Dr
Tsukada Kazuaki
(Japan Atomic Energy Agency)
Prof.
V. Kratz Jens
(Institut für Kernchemie, Universität Mainz)
