Heaviest Atoms Spotlight

First spectroscopic examination of the element Nobelium

The analysis of atomic spectra is of fundamental importance for the understanding of atomic structure. So far, the heaviest elements for optical spectroscopy studies were not available, as they do not yet exist in nature may be artificially produced in ponderable quantities. At atoms of the element Nobelium with the atomic number Z = 102, which it produced at the GSI accelerator, it is scientists managed a look at the internal structure of very heavy atoms to throw.

Using laser spectroscopy, the researchers were able to study individual atoms of element and demonstrate different atomic excitation states. The experiment was the physics under the direction of the department superheavy elements GSI Helmholtz Centre for Heavy Ion Research carried out by an international collaboration, at the Prof. Dr. Thomas Walther from the Institute of Applied Physics of the TU Darmstadtwith his doctoral Felix Lautenschlager and Premaditya Chhetri was involved.

The experiments were performed jointly by scientists at the GSI Helmholtz Centre for Heavy Ion Research, the University of Mainz, the Helmholtz Institute Mainz, Darmstadt Technical University, KU Leuven (Belgium), the University of Liverpool (UK) and the TRIUMF (Vancouver, Canada ) carried out. on their findings, the researchers report in the journal Nature .

Mystery of the internal structure
From most of the currently known elements 118 the energy spectra are known. The elements beyond fermium, called transfermium elements with more than 100 protons in the nucleus and the corresponding same number of electrons in the electron shell, but are not subject to date experimental investigating. But just the relativistic effects, caused by the high speeds at which the electrons move around atomic nuclei with such a high number of protons, and the interactions between the many electrons largely determine the internal structure of atoms. Like all transfermium elements is also Nobelium experimentally very difficult to access. It does not occur in nature and can only be artificial and produce in small amounts. Therefore, its characteristics and the internal structure are largely unknown.

"Our collaboration has succeeded in reducing carry out laser spectroscopy on elements that are heavier than atomic number 100. It was possible to identify for the first time the first excited state and Rydbergserien.This work is extremely challenging, because only a few atoms are produced in fusion reactions, and these must be investigated spectroscopically. Moreover, they are unstable and the energies of the states are insufficiently known. This work actually like the proverbial needle in a haystack search. Such research studies are, however, important to gain insights into the core structure of these heavy elements. "

Prof. Dr. Thomas Walther, laser and quantum optics, Institute of Applied Physics, TU Darmstadt

detected atomic excitation states
With a highly sensitive method, the Institute of Physics and the Institute of Nuclear Physics of the University of Mainz has been developed in the research group of Professor Hartmut Backe and Dr. Werner Lauth since the early 90s, it is the researchers were successfully able atomic excitation states in Nobelium detected and characterized.

"At the GSI accelerator we merged by bombarding thin lead foils with calcium projectiles the atomic nuclei of the reactants to the isotope Nobelium 254th On operating at GSI SHIP separator We then isolated the Nobelium isotopes and so irradiation allows laser light ", Professor Michael Block, head of the department describes superheavy elements physics at GSI and the section Super Heavy Elements Physics at HIM, the experiment.

The energy gaps in the electron shell determines the team, by varying the energy of the irradiated laser light. Adjusts the distance, the laser light is absorbed and an electron is removed from the atom, so that the atom is a positively charged ion. This ion is then clearly demonstrated by its radioactive decay. "The experimental setup is so sensitive that to carry out our investigations, a generation rate of a few atoms per second is sufficient. The radioactive nobelium atoms exist just by 50 seconds before decaying again, "says Dr. Mustapha Laatiaoui, GSI scientists and the experimenter.

extended studies
After the first atomic transition in Nobelium-254 was determined, the investigation could even be extended to the short-lived isotope nobelium-252, which can be generated only with a five-fold lower production rate as Nobelium 254th The measurement of the energy shift of an atomic transition between different isotopes provides information about the size and shape of the particular atomic nuclei.

The experiment is the first successful, studies of the atomic structure of an element transfermium example Nobelium (Z = 102) carried out by means of laser spectroscopy. The extremely high precision with which the energies of atomic states in laser experiments can be measured, provides the basis for further theoretical work and opens new perspectives for future precision experiments for measurements of atomic and nuclear properties of unstable atomic nuclei in the superheavy elements.