Nov. 18, 2011 In order to find the chemical properties of super-heavy elements, chemists must conduct one of the world's most demanding chemical experiments in a matter of seconds. When scientists discover new elements, that is just the beginning of a voyage of discovery in the world of chemistry.
Chemists are not just interested in knowing the number of protons and neutrons in the new, super-heavy elements. They also want to discover their physical and chemical properties, such as their boiling and melting points, whether the element is soluble in water or acid and how the element binds and reacts with other atoms and molecules.
Of course, it is not possible to directly measure the boiling point of super-heavy elements, but the chemists can get an indirect answer by measuring the volatility; i.e. how strongly the element binds to a metal surface.
It is only possible to conduct such experiments in a very small number of laboratories in the world, e.g. the GSI Helmholtzzentrum für Schwerionenforschung in Germany and the Joint Institute for Nuclear Research in Dubna, Russia. The University of Oslo is cooperating with both of these centres.
The experiments are expensive to conduct, and it is difficult to gain access to these laboratories. Therefore, it is absolutely necessary for the chemists to make highly elaborate preparations for the experiments beforehand.
These preparations take place in a particle accelerator (cyclotron) connected to a chemical laboratory.
Charged Hydrogen and Helium nuclei are accelerated up to enormous speeds and bombarded against thin metal foils.
This gives rise to radioactive metal ions that resemble the super-heavy elements. The chemists can then perform experiments on the metal ions in the chemical laboratory.
Only a very few research institutions have their own cyclotron in the basement. Even fewer have an automatic connection between the cyclotron and a chemical laboratory. The University of Oslo is one of the few places in the world that has both.
"Our facility arouses interest abroad. After we have checked to make sure that our self-invented equipment is functioning properly, we will load up a van and take it with us to the experiment abroad," says Professor of nuclear chemistry, Jon Petter Omtvedt, at the SAFE-Centre for Accelerator-based Research and Energy Physics at the University of Oslo.
Extremely short lifetime
On the University campus at Blindern in Oslo, the elements are projected straight from the cyclotron through a twenty metre long tube into a chemical laboratory. Much of what transpires is fully automatic. There is unbelievably little time. Since the half-life of the elements is extremely short, the chemists do not have time to perform the experiment in a normal way. The lifetime of the element is less than one minute. Many of the super-heavy elements that they want to experiment with only last a few seconds before they decay.
Thus, it is no use putting them in classic test tubes to be analysed later. That takes far too much time. Sometimes, the chemical reactions must occur within the actual detector in order for the substances to be detected before they disappear.
The detector only detects what happens with the one atom at the moment it disappears. Then it sends out a special radioactive signal. It is this signal that is detected.
The heaviest elements of all have such short lifetimes that it is not possible to examine them chemically. It does not make it any easier that it is only possible to experiment on one atom at a time.
Jon Petter Omtvedt has spent the last fifteen years developing the laboratory facilities at Blindern.
His specialisation is a special type of detector system that measures a particular type of radioactive radiation, called alpha rays, from a fluid. His other specialisation is the advanced, automated conduct of experiments in so-called "wet chemistry."
"Since the lifetimes of these substances are so brief, we have to be lightning fast. All of the steps in the experiment must function simultaneously. We push the limits to the utmost. You can compare this with studying the outermost reaches of space. There are not many detectors in the world that can find one or two atoms of a special element, especially when there is a lot of turbidity in the mixture," notes Omtvedt. He was involved in the chemical research on element 104, Rutherfordium, a few years ago.
Repeating the experiment
Now Omtvedt is participating in a major international team of scientists in order to study the chemical properties of the super-heavy element 114.
In order to obtain good enough data, the chemists have to run the same experiment a number of times. Each time, they test whether the atom binds to other molecules. By repeating the experiment a number of times, they can determine the approximate probability of how often the atom will be bound. Omtvedt would also like to study the ways in which super-heavy atoms react with each other, but since the cyclotron only manages to create one super-heavy atom at a time, this task is impossible to solve.
The world's heaviest elements, 119 and 120, which will hopefully be detected this autumn, will have such brief lifetimes that they will not last long enough for the chemical experiment. Therefore, there is an upper limit on how heavy an element may be that is still possible to study chemically.
Better chemical models
If the chemists understand more about how the super-heavy elements behave chemically, it may come as a surprise to the layman that they may then be able to learn more about the chemical properties of the lighter elements.
Although this is basic research in its truest sense, these discoveries may improve current mathematical chemical models. These models are the basis for all chemistry. The chemists use them to predict chemical reactions.
"The data from the experiments may push the models to give even better results.
The electrons become heavier
Einstein's theory of relativity is an important component of these chemical models. The heavier the elements become, the higher the velocity of their electrons will be. When the electrons move faster and faster, they also become heavier and heavier. Modern mathematical descriptions of atoms are dependent on this relationship. That is where the theory of relativity comes in.
One amusing example: if gold did not have relativistic properties, gold would have been white.
In the GSI Helmholtzzentrum für Schwerionenforschung, Omtvedt's Russian colleague, Valeria Pershina, is working exclusively on theoretical calculations of the properties of atoms.
"She can predict chemical reactions. Now and then, her theory does not agree with our experiments. The question then is who has made a mistake," concludes Omtvedt.
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