Nov. 17, 2011 All elements heavier than iron are formed in supernovas. A supernova is a gigantic stellar explosion that releases enormous amounts of energy. By comparison, the energy of the sun is so low that it can only form the light elements.
This autumn, two international teams of scientists are competing to see who can create the heaviest element in the universe in a laboratory.
Super-heavy elements are those with an atomic number above 104. This number indicates the number of protons in the atomic nucleus. Several years ago, scientists managed to create element 118. Now it is time to try elements 119 and 120.
Jon Petter Omtvedt, professor of nuclear chemistry at the University of Oslo, Norway, is a member of one of the teams. He has been studying super-heavy elements for twenty years. Working together with scientists from a number of Western European countries, Japan and the USA, he hopes to win the prestigious competition. The experiment is being conducted at the German GSI Helmholtzzentrum für Schwerionenforschung, which is almost as large as the CERN Big Bang research facility, where research in nuclear physics is conducted.
The competitors, a team of Russian and American scientists working at the Joint Institute for Nuclear Research in Dubna, Russia are just as eager to win the competition. It is not yet clear which team will emerge victorious.
"The competition is razor-sharp. Super-heavy elements are highly unstable and very difficult to create. It is like finding something unknown in outer space. We are working right at the cutting edge of what is experimentally possible. In order to study the heaviest elements, we have to stretch the current technology to its utmost and even a little further," explains Omtvedt.
Although it is sufficient to create one single atom of the new element, that is not enough to be construed as a scientific proof.
"No one will gain any recognition until another laboratory manages to recreate the experiment. In the worst case, it may take several decades before the experiment has been verified.", Omtvedt says to the research-magazine Apollon at University of Oslo.
One atom per month
The scientists are already busy trying to create the first atom of element 120. The production time for super-heavy elements gets longer the heavier they are. When scientists discovered element 106, they managed to create one atom per hour. The half-life, i.e. the approximate lifetime of an atom, was twenty seconds. That means that half of the substance decayed into other, lighter elements in 20 seconds time.
In the search for element 118, they managed to create one atom per month. In that case, the half-life was down to 1.8 milliseconds.
"There is a very definite possibility that it will be even more difficult to create even heavier atoms. Moreover, we must expect ultra-short half-lives.
The race to create element 119 started two weeks ago when the nuclear physics facility at Oak Ridge National Laboratory in the USA produced 20 mg of the extremely radioactive substance, Berkelium. Berkelium, which must be created artificially in very special nuclear reactors, is heavier than Uranium and extremely difficult to produce in pure concentrations.
Each of the teams of scientists received 10 mg. In order to create element 119, they will bombard a metal plate laced with Berkelium atoms with a beam of Titanium atoms. The Berkelium has to be used quickly before it disappears. Berkelium is a perishable substance. It has a half-life of 320 days; i.e. half of the Berkelium will have decayed into some other substance after 320 days.
Billiard balls fusing together
The goal is to induce a Titanium atom to fuse together with a Berkelium atom.
Titanium has an atomic number of 22. Berkelium has an atomic number of 97. Together, these two atoms have a total of 119 protons; i.e. exactly the right number to create an atom of element 119.
"It is extremely difficult to create intense Titanium beams. To accomplish this, we have secrets that we will not share with others. We shall bombard the plate with a beam of five trillion Titanium atoms per second. It will be like bombarding the plate with billiard balls, but the probability of a direct hit is extremely low.
"When the atoms collide with each other on rare occasions, they are usually merely shattered or partly destroyed in the collision.
"However, less than once a month, we will get a complete atom. The probability of doing so is lower than the chance of winning the jackpot in Lotto. The problem is that you will have to detect this one atom on a metal plate where more than 100,000 superfluous events are occurring each second."
Detected when the atom disappears
The only way to do this is to measure the radioactive radiation at the moment when the atom decays.
"This means that we cannot detect the atom by measurement until it is gone. Not before that!"
The surest way to detect the atom is to examine all of its "daughters" when it decays.
Such a chain of fissions may progress in five to eight steps. The scientists can only be certain that they have found the new element when the chain of reactions occurs in a particular way.
It is not easy to detect atoms with such a short half-life. The current detectors need a certain amount of time to "digest" each event. That means that they are not immediately ready to detect the next event.
Therefore, the team of scientists has developed even faster detectors. "They are capable of measuring the ultra-short half-lives."
The scientists also want to know how an element is composed and why some elements are unstable.
"Super-heavy elements are very large and can easily decay.
An atomic nucleus consists of protons and neutrons. The larger the atomic nucleus becomes, the more difficult it is for the forces among the protons and neutrons to hold the nucleus together.
"It is not sufficient that the neutrons and the protons be at the same place simultaneously. They must have been bound together for at least a few fractions of a micro-second in order to be characterised as an atomic nucleus. One of the biggest and most exciting questions is to find out how heavy an element we are capable of creating. Even though it is extremely difficult to create elements 119 and 120, we do not believe that these elements will be the end of the periodic table," says Jon Petter Omtvedt.
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