Matter of stability

Serious efforts are being made to find out superheavy elements that could be stable

Published: Saturday 31 January 1998

nuclear physicists are making serious attempts to prove the theory wrong that as the size of superheavy elements increases, they become more unstable. Researchers predict that around element 114, there is an "island of stability", which is yet to be explored. Element 114 is postulated to have unusually long life.

There are 94 elements found in the nature that range from the lightest hydrogen to the heaviest plutonium. However, scientists have produced several new elements that have increased scientific understanding of the fundamental structure of matter. The discovery of new elements has also made possible to predict the existence and basic properties of elements much heavier than uranium. These elements are unstable that last for merely a few hundred microseconds.

Scientists at the Lawrence Berkeley National Laboratory (lbnl), California, usa , and the Institute of Heavy Ion Research (gsi), Darmstadt, Germany and the Joint Institute for Nuclear Research (jinr) , Dubna, Russia, are actively involved in this pursuit. They plan to synthesise superheavy elements, including element 114 (Science , Vol 278, No 5338).

The lbnl plans to add new facilities such as the Gas-filled Separator to its existing accelerator. The arrangement would help in separating the superheavy elements. The researchers at the lbnl would bombard plutonium-244 with calcium-48 in an attempt to create element 114 with 174 neutrons. Such an isotope should be far more stable. An isotope is one of two or more varieties of a particular chemical element which have different numbers of neutrons in the nucleus, and therefore different relative atomic masses and different nuclear properties.

On the other hand, scientists at gsi are already conducting trials to calculate the experimental parameters needed to produce the much sought element. Both the groups hope for some results early next year, which may prove or disprove one of the favourite guesses of nuclear physics.

Elements are labelled by the number of electrons or atomic number. The atomic number of hydrogen is one because it has got one electron in its outermost orbit. Whereas the atomic number of plutonium is 94. The number of protons in the atomic nucleus is equal to the number of electrons. But the number of neutrons can vary, leading to different isotopes of the same element. Thus hydrogen can exist in a form that may have one proton and no neutron or as deuterium or heavy hydrogen with one proton and one neutron.

At present, theorists believe that neutrons and protons arrange themselves into shells in the nucleus. Each shell has a certain number of empty places that can get filled with the neutrons or protons. When the shell is full then the nucleus is usually seen to be stable against radioactive decay. For instance, helium, tin and lead have got a full shell with so-called magic numbers of protons. If the number of neutrons are also magic, then the isotope is said to be doubly magic and is thought to be very stable. At present, Lead 208 is the heaviest doubly magic isotope with 126 neutrons and 82 protons.

Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.