It’s a bit like buses, you wait for ages then four come by at once. Of course the big news story this week is the positive identification of four new elements 113, 115, 117 and 118. (For those of you a long time out of the classroom this number is the atomic number which is the number of protons found in the nucleus). The actual names for these elements are up for discussion with debates over whether they should be after people, countries, minerals or places to name a few suggestions. There have been lots of articles about these elements, a great graphic by compound interest and an excellent blog post by Dr Eric Scerri.
It popped up as a question on the BBC quiz show Pointless and I even spotted a petition on Twitter to name element 117 octarine in honour of Terry Practchett. Oh and my favourite -naming one after Lemmy, the bassist of the heavy metal band Motörhead.
But what I want to talk about is the island of stability. In nuclear physics, the island of stability is the prediction that a set of heavy isotopes with a near magic number of protons and neutrons will temporarily reverse the trend of decreasing stability in elements heavier than uranium. Now magic is not something that you usually hear scientists talk about but it refers to the numbers of protons and neutrons that give stable atoms. It goes against everything we’ve been taught in that as nuclei get bigger they get more unstable, and that any element greater than uranium in the Periodic Table does not occur naturally. So where do we find this island and why an island ? If you look at the graphic above which is the relationship between nucleons and stability and use a bit of blue shading it becomes clearer. The island of stability is a region of the periodic table where elements’ half-lives increase after a large group of elements with very short decay times. This is were we find the super heavy elements who have atomic numbers greater than or equal to 112. The discovery of element 114 back in 1998 was the beginning of the this quest for the island of stability. And why are some of these super heavy elements stable – I think I’ll leave that to the nuclear physicists to explain.
Making these super heavy elements is no mean feat and there are only certain places in the world with the capabilities to do so including the RIKEN Institute in Japan, Joint Institute for Nuclear Research in Russia, and Lawrence Livermore and Oak Ridge national laboratories in the U.S. These elements have been reported in the literature for quite a while now with first experiments on 113 and 115 starting in 2003. To create these elements researchers smash smaller elements together. For instance, to make element 117, calcium nuclei (20 protons) were smashed into a target of berkelium (97 protons). Interestingly they never actually recorded the new element itself but evidence of its decay products. Why bother spending so much time making these elements that really do not have any everyday uses – it’s that old science chestnut, we add to the bank of scientific knowledge and we learn a bit more about atomic structure. As some may have longer half lives we may be actually able to do experiments with them and one day who knows where that could lead !