How are new elements discovered?

Several experimental techniques have been used to make new chemical elements.

Some of these include

i)              heavy ion transfer reactions,

                 ii)      cold or hot fusion evaporation reactions,

iii)             neutron capture reactions,

                Iv)       light-ion charged particle induced reactions, and

                 V)        even nuclear explosions.

These techniques each have advantages and disadvantages making them suitable for studying nuclei in certain regions.

The types of nuclear reactions that have been successfully used to produce new elements in the last decade are cold fusion reactions and hot fusion reactions. 

Cold fusion reactions use beam and target nuclei that are closer to each other in mass in order to produce a compound nucleus (the complete fusion of one target nucleus with one beam nucleus) with generally lower excitation energy that typically requires evaporation of one or no neutrons. This generates fewer neutron-rich isotopes of an element that have higher survival probabilities with respect to fission, but have lower fusion probabilities. An example of this type of reaction is⁷⁰Zn + ²⁰⁸Pb → ²⁷⁷112 + 1n with a cross-section of ~1 picobarn.

Because the 112 isotope ultimately decays by α emission to known nuclei [namely isotopes of elements 102 (No) and 104 (Rf)], identification of this element is straightforward. Hot fusion reactions use more asymmetric beam and target nuclei, produce a compound nucleus with generally higher excitation energy that typically requires evaporation of three to five neutrons, generate more neutron-rich isotopes of an element, have lower survival probabilities with respect to fission, but have higher fusion probabilities.

 An example of this type of reaction is ⁴⁸Ca + ²⁴⁴Pu → ²⁸⁸114 + 4n with a cross-section of ~1 pb. Because of the neutron-richness of this isotope of element 114, it never subsequently decays to any known isotope, and thus its identification is more problematic. Cold fusion reactions have been successful in producing elements 104—112 and hot fusion reactions have recently provided evidence for elements 113—118.