Nihonium (Nh) is a synthetic element with atomic number 113. Being synthetic, a standard atomic mass cannot be given and like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 284Nh as a decay product of 288Mc in 2003. The first isotope to be directly synthesized was 278Nh in 2004. There are 6 known radioisotopes from 278Nh to 286Nh. The longest-lived isotope is 286Nh with a half-life of 19.6 seconds.
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Notes
Nucleosynthesis
Super-heavy elements such as nihonium are produced by bombarding lighter elements in particle accelerators that induce fusion reactions. Whereas most of the isotopes of nihonium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higher atomic numbers.
Depending on the energies involved, the former are separated into "hot" and "cold". In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets (actinides), giving rise to compound nuclei at high excitation energy (~40–50 MeV) that may either fission or evaporate several (3 to 5) neutrons. In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions. As the fused nuclei cool to the ground state, they require emission of only one or two neutrons, and thus, allows for the generation of more neutron-rich products. The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion).
Cold fusion
Before the successful synthesis of nihonium by the RIKEN team, scientists at the Institute for Heavy Ion Research (Gesellschaft für Schwerionenforschung) in Darmstadt, Germany also tried to synthesize nihonium by bombarding bismuth-209 with zinc-70 in 1998. No nihonium atoms were identified in two separate runs of the reaction. They repeated the experiment in 2003 again without success. In late 2003, the emerging team at RIKEN using their efficient apparatus GARIS attempted the reaction and reached a limit of 140 fb. In December 2003 – August 2004, they resorted to "brute force" and carried out the reaction for a period of eight months. They were able to detect a single atom of 278Nh. They repeated the reaction in several runs in 2005 and were able to synthesize a second atom.
Hot fusion
In June 2006, the Dubna-Livermore team synthesised nihonium directly by bombarding a neptunium-237 target with accelerated calcium-48 nuclei:
23793Np
+ 48
20Ca
→ 282
113Nh
+ 1
0n
Two atoms of 282Nh were detected.
As decay product
Nihonium has been observed as decay products of moscovium. Moscovium currently has four known isotopes; all of them undergo alpha decays to become nihonium nuclei, with mass numbers between 283 and 286. Parent moscovium nuclei can be themselves decay products of tennessine. To date, no other elements have been known to decay to nihonium. For example, in January 2010, the Dubna team (JINR) identified nihonium-286 as a product in the decay of tennessine via an alpha decay sequence:
294117Ts
→ 290
115Mc
+ 4
2He
290
115Mc
→ 286
113Nh
+ 4
2He
Evaporation residue cross sections
The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels. The channel with the highest expected yield is given.
DNS = Di-nuclear system; σ = cross section