[gippgig]

DOI: 10.1103/PhysRevLett.112.172501
They also identified ²⁶⁶Lr.

[ik3]

The nucleus ²⁶⁶Lr would be the heaviest β⁻ decay nucleus observed so far, supposing the β-stable line of odd-Z nuclei is extrapolated along the 2Z−N=44 line (²⁴⁷Bk, ²⁵³Es, ²⁵⁹Md, ²⁶⁵Lr, ²⁷¹Db and so on). The coincident SF signal of the daughter nucleus ²⁶⁶Rf with a short SF half-life may support the identification of the β⁻ decay of ²⁶⁶Lr, similar to the case of ²⁶²Lr and its EC daughter ²⁶²No with a half-life of 5mesc.

[Dan1195]

RE: SF vs EC/β- decay for ²⁷⁰Db and SF vs β- decay for ²⁶⁶Lr

Based on the limited SF data we have for adjacent nuclei and the knowledge that unpaired nucleons create a hindrance factor of 500-1000 for SF decay it is very probable that we observed the Even-Even daughter fission and not direct fission of ^270Db or ²⁶⁶Lr. Lets look at each isotope separately:

²⁶⁶Lr: Only adjacent nucleus with a known SF lifetime is ²⁶⁷Rf at ~1.3 hours based on 2 decays. A hindrance factor of 500 would result in a SF lifetime of >10 days. Much greater than the 11 hour SF activity observed. This is likely β-.

²⁷⁰Db: Only adjacent nucleus with SF decay reported is ²⁷¹Sg (~6 m SF partial based on 1 SF and 2 α decays).  A ~10 hour SF partial lifetime for ²⁷⁰Db would mean a hindrance factor of ~100 compared to ²⁷¹Sg. This has a better chance to be direct SF. 

[Dan1195]

This study makes me wonder if potential alpha branching of ²⁶⁸Db was also missed due to the longer lifetime of the nucleus. The longer lifetime may make detection more difficult but at the same time the experiment can be done without the limitations associated with the Berkelium target (i.e. short half-life, handling issues, etc.)