[Dan1195]

New isotope in Phys Rev C 79, 011602(R) (2009). An alpha emitter with 0.74 ms half-life. Of additional interest is Chain #4 ends with a SF assigned to ²⁵⁹Sg. This is the first report of an SF branch of this nuclide and when combined with previous data results in an partial SF half-life close to 10 seconds in good agreement with existing Sg Odd N SF data. ²⁶¹Sg has a partial SF of 31 seconds, ²⁶⁷Sg (with limited data) about 100 seconds.

[Dan1195]

Just an update, ²⁵⁹Sg was also recently produced directly in Phys. Rev. C 79, 027602 (2009). No SF from ²⁵⁹Sg was reported here, which is a bit puzzling considering the higher number of decays observed. It is possible the SF branch is a bit smaller than the Phys Rev C 79, 011602(R) (2009) data would seem to indicate, which is quite possible and results in a partial SF half-life still consistent with SF systematics in the region.

[Dan1195]

One thing I forgot to point out in the previous post is decay branches of <5% are almost impossible verify with any accuracy without observation of hundreds (or more) decays. It took a study with ~1600 decays to confirm the small EC/SF branches in the ²⁶¹Sg->²⁵⁷Rf chain.  One SF decay doesn't tell us very much about branching ratio. It is entirely feasible to record 1 alpha, 1 SF, then 98 more alphas, or just 1 alpha and 1 SF if you have a very low cross section.

[Grejak]

²⁶³Hs was also recently observed at GARIS and published in J. Phys. Soc. Japan 78(2009) 035003.  They also observed SF decay of ²⁵⁹Sg, so looks like this is another case of direct vs. indirect production isomers (also observed in ²⁶³Sg, for example).  The chains look good, although the cross section calculations seem a bit strange.

[Dan1195]

If there is an isomer in ²⁵⁹Sg, it is not readily apparent in the current data. Both the alpha's from direct and indirect production cover the same energies, the strong line at ~9620 keV in particular shows up in both at similar branching ratios (50-60%). This is in contrast to ²⁶⁵Sg, where different alpha spectra were observed. It may be just a case of randomness due to the very low probability of SF from ²⁵⁹Sg relative to number of observed decays.

A combined analysis of the decay of the ²⁵⁵Rf decay product from the ²⁶³Hs and ²⁵⁹Sg data shows evidence of a ~7% EC branch of this nuclide. There are 3 chains where it appears the 8247 keV alpha line of the 2.5 second ^255mLr was observed. GARIS chain #9 was assigned in this manner by the authors. Chains 13 & 19 from the LNBL ²⁵⁹Sg study also show this line. In #13 this alpha was assigned to ²⁵⁵Rf followed by ²⁵¹No EC and ²⁵¹Md alpha. EC decay of ²⁵¹No is likely a very low probability event (<1%) and ²⁵¹Md itself only has a ~10% alpha branch. with #19 the chain is lost after the 8481 keV alpha. The obvious question is why hasn't the 8247 line shown up in direct ²⁵⁵Rf production. As with ²⁵⁹Sg the the lines observed from direct and indirect production are similar, decreasing the likelihood of an isomer.

[Dan1195]

Couple other thoughts Re: Small EC branches in transactinides. They are much easier to detect in Odd-Odd nuclei than Even-Odd for a few reasons, assuming enough decays are observed:

1. The decay following the EC of an O-O is almost always SF. This is because Rf & Sg isotopes w/ N<162 all fission at >75% branching, many very close to 100%.

2. The SF observation in O-O decay chains almost has to be from an EC daughter. The very high hinderance factors from the odd proton and neutron make direct SF decay a very unlikely observation. We would see significant SF branches in adjacent O-E nuclei before direct O-O fission would be detectable at the cross-sections currently obtainable in the Db/Bh region.

3. A negative factor in detecting small E-O EC branches is the EC daughters often have ground or excited states with similar alpha energy and lifetime as the alpha daughter. In the case of ²⁵⁹Sg, both it and ²⁵⁹Db fit this example. GARIS chain #9 above for example shows a 0.173 s 9460 keV alpha preceding the alpha assigned to ^255mLr. This would be compatible with ²⁵⁹Sg or Db. Hence, No real way to detect any ²⁵⁹Sg EC branch (likely a couple of %, like the 1.3% EC branch of ²⁶¹Sg) without observation of 1000+ decays (like with the ²⁶¹Sg study where 1600 decays were observed), where all parents of ²⁵⁵Lr assigned events in the chains would be examined to see if a significant higher ratio of 9470 keV alphas occurred here as compared to the primary ²⁵⁵Rf->²⁵¹No decay path.

[gippgig]

Has that study of ~1600 ²⁶¹Sg decays been published?

[Dan1195]

Unsure whether it has appeared in a peer reviewed journal as of yet. According to this thesis, http://javier.dnp.fmph.uniba.sk/sok11249/works/streicher-1150726366-thesis.pdf, the two experiments were run at GSI, in 2003 and 2006. The actual number of decays is not actually referenced in here but was at a conference ppt presentation I saw (forget where).

[Grejak]

It has been published twice that I know of:

Antalic: Acta Physica Slovaca 56 (2006) 87
Streicher: Acta Physica Polonica B 38 (2007) 1561.

Both are a 'bit' light on details, so thanks for the thesis reference