[Dan1195]

An analysis has been performed on the observed chains to date previously assigned to ²⁸⁸115 and ²⁸⁹115 parents. Preprint is available here: http://xxx.lanl.gov/pdf/1502.03030.pdf

Previously Dubna had assigned all chains ending in SF of Rg to ²⁸⁹115 as they were all the same length. The above analysis includes the new GSI chains and suggests many of the chains assigned to ²⁸⁹115 should be assigned to ²⁸⁸115. If correct, the SF observed is very likely decay of the Even-Even EC daughters as the straight SF lifetimes of the odd-odd nuclei ²⁸⁰Rg and ²⁸⁴113 should be hindering significantly relative to adjacent nuclei with only one odd nucleon.

Couple things to think about:

1. If ²⁸⁰Rg has a ~10% EC branch, its partial EC half-life is ~45 seconds. This means ²⁸²Rg would likely have a significant EC branch (partial EC lifetime prob. ~2 to 10 minutes based on stepping of EC lifetimes seen elsewhere in the nuclear chart).

2. This means a separate reanalysis is probably going to be needed to the chains assigned to ²⁹⁴117 and ²⁹³117. Some of the chains currently assigned to ²⁹³117 have multiple members with rather long lifetimes compared to the rest. Would appear just on visual inspection of those chain 4-5 of those may actually be ²⁹⁴117 chains resulting in a ~33% EC branching for ²⁹⁴117 and a partial EC lifetime of ~4-5 minutes for this nuclide. Probably need additional data here for this, unfortunately availability/short lifetime of ²⁴⁹Bk makes producing element 117 more challenging.

3. Chain D3 mentioned in the paper. Resembles the longer chains I mentioned in #2. However I think the 1n channel leading to ²⁹⁰115 is hardly a practical explanation (1n channel has yet to be observed in "hot fusion" reactions). Isomeric state?

[Dan1195]

Took another look at the data, particularly chain D4. Assigned to ²⁸⁹115 in the paper, however the high E_α for Z=113 combined with the short SF lifetime for Rg put some question into the assignment. One possibility not mentioned in the paper is that chain D4 belongs to ²⁸⁷115 and the SF belongs to ²⁷⁹Rg. Lifetimes of all three members of this decay appear compatible with this decay sequence. The E_α for Z=115 is ~300 keV lower then the three other assigned members of this decay sequence, but this is not too unusual in odd Z nuclei. The resulting significant SF branch for ²⁷⁹Rg (~25%) is quite reasonable as its neutron number (N=168) is at the already known fission barrier minima between the deformed N=162 and spherical N=184 shells. Would results in a partial SF lifetime ~320 ms very close to that of the N=169 nucleus ²⁷⁹Ds (~230 ms).

[ik3]

Based on your assignment that the chain D4 belongs to ²⁸⁷115 and is terminated by the SF of ²⁷⁹Rg, the SF lifetimes of unhindered e-e nuclei of N=168 can be estimated roughly. Assuming the hindrance factor of odd nuclei as about 10³, the SF lifetime of the nucleus ²⁷⁸Ds (Z=110, N=168) is estimated at an order of 100μs from the neighboring e-o nuclei ²⁷⁹Ds (230ms) and ²⁷⁹Rg (320ms). In a similar way, that of ²⁷⁶Hs (Z=108, N=168) is estimated at an order of 1µs from ²⁷⁷Hs (3ms) and ²⁷⁷Mt (5ms). This sudden decrease of SF lifetime of 276Hs suggests that the bottom of the SF valley is located at the lower Z side of N=168. However, the α-decay lifetimes of N=167 nuclei too short to branch EC-decay, thus no feasible method to product such e-e N=168 nuclei of Z≤110.

[gippgig]

The fact that they found a plausible theoretical basis for the existence of parallel decay chains for isomers of ²⁸⁹115 suggests that the seemingly ridiculous idea that this could explain the first candidate for 114 might actually be correct. Note that a much less extreme version of this has been found; ²⁶⁵Sg has 2 isomers that preferentially decay to different isomers of ²⁶¹Rf. Observation of rare cross-pathway decays would confirm this (as always, we need more data).
The even-Z odd-A decays should also be reexamined.

[Dan1195]

There are examples of parallel alpha decay chains elsewhere in the nuclear chart, looking the Z>82 N<126 vicinity especially

e.g.

¹⁹⁹Fr (1/2+) 4.5 ms > ¹⁹⁵At (1/2+) 290 ms > ^191mBi (1/2+) 125 ms
^199mFr (7/2-) 6.2 ms > ^195mAt (7/2-) 143 ms > ¹⁹¹Bi (9/2-) 12.4 s

Due to the large spin+parity change the two decay sequences are somewhat independent from each other (^195mAt has a 12% IT branch to the ground state, ^191mBi has 32% IT branch)
 

[Dan1195]

Another thing I was thinking about when looking over the published ²⁸⁸115 chains and alpha decay systematics in the vicinity of the N=162 shell, where is the alpha branching of ²⁶⁸Db? The alpha half-lives for ^270,272Bh are about 60 seconds and 10 seconds respectively. Partial alpha half life of ²⁷⁰Db is ~1 hour, which implies a possible ²⁶⁸Db partial half-life of a few hours from systematics. It was very likely the Dubna studies were not set up to find the longer lived alphas (as suggested in the GSI Z=117 confirmation paper). However GSI didn't find any alphas from this nucleus either in their most recent experiment, though it is unclear where <8000 keV alphas with lifetimes >1 hour were looked for here.

[ik3]

For the α-decay branch of ²⁶⁸Db, one of the possible scenario is longer lifetime (more than 20hours) of ²⁶⁸Db and shorter lifetime (less than a few hours) of ²⁶⁴Lr, which is the daughter nucleus of ²⁶⁸Db. Based on the systematics of neighboring nuclei, the decay mode of ²⁶⁴Lr is expected to be EC or SF. The t_SF of ²⁶⁴Lr is estimated to be much longer than a day, which is so long that may cause the escape of SF event detection. (The hindrance factor of the 103rd proton is roughly estimated to be 20000 based on ²⁵⁸No/²⁵⁹Lr and ²⁶⁰No/²⁶¹Lr pairs. The roughly estimated t_SF of ²⁶⁴Lr is 30days that is multiplied 20000 by 2.5 minutes, which is the t_SF of the N=161 even-odd isotone ²⁶⁵Rf (only a single decay observed so far) instead of the unknown isotope ²⁶³No.) ²⁶⁴Lr is the one-neutron-deficient nucleus from the β-stability line. The t_EC  of such odd-odd nuclei in the heavy (Z>90) region are widely distributed from 57 minutes (^258mMd) to 1.54×10⁵ years (²³⁶Np). If t_EC of ²⁶⁴Lr is less than a few hours like as ^258mMd, this matches to the scenario described at the beginning.

[Dan1195]

I mentioned above that a reanalysis should probably be done on the Z=117 chains, the exact test performed in the above paper is a little over my head, but I did do a simpler test where I took the currently assigned ²⁹³117 decay chains and looked at the average ratio of the lifetime of members of each chain relative to the current half-lives based on existing chain assignments.

It appears five of this chains (original JINR chains #1 and #5 from 2010 w/17.01 ms and 20.24 ms Z=117 and JINR chains  #7, #12 and #25 w/109.898 ms, 153.948 ms and 10.547 ms Z=117) may possibly be better fits with ²⁹⁴117. When those five chains are isolated from the rest one also notices that those chains include predominately decays of Z=113 w/alpha energies <9700 keV. Couple of red flag do pop up, one is that the of the five Z=111 (Rg) atoms in the chains listed above have a half-life of ~45 seconds, a fair bit below the current ²⁸²Rg half-life of ~130 seconds. another is that chain D3 in the paper in the first post would also appear to fit with these other five, but I find it hard to believe the 1n channel was available there.