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Author Topic: Element 115 chain analysis  (Read 7856 times)

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Dan1195

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Element 115 chain analysis
« on: February 15, 2015, 11:37:18 AM »

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?
« Last Edit: February 15, 2015, 12:04:23 PM by Dan1195 »
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Dan1195

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Re: Element 115 chain analysis
« Reply #1 on: February 20, 2015, 07:39:26 AM »

Took another look at the data, particularly chain D4. Assigned to 289115 in the paper, however the high Eα 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 Eα 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).
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ik3

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Re: Element 115 chain analysis
« Reply #2 on: February 23, 2015, 03:59:23 AM »

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.
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gippgig

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Re: Element 115 chain analysis
« Reply #3 on: February 26, 2015, 05:51:31 PM »

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.
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Dan1195

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Re: Element 115 chain analysis
« Reply #4 on: March 14, 2015, 04:42:05 AM »

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)
 
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Dan1195

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Re: Element 115 chain analysis
« Reply #5 on: March 21, 2015, 12:21:14 PM »

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.
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ik3

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Re: Element 115 chain analysis
« Reply #6 on: March 23, 2015, 04:59:13 AM »

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 tSF 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 tSF of 264Lr is 30days that is multiplied 20000 by 2.5 minutes, which is the tSF 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 tEC  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 tEC of 264Lr is less than a few hours like as 258mMd, this matches to the scenario described at the beginning.
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Dan1195

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Re: Element 115 chain analysis
« Reply #7 on: March 28, 2015, 03:28:28 PM »

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.
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