[Dan1195]

In the pdf report of the recommendations of 31st meeting, PAC for Nuclear Physics 25 – 26 January 2010, they report the discovery of two isotopes of element 117. From their statements about the channels involved(3n and 4n), the two chains appear to be ²⁹⁴117>²⁷⁰Db (3n, 6 alphas observed) and ²⁹³117>²⁸¹Rg (4n, 3 alpha observed). I suspect that ²⁸¹Rg ended in SF as N=170 isotones appear to have low SF lifetimes (a fisson valley as nuclei change from deformed to spherical).

The pdf is here http://www.jinr.ru/img_sections/PAC/NP/31/PAK_NP_31_recom_eng.pdf

It can be found on the JINR website via main page>information>materials of governing and advisory bodies>materials of programme advisory committee>programme advisory committee for nuclear physics.

hopefully a paper will soon be submitted for journal review.

[gippgig]

That might be ²⁹³117>²⁷⁷Mt; "twice longer" = 2 additional (6 instead of 4) alphas.

[Dan1195]

Yeah, that appears so. the wording is just kind of funky. I suspect alpha may actually be a fairly competitive decay mode (here i.e. >5% branch)  but almost certainly only a few atoms were observed so it wasnt found. I suspect if you could get beyond that nuclide the chain would get down to Db as well (SF lifetimes rise as you approach N=162. This is what happened with ²⁷⁹Ds, where once you got beyond that nuclide the chain continued to ²⁶⁷Rf in 2/3 chains. Both of those chains have one odd nucleon in the same alpha chain line (A=2z+59) as well.

[gippgig]

I noticed that the isotope chart on page 27 of this reference shows ²⁵⁷Es as an 8 d SF activity. I've never heard of that isotope. Does anyone have any idea where this came from? (This chart still lists ²⁶⁶Sg as a 21 s alpha emitter so I don't trust it.)

[Dan1195]

Many isotope charts (and the ENSDF data set at NNDC) still have the incorrect properties for ²⁶⁶Sg. As has been discussed before ²⁶⁶Sg is a 360 ms SF emitter and previous studies identifed the one of the isomers of ²⁶⁵Sg as it in error.

Re: ²⁵⁷Es. 3 Russian refences from 1987-91 all from same authors in the ENSDF file discuss this nuclide. Has not been confirmed by anyone else apparently.

[Dan1195]

A Powerpoint presentation on their discovery of 117 is now available on the Dubna website (decay chains included) on the SC107 Programme [http://ftp.jinr.ru/Prog_SC107-e.htm. Note they doubled on the extention for some reason, just take out the 2nd extension to open.

They have reported 1 chain from ²⁹⁴117 and 5 chains from ²⁹³117. The 294 chain ends in the (apparent) SF of ²⁷⁰Db. The 293 chains all end at the N=170 isotone ²⁸¹Rg. Whether the Odd-Odd Db in that region decay by SF or EC is still unclear as EC cannot be dectected here. A couple members of that chain (²⁹⁰115 & ²⁸²Rg) have alpha decay lifetime that look rather short. I suspect its the result of only seeing one atom. although an isomer is possible. N=170 nuclides all have short SF lifetimes. The Rg isotope is the first odd Z above Db where SF has been observed and clearly not EC followed by fission. This will be a roadblock if more neutron rich SHE are produces (except for Odd-odd which are most stable against fission).

Edit: Re-looked at the Db data. ²⁶⁶Db is almost certainly EC. Its lifetime is less than ²⁶⁷Db which has less fission hindrance. ^268,270Db are less clear.

[Dan1195]

Reading through the announcement yesterday is appears no additional chains were discovered beyond the 6 previously mentioned.

²⁸¹Rg should have a detectable alpha branch, If the alpha branching of ²⁸¹Ds is 5-10% (combining Dubna & GSI data) than the partial alpha for this nuclide is 100-200 seconds. No alphas for ²⁸¹Rg implies an alpha half-life of at least approaching 100 seconds. unfortunate that they didn't find it as I am sure the chain would have continued to ²⁶⁹Db which would have been helpful as EC would not have been a decay option for this nuclide (it is expected to be beta stable).

[Grejak]

The paper came out today.

[Dan1195]

One of the most interesting statements in the paper was that when the ²⁹⁴117 chain was observed ~30% of the BK sample had decayed to Cf. With the cross sections you are dealing with you are really at the limits of what you can achieve right now. Using another Bk source (this one will become mostly Cf before they could use it again) to try for 119 is not really feasible. Some estimates drop the cross sections for 119 and 120 down to levels close to what RIKEN had to deal with w/113. 129 might be possible with a long enough irradiation time.

In general the most promise short term idea appears to be to use reactions involves collisons between actinides resulting in matter transfer. This would theoretically result in isotopes of 104-110 along the beta stability line. Other options being looked at such as accerating fission fragments hold a lot less promise it appears.

Actually getting to the N=184 shell enclosure appears infeasible for now though.

[gippgig]

A review of this work by Sigurd Hofmann of GSI with a free download of the 117 paper is available by going to the paper link above then clicking on "Viewpoint: Exploring the island of superheavy elements" at the upper right.

[Dan1195]

Had a typo above...heh..meant "120" not 129..

[Dan1195]

FYI in the The 109th Session of the JINR Scientific Council http://indico-test.jinr.ru/conferenceDisplay.py?confId=95 the presentation by Greiner shows the preliminary finding of two more partial chains originating from ²⁹⁴117. Both chains have multiple missed alphas so the data quality isnt as good. Key thing I see from those chains is the half-life for ²⁸²Rg now comes out to 41 s if all 3 chains are taken together. which makes more sense from a alpha systematics point of view relative to the lifetime of ²⁸⁰Rg in particular. This also tells me that ²⁸¹Rg should have a fairly significant alpha branch.

[Dan1195]

EDIT: In those 2 chains elements 115 & 117 were undetected as these were part of the element 113 chemistry study.