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Topic: Hs-263  (Read 10536 times)

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Offline Dan1195

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Hs-263
« on: February 07, 2009, 09:34:55 AM »
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.

Offline Dan1195

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Re: Hs-263
« Reply #1 on: February 14, 2009, 09:04:01 AM »
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.

Offline Dan1195

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Re: Hs-263
« Reply #2 on: February 14, 2009, 03:48:25 PM »
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.

Offline Grejak

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Re: Hs-263
« Reply #3 on: March 11, 2009, 03:11:49 AM »
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.

Offline Dan1195

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Re: Hs-263
« Reply #4 on: March 15, 2009, 01:58:46 PM »
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.
« Last Edit: March 15, 2009, 02:31:37 PM by Dan1195 »

Offline Dan1195

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Re: Hs-263
« Reply #5 on: March 16, 2009, 09:02:51 PM »
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.

Offline gippgig

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Re: Hs-263
« Reply #6 on: March 16, 2009, 11:28:53 PM »
Has that study of ~1600 261Sg decays been published?

Offline Dan1195

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Re: Hs-263
« Reply #7 on: March 17, 2009, 07:02:51 AM »
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).

Offline Grejak

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Re: Hs-263
« Reply #8 on: March 17, 2009, 01:08:46 PM »
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 :)

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