[gippgig]

According to their web site, JINR will try to make element 117 in the fall by bombarding ²⁴³Am with ⁵⁰Ti. Why not ²⁴⁹Bk + ⁴⁸Ca?

[Dan1195]

Good question, I would have assumed ⁴⁸Ca would allow for a higher cross-section due to its double magicity, besides the fact that combination you refer to leads to a compound system with 4 more neutrons. Only a couple reasons I could think of are 1) that they were unable to get enough ²⁴⁹Bk, which I would assume is in limited supply 2) They are looking at the viability of using projectiles heavier than ⁴⁸Ca moving forward since using i⁴⁸Ca on ever heavier actinide targets in not viable beyond element 118 due to the short lifetimes of heavier potential targets.

[gippgig]

According to the Flerov Lab website (click on "Experiments" under "Research") the ²⁴⁹Bk + ⁴⁸Ca reaction is currently scheduled (from July at least until the end of the year) at the U-400 cyclotron. We should soon have 117.

[Dan1195]

Assuming (as expected) cross sections are similar to what was observed with 118..

Btw, recently I found a conference presentation where Dubna presented some results from the recent ²⁷⁰Hs experiment. http://www.np.ph.bham.ac.uk/IOP09/iop_talks/07_04_09_Parallel_2/07_04_09_Parallel_2.htm select Y. Tsyganov.ppt. Both the ²⁷⁰Hs and ²⁶⁶Sg daughter decay properties were confirmed and the half-life of ²⁷⁰Hs was actually measured (7.6 s) for the first time. The previous experiment was able to measure the alpha energy only.

[gippgig]

See www.russiatoday.com/Sci_Tech/2009-07-01/New_chemical_element_to_be_synthesized_in_Russia.html?fullstory for a story on the preparation of the ²⁴⁹Bk target for this experiment.

[Dan1195]

The 330 day half-life of ²⁴⁹Bk obviously limits the time within which the experiment can be run. Even with the 3-4 month window Dubna is using to perform the experiment, the half-life of the target is short enough that the chance the ⁴⁸Ca fuses with the Beta decay product of this nucleus, ²⁴⁹Cf instead of the intended target is high enough that it cannot be dismissed out of hand. Perhaps the beam energy used (which might be slight different that the 118 experiments, I haven't looked at that) may reduce the likelihood of this enough so the chance is negligable.