Thanks for the heads up about this post. I have not had the time to do an in-depth analysis of the paper yet. Nonetheless, there are a few things that are quite interesting.
Surprisingly the article wasn't published in Nature or Physical Review Letters, but in Phys Rev C (PRC).
This surprised me as well initially. Looking over the papers I have, 114 was published in PRL and Nature, but 116 only warranted a PRC publication. Since the Dubna group has previously published part of the 118 results in both a JINR Preprint
and also in NPA
, the paper may not have been “new” enough for nature/PRL.
212Pom has the exact same alpha energy of 11.65MeV. One would also expect to see 212Pom as a common transfer product contaminant in these reactions.
Agreed. If you look at figure 1, it clearly shows a peak corresponding to 212
Po, so you would expect that 212
is also populated in the transfer reactions and would provide some background at the higher energies. This would not explain the EVR-alpha correlations though, as 212
has a half-life of 45.1 seconds and the two alphas assigned to 118 were correlated to EVR’s within 3 ms.
I also find the 11.8(5) MeV alpha event quite interesting. Mostly because this is listed as an “escaped alpha particle registered by focal-plane detector without position signal because of low deposited energy.” Correct me if I am wrong, but 11.8 MeV seems like more then enough energy to register a position. The absence of a position leads me to believe that the alpha energy listed was not the energy observed in the focal plane. I suspect that the listed energy is actually an estimated based off of energy deposited and possible angles of escape, which I do not like.
Also, from what I understood from their data analysis code, the first alpha in strip 3 should of turned off the beam, and I didn't see where they explained why it didn't.
This work contains results from 2 experiments separated in time by a few years. In the first set of experiments with 48
Ca projectiles, it was assumed that all decay chains would end in a spontaneous fission. The early experiments did not employ fast shut-offs, instead they looked for spontaneous fissions and then searched back in time for alpha chains. It was only in the later experiments, after they knew alpha energies for the first few isotopes, that fast shut-offs were employed. The first chain listed comes from experiments performed prior to the use of fast shut-offs for superheavy elements, the other chains come from a later experiment.
Also, having a mean life-time, for 118, ranging from 98ns to 42ms seems too large, even for just 3 events.
116 actually, but you are correct. I went through and ran a Monte Carlo simulation that randomly generated 1 000 000 sample sets with the same half-life (9.98 ms) and number of events (3). Of these 1 000 000 sets, only 1.4% had a lifetime distribution broader than the experimental one. Including the 3 decays from the 118 chains, there are a total of 10 decays of 290
116 where a lifetime was recorded. I did the same simulation with these values (10 events, 7.08 ms half-life). Again, only 1.9% of randomly generated sets were had a wider lifetime distribution. If I ignore the 290
116 decays from the 118 chain then the results are a little better with 5.1% of trials having a wider distribution. The other possibility is that there is an isomeric state in 290
116, although that would be difficult to distinguish based off of the alpha energies given.
Who knows, maybe pxn exit channels become probable in that region and what they saw was the discovery of element 117.
No, that does not work very well. The efficiency of the DGFRS for a pxn reaction is likely much less than 1% when it is tuned to look for the xn reaction products. By evaporating the additional proton, your average charge state will change a lot more than it would if you were evaporating just neutrons. Additionally, that would not explain the chemistry experiments on 112. Specifically the most recent ones where they made 114, which decayed in the recoil chamber, and then looked for the decays of 112 on gold plated detectors. There they saw mercury like behavior, which would indicate 112, not 111.
At the moment, I am finding the 116 chains to be much more interesting than the 118 chains. The first thing of interest is the decay times. I already mentioned that the distribution of 290
116 half-lives is abnormally wide. However, 2 more decays down, the distribution of 282
112 half-lives is abnormally narrow
. Based off of the 5 events, only 1.6% of randomly distributed sets were narrower. Eventually I will get around to adding in all the 282
112 decays to see if that changes.
The alpha events listed for 290
116 are also quite interesting. Of the 12 events listed (including the ones from 118), three were not observed, three were only detected in the upstream detectors and one was an escape. Again, the escape event has no position listed as it is said to have had too low of an energy for position resolution, although 11.15(31) MeV seems like plenty of energy for position resolution. Unfortunately, not much more information about these are given in the paper.
Two of the spontaneous fissions listed in the table are out more than 3 mm from the EVR. For one of these events (out 3.4 mm), the FWHM position resolution is 1.1 - 2.2 mm (I assumed 2.2), giving a standard deviation of 0.93 mm, making the SF event out more 3.6 standard deviations. For the second event, the FWHM position resolution for EVR-SF events is 0.4 - 0.8 mm (I assumed 0.8 ), which gives a standard deviation of 0.35. The SF listed in the correlation is then 14.6 standard deviations outside of the mean. In the paper they state “…one of them was detected during a beam-off period and the probability of observing it as a random event is extremely low. For the second SF, this probability if about 1%”. However, I seem to recall that the DGFRS has a small SF background. One of these SF events follows an escape alphas, so I suspect that it is actually a background event. For the other event, I am weary of anything being 14.6 standard deviations out.
Anyway, that is all I have had time to think about, I still need to go over the paper in detail.