nuclear chemistry

Discovery of Mg-40, Al-42, and Al-43

Baumann et al. have recently reported the discovery of three new isotopes 40Mg, 42Al, and 43Al. The discovery is notable for producing an isotope that neither the finite range droplet model (FRDM) nor the Hartree-Fock-Bogoliubov (HFB-8) predicted should be bound.

neutron rich low z chart of nuclides

Of the 3 isotopes, the discovery of 42Al is an unexpected surprise and thusly the most fascinating. As we all know from undergraduate nuclear chemistry the Weizsäcker’s formula contains a pairing term (d) approximately equal to 34*A-3/4 MeV. The term increases the binding energy for an even number of protons (Z) and neutrons (N), decreases it for an odd Z and N, and of course is zero for an odd atomic number (A). 42Al contains 13-protons and 29-neutrons, lies on the extreme neutron-rich side, and thus was not predicted to exist in a bound state.

Theory can be seen to be in contradiction from experimental data as seen below.

Mg-40 Data2
Reprinted by permission from Macmillan Publishers Ltd: Nature 449, 1022 – 1024 (25 Oct 2007).

To the immediate left of the 43Al dot is the collection of 42Al events. The 43Al event had a probability of ~2 x 10-3 of arising from the Al-42 cluster of events.The tantalizing conclusion of this work is that the neutron-drip line may reside further than even the next generation nuclear facilities could explore for Z>12.

Link to article: http://dx.doi.org/10.1038/nature06213

Mitch

By November 21, 2007 0 comments nuclear chemistry

Morita’s Element 112 Confirmation: 112-277

Morita et al.1 have recently published the details of their confirmation experiment of the German’s claim for the discovery of element 112.2,3 The paper reports similar decay properties to the Germans, and for all intents and purposes it looks like element 112 has now been confirmed. Fortunately, the paper is a really good and easy read. There is no scandal or fishy decay chains anywhere in it. Since I’m a fan of decay chains, a summary of all known and not faked3 decay chains of 277112 are shown below.


Morita

A summary of the table above in an easy, digestible, fun and always enthralling Nuclear Trading Card format is shown below.

Remember, the yellow means alpha-emitter and t1/2 is the half-life.

Enjoy the newest trading card! An element needs a confirmation experiment before it can be given a name. The only remaining question is, “What will the name be?” Ghiorsoium anyone?

[1]Japanese confirmation: http://dx.doi.org/10.1143/JPSJ.76.043201
[2,3]Germans: http://dx.doi.org/10.1007/s002180050036, http://dx.doi.org/10.1140/epja/i2001-10119-x

Mitch

By May 8, 2007 1 comment nuclear chemistry

The difference between cold fusion and cold fusion

In a recent article in C&EN, Steve Ritter writes about a cold fusion presentation at the recent ACS Chicago meeting. The article can potentially be read as lumping the loony-toony crack-pot conspiracy theorists cold fusion with the very real and valid field of low-energy nuclear reactions dealing with cold fusion. So, lets talk about the differences…

Article: http://pubs.acs.org/isubscribe/journals/cen/85/i17/html/8517sci2.html

Low Energy Nuclear Reactions
In this branch of nuclear chemistry there is a subfield called cold fusion. In “cold fusion” a heavy nucleus (Z>2) is accelerated and bombarded against a target composed entirely of Lead(Z=82), or Bismuth(Z=83), or other near neighbor. The term cold fusion is applied for these reactions because when these two nuclei come together they have an excitation energy of ~10-15MeV which is very small when you compare it to other types of nuclear fusion. Since the excitation energy is so low, the newly formed element is stable to fission and thus tends to stick around long enough to be detected by “conventional” means. Some examples of cold fusion reactions exploited in this way are shown below.

  • 209Bi + 58Fe -> 266Mt + 1n <~~Reaction lead to the discovery of Mt
  • 208Pb + 58Fe -> 265Hs + 1n <~~Reaction lead to the discovery of Hassium

Loony-Toony Cold Fusion
Loony-Toony Cold Fusion is the fusion of two light nuclei at room temperatures. The following 4 reactions are the typical cold fusion reactions investigated by the crack pots.

  • 2H + 2H -> 3He + 1n(2.45 MeV) (eqn.1)
  • 2H + 2H -> 3H + 1H(3.0 MeV) (eqn.2)
  • 2H + 2H -> 4He + gamma-ray(23.8 MeV) (eqn.3)
  • 1H + 2H -> 3He + gamma-ray(5.5 MeV) (eqn.4)

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Here is how the non-nuclear chemists test for cold fusion. They stick D2O in an electrochemical cell, turn it on, measure the heat coming out and compare it to the amount of energy that went in. Sounds like a very reasonable scientific thing to do; If the
heat out is greater than the energy in, than a fusion event has to of occurred to account for this mythical-ether like heat output. However, this is a horrible prehistoric way to look for fusion; It would be like calculating an area of an integral by cutting it out from a sheet of graph-paper and weighing it.

Reasons Why Loony-Toony Cold Fusion is bull…

  • We’ve looked for the heat and can’t find it. There is no excess heat generated from these kinds of reactions that can not be accounted for. See Henderson et al.’s paper: http://dx.doi.org/10.1007/BF01588282
  • Lets just do the freshman Physics and see if it makes sense with our knowledge of physical chemistry.
    In order to fuse, two nuclei need to overcome the coulomb force and touch each other, so lets calculate the coulomb energy for this configuration.

    So, for the case of a deuteron on deuteron…
    k = 8.9876×109 N m2 C-2, q1=q2=1.602×10-19 C, r = 2.8 x 10-15 m.
    Which by my calculation equals to 8.2 x 10-14 J

    Now we know the energy necessary to put two +1 charges close enough in order to undergo fusion. How fast must the two nuclei travel in order to have enough kinetic energy to overcome this 8.2 x 10-14 J barrier?
    The Total Kinetic Energy(KE):
    KE = .5(mass of deuteron)(velocity)2 + .5(mass of deuteron)(velocity)2 = (mass of deuteron)(velocity)2

    velocity = [KE / (mass of deuteron)]1/2
    velocity = [ 8.2 x 10-14 J / (3.3 x 10-27 Kg) ]1/2
    velocity = 4,984,825 meters per second!

    To get atoms moving that fast will require a high temperature, higher than can be achieved with water for sure. We’ve all taken Physical Chemistry so lets see what Temperature it will take to have gas molecules traveling that fast (notice how I already assume that fusion in the liquid phase is phony-bologne). If I assume the deuteron behaves as a monatomic gas then…

    Translational kinetic energy = (3/2)kT, where k is the Boltzmann constant and T is temperature.

    T = (2/3)KE / k = (2/3)(8.2 x 10-14 J) / (1.381×10-23 J / kelvin) = 3,958,484,190 Kelvins

    This temperature can not be reached by an electrochemical cell! This is all just complete rubbish.

    (Notes: (1) It would of been proper to use the energy in the center of mass instead of the lab-frame. (2)The correct coulomb barrier for real nuclei is approximately half of what was calculated using the formula above, which is only meant for rigid hard charge spheres.)

  • In (eqn.3) and (eqn.4) above, a very high mono-energetic photon(gamma-ray) is emitted. It is ridiculously simple to put a gamma detector in front of the electrochemical cell and look for the very specific photon that comes out with an energy of 23.8MeV or 5.5MeV respectively. From (eqn.1) an energetic neutron is emitted; it is also very simple to put a scintillating liquid around the electrochemical cell and look for the stereotypical slow-rise time of a neutron signal.

In conclusion, giving coverage to this fringe science only helps perpetuate the false belief that there exists any viability in cold fusion. The C&EN readership would be well served if more coverage of valid nuclear chemistry research was reported too. Hint-hint. Wink

Link to article:

http://pubs.acs.org/isubscribe/journals/cen/85/i17/html/8517sci2.html

Mitch

By April 23, 2007 8 comments nuclear chemistry

New Isotope Discovery: Hassium-270

So why study elements at the extreme of the periodic table? Because we want to learn about their Chemistry! This has been made easier with the recent work of Dvorak et al. The work created 4 atoms of the heaviest element we can currently do Chemistry with, element 108(not sure if the 112 chemistry paper is out yet). The paper focuses on the isotope’s physics, which it has lots of interesting bits and pieces to it,  but I’ll be focusing on Chemistry, sort-of.

The new isotope Hassium-270’s decay chain from the paper is shown below.

Since that’s an ugly way to show decay information, I’ll summarize it myself with the isotope trading cards method. The decay properties of Hs-270 and Sg-266 from this experiment are shown together below.

The yellow signifies it’s an alphe emitter and the green signifies it decays by spontaneous fission. The star on the half-life is meant to signify that the half-life wasn’t measured by the experiment, but determined from systematics.

Now quickly to Chemistry.
When Nuclear Chemists make heavyelements, we also make a bunch of other elements from all over the periodic table too. So we have to separate what we want from the junk. The two methods of choice are either a physical separation (magnets and electric fields) or by a chemistry separation (in this case the formation of a volatile tetroxide). To prove that their chemical separation method was indeed only separating out group 8 elements, they also produced some Osmium in tandem with Hassium and observed both their decay signatures in their detectors, the paper notes they had trace Actinium contamination coming to their detectors too.

Now the question for the audience of Chemists.
The heavyelement community now has ready access to a long lived group 8 element, do you have any suggestions for interesting chemical investigations with it? Remember, due to the short half-life of 108 and the current experimental setup, any ligands or chemistry would have to occur in the gas-phase so modest volatility is a must. If you have any suggestions post them here.

Mitch being a smart-ass.
Note 1: Chemistry and Engineering News put out a note about the discovery too: http://pubs.acs.org/cen/news/84/i52/8452hassium.html . Thanks Mark K for pointing it out, link to his soccer website.
Note 2:The following picture was taken from that article:

Note 3: Couldn’t wear a nicer shirt Honza(Jan Dvorak) for the photo? Wink
Note 4: I don’t see Honza wearing a face shield or safety thermal gloves, how unsafe. Is the cap still on the detector your filling? Tongue

Edit 1: Link to discovery paper.

Mitch

By December 28, 2006 0 comments nuclear chemistry