nuclear chemistry

nuclear?

Like Albert, I’ve also been asked to fill in for Mitch while he’s gone. Since Mitch is a nuclear chemist, I wanted to do something related to that. Unfortunately, in the process, I realized that most of what I know about nuclear science, I learned from the Simpsons. Since I’ve never had a class in nuclear chemistry, the extent of what I’ve learned about it in school is “There’s a hot spot by the sink, so don’t get too close if you want children.” (The class was held in an old radiochemistry lab.)
I wanted to take a picture of the local Van de Graaff accelerator, but it doesn’t look so exciting from the outside, so here is a more impressive-looking picture from the ESA.

Van de Graaff accelerators are used to cause nuclear reactions, producing radioactive isotopes, such as 15O and 13N. They can also be used to produce neutron beams for spectroscopic use. Neutron spectroscopy is pretty cool, for people interested in vibrational modes of crystals.
For people like me who shudder at the mention of the word “phonon,” the nucleus is also involved in a more familiar type of spectroscopy: NMR!!! Remember, NMR requires a magnetically active nucleus such as 13C or 1H. (Not to be confused with a radioactive nucleus like 235U.)

Enjoy your time off, Mitch!

Psi*Psi

By December 22, 2006 0 comments nuclear chemistry

Calculating the Bass Interaction Barrier

So we talked about Interaction Barriers previously, but I didn’t really mention how one would go about and calculate it. I won’t go in details on how it is done, but I’ll show you all the equations you’ll need to calculate them yourself. The formula I’m using is called the Bass Interaction Formula and is taken mainly from Nuclear Physics A231 (1974) 45-46.

Where Zt and Zp are the number of protons in the target and projectile respectively. e2 is the familiar e2 which equals 1.44 MeV*fm. d (range parameter) is 1.35fm and Dint (interaction distance) is 2.70fm, but these 2 values are the adjustable parameters. r12 is given as , where Ap and At are the mass numbers of the projectile and target nucleus respectively, and where r0 is 1.07fm. Finally x is the ratio of the coulomb force with the nuclear force and is calculated in the equation below.


Where as is the surface constant from the semi empirical mass equation and is taken as 17.0 MeV.

Bass also has an other equation named after him often referred to as the Bass Fusion Barrier Equation and we’ll get to that in the next couple of days. Hope this is useful to someone out there.

Note1: Using a calculator, the calculated barriers seem to vary from 0.1MeV for light projectiles to 0.8MeV for Krypton. When I only use 3 significant figures in the calculation it did a much better job replicating his calculated barriers in the paper.

Mitch

By November 6, 2006 0 comments nuclear chemistry

Nuclear Chemistry Vocabulary: Nuclear Interaction Barrier

I can’t always be gentle with the reader and clearly define and explain in simple English why we are interested in what nuclear chemists find interesting. That being said, I’ll jump into this next topic.

I’ve come across the term, Interaction Barrier, several times now and I’ve finally figured out what it means. At first I thought the interaction barrier was a nicer way to say the coulomb barrier. I thought it was a term that the learned nuclear scientist used to describe the point where the attractive nuclear force and the coulomb potential would equal each other. Unfortunately I was wrong, I was misled to this conclusion by several recent (recent being defined as anytime from today to 5 years ago) pieces of literature that I have read, but I’ll be nice and not point them out here.

The formal definition of the interaction barrier is (as defined by Mitch rewording Reiner Bass):
The interaction barrier is the threshold bombarding energy in the center-of-mass system which is needed classically for two fragments to undergo a nuclear reaction. Noting that a nuclear reaction is defined liberally and involves any inelastic process.

The informal definition that you can use to make yourself sound smart (which others do retardedly often Roll Eyes):
The interaction barrier, unlike the coulomb barrier which assumes 2 charged-spheres in a static and rigid touching configuration, describes the minimum distance Rint two fragments need to be to undergo a dynamic inelastic non-negligible mass-energy exchange. Where Rint approximately equals R1 + R2 + 3fm, where R1 and R2 are the classical nuclear radii one would calculate for a projectile and target nucleus.

A figure plotting the coulomb potential (solid-line) and the actual nuclear+coulumb potential (dash-line) is shown below. The figure is for 20Ar + 208Pb.

As can be seen in the figure, the interation barrier (Bint) shows the boundary where the interesting physics begins. While the calculated coulomb barrier shows some useless point far above and behind the actual fusion barrier. No wonder “sub-coulomb barrier” reactions seem to occur so readily in our field! They may be sub-coulomb, but the only important barrier is the fusion barrier! This might stand out to others, but took me sometime to realize the importance.

If you are interested in more physics of nuclear reactions with heavy ions. See this book. . I’ve been secretly borrowing it from Walt for 2-weeks now, shhhh….. If you want the book too, please purchase through this link: Nuclear Reactions With Heavy Ions, it’ll give me a few quarters.  Wink

Mitch Rating for Interaction Barrier:
Complicated Soundingness: 3/10
Usefulness: 6.5/10

Next Week’s Term: Sommerfeld Parameter

Mitch

By November 2, 2006 0 comments nuclear chemistry

The Physics of Seaborgium-264: 264Sg

I can finally talk about 264Sg since Gregorich’s paper came out this week. The paper is cool for many reasons and not only because I’m a co-author. The paper recounts the Seaborgium-264 discovery by our group earlier this year from the nuclear reaction of 238U(30Si,4n)264Sg. We observed a total of 5 events of Seaborgium. The events are summarized in the figure below.


Taken from: http://dx.doi.org/10.1103/PhysRevC.74.044611

It sucks to read a table, like the one above, to try and figure out general decay properties of a nuclide. So instead of reading through all the known literature values for a nuclide, we’ll condense the above information into a little box like this one I made (shown below).

The percentage of green signifies the probability it will undergo spontaneous fission. For 264Sg it will undergo spontaneous fission 100% of the time, thus the box is completely filled green. These decay boxes are traded between nuclear chemists as kids trade with Pokemon cards. All nuclear chemists want to keep up to date on the latest decay systematics for any given nuclide, but it’s a pain to always track them down and then update your existing files with new data and making sure you didn’t miss any other data from the literature. So I’ll most likely use this blog as one mechanism I’ll incorporate to keep track of new data.

Very recently Nishio also published some of his results regarding Sg-264.

Taken from: http://dx.doi.org/10.1140/epja/i2006-10091-y

Nishio calculated a half-life of 120.7 ms from 3 atoms detected. Summing Nishio’s work with our experiment we can have a better value for 264Sg true decay properties, shown below.

Enjoy the latest trading card.

Mitch

By October 24, 2006 0 comments nuclear chemistry