Monday, September 29, 2008

How to arm Bridezilla

A couple of years ago, (which is an epoch on blog timescales), Jen over a cocktail party physics blogged about diamonds, gold, and other constituent materials of engagement rings. Since I did my PhD on diamonds, we had a bit of a discussion on the subject. Not long afterwards, her cat evidently lost said ring, generating predictable distress.

Since Jen is a journalist, and Sean is a theoretician, I planned a blog entry describing a variety of non-destructive analytical techniques which they could use to find said article of jewelry. This way, should one of them go Bridezilla (or Groomzilla), they would have a variety of caustic, ionizing, and nuclear tools at their disposal. Unfortunately, said post languished in my half baked finished box for the better part of a Wilson cycle. However, as today is their wedding anniversary, I figured I might excavate it, dust it off, and post. So without further ado:

Engaging ways of finding a ring


The following analytical techniques are standard geochemical techniques that have been used to analyse diamond and/or gold by various scientists over the years. Destructive techniques, though generally more effective, have been excluded from this list. Each method consists of a short description of how it works, and summary of the experimental setup you will need, and a brief description of what the side effects might be for the cat. They are listed in increasing order of impracticality.

Xray induced optical fluorescence


Theory: Most diamonds fluoresce in the optical wavelengths when illuminated by X-rays, as a result of impurities and structural defects. In fact, this technique is usually what is used to recover the diamonds from the kimberlite ore in the first place. The ground ore is illuminated with X-rays, and anything that glows is retrieved (all in a highly automated process).

Method: Black out apartment. Irradiate everything in it with X-rays. Grab anything that glows.

Effect on cat: increased cancer risk from moderate X-ray dosage.

X-Ray fluorescence


High energy X-rays will knock inner shell electrons out of the atom. When outer shell electrons fall down to fill the vacant shell, an X-ray is emitted. These X-rays can be detected with an X-ray spectrometer, which will identify the element being irradiated. Since most apartments don’t have a lot of gold lying around, looking for Au K , L, and M band X-rays will detect the gold instead of the diamond. Better yet, the K and L X-rays are quite energetic, so if the ring is obscured by a low Z number object (like a cat), they may be able to penetrate it.

Method: as above, but with a high energy, brighter source (Is there a synchrotron in your block of flats?).

Effect on cat: Chronic radiation damage, but with a higher dose.

Gravimetric/ magnetic separation


Theory: Diamonds and gold are both denser than wood, plastic, concrete, and most other building and furnishing materials. Unlike steel, they are not ferromagnetic. So a gravimetric and magnetic separation should reveal the ring.

Method: grind apartment into gravel-sized bits. Use a magnet to pull out any steel. Dump the remains in a heavy liquid (a variety of iodine or bromine organic molecules are available for this purpose) which will float the concrete (as well as plastics and wood) Your ring should sink and be recoverable.

Effect on cat: The grinding step may produce physical damage. In addition, most heavy liquids are extremely toxic.

Acid dissolution


Theory: diamond and gold are both very insoluble in most caustic liquids. Dissolving the apartment with increasingly aggressive solvents should leave the ring untouched.

Method: dissolve plastics in the appropriate organic solvents. Dissolve wood in this stuff. Dissolve concrete, ferrous, and base metals in sulphuric acid.

Effect on cat: Ends up in a solution of the fairly final variety.

Mössbauer Spectrometry


Theory:197Au, the only stable isotope of gold, has an excited isomer which decays back into the stable isotope with a half life of 7 seconds. By irradiating stable gold with gamma radiation of the exact energy required (about 400 KeV), a nuclear transition to the excited state can be induced. This will then decay with the same characteristic energy, which can be detected with a gamma ray spectrometer.

Method: Irradiate the flat with gamma rays of the appropriate energy to excite the Au nucleus. Then switch on your GRS and home in on the emitter.

Effect on cat: Gamma ray irradiation is similar to X-ray damage described above, but potentially more penetrating.

PIXE


Theory: Proton-Induced X-ray Emission. This is similar to XRF, except that high energy protons are used instead of X-rays. The disadvantage is that you need a particle accelerator- nothing LHC sized,as a few MeV is the energy most commonly used. The advantage is that proton beams can be focused better than X-rays, allowing you to target your search more carefully.

Method: Remove an elevator and install a particle accelerator in shaft. Evacuate apartment. Raster beam across all potential hiding places, and use an X-ray detector to spot emission from inner shell ejection of electrons from the gold atoms.

Effect on cat: death by asphyxiation. Potential additional radiation damage from proton beam.

Neutron activation


Theory: 197Au will fairly easily absorb a neutron, transforming to the radioactive isotope 198Au. This isotope decays so 198Hg with a half-life of a couple of days, releasing a characteristic gamma ray in the process. Both neutrons and gamma rays can easily penetrate all but the best shielded of hiding places, making this method ideal. Note that only a tiny fraction of the gold atoms are transmuted, so the mercury toxicity threat and loss of gold from the ring are both minimal.

Method: Construct an unshielded nuclear pile in your living room. Flood flat with neutrons. Afterwards, send in a radiation-shielded robot with a gamma ray spectrometer to detect 198Au decays. The apartment (and most of the building) will be uninhabitable for a few decades due to the production of radioactive elements, but the ring will only be too hot to handle for a month or so.

Effect on Cat: Death from acute radiation poisoning.

So there you have it. Jen, Sean: Happy anniversary. And just remember, if you ever need to find anything, science is always on your side.

3 comments:

Chris Phoenix said...

Love it! Thanks!

I note that "the cellulose in wood can be efficiently converted into glucose." This implies that, with proper chemical separation, we could use wood (grass, etc) as a food source. I find that more exciting than biofuels (albeit somewhat scary).

Chris

dublin said...

nice article... even if it doesn't help me to buy my engagement ring!

Jennifer Ouellette said...

This is an awesome blog post. Thanks! (The cat, however, is not amused.) )