Some elements are incredibly common and have been studied for hundred of years in one form or another. Abundant elements like oxygen, nitrogen and hydrogen are easy to find as they are literally all around us. Other elements like gold, lead and copper are unreactive and so are easily found lying around most of the time in their elements form or in an easily extractable ore. Elements near the bottom of the periodic table, in the radioactive set, are not only rare as they are constantly decaying but also are quite reactive. The example under examination today is one that most people will have heard of as it is that of plutonium. Samples of plutonium have over recent years been subject to a series of experiments and associated theoretical treatment from X-ray spectroscopy to neutron scattering.
Alfvén waves, named after the man who suggested them in 1942, are waves that exist in conductive fluids. Normally they are talked about when it comes to plasmas but they were originally shown to exist in mercury as this too is a conductive liquid that a magnetic field can permeate. The magnetic field acts as the restoring force for the oscillations that make the Alfvén waves exist in the first place. For an ideal Alfvén wave the particles receive no energy as the wave propagates and this is close enough to being true for a significant amount of the time. However, as the oscillations increase in speed, or the wave decreases in size, it can begin to excite the ions through the production of its own electric and magnetic fields. This naturally results in a loss of energy from the wave and is actually one of the most important mechanisms is solar physics for the transfer of energy from electromagnetic waves to the kinetic energy of particles.
I have previously written a post on the concept of reverse Cherenkov radiation, almost like the sonic boom of light. The reverse aspect is where Cherenkov radiation is produced in a metamaterial with negative refractive index. The result is as if a sonic boom cone was flipped and so was flung forwards of the plane. Despite constant research being focused on the subject of reverse Cherenkov radiation since 2003, there has never actually been an observation and measurement made. Attempts have failed either because the negative refractive index material was not pure enough to produce the effect of because the detectors for the radiation encountered problems. Now, fourteen years after the quest began, the official detection of this reversed radiation has been made in a completely metal metamaterial.
Nuclear ceramics are quite simply ceramic materials that are used as part of the nuclear industry. There are many different types of ceramics that can be used for many different purposes such as the uranium oxide ceramics that are used as fuel pellets and coating nuclear waste in dense ceramics in order to limit the radiation output. One of the most common ceramics used is silicon carbide (SiC) although there is a concern. Even after decades of effective use we still are not exactly sure how defects develop and then transfer within the silicon carbide. The simple fact is that over time radiation, specifically ionised particles, can produce persistent errors in the lattice structure which is not ideal for when SiC is going to be used in high dosage environments.
Separating isotopes has always been a bit of a challenge. Traditionally there are five methods for isolating isotopes these being: containing the gas with a semi-permeable membrane as lighter isotopes will diffuse through faster; electromagnetic deflection where heavier isotopes will experience less acceleration for a given force; centrifuges where lighter elements are thrown outwards more; electrolysis where the heavy ions, having less mobility, are evolved less often at the electrodes; and finally there is a method involving two plates, one hot and one cold, as thermal diffusion rates leave the heavy isotopes nearer the cold wall. (There is technically also a sixth way as some chemical reactions of exchange develop biased isotope concentrations such as the catalysed reaction between hydrogen and water vapour where the water is found to contain almost three times as much deuterium as the hydrogen gas does.)
Stars are well known to have magnetic fields surrounding them like many planets do. These magnetic fields are generated due to the movement of the plasma, which is of course charged, inside the star. It is through a series of convection currents that the dynamic action of the plasma keeps going and so the magnetic field remains. As magnetic fields themselves exert forces on plasma this creates a very interesting effect where without a density change the internal pressure of the star can change. This is one of the aspects that makes the modelling of stars as perfect gasses a foolish task. Although it was believed for some time that the swirling plasma must cause the magnetic fields recent observations have shown that even the calmer, static regions of the Sun maintain a magnetic field over them.
Helium-3 is the most important isotope there is for detecting neutrons. Because helium is roughly the same size as a single neutron (much closer than all other elements other than hydrogen) it removes quite a lot of a neutrons kinetic energy in a collision and so has a high absorption cross section, which is a fancy way of saying it is quite likely to absorb a neutron in an impact. On absorption the helium-3 breaks up into hydrogen and tritium (hydrogen-3) which are then easily detected. The United States government had a plan to use the neutron emissions to detect plutonium even when hidden out of sight. Unfortunately as nuclear tests aren’t in the numbers they used to be the quantity of helium-3 required would be unobtainable at a reasonable price and so the plan is to use boron-10 instead in boron trifluoride (BF3).