Nuclear weapon testing has been both a good and a bad thing for the study of radioactive dating. On one hand the nuclear material released into the atmosphere has made it more difficult to accurately determine ages as the released radioactive material alters the naturally present concentrations in the atmosphere. On the other hand it can actually be beneficial in cases such as limnology. If some freshwater is found checking the radioisotopes present will reveal whether it has been recycled during the nuclear age. Another good example is to use the great increase in unnatural radioisotopes produced during a nuclear detonation, caesium-137 for instance, to calibrate other dating techniques. Since we know the exact dates of these explosions we can find the soil layer containing large amounts of caesium and check other dates compare to it.
Stopping power is the ability of a material to slow down charged particles (stopping power is only used for charged particles) passing through it by removing their energy through interactions with the particles in the material. In the early 1930s a physicist named Hans Bethe developed the Bethe formula for calculating the average energy loss over a distance within a material:
where me and e are the mass and charge of an electron; I is the average potential of the electrons in the material and n is their number density; and v and z both refer to the particle being retarded, being velocity and charge respectively (it should also be noted that this is a simplification for a non relativistic particle. Electrons and fast moving particles require corrections to the above formula). Continue reading Calculating Distance Over Which Charged Particles Pause
Nuclear fusion is quite a way off becoming viable although progress is being made with larger and larger fusion reactors being created all the time. So far the largest reactor that is being built at the moment, ITER, will have an exhaust power of about 150 megaWatt. When a proper fusion power plant is created it would have an exhaust power of about 800 megaWatt. A divertor is a component of a fusion reactor which uses a magnetic field to define a plasma boundary. The divertor can be controlled to manage and shape the plasma into a D-shape plasma (a more elongated ovular form). In this state, the heavy ions, which are the main component of the “exhaust” of the fusion, are flung out and separated with greater ease. Unfortunately the current limit of divertors are 10 megaWatt per metre squared and it doesn’t seem this limit is set to increase. Radiative cooling has to be employed in future reactors if they can’t provide the exhaust space for the current divertor ability.
There is condensed matter physics, where particles have to adhere to eachother (hence the word condensed). There’s plasma physics, where electrons have stripped from all the atoms leaving just a gas of ions behind. There is also an intermediate step. This is where the temperature is such that the average kinetic energy of the electrons is about equal to the binding potential energy that holds them to the nuclei. This means it is too cold for condensed matter physics where its a guarantee that the electrons will be liberated, but too hot for condensed matter physics where the electrons are guaranteed to be bound. This is called warm dense matter and is not easily modelled by either branch of physics.
The importance of the Sun in our solar system cannot be overstated. When considered, it is quickly realised that almost all sources of energy on this planet come from the Sun. For solar power it is obvious, but wind power is caused by the temperature gradient the Sun produces and fossil fuels originally started out as plants absorbing energy through photosynthesis. The two main exceptions are tidal power, which is a conversion of the Earth and Moon’s rotational kinetic energy, and geothermal power, which is gained from nuclear decay in the Earth’s core.
Ultra high energy cosmic rays (UHECR) are cosmic rays which are measured to have over 1018 eV of kinetic energy. Many of these particles exist beyond the Greisen–Zatsepin–Kuzmin limit, a theoretical limit based on the interaction of the cosmic rays above a certain energy threshold and the photons of the cosmic microwave background radiation. In essence if the particles were of too high energy they would have interacted and slowed down, but this restriction only applies over a certain distance. UHECRs are believed to be produced locally and so are not restricted by the limit. There is also a possibility that heavier nuclei may circumvent the limit also, but what particles make up UHECRs are still unknown. Despite this the mass compositions have been measured by the Pierre Auger Observatory in Argentina which is believed to show particles of higher mass than helium with an upper limit of about iron.
The discovery of nuclear magnetic resonance is described as one of the great scientific achievements of the last century. It was found that any atom with an odd number of nucleons in the nucleus would exhibit a magnetic moment. Luckily common isotopes such as hydrogen-1, carbon-13, fluorine-19, and phosphorous-31 exist which can be easily analysed (technically hydrogen-2 and nitrogen-14 also have magnetic moments but there are difficulties present in these cases). When anything with a magnetic moment is placed in a magnetic field it will experience a torque which rotates it, for objects the size of nuclei the magnetic field needs to be great, many Tesla normally.