The Prize:
The 1938 and 1951 Nobel Prizes in Physics went to scientists who laid the groundwork for modern particle physics.
The Science:
Particle accelerator science, sometimes called the science of “atom smashing,” began when Ernest Rutherford. Rutherford (Nobel Prize, 1908) performed what can be thought of as the first modern atomic experiments by aiming alpha particles at a metal target to discover the atomic nucleus. Alpha particles are emitted during some types of radioactive decay. They are positively charged, so when they encounter an atom’s nucleus (which is also positively charged) they are deflected. Rutherford was the first to see this, allowing him to make the conclusion that the nucleus is compact and positively charged.
Particle accelerators can be likened to a super-powerful microscope. The resolution of your final image reflects the wavelength of the particle used to create it. When observing a cell using a light microscope you are essentially following the path of a beam of light (made up of photons) to create the image. To see smaller, sub-cellular structures, an electron microscope may be required in which a beam of electrons replaces the photons of a light microscope. Because electrons have much shorter wavelengths than photons, electron microscopes can generate more detail on a smaller scale than light microscopes.
Particles with shorter wavelengths have a correspondingly higher energy and Rutherford understood that “visualization” of sub-atomic particles would require something with a shorter wavelength, and therefore higher energy, than the alpha particles he used to identify the atomic nucleus. He presented his results at the Royal Society in London, urging other researchers to develop a method to generate more powerful beams composed of higher energy particles in an effort to get better resolution of the atom. So began the race to make the first particle accelerators with the ability to unlock the secrets hidden inside the atom.
Sir John Douglas Cockcroft and Ernest T.S. Walton were among the first to heed Rutherford’s call. In 1932 they published the results from their Cockcroft-Walton high-voltage generator, which was an electrostatic accelerator. It worked by lining a column with a number of high-voltage condensers to accelerate protons. They used it to add a proton to a lithium atom and watch it decay into two helium nuclei. This work won them the 1951 Nobel Prize in Physics. Their experiments marked the first time that scientists could artificially change the “chemistry” of an atom without using a natural source of particles like Rutherford had. It was the first step into a new world for physics.
In 1929, Ernest Lawrence was leafing through a paper written by Rolf Wideroe that described the first steps in the development of a linear accelerator. Not able to read German, Lawrence followed the mathematics and drawings. The paper inspired Lawrence’s invention of the cyclotron (Nobel Prize, 1938), a particle accelerator that uses magnetic charge to bend the path of particles into a circle. Protons accelerated in a cyclotron can be sped up by incrementally increasing the voltage as they spin around.
Lawrence’s work on particle accelerators, however, did not end here. It could be said that Lawrence was one of the early fathers of particle acceleration as he mentored many scientists who themselves went on to further the field. He was very influential in attracting attention and funding to this new field of science and has been credited as one of the first scientists who could effectively petition donors and government to give science projects large donations. He was also one of the first scientists to exploit the value of bringing together groups of scientists with different sub-specialties to work towards a common goal. He is the founder of the Lawrence Berkeley National Laboratory, the site of many discoveries in physics with 11 of its researchers having won the Nobel Prize.
Since the development of the early particle accelerators, other types of accelerators such as cyclotrons, betatrons, and synchrotrons have emerged. They differ in the path that the particles take and the types of particles that are accelerated, but overall, they share common design principles with their forbears. Perhaps the most exciting work in particle physics today is coming from experiments performed in colliders.
A collider aims two beams of particles at each other in opposite directions. This is in contrast to other particle accelerators where a beam of high-energy particles is aimed at a fixed target. At very high speeds, subatomic particles can be “smashed” into each other and experimenters can observe what the high-energy, high-speed collisions create. When two high-energy particles slam into one another they often create new particles.
The standard model of physics nicely explains most of what we’ve observed about particles such as the electron, proton, and neutrino. It helps us to understand the forces that determine their behaviour, and the smaller “massives” that make up sub-atomic particles. What the model is missing, however, is a description of why sub-atomic particles have such different masses. The current hypothesis is that another “force” particle, called the Higgs boson, is the missing piece. This particle has never been observed but is predicted by the symmetry of subatomic particles. There is only one accelerator on earth powerful enough to create and detect a Higgs boson: the Large Hadron Collider on the shores of Lake Geneva.
The LHC is a massive, underground collider that aims two beams of protons at one another. The 27-kilometre tunnel running under the French-Swiss border became operational in September 2008, but has been rife with problems ever since. The latest bad news: it will run at only half its maximal power for at least another two years, will be out of use in 2012 for repairs, and not back up and running until 2013. This is because of faulty electrical connections that brought the LHC down for 14 months only nine days after its first experiments were recorded. The safer, lower power currently in use at the LHC significantly reduces the chances of scientists finding the elusive Higgs boson.
The Significance:
Certain aspects of the “string theory” of physics suggest that a high-energy collision could potentially create a black hole within a particle accelerator. This possibility has been jumped on by popular culture and fueled public fear of high-energy physics experiments. However, top physicists assure us that the LHC, and other colliders, are safe. Even if a black hole is created in a collision, its lifetime is predicted to be so short it would not pose any danger.
In his book Angels and Demons, Dan Brown creates a plotline around the use of anti-matter, created at the LHC, as a weapon. This has no grounding in scientific fact.
Today, dozens of large particle accelerators can be found all over the world—the cathode ray tube at the back of your old TV is one (small) example. None of these pose any risk of creating dangerous black holes or sinister particles that can be used to take over the world.
What colliders have done is offer particle physicists the opportunity to study the smallest objects in the universe (at least, the ones that we know of). Particle accelerators have aided the discovery of a whole host of subatomic particles and are slowly etching the unknown forces that keep the atom together and influence its behaviour. The Nobel Prizes devoted to discoveries made possible by the particle accelerator are too many to number.
Yet not all accelerators in use study the atom. Many accelerators are used in medicine and industrial sterilization methods. Lawrence’s own mother’s life was saved with radiation therapy generated by an x-ray tube that Lawrence developed with David Sloan.
Accelerators also produce radioisotopes for use in medicine as surgical tools and in cancer therapy. Some larger hospitals make their own radioisotopes in basement-cyclotrons. Ironically, they have also been used to enrich uranium for use in atomic bombs. Lawrence has regretted this application as his lab provided the American government with all of the radioactive uranium dropped on Japan during the Second World War.
A notable setback in accelerator science occurred in Texas. In the early 1980s the Department of Energy chose a site just south of Dallas as the location for a “super-collider” that would have been three times as powerful as the LHC—more than enough power to discern the putative Higgs boson. Congress scrapped the plans for the SSC, as it was called, as the projected cost ballooned. Almost $2 billion had already been spent on its construction.
The loss of the SSC means that, for now, the holy grail of particle physics rests on a fully functional LHC. In addition to observing the elusive Higgs boson, this collider promises to finally experimentally challenge aspects of the highly controversial, grand-unifying, “string theory.” Unfortunately, we likely have a few more years to wait before these tests can truly get underway.
