By Les Hearn
What do they do at CERN? It’s simple — they smash things, ions for example, together at high speed. Why do they do that? It’s even more simple — to see what happens! CERN is an example of “blue skies” research: particles are not smashed together to solve any practical problem but to test theories of matter and energy. We’re paying for it — and we should be!
Physicists have been smashing particles for quite a long time, over 50 years at CERN and about 100 years altogether. It first revealed the structure of atoms. In 1911, Rutherford’s team bombarded gold atoms with fast-moving alpha particles. Their behaviour showed that atoms are almost entirely empty space populated by some electrons, with an incredibly dense nucleus (1 cubic millimetre of nuclei would weigh about 200000 tonnes). This “blue skies” research gave rise to modern atomic theory and the nuclear age.
More recently, particle accelerators proved a theory about the forces of nature. In 1983, particles predicted by the proposed unification of the electromagnetic and weak forces, vector bosons, were produced at CERN. This helped support the so-called Standard Model which seeks a unified description of three of the four forces of nature.
What is the Large Hadron Collider (LHC)?
The LHC is a colossal piece of apparatus designed to produce the predicted Higgs boson, a particle that gives mass to other particles. This would further confirm the Standard Model.
It accelerates two beams of charged particles round a 27km tunnel beneath the Swiss-French border until they almost reach the speed of light (c), nearly 300,000km/s. They circulate some 10,000 times per second.
Bending their paths to follow the tube requires thousands of the most powerful electromagnets which require enormous electric currents. Normally, the heat released would vapourise the whole lot so superconducting wires are used. Cooled to -271 ºC (colder than outer space) by liquid helium, these conduct without any resistance whatever.
When the particles collide, their (increased) mass is converted into energy, simulating the conditions of the “Big Bang”. The energy then condenses into new unstable particles. These decay into gamma rays, X-rays, and other particles, identified using six enormous detectors in huge caverns; one, ATLAS, weighs 7,000 tonnes.
ATLAS, one of the largest physics collaborations ever, involves 1,800 physicists in 35 countries collecting and analysing data. Communication of the data would be virtually impossible without the internet.
CERN is arguably the wonder of the modern world.
What are accelerators?
Accelerators apply electric fields to charged particles, electrons, protons or ions. These make the particles move faster and faster. For instance, one volt gives an electron one electron-volt (eV) of energy and accelerates it to about 2% of c. The LHC produces energies of 7 TeV (tera = million million). Old TV sets used 5,000V to accelerate electrons to about a quarter of c before smashing into the screen and causing a flash (Yes! We had particle accelerators in our living rooms. Who knew?).
Developed for fundamental, curiosity-driven, research, there are now about 30,000 accelerators worldwide, mostly in industry and health (see spin-offs).
Research accelerators operate at such high voltages that the particles are moving at a fraction below c. They can’t exceed this because as they get closer some of the extra energy is converted into mass and the particles become heavier, as Einstein predicted. At 99.9998% of the speed of light, a mouse would weigh as much as an elephant, and the LHC can accelerate particles more than this.
Some spin-offs from particle acceleration research
• Radiation therapy. Proton/carbon ion treatment: ions accelerated to appropriate speed (kinetic energy) to reach the tumour; they penetrate healthy tissue but deliver most of their energy to the target tumour, damaging the cancer cells’ DNA so much that they die.
• Ion implantation. Used for making semiconductors and hardening/corrosion-proofing metal tools. Ions of particular elements are accelerated and then bombard the surface of silicon chips, metal tools or artificial joints. The elements alter the electrical properties of the silicon, and make metal surfaces resist cracking and corrosion.
• Detectors. PET scans result in emission of positrons from radioactive isotopes passing through blood vessels. These annihilate when they meet ordinary electrons, emitting two gamma rays. Detectors are used to build up a pattern of blood flow in the body, highlighting any abnormalities. And the isotopes are made in accelerators.
• Super-conducting electromagnets. Used in MRI scanners.
• Data handling. CERN generated greater and greater amounts of data as time went on. This led computer scientist Tim Berners-Lee to invent the World-Wide Web in 1989 as a way of sharing information between scientists; it was opened up to the world in 1994. It is obviously the most far-reaching spin-off from CERN, though there is no way it could have been predicted.
• Safer nuclear power. An exciting potential use is in accelerator-driven systems (ADS) firing neutrons at thorium fuel, releasing energy. Unlike conventional nuclear reactors, the process can be immediately stopped by switching off the accelerator. The other advantage of ADS is that they can burn up nuclear waste, reducing drastically the problem of disposal. India is planning a pilot thorium-fuelled ADS by 2020.
Fundamental research — is it worthwhile?
Populist politicians often point to tax-payers’ money being “wasted” on the curiosity of scientists. Governments often favour applied research, cutting fundamental research to save money in the short term.
Looking at some spin-offs from particle accelerators shows how unwise this is. And CERN’s originating the internet is alone enough to justify all the money spent.
Two hundred years ago, applied research into lighting would have meant better candles or gas flames. No one could have predicted that Faraday’s research would lead to using electricity to make clean bright light anywhere. When Faraday was asked what good his discoveries were, he replied “What good is a new-born baby?