Why do we need particle accelerators Two reasons The higher energy the beam of particles in the collision the more massive or energetic the particles will be that we can create. To see or detect small particles we need diffract the particle beam around the particles. A particle’s de Broglie wavelength (in the beam) needs to be close to the separation of the particles (in the target) to allow the particles to diffract around them and be “seen”

Key old equations to remember

Producing new particles Head on collision- all the particles energy is turned into energy available for the creation of new particles. Stationary target – some of the energy created is not available due to the conservation of momentum

Predicting energies and masses

Particle Detectors

Particle detectors – Bubble chamber Tank of pressurised liquid hydrogen kept at just below boiling point. Pressure is suddenly reduced by an expansion in the chamber Liquid hydrogen is said to be SUPERHEATED and begins to boil. As particles enter the chamber, they will cause ionisations along their paths

Bubble Chamber By placing the whole chamber in a magnetic field the paths of the particles can be deflected and this helps identify CHARGE and MOMENTUM Photographs are taken and recorded of the tracks produced

Example bubble chamber photo

Particle Detectors- Wire Chamber Similar to the operation of a GM tube (from iGCSE) Particle enters the chamber and ionises a gas atoms in its path. These ionisation events are detected by a series of very fine wires above and below the gas. The position of the wire that senses this pulse if current identifies one position on the particle’s path Many wire chambers in sequence can be used to record a particle’s path

Wire Chamber

Particle Detectors - Photomultiplier Many of the particle events that are looked at produce photons. Photons are not easy to detect in the other detectors because once they interact with matter they disappear completely so leaves no path. The photoelectric effect is used to change the photon into an electron. The electron is then accelerated over a set of positive dynodes (each with increasing positive potential)

Photomultiplier Each time the electron strike the subsequent dynodes additional electrons are released. By the end of the tube (the anode) there are enough liberated electrons to have a measurable change in potential and is measured as a pulse of current. This coupled with a SCINTILLATOR produced the information required to detect the photons

Scintillator A screen made out a material (such as mercury) that emits visible light photons when struck by high energy gamma rays.

Should we allocate funding to research FOR Understanding the universe is one of the most fundamental quests for humans and therefore deserves to be properly resources All research has the potential to give rise to new technology and improve the quality of life for many International particle physics projects provide opportunities for citizens of different countries to collaborate. Even at the height of the Cold War Western and Soviet scientists collaborated in this field

Should we allocate funding to research AGAINST The money would be better spent providing food, shelter and medical care to the many people of the world suffering hunger, homelessness or diseases Is the information gained really worth the cost It might be more beneficial to fund many more small pieces of research rather than one big expensive area Medical research offers the immediate possibility of saving lives and improving quality of life so should get the funding