Acceleration of Particles

“I need to talk of what I don't know yet, So that I may perceive whatever holds The world together in its inmost folds, See all its seeds, its working power…”
Goethe, Faust

One of the effective ways to analyze the structure of matter is to allow an energetic charged particle to collide into a solid target, or into another energetic charged particle. Studying the debris of the collisions is a very effective way to learn about the nature of the particles of matter. Charged particles can acquire the required for collision kinetic energy in acceleration process “falling” through potential difference or centripetal acceleration in magnetic field. Since it is difficult to establish necessary potential difference for higher energy particles, a charged particle can accelerate in magnetic field with periodic electrical boost (~100 keV per revolution). The device cyclotron is a particle accelerator that uses magnetic field to hold charged particle on circular orbit so that the modest accelerating potential can act on it rapidly, resulting in high energies. The frequency of circulation of the particle equals to the frequency of electrical oscillator.
q*B = 2 Pi* m* f. At proton energies above 50 MeV, cyclotron begins to fail; as the speed of charged particle begins to approach the speed of light, the frequency of the particle decreases. The required radius of dees is increasing greatly (for 500-GeV proton in B=1.5T, r = 1.1 km). A synchrotron avoids these difficulties: Both B and f are programmed to change cyclically. The particle acquires high energy (~1TeV in Fermilab synchrotron, ~20TeV in CERN ), going in constant orbital radius. Learn about different types of particle accelerators (cyclotron, synchrocyclotron, linac, synchrotron) and ways to detect/observe particles.
Compare different types of particle accelerators, provide analysis of methods used for accelerating particles, particles accelerated, energies achieved.

What kind of the basic research can be done using various types of particles accelerators (gold-foil alpha scattering, early cyclotrons, synchrocyclotrons, linacs, Tevatron, CERN LHC? Provide ranges of typical particle energies for each type of accelerator and resolving ability of the particles (de Broglie wavelength lambda = h / (mv)).

Explain why high-energy particles are effective tools for resolving the finer details of the working of atoms.

Radioactive Decay

“I have always looked upon decay as being just as wonderful and rich an expression of life as growth.” Henry Miller

Naturally occurring radioactive nuclides provide ways to estimate the dates of historic and prehistoric events. The concept of half-life is used to model the process of radioactive decay: the time required for one half of the particular type of radioactive nuclei to decay is constant. The approach is based on statistical analysis (decay of a nucleus is a random event). Rate of decay represents the radioactivity of the unstable nuclei and is calculated as a number of disintegrations per time interval. Activity is measured in decays per second, Bq (SI), Ci. The amount of radioactive substance after some time can be calculated using the model N = No (2) (-t/T); the activity of the substance A= Ao (2) (-t/T). Organic material can be dated by measuring their 14C content, rock samples can be dated analyzing radioactive 40K. Learn about radioactive decay and answer the following questions.

Radiometric dating has helped to determine that life has appeared on Earth approximately 3 billion years ago. Describe how you would estimate this.

A chunk of carbon, assumed to be ashes from an ancient fire, has activity of 89 Bq. The initial activity is estimated to be 105.4 Bq. Estimate the age of the sample.

The half - life period of a radioactive substance is 32 hours. After how much time will 6.25% of the radioactive material remains?

Four units are used to describe the exposure to ionizing radiation. The Curie measures the activity of the source. The roentgen is a unit of exposure. The Rads are used to measure the amount of energy absorbed. The Rems are units for measurement of biological effects of absorbed energy. Research the methods used in mining radioactive substances, such as uranium. What are the biological effects of exposure to radiation? Briefly describe some of the safeguards taken to protect the health of the miners.

Describe some medical of applications of radiation.

Physics SPH4U: Radioactivity

“If circumstances lead me, I will find where truth is hid, though it were hid indeed within the center.” – Hamlet

At the beginning of the last century the significant break through was done in the theory of atomic structure: 1911 - E. Rutherford discovered atomic nucleus, he proposed that positive charge is densely located at the center of the atom, and it has the most of the mass of the atom. An atom is mostly empty space. Nuclei are made of protons and neutrons. Atomic number shows the number of protons Z, mass number A shows the number of nucleons (protons and neutrons). A = Z+ N. Nuclides with the same atomic number and different numbers of neutrons are called isotopes.

Nuclear masses are measured in atomic mass units: 1u = 1.661x10^-27 kg. Einstein’s E=mc^2 relation governs energy-mass transformations in nuclear reactions. The energy equivalent for atomic mass 1u is 932 MeV. The total energy needed to separate nucleus into protons and neutrons is binding energy. Nuclei represent different energy levels: when they make transition from one level to another the photon (gamma particle) is emitted. Many particles have intrinsic angular momentum – spin. There is a strong attractive nuclear force that binds nucleus together against the force of repulsion. Many nuclides are radioactive. Radioactivity is the spontaneous disintegration of nuclei. The most common types of radioactivity: alpha-particles, beta- particles, and gamma radiation.

Learn about different types of radioactivity and answer the following questions:
- Compare three types of radioactive emission analyzing mechanism, mass, charge, speed, penetrating ability, and ionization ability.
- In general, which nuclei (small or large) would tend to be more unstable? Explain your reasons.
- Why does the relative importance of the Coulomb force compared to the strong nuclear force increase at large mass number?
- List some of the things/ materials/ devices surrounding you that contain radioactive substance. Explain the purpose of the radioactive material in the device.

Post your thoughts before May 31, 2006

Physics SPH4U: Elementary Particles Unit by Ms. Olga Sediako. Trip to NRC

Welcome to the on-line Students' Journal on Elementary Particles.
Your Assignment will be based on the information from the oncoming field trip on May 23, 2006 and your independent study.
During the NRC visit learn about the history of development of experimental particle physics in Canada; get an information about current research projects and major directions/perspectives of future developing; acquire an information about subatomic and elementary particles used in the NRC projects, equipment, and facilities.

Reflect on your visit to NRC, answering the following questions.
How neutrons can be emitted?
Why do we need to study subatomic and elementary particles?
What is neutron scattering used for?
Where neutrons can be found?
Why is neutron penetrating capacity higher than the penetrating capacity of other particles?
Why penetrating capacity of neutrons is so important?
Are neutrons dangerous?
If penetrating capacity is so great how do we protect ourselves from radiation?
What properties of neutrons make them useful in research in material science?
Name several practical applications of neutrons.

Post your thoughts, comments, questions and ideas by May 26, 2006