Questions and Answers on Particles

My responses have not been proof read.

Q
Harvesting energy from annihilation
When a particle and its respective antiparticle annihilate each other, they produce a 'star-burst' of energy. Considering the amount of energy required to create an antiparticle, and the difficulty in creating such a reaction, could this particle / anti-particle annihilation be used as a feasible energy source? If so, how easy would it be to harness the energy produced?
A
The energy from annihilation is usually in the form of electromagnetic wave. This is a large amount of energy in comparison to atomic events. However, the amount of energy is not economical in terms of using it to warm the house or propelling the automobile.

Q
Number of photons in annihilation Is it possible that, during the annihilation of a electron-positron pair, that more than 2 photos are emitted? if so, what determines the number of photons?
A
Experiments showed that annihilation of positrons and electrons results in emitting two photons in opposit directions. Their total energy is equal to the energy of the two photons. Thus, no other particles are emitted due to conservation of energy.

Q
5th force?
Is there a 5th force other than the 4 fundamental forces? Is there a pure repulsive force?
A
I've heard of a 6th sense, but only 4 fundamental forces are circulating in the science community so far.

Q
Other antiparticle
After the discovery of positrons, antiprotons and antineutrons, what are the fourth, fifth, etc antiparticles discovered?

What is the first known particle of antimatter?
A
Science historians probably will keep track of the time of discovery, but many more antiparticles have been confirmed as given in the Module.

Positron is an antiparticle first discovered.

Q
Antiparticles in ordinary matter
Why antiparticles are not mentioned or involved when we talk about the basic structure of the elements?
A
Since antiparticles are not part of the structure of ordinary matter.

Q
Atoms are stable
If atoms/matter are composed entirely of Quarks and Leptons; each with extremely short life times, then how do atoms remain? Why do the atoms not "wink out" as each Quark and Lepton burns out?
A
Existing atoms are stable states of energy, and they remain for us to observe. As to why, I am afraid to guess, but its natural. Since they are stable, they do not wink out.

Q
Conservation of quarks
How come in decay reactions, the number and type of quarks are not conserved? For example, K0 -> p+ + p-, where the quark composition is:

K0 = ds'
p+ = du'
p+ = ud'
A
Interesting note. Note however that strange is a second generation quark. Material made up of first generation and second generation quarks are not stable, and they convert to energy and ordinary material.

Q
Color
What is the basis, theoretical or experimental, for the concept of colour introduced by QCD?

Quarks exist as one of 6 varieties of type: u, d, s, c, b, and t. However, they also exist as one of 3 varieties of colour: red, green, and blue. Does this mean that there are really 18 different quarks and how can the colour of a quark be "measured"?
A
I think color is used to differentiate the many kinds of force carriers and wavefunctions. They can also be called A, B, C, ... etc.

Colored quarks are not discussed in my lecture (notes), but some of you may have learned the color in other places. The quarks do not have color. However, there are many kinds of strong force carriers, and color has been used to differentiate them.

Q
Number of quarks
Can you derive the number of quarks with a given number of hadrons, mesons? What is the relativistic mass and how does it effect the Dirac Equation??
A
Actually, the number and kinds of quarks are proposed from the analysis of and relationships among mesons, hadrons etc.

Q
Storing antimatter
How would antimatter be stored? Since they would annihilate each other, is there technology to keep matter and antimatter separate? Would a strong magnetic field do?

How are antiparticles be created/collected for experimentation?
A
Positron/electron pairs generated by gamma-rays are accelerated. They travel in opposit directions and are kept separate until they reach the collision station, at which their products are analyzed. So are protons and antiprotons.

Q
Two modes of interaction between proton and antiproton
On page 153 of the course notes, you discuss the annihilation of a proton and an anti-proton. However, the next page discusses Bruce Cork's theory, where a proton and an anti-proton don't really annihilate, but instead convert to a neutron and an anti-neutron. Which theory is correct?
A
There are two modes of interaction between protons and antiprotons. They annihilate and they also carry out the charge transfer to become neutrons and antineutrons.

Q
Total energy and speed of particles
In the self-assessment for chapter 5, your answer for question 6 is that total energy of a particle becomes more negative as its speed increases. Isn't this only true for total negative energy? Doesn't total positive energy increase as the particle's speed increases, as stated on page 151? Also, are Dirac's equations just a validation of the fact that total energy stays constant?
A
Total energy of antiparticles decreases as their speed increases.
Total energy of particles increases as their speed increases.
Dirac's equation agrees with the fact that total energy stays constant.

Q
Angular momentum quantum number
I find the paragraph on page 169 about the angular momentum quantum number and their parity to be completely mystifying. Could more explanation on this subject be supplied?
A
Actually, all the quantum numbers are mystory at this point. Quantum numbers, including the angular momentum quantum number, are the results from solving the differential equations with boundary conditions. At this level, don't worry too much about them except consider them as labels of energy states. Take a course in nuclear physics or quantum mechanics to learn more about quantum numbers.

Q
Determination of half lives
Even though the half lives of most radioactive elements are much longer than the lifetime of a single human being, they can be determined with a great degree of certainty. Do anthropological interferences such as nuclear weapons testing and air pollution have to be considered in the determination of half lives?
A
Actually, half lives of radioactive nuclides (not elements) vary from pico seconds to trillions of years. There are many methods to determine half lives. We really do not need to measure them for a period of their half lives.

Q
Deriving Dirac's equation
Paul A. M. Dirac combined the theory of relativity with quantum mechanics. Can you derive Dirac's equation from Albert Einstein's relativity equation, E^2=(mc)^2? How does this equation suggest the existence of antimatter or antiparticles?
A
The derivation is given in the Lecture Notes, from

E = m c2. Your formulation has an error.

Q
X-rays from nuclear phenomena
Where exactly does X-ray emission occur in nuclear phenomena? Is there any other X-ray producing situation other than electron capture?
A
In the module when we discuss Interaction of Radiation with Matter, we shall point out the emission of X-rays as well.
Don't worry about all nuclear phenomena that generate X-rays at this point. Electron capture does produce X-rays.

Q
Scientific Theories
In observing the vast number of scientific fields of study, nuclear science is one of the very few based on statistical observation to confirm empirical observations. Other statistical based sciences are established because of an inability to completely determine initial conditions and system parameters, thus only statistical probabilities can be offered. Particle theory however, claims to describe matter in it's most basic form - quarks, and then builds upon that to describe particles that are combined of these basic building blocks. How can a basic theory be considered valid when it fails to describe all aspects of empirical observations (for example, the unity of gravity, strong, weak and electrostatic forces), or arising from the Heisenberg uncertainty principal fail to make desired system predictions, instead being forced to rely on statistical probability.
A
This comment is a result of deep thinking. The following are my addition.

Nuclear Science involves many theories, some of which involve statistics and others are based on experimental observations. However, some are based on statistical methods.

The analysis of particles and the study of particle relationships led to the conclusion that there are 6 fundamental quarks and leptons. I try to show how these fundamental building blocks are related to ordinary matter that we encounter daily. I do not want students to have the impression that we have now a unified theory about matter and materials.

The validity of a theory is destroyed whenever a contradiction is found. Yes, theroies help us predict the outcome from a certain set of conditions. The outcome may be subject to statistical, however.

Q
More particles to be discovered
Do you believe the discovery of more new particles will continue in the future? Do you think it is possible that all of the currently discovered particles could be composed of even smaller particles that have yet to be discovered?
A
Yes, I believe more particles will be discovered, and may be we will see new theries emerge on the foundamental particles.