Physics Chapter 10 Nuclear Physics By: J. Rowe

Planetary Model Electron Cloud Model

Basic Concepts There are 3 different types of particles we find within the atom. These are known as the Proton, the Neutron, and the Electron. ProtonNeutronElectron Size1 amu Negligible Mass1.67x x Charge+1e--1e e, or elementary charge, is the basic charge used by the particles of the atom. Elementary charge is always 1.60x C.

Basic Concepts Cont. The Proton and the Neutron are found in the nucleus of the atom. Whereas the Electron is found outside the nucleus of the atom, it circulates around the nucleus either as the Planetary model of the atom or as the Quantum Mechanical model of the atom. The Quantum Mechanical model of the atom, or the electron cloud, is a more recent finding on the structure of an atom. It shows that electrons do not circulate around the nucleus in a planetary fashion, but instead they follow their own orbitals, and it is next to impossible to locate the exact location of an electron except for knowing the orbital that the electron circulates on.

Planck’s Photon: Preface During the time of Einstein and other scientists were well on their way of discovering the different properties of light, two well known theories, both backed by scientific evidence, were accepted as answers to what light could be constructed from. The first theory was the particle theory. This entailed that light was an array of particles made from tiny, massless particles called photons. It was this theory that was backed by Albert Einstein. The second theory was the wave theory of light. This theory was brought about by Christiaan Huygens and suggested that light was in fact, a wave. This was further backed by Thomas Young’s famous Double-Slit experiment. In the end, the two theory’s were equal, but was light a particle, or a wave?

Planck’s Photon: Preface Cont. The answer, is both. In the 1920’s, Louis De Broglie had hypothesized that any quantum particle, whether it be an electron, or a photon, exhibits both particle like and wave like properties. The reason was because of the way we interact with the particles themselves. When the Compton effect was done, we could see that light was obviously a wave. However when the Double-Slit experiment was completed, we could evidently see that light was a wave instead of a particle. Wave-Particle Duality was formed when Do Broglie realized that both could be used in conjunction with one another to explain that light in fact reacts to the way we test it. It was Albert Einstein who would be able to back De Broglie’s findings.

Planck’s Photon After that, Planck was able to put his own constant (h = 6.63 x ) That was used to equalize both ends of the equation. Because of Planck, Einstein, and De Broglie, we are now able to calculate the frequency, energy, and wavelength of a photon. Under the photon theory of light, a photon is a bundle of electromagnetic energy. Photons are always in motion and have a constant speed of light to all observers, at the speed of light. The formula for speed of light is c = x 10 8 m/s.

Planck’s Photon We now know that Albert Einstein, had used De Broglie’s findings to spearhead the particle wave duality. The reason that Einstein had agreed with the link between particles and waves was because of Max Planck. Planck had been tackling the problem of blackbody radiation (not important). In order to do so, he had decided to quantise energy. He called it photons. He had theorized that photons had different amounts of energy, and that the frequency of the photons (remember particle wave duality) was proportional to each other. This can be read as (The energy of a photon is equal to the frequency of a photon as well.

Binding Energy When doing the electricity unit, we found that like charges would repel each other, and that opposite charges would attract each other. Let’s think about the atom. We know that the positive protons are all centered in the nucleus, whereas all the negative electrons are scattered in a cloud out side the nucleus. Has it ever occurred to you as to why the protons don’t repel away from each other, and why the electrons don’t just stick to the nucleus instead?

Binding Energy Cont. The answer is known as the Strong Nuclear Force. The Strong Nuclear Force is a fundamental for of nature that exists between Neutrons that stops that from them from separating due to the opposing forces that exist protons. Mass and energy are proportional and equal to each other. There is always an equal amount of mass and energy in the universe. But they are always converting to each other. For example, an atom’s weight is 1 but if you were to take apart the atom it would weigh more. This is because when the particles are put together, energy is used to combine them and it is converted. Mass is converted to energy to hold the atom together.

Radioactivity Sometimes, in unstable isotopes of atoms, the Strong Nuclear Force is unstable, the result, is small bits and pieces of energy are converted to mass and are ejected from an atom. There are 2 different types of decay we need to know about. Nuclear Reactions are reactions that happen within the atom, for example, Alpha decay could be considered a nuclear reaction. Essentially a nuclear reaction is when atoms add together to form bigger atom (fusion) Or they break onto two smaller atoms (fission)

Alpha Decay Alpha decay can most simply be described like this: 1) The nucleus of an atom splits into two parts. 2) One of these parts (the alpha particle) goes zooming off into space. 3) The nucleus left behind has its atomic number reduced by 2 and its mass number reduced by 4 (that is, by 2 protons and 2 neutrons).

Beta Decay Beta decay is somewhat more complex than alpha decay is. These points present a simplified view of what beta decay actually is: 1) A neutron inside the nucleus of an atom breaks down, changing into a proton. 2) It emits an electron and an anti-neutrino which go zooming off into space. 3) The atomic number goes UP by one and mass number remains unchanged.

Are all these processes & particles related ??? Is the atom really the smallest functional aspect of matter ?? Is there anything smaller than the proton & neutron or electron ? What makes up a proton or neutron ? Are there other particles besides PEN, photons & neutrinos ?

Particles of Matter : 1 - Elementary / Fundamental Particle – the smallest indivisible portion of matter a.k.a. not made up of any other functional substance a.k.a. They have no measurable internal structure. There are 17 types of fundamental particles e.g. quarks, gluons, photons, gravitons etc… These are the fundamental objects of The Quantum Field Theory and are divided up in many families and sub-families. Elementary Particles are grouped based on their spin: Fermions have ½ integer spins while Bosons have full integer spins There are 2 types: Elementary Particles & Composite Particle

What is Integer Spin ?? All particles have an intrinsic angular momentum, as if they were little spinning balls of energy Since we are talking about sub-atomic particles, we refer to sub-atomic energy as Quantum Energy. The basic Quantum Energy in a spinning particle can be calculated using the formula E = h , with E = energy, h = Planck’s constant & , = angular velocity or frequency If an object spin has enough energy to = 0,1 etc full integer increase/decrease in Plank’s constant, it has full integer spin If an object’s spin is only a fractional increase / decrease in Planck’s constant, it has a ½ integer spin Planck’s constant, is h = × m 2 kg / s

Elementary Particles

Fermions Fermions have mass and are the building blocks of matter Named after Enrico Fermi & have a spin number of -½ or ½ There are 12 types & each type is called a “flavor” Fermions are divided into 2 groups based on their interaction with the Strong Binding Force. Quarks: up, down, strange, charm, bottom, top. Quarks come in three pairs, called "generations." One member of each pair has a charge of ⅔. The other member has charge - ⅓. Leptons: electron, muon, tau, electron neutrino, mu neutrino, tau neutrino. The neutrinos have charge 0, hence the neutr- prefix. The other leptons have charge -1. Each neutrino is named after its corresponding original lepton: the electron, muon, and tauon.

Elementary Particles

Bosons bosons are mass-less and behave as force carriers for fermion interactions Bosons all have full integer spins. Bosons include: photons and gluons, higgs boson, graviton, Z & W bosons o Photons – mediate electromagnetic radiation, o Higgs Boson – mediates mass transfer between elements o Z & W Bosons – mediate nuclear radiation energy transfer o Gravitons – mediate the gravitational forces

2 – Composite Particle – or Hadron is formed from a group of elementary particles. Composite or group particle can be formed from fermions (called baryons) or from bosons (called mesons) Composite fermions, in which case they are called baryons. Composite bosons, in which case they are called mesons. Baryons (3 types) Nucleons are the fermionic constituents of normal atomic nuclei: Protons, composed of two up and one down quark (uud) Neutrons, composed of two down and one up quark (ddu) Particles of Matter : There are 2 types: Elementary Particles & Composite Particle

Composite Atomic Nuclear Structure The Nucleus The Neutron The Proton

How do these Particles behave ? The Standard Model is the most accepted way to explain how particles behave, and the forces that affect them. According to this model, the elementary particles are further grouped into quarks, leptons, and gauge bosons, with the Higgs boson having a special status The Standard Model to the rescue !!!

Summary

The End …. Right ??