13.+Nuclear+Physics



**Nuclear physics** is the branch of physics concerned with the nucleus of the atom.

Changes can occur in the structure of the nuclei of atoms. These changes are called **nuclear reactions**. Energy created in a nuclear reaction is called **nuclear energy**, or **atomic energy**. Nuclear energy is produced naturally and in man-made operations under human control. Nuclear energy is produced in two different ways, in one, large nuclei are split to release energy. In the other method, small nuclei are combined to release energy. For a more detailed look at nuclear fission and nuclear fusion, consult the nuclear physics page.
 * **Naturally:** Some nuclear energy is produced naturally. For example, the Sun and other stars make heat and light by nuclear reactions.
 * **Man-Made:** Nuclear energy can be man-made too. Machines called **nuclear reactors**, parts of **nuclear power plants**, provide electricity for many cities. Man-made nuclear reactions also occur in the explosion of atomic and hydrogen bombs.
 * **Nuclear Fission**: In nuclear fission, the nuclei of atoms are split, causing energy to be released. The atomic bomb and nuclear reactors work by fission. The element uranium is the main fuel used to undergo nuclear fission to produce energy since it has many favorable properties. Uranium nuclei can be easily split by shooting neutrons at them. Also, once a uranium nucleus is split, multiple neutrons are released which are used to split other uranium nuclei. This phenomenon is known as a **chain reaction**.

**Nuclear Physics Terms** > **Proton**: A positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element. > **Neutron:** A subatomic particle forming part of the nucleus of an atom and having no charge. > **Nucleon:** A proton or a neutron. > **Atomic Number:** The number, equal to the number of protons in an atom that determines its chemical properties. Symbol: Z > **Atomic Mass:** The mass of an atom expressed in atomic mass units. > **Strong (nuclear) Force:** A fundamental force that is associated with the strong bonds between quarks and other subatomic particles. > **Weak (nuclear) Force:** One of the four fundamental forces that is associated with nuclear decay. > **Binding Energy:** The energy needed to separate the constituent parts of an atom or nucleus > **Mass Defect:** The difference between the mass of an atom and the sum of the masses of its individual components. > **Electron-Volt:** A unit of energy > **Mass-Energy Equivalence:** All mass represents an equivalent amount of energy. 1 amu = 931 MeV. > **Radioactivity:** Emission of radiation as a consequence of a nuclear reaction, or directly from the breakdown of an unstable nucleus. > **Half Life:** The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay. > **Alpha Particle:** A positively charged helium nucleus (consisting of two protons and two neutrons). > **Beta Particle:** An energetic electron produced as the result of a nuclear reaction or nuclear decay. > **Gamma Particle/Ray:** Very high frequency electromagnetic radiation emitted as a consequence of radioactivity. > **Fission:** The process whereby one item splits to become two. > **Tomography:** Imaging by sections or sectioning.

An atom consists of a positive charged atomic nucleus where you can find protons and neutrons and it consists of a negative charged atomic shell with electrons. In every atom the number of the electrons is equal to the number of the protons so it is neutral. The number of the protons decides which chemical element the atom is. The first element in the "Periodic table of the elements" is hydrogen. The elements in the "Periodic table of the elements" are sorted by the number of the protons. The atomic nucleus of a hydrogen atom consists of only one proton. But there are a few isotops of every element. Isotops are atoms with the same number of protons, but another number of neutrons. The different isotops of one element do not differ in their chemical properties. There are for example three isotops of hydrogen. The first isotop is the one I wrote about. The second isotop of hydrogen is deutrium with one proton and one neutron in his atomic nucleus and the third isotop is tritium which has got one proton and two neutrons in his atomic nucleus. In the atomic nucleus of a tritiumatom there is no balance between the protons and the neutrons so it is instable and decays. The particle which is emited from this decay is radioaktiv and it is charged. You can make ions of atoms. We can say that an ion is an atom which has got less or more electrons than protons. An ion is not neutral an so it is radioactif.






 * Radioactivity **

Radioactivity means that atoms decays. The reason for this decays is that they are instable. A atomic nucleus is instable when he is to heavy or when a balance is missing between the protons and the neutrons. Every atom which has got a higher number of nucleons (protons and neutrons togehter) than 210 is instable. There are three types of decays: alpha decay, beta decay and gamma decay. Because it is impossible today to say which atomic nucleus will be the next who decays there statistics. We can say how many atomic nucleus will decay in a certain time. This is the princip for half lifes. After one half life a half of the atomic nucleus of a certain material decayed. Plutonium-239 for example has got a half life 24,000 years, radium-228 has got a half life of 6.7 years, thorium-232 has got a half life of 14,000,000,000 years and polonium-212 has got a half life 0.0000003 seconds. The activity is the number of decays devided by a certain time. the unit of the activity is becquerel. 1 becquerel is one decay per second. So 20 becquerels are 20 decays per second. To prove these decays there is a geiger counter. It consists of a closed tube which is often filled with argon. At the end of the tube there is a wire, which is not allowed to touch the other end of the tube or the walls. The wire is charged positive and the walls are charged negative. A radioactive particle which flows into the tube ionizes one or a few gas atoms. The out-pushed electrons go to the wire. The consequence is a voltage surge. This voltage surge is shown on an output device as a decay. On the photo there shown a geiger counter. Geiger counter detects radiation.



**The Alpha Decay**

When we talk about the alpha decay then it means that a twice positive charged heliumion (helium atomic nucleus) is emited from the atomic nucleus. Then we find two protons ans two neutrons less in this atomic nucleus, so it is lighter. The alpha radiation is the most dangerous of the three types of radiation, but a sheet of paper is enough to protect oneself. The skin protects us also from alpha radiation.




 * Beta Decay **

There are two types of the beta decay. The one is the beta minus decay and the other is the beta plus decay. When we talk about the beta minus decay a neutron decays into a proton, an electron and an antineutrino. The electron and the antineutrino are emited. The radioactive particle is the electron. The number of nucleons do not change, but we have got one proton more than before the decay. 2 or 3 cm of wood are enough to protect oneself.



**The Beta Plus Decay**

When we talk about the beta plus decay a proton decays into a neutron, a positron (the antiparticle of the electron) and a neutrino. The positron and the neutrino are emited. The radioactive particle is the positron.



**The Gamma Decay**

When we talk about the gamma decay high-energy electromagnetic waves are emited from the atomic nucleus. This waves are photons, which have got a higher frequency and less wave long than light. A gamma decay can happen after an alpha decay or a beta decay, because the atomic nucleus is very energitif. You need a big wall of lead to protect yourself from gamma radiation.



**__Nuclear Reactions and Their Applications__**

The animation of a nuclear fission:



We must begin which Einstein's famous formula: E=mc2 (E stands for energy, m stands for mass and c stands for the speed of light in the vacuum). This formula makes it possible transform masse in energy. Atomic nucleus have got different binding energy. The binding energy is the energy which holds the nucleons together. Because of this fact there is in every atomic nucleus a mass defect. A free proton and a free neutrons weighs more than deutrium (heavy hydrgen, consists of one proton and one neutron). Iron has got the highest binding energy and stands in the middle of the "Periodic table of the elements". When somebody goes closer to this middle with fissions or fusions a part will be transformed into energy.

The animation of a nuclear fusion:



in which //E// is the energy equivalent (called **mass energy**) of mass //m//, and //c// is the speed of light.
 * Mass and energy are related by what is certainly the best-known equation in physics:

**Examples of E=mc^2:**

For a proton: m = 1.67 x 10 -27 kg

E = mc 2 E = (1.67 x 10-27 kg) (3 x 108 m/s)2 = 1.5 x 10-10 J  Convert joules to energy in eV: E = (1.5 x 10 -10 J)(6.24 x 1018 eV/J) = 938 MeV

1 u = 931.5 MeV/c 2

In the equation E=mc2

E is energy

m is mass

What is that c is the speed of light, but why use the letter c? What does c stand for?


 * __ General Applications Of Nuclear Physics __**


 * __Medical Imaging__-(such as CAT scans and MRI) is used to determine the amount of radiation a person has been exposed to. There have been quite a few different techniques and more are still being developed and improved presently.
 * __Radioactive Dating__-uses radioactive properties of certain elements to determine the age of something such as an ancient person.
 * __Radiation Detection__-involves different instruments used in order to detect radiation present somewhere.

=Nuclear Weapons and War =

**The Facts**: It is known that there are more than enough nuclear weapons in existence today to kill everyone in the world. Many countries have nuclear weapons, and the threat of a nuclear war brings fear to many. Some people believe that it is necessary to have nuclear weapons. Others believe that all nuclear weapons should be disposed of and further manufacturing of them should be deemed illegal by international law. Still others are content with the existence of nuclear weapons, but seek stricter methods to control their use. Here, we examine some facts about nuclear weapons and differing viewpoints.
 * The atomic bomb that the U.S. dropped on Hiroshima killed over 100,000 people and the radiation left from it posed a risk to even more people.
 * A new bomb, the hydrogen bomb, has already been developed. It is over one thousand times as strong as an atomic bomb. In fact, it needs an atomic bomb just to start its explosive reaction.
 * Many countries, including the U.S. and Russia, have nuclear weapons.
 * Many other countries are developing nuclear weapons. Some are suspected of already having them. These countries include North Korea, Israel, South Africa, India, Iraq, Iran, Syria, Libya, Algeria, and Pakistan.

Essential Questions for your Use
 * 1) How many people where killed in the Atomic Bomb droppping on Hiroshima?
 * 2) What formula is repersented by mass and energy?
 * 3) What is Nuclear Physics?
 * 4) What is energy created in nuclear reactions?
 * 5) When talking about Alpha decay what does it mean?
 * 6) What are the two types of Beta Decay?
 * 7) What decay has to do with the atomic nucleus being very energitif?
 * 8) What can you use to protect yourself from Gamma Radiation?
 * 9) Name two countries that are developing nulcear weapons?
 * 10) What is the name of this website?

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