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Physics - Objectives
Nuclear Physics
| Term | Definition |
|---|---|
| Atomic Mass | an atoms total mass in atomic mass units = protons + neutrons |
| Atomic Number | no. of protons |
| Protons | positively charged subatomic particles |
| Electrons | negatively charged subatomic particles |
| Neutrons | Neutral subatomic particles |
| Nucleons | Neutrons + protons form nucleus of an atom |
| 4 fundamental forces | Gravitational force, Electromagnetic force, Weak nuclear force Strong Nuclear force |
| Electromagnetism | refer to the interactions between charged particles consisting of an exchange between photons. Moving charges can create magnetic fields and therefore exert forces onto each other. |
| What does Electromagnetism Consist of? | electrostatic forces which are specifically on charged, static particles such as the repulsion between like charges and attraction between protons and electrons - this force helps hold the atom together, contributing to its stability |
| Strong Nuclear Force | binds the protons and neutrons in a atoms nucleus together and is much stronger than the electromagnetic force but can only operate within very short distances |
| How can an atom be stable? | For an atom to be stable, the strong nuclear force must be large enough to counteract the electromagnetic force and this is dependant on the number of protons and neutrons. |
| If nucleus isn't stable? | The atom will undergo radioactive decay releasing high energy alpha or beta particles, or electromagnetic photons (gamma rays). This process repeats until the SNF and electromagnetic forces are balanced |
| Radiation | energy travelling in the form of waves or particles as heat, light, sound etc. Radiation is a natural phenomenon making up the background radiation we experience daily from natural sources |
| Natural sources of radiation | Radioactivity from living organisms, sun+space, infrastructure, Earth's surface, Industrial uses of radioactive materials, radioactive waste |
| Electromagnetic waves | travel at a constant velocity in a vacuum, non-mechanical; does not require matter/medium for energy transfer, all transverse waves |
| Electromagnetic spectrum | Radio waves, microwaves, infra-red, visible light, ultra waves, x rays, gamma rays |
| Main properties of EM Radiation | 2 frequency and intensity, from left to right of the spectrum, frequency increases and wavelength decreases |
| Alpha, Beta and Gamma Radiation | All are ionising radiation, can break chemical bonds and can potentially cause harm to cells with prolonged exposure. |
| Ionising Radiation | carry enough energy to ionise an atom (gain or lose and electric charge). |
| Alpha radiation | Occurs when there is too much mass in an atom for its nucleus to remain stable and the atom emits an alpha particle to become more stable. 2 protons & 2 neutrons (called alpha particles are released as a helium atom |
| Properties of alpha radiation | are heavy, so their travelling speed is slow, high ionising ability, low penetrating power (highly ionising over short distances like few cm through air) but can be stopped by paper. |
| Beta Radiation | Occurs when there are too many neutrons in the nucleus. Neutron is changed into a proton and an electron. Newly created electron shoots out at 98% of the speed of light and this is the beta particle whereas the proton remains. |
| Properties of Beta Radiation | Much smaller than alpha particle, Very light (1/2000 AMU), Very fast (98% speed of light), medium ionising ability (sometimes metres) and penetrating power (few mm of skin), can be stopped by aluminum |
| Gamma Radiation | Excited nucleus is unstable and releases a gamma ray, could be excited due to prior alpha or beta decay and gamma radiation only result in de-excitation of the nucleus. |
| Properties of Gamma Radiation | made of photons, massless particles which travel in waves at the speed of light. Same energy as the X-rays but X-rays originate in the atomic shells. No mass, no direct ionising ability, high penetrating power, mostly stopped by lead |
| Half life | The time taken for half of the atomic nuclei of a sample to decay, different radioisotopes have different number of neutrons in the nucleus, hence their stability varies and can have different length half lives, more unstable nuclei decay quicker |
| Fission | a large unstable atom absorbs a slow neutron, which causes it to split into 2 smaller more stable nuclei. Also releases neutrons and energy in the form of heat. |
| Fusion | A nuclear reaction in which two or more light atomic nuclei combine to form one of more different, heavier atomic nuclei and subatomic particles |
| Mass defect | difference in mass between sum of individual protons and neutrons in a nucleus and the total mass of the nucleus due to binding energy. To find mass defect in fusion reactions, mass reactants - products |
| Binding energy | amount of energy required to split a nucleus into nucleons. |
| Isolated nucleons assemble | into a stable nucleus a small fraction of nuclear mass is converted into energy. |
| Formula: e=mc^2 | E = energy in MeV or J, M = mass defect, c^2 =931.5MeV or c=3*10^8ms^-1 speed of light |
| Nuclear power plants - Main components | Reactor vessels, Control rods, Fuel rods, Heat exchanger, Moderator, Radiation Sheild |
| Reactor vessels | encase and prevent radiation from escaping |
| Control rods | contain materials that absorb neutrons (like Cadmium and Boron) to control nuclear reaction. Lowering them increases neutron absorption, slowing down rate of reaction |
| Fuel rods | aluminium rods contain uranium isotopes (V-238 non fissile to absorb neutrons and U-235 fissile) |
| Heat exchanger | consists of many mini tubes with large surface area. Heated water is pressurised and runs through the tubes which heat a separate water source to create steam which spins the turbine and the generator converts this into electrical energy. |
| Moderator | slows down fast moving neutrons by making them lose kinetic energy as they collide with the moderator. Most effective with substances with small nuclei including graphite, normal water, carbon dioxide, or heavy water containing deuterium. |
| Radiation sheild | encases the core with 2m thick shield made from layers of concrete, graphite (reflects neutrons back into core) and lead to prevent gamma rays and neutrons from excaping. |
| Steps to electricity generation 1-3 | 1. Fission in the core releases a vast amount of heat energy 2. Core temp = 500-1500degC 3. the heat energy is removed from the core by pipes containing coolant |
| Coolant | Coolant = liquid sodium, water, CO2 or heavy water |
| Steps to electricity generation 4-6 | 4. The coolant enters a heat exchanger where the heat energy is transferred to pipes containing water. 5. The water is converted to steam 6. The steam rotates a turbine that drives the generator |
| Uncontrolled Reactions | when neutrons escape too quickly to maintain the steady chain reaction leading to a rapid release of nuclear energy almost instantaneously causing an explosion. Magnifies chain reaction effect too quickly - so used in bombs |
| Controlled reactions | allow for a steady and controlled chain reaction to occur through absorption and reduced speed. Used in nuclear power plants. |
| Advantages of Nuclear energy | Clean energy source, creates lots of jobs, international relations, low running costs and longevity, variety of uses, efficiency |
| Disadvantages of nuclear energy | radioactive waste, weapons and war, resource scarcity, indirect energy - greenhouse gases, set up costs, Uranium mining - not ecofriendly |
Created by:
meena.srinivasan
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