Chapter 7 - Radioactivity

1m can fit 10,000,000,000 atoms side by side.10,000 nuclei side by side fit in an atom.Radiation comes in the form of alpha, beta and gamma particles. Alpha has 2 protons and neutrons, beta is an electron; and gamma is high energy light. Background radiation consists of many things, including radon gas, rocks, human body, food, cosmic rays, artificial sources, medical, nuclear power, weapon tests, and many more

Key words:

Isotope - an isotope of an element has the same atomic number, but a different number of neutrons. This means it has a different atomic mass

Atomic number - number of protons.

Atomic mass - number of protons and neutrons.

Radioactive - material made up of atoms that are likely to decay.

Radiation - particles of energy that is released when a radioactive material decays.

Democritus (400BC) The atom - Democritus was thinking about matter. He imagined cutting his cheese in half, and half again, and half again... What would it look like when he couldn't cut it anymore? Small, solid spheres whose surface determines the materials properies.

JJ Thomson (1880) The plum pudding model - Thomson was investigating charges, electrons and static energy. He rubbed amber wih fur, which caused a static effect. He realised that for objects become statically charged it hase to loose an electron. 

Ernst Rutherford (1910) Nuclear model - He uses alpha ray and cathode ray to prove the plum pudding model. His PhD student, Geiger, to fire alpha particles at thin gold foil. He expected alpha particles will travel through the atom, and there will be little or no scattering. They discovered that most passed straight through, some deflected and very view deflected back. They concluded that most of the atom is empty space, there must be a small area of positive charge, that must be very small but very dense

Alpha - stable way of removing charge from larger unstable nuclei. Made from 2 protons and 2 neutrons (helium nucleus). Relative mass of 4. Charge of +2.

Beta- way of changing the ratio of protons to neutrons in smaller unstable nuclei. Made from an electron. Relative mass of 0. Charge of -1.

Gamma - way of reducing energy in a nucleus without changing it. High energy electromagnetic wave (light). Relative mass of 0. Charge of 0.

It takes energy to rip electrons from a nucleus.

Ionisation occurs when enough energy is transferred to an atom. This removes an electron, leaving the atom charged. The energy can be delivered in two ways by radiation: through a direct collision, or at a distance by charge attracting or repelling the electron.

Alpha is the most ionising because it has the largest mass (4) and the most charge (+2). Then, Beta is the second as it has the second largest mass (1/2000) and the second largest chage (-1). Gamma is least ionising because it has the smallest mass (0) and the smallest charge (0).

Alpha transfers energy very easily and loses energy, so stops easily. Gamma does not transfer easily and loses energy slowly, so takes a long time to stop.

Sample - a given amount of material within which atoms are active and decaying.

Activity - the amount of decay occuring each second.

Decay - the random process where an unstable isotope in a sample changes to become more stable by emitting radiation.

Half-life - the time it takes for a sample of radioactive isotopes to decay to half that number.

Tracers is a radioactive isotope that emits gamma radiation. It is allowed to pass through an organ. It emits gamma so is less likely to ionise the body and cause damage; it can penetrate through the body to a detector. Tracers are used to locate growths, detect blood flow, and see bone growth.

Precautions that are used include lead lined suits, lead on syringes and the radiation is handled in a protected box. Gamma radiation carries energy that ionises the cell. If enough energy is transferred, the cell will be destroyed. It must be gamma because it is able to penetrate the body furthest, and be focussed.

Radioactive implants are invasive and can be referred to as a 'seed'. It could be gamma or beta, and it can have a longer half-life.

Alpha can be used in smoke alarms, beta can be used to measure paper or foil thickness, gamma can be used in sterilization and medical treatment and tracers.

Nuclear fission is when the nucleus splits, it only occurs in larger nuclei.

A neutron is absorbed, the nucleus then becomes unstable. The nucleus breaks apart into two, roughly even, isotopes. This releases gamma radiation and 2 or 3 neutrons. This could be unstoppable because it creates a chain reaction. 

Control rods absorb neutrons and can be raised or lowered to control the rate of the chain reaction.

Concrete sheild absorbs radiation and makes it safe to work around the site.

Water moderates and slows neutrons and conducts heat to keep them safe. It also transfers energy and turns into steam to drive the turbines.

Fuel rods are only 3% Uranium-23 and reduces the rate of the chain reaction.

Heat exchangeallows heat to transfer out of the sheild without the contaminated water/steam.

This is when two nuclei interact and join to become a larger nucleus. It relies on the nuclei having high temperature and high pressure.

There must be high pressure so the particles will collide more frequently to overcome failures. There must be high temperature so the particles will collide with high speed and energy to overcome the repulsion of the positive nuclei.

Nuclear fusion occurs naturally in stars, like the sun. It can happen there because there is high temperature and pressure, combined with gravity. Hydrogen isotopes fuse and becomes helium. 5,000,000,000kg of mass is converted to energy each second.

Nuclear power - the raw materials are sourced in the sea, with the waste product of tritium and helium, created at 150,000,000 degrees centigrade. Magnetic fields can't contain the plasma . it is safe, it doesn't create a chain reaction.

There are bad sides, such as nuclear weapons, waste, accidents and disasters. It takes thousands of years to decay to safe isotopes. Chernobyl and Fukashima had to close vast areas of land for a long time; also leads to contamination and thousands of deaths.

Also, there are good sides, such as that it will save lives and has next to no carbon emissions, and new technologies will be developed. There is a huge amount of energy per kg to meet demand reliably. There are fewer deaths due to reduction of the use of fossil fuels. Additionally, it slows global warming.

Radioactive dose is how much radiation on average each person gets in a year from each person, measured in sieverts.

Most background radiation comes from radon gas, which seeps from radioactive sources deep underground. It is very dangerous as we cannot protect ourselves from it. It emits alpha radiation, and is in the air so we can do nothing but breathe it in.