7 Radioactivity and particles

7.03 know the terms atomic (proton) number, mass (nucleon) number and isotope

Atomic (proton) number is the number of protons in the nucleus of an atom.

Mass (nucleon) number is the total number of protons and neutrons in the nucleus of an atom.

An isotope is an atom of the same element, i.e. it has the same number of protons/same atomic number, but has a different number of neutrons/different mass number. Two atoms with the same atomic number but different mass numbers are isotopes 

see 7.02 for example 

7.04 know that alpha (α) particles, beta (β−) particles, and gamma (γ) rays are ionising radiations emitted from unstable nuclei in a random process

There are three types of ionising radiation:

Alpha (α), Beta (β) and Gamma (γ)

One radioactive source can release different types of radiation.

Ionisation is when an atom loses or gains an electron, causing it to become an ion (an atom which is positively or negatively charged).

7.07 describe the effects on the atomic and mass numbers of a nucleus of the emission of each of the four main types of radiation (alpha, beta, gamma and neutron radiation)

Alpha decay:

·         2 protons and 2 neutrons are lost.

·         Mass number decreases by 4

·         Atomic number decreases by 2

Beta decay

·         1 neutron is converted to an electron (lost from the atom) and proton

·         Mass number is unchanged

·         Atomic number increases by 1

Gamma decay

·         Energy is lost from an atom in the form of an electromagnetic wave

·         Mass number is unchanged

·         Atomic number is unchanged

7.13 use the concept of the half-life to carry out simple calculations on activity, including graphical methods

Numerical:

A radioactive source has a half-life of 2 hours. If the mass starts at 40mg, what will the mass be after 4 hours?

 

 

Graphical:

Several different times for the half-life can be calculated and averaged.

7.14 describe uses of radioactivity in industry and medicine

Gamma radiography:

Medical tracer:

–          Radioactive tracer put in body (swallowed/injected)

–          Detector put around body

–          Computer generates an image

Gauging:

–          Coal absorbs a lot of radiation

–          If only a small amount of radiation is detected back after it is reflected by what you are trying to gauge, lots of coal is present.

Radiotherapy

  • High doses of radiation are directed at cancer cells
  • Cancer cells are killed

Pipe tracers:

–           A radioactive material which emits gamma radiation with a short half-life is put in the water

–          A detector is placed above the pipe

–          A spike in detected radioactivity suggests a leak in the pipe

Sterilisation:

  • Medical equipment irradiated
  • Kills all living matter on tools (e.g. bacteria)

Carbon dating:

7.17 know that nuclear reactions, including fission, fusion and radioactive decay, can be a source of energy

  • Nuclear Fission:

The process where heavy atoms are split into smaller, lighter atoms. This releases energy.

  • Nuclear Fission:

The process where lighter atoms are forced to join together to make heavier atoms. This releases energy.

  • Radioactive Decay:

Within the core of the Earth, radioactive isotopes of elements such as uranium, thorium and potassium provide a large proportion of the heat within the Earth through radioactive decay.

7.20 describe how a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei

Chain Reaction:

  • The three neutrons produced by the fission may hit other nuclei of uranium 235, causing the process to repeat.
  • For a chain reaction to occur, there is a minimum mass of uranium 235 required. This is known as the critical mass.

7.21 describe the role played by the control rods and moderator in the fission process

Moderator:

  • Graphite is used as a moderator.
  • The purpose of the moderator is to absorb some of the kinetic energy of the neutrons to slow them down.
  • This is because slow neutrons are more easily absorbed by uranium 235 nuclei.

 

Control rods:

  • Made of boron or cadmium.
  • The purpose of the control rods is to absorb neutrons and completely remove them from the fission process.
  • Helps adjust the rate of nuclear fission in the reactor.

7.26 explain why nuclear fusion does not happen at low temperatures and pressures, due to electrostatic repulsion of protons

  • For nuclear fusion to occur, very high temperatures are required to overcome the repulsive force between the positively charged nuclei of each isotope.
  • High pressures are also needed to increase the chance of fusion between the nuclei.
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Section 1: Principles of chemistry

      a) States of matter

      b) Atoms

      c) Atomic structure

     d) Relative formula masses and molar volumes of gases

     e) Chemical formulae and chemical equations

     f) Ionic compounds

     g) Covalent substances

     h) Metallic crystals

     i) Electrolysis

 Section 2: Chemistry of the elements

     a) The Periodic Table

     b) Group 1 elements: lithium, sodium and potassium

     c) Group 7 elements: chlorine, bromine and iodine

     d) Oxygen and oxides

     e) Hydrogen and water

     f) Reactivity series

     g) Tests for ions and gases

Section 3: Organic chemistry

     a) Introduction

     b) Alkanes

     c) Alkenes

     d) Ethanol

Section 4: Physical chemistry

     a) Acids, alkalis and salts

     b) Energetics

     c) Rates of reaction

     d) Equilibria

Section 5: Chemistry in industry

     a) Extraction and uses of metals

     b) Crude oil

     c) Synthetic polymers

     d) The industrial manufacture of chemicals