Radioactivity , and ; their properties and experimental identification; applications, e.g. to relative hazards of exposure to humans

The experimental investigation of the inverse square law for  rays

Applications, e.g. to safe handling of radioactive sources

Background radiation; its origins and experimental elimination from calculations

• recall the charge, mass, penetration power (hence how to distinguish them) and ionizing power of each type of radiation
• recall how to perform an experiment using a radioactive source safely.
• Explain how the ISL relates to safety rule of keeping the source as far from you as possible.
• Recall sources of background radiation and how to eliminate it from calculations and practical data.

Exponential law of decay Random nature of decay

Half-life and decay constant and their determination from graphical decay data

Applications, e.g. relevance to storage of waste radioactive materials; radioactive dating

• recall tha radioactive activity is spontaneous (it cannot be changed by changing pressure/temperature etc.)
• it is also random - direction that ray is emitted and which nucleus will decay when - is impossible to say! But when dealing with large numbers of atoms the mathematics of probability can be employed.
• Recall that radioactive decay is an exponential process therefore portability is applicable!
• You should be able to sketch a graph of number of nuclei against time (marking on multiples of N_o and T (half) to show th exponential relationship)
• recall that the rate of decayN/t (or Activity of the sample) is proportional to the number of atoms of the radioisotope present in the sample.
• Recall that the decay constant () is the constant of proportionality between activity and sample size. It gives a measure of the probability that a particular nucleus in a sample will decay in a given time. It has units of time^-1.(The negative sign before it is because the number present decreases with time - so that would lead to a negative constant!)
• recall that the half life of a radioisotope is the time taken for half of the radioactive nuclei of that isotope substance in a sample to decay. This is constant for any given isotope. The units are those of time.
• appreciate the variation in natural half-lifes from nanoseconds to millions of years and the affect this has on uses and safeguards when disposing of waste.
• know about carbon dating.

Variation of N with Z for stable and unstable nuclei

Graph of N against Z for stable and unstable nuclei

• recall that Z is the atomic number (proton number)
• sketch this graph - with labelled axes and values!
• mark in alpha, beta and positron emitters
• know that positron emitters are the result of artificial transmutation experiments

Possible modes of decay of unstable nuclei , +, -, nucleon emission, electron capture

Changes of Z and A caused by decay and representation in simple decay equations

• modes of decay - don't forget the neutrinos! - check out the Feynman diagrams that you did in module 1
• decay equations should be most simple for you!

Existence of nuclear excited states

ray emission

Application, e.g. use of technetium 99m as a gamma source in medical diagnosis

• when the nucleus emits a radioactive particle the nucleons left are not all necessarily in their lowest possible energy state - they therefore emit a gamma ray as the 'rearrange' themselves into a more stable configuration
• You should know the reasons why Tc99m is so valued and how it is used

Probing matter

Scattering as a means of probing matter, including a qualitative discussion of the choice of bombarding radiation or particle, the physical principles involved in the scattering process, the processing and interpretation of data

• probing matter can be done by shooting particles into the nucleus (scattering) and making conclusions on its structure by what happens (recoil, deflection or the knocking out of another particle)
• revise the Rutherford experiment from Module 1
• as well as alpha particles high energy protons, neutrons, deuterium nuclei and electrons can be used (see particle accelerators as to how they are produced)
• be able to interpret the way that the particles produced make traces in a magnetic field (charged ones get deflected - use FLHR to determine the charge)

Nuclear radius

Estimation of radius from closest approach of alpha particles and determination of radius from electron diffraction; knowledge of typical values

Dependence of radius on nucleon number

derived from experimental data

• understand that if an alpha particle is shot at a nucleus it will experience electrostatic repulsion and come to a stop a distance from the centre that depends on the charge in the nucleus and the kinetic energy of the particle projected at it.
• be able to evaluate the distance of closest approach as the kinetic energy of the particle would be changes into potential energy at the point of closest approach (see text book page 151 for calculation and Sang page 8)
• recall that the nucleus has a value of a few femtometres (in Rutherfords day it was thought to be of the order of 10^-14m)
• understand that measurements of nuclear size can be found from electron diffraction patterns (Sang page 11-13 and text book page 152 to 153)
• know that nucleons are close-packed within the nucleus making all nuclei have the same density.
• know what to plot as graphs from the equation to find r_o