Ionizing Radiation From The Nucleus
Overzicht
Put a radiation counter on a bench in an empty room, switch it on and walk away. It clicks. Not steadily, and not because anything in the room is broken: a click now, two more a second later, then a pause, then another. Those clicks have been arriving since long before anyone built a counter to hear them, and they are coming from the bricks in the wall, from the food in your bag, from the air you are breathing and from the depths of space. Somewhere inside each of those sources, a nucleus that had held together for a million years chose this particular second to fall apart, and nothing that has ever been done to it changed that choice by a fraction of a second.
This lesson is about that behaviour and about how physicists learned to work with it without ever being able to predict any single event. You will find out what an unstable nucleus throws out and why, why a sheet of paper stops one kind of radiation while several centimetres of lead only weaken another, how to strip the ever present background out of a reading before you trust it, and how a table of counts against distance can name an invisible emission you never saw. Extension Tier candidates go one step further and write the decay down as an equation, using nothing harder than subtraction. By the end you will be able to look at a set of detector readings and say what the source is doing.
Doelstellingen
- Some atomic nuclei are unstable. The nucleus emits particles or radiation and the nucleus changes to that of a different element and becomes more stable. This is a random process called radioactive decay.
- Energy is emitted by changes in the nucleus.
- Unstable nuclei emit alpha particles, beta particles, or neutrons, and electromagnetic radiation as gamma waves. Neither chemical nor physics processes affect this behaviour. These substances are said to be radioactive and although the general process follows a pattern this radioactive decay is a random process. It is impossible to predict when a particular atom might decay.
- Background radiation is around us all of the time. It comes from a range of sources, such as radioactive substances in the environment, from space or from devices such as X-ray machines in hospitals.
- An alpha particle consists of two neutrons and two protons (i.e. a Helium nucleus). A beta particle is a high speed electron ejected from the nucleus as a neutron turns into a proton. Gamma radiation is electromagnetic radiation from the nucleus.
- Nuclear equations are used to represent radioactive decay. Students will be required to balance equations for single alpha and beta decay, limited to the completion of atomic number and mass number. The identification of daughter elements from such decays is not required.
- Properties of the alpha, beta and gamma radiations are limited to their relative ionising power, their penetration through materials and their range in air.
Mindmap
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- What is an alpha particle? A. A high speed electron from the nucleus B. Two protons and two neutrons C. Electromagnetic radiation from the nucleus D. A neutron ejected from the nucleus Answer: B
- A nucleus has mass number 210 and atomic number 84. It emits an alpha particle. What are the mass number and atomic number of the nucleus produced? A. Mass number 206, atomic number 82 B. Mass number 210, atomic number 85 C. Mass number 206, atomic number 86 D. Mass number 209, atomic number 83 Answer: A
- Which radiation has the greatest ionising power and the shortest range in air? A. Alpha B. Beta C. Gamma D. All three are the same Answer: A
- A radiation passes through a sheet of paper without being reduced, but is stopped by 3 mm of aluminium. Which radiation is it? A. Alpha B. Beta C. Gamma D. A neutron Answer: B
- A counter reads 264 counts per minute next to a source. With the source removed it reads 24 counts per minute. What is the corrected count rate? A. 24 counts per minute B. 240 counts per minute C. 264 counts per minute D. 288 counts per minute Answer: B
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