PHYSICS – Radioactive Decay

LEARNING OBJECTIVES Core • State the meaning of radioactive decay • State that during α- or β-decay the nucleus changes to that of a different element Use the term half-life in simple calculations, which might involve information in tables or decay curves Recall the effects of ionising radiations on living things Describe how radioactive materials are handled, used and stored in a safe way Supplement Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Calculate half-life from data or decay curves from which background radiation has not been subtracted

Radioactive decay

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay.

Radioactive decay Radioactive decay is a random event – When a nucleus decays it becomes more stable, but the loss of protons and neutrons makes it a different element. The original nucleus is called the parent nucleus. The nucleus formed is known as the daughter nucleus. Both are called the decay products. Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay.

Radioactive decay He Radioactive decay is a random event – When a nucleus decays it becomes more stable, but the loss of protons and neutrons makes it a different element. The original nucleus is called the parent nucleus. The nucleus formed is known as the daughter nucleus. Both are called the decay products. Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Mass number (nucleon number) = total number of nucleons (protons + neutrons) in the nucleus 4 He 2

Radioactive decay He Radioactive decay is a random event – When a nucleus decays it becomes more stable, but the loss of protons and neutrons makes it a different element. The original nucleus is called the parent nucleus. The nucleus formed is known as the daughter nucleus. Both are called the decay products. Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Mass number (nucleon number) = total number of nucleons (protons + neutrons) in the nucleus 4 He 2 Atomic number (proton number) also shows the relative charge on the nucleus.

Four nucleons, relative charge of +2 Radioactive decay When a nucleus decays it becomes more stable, but the loss of protons and neutrons makes it a different element. The original nucleus is called the parent nucleus. The nucleus formed is known as the daughter nucleus. Both are called the decay products. Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Mass number (nucleon number) = total number of nucleons (protons + neutrons) in the nucleus Alpha particle 4 + 4 He α 2 2 Atomic number (proton number) also shows the relative charge on the nucleus. Four nucleons, relative charge of +2

Four nucleons, relative charge of +2 Radioactive decay When a nucleus decays it becomes more stable, but the loss of protons and neutrons makes it a different element. The original nucleus is called the parent nucleus. The nucleus formed is known as the daughter nucleus. Both are called the decay products. Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Mass number (nucleon number) = total number of nucleons (protons + neutrons) in the nucleus Alpha particle Beta particle 4 + 4 He α β 2 2 -1 Atomic number (proton number) also shows the relative charge on the nucleus. Four nucleons, relative charge of +2 An electron, charge of -1

Radioactive decay Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted

Let’s have a look at some examples! Radioactive decay Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Let’s have a look at some examples!

Let’s have a look at some examples! Radioactive decay When radium-226 decays, it does so by emitting an alpha particle. This means that the ‘daughter’ nucleus now has 2 protons and 2 neutrons less than it did before. We can write this as a nuclear equation. Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Let’s have a look at some examples!

Let’s have a look at some examples! Radioactive decay When radium-226 decays, it does so by emitting an alpha particle. This means that the ‘daughter’ nucleus now has 2 protons and 2 neutrons less than it did before. We can write this as a nuclear equation. Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Let’s have a look at some examples! 226 222 4 Ra Rn + α 88 86 2

Let’s have a look at some examples! Radioactive decay When radium-226 decays, it does so by emitting an alpha particle. This means that the ‘daughter’ nucleus now has 2 protons and 2 neutrons less than it did before. We can write this as a nuclear equation. Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Let’s have a look at some examples! 226 222 4 Ra Rn + α 88 86 2 A new element, radon, has been formed from the decay of the radium.

Let’s have a look at some examples! Radioactive decay Thorium-232 also undergoes radioactive decay, again with the loss of an alpha particle (helium nucleus). Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Let’s have a look at some examples! 232 228 4 Th Ra + α 90 88 2 The element radium has been formed from the decay of the thorium.

Radioactive decay Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Both examples involved alpha decay. Let’s now look at an example of beta decay

Radioactive decay In beta decay, a neutron changes into a proton plus an electron. The proton stays in the nucleus and the electron leaves the atom with high energy. The mass number remains unchanged (one neutron lost, one proton gained) but the atomic number increases by one. Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Both examples involved alpha decay. Let’s now look at an example of beta decay

+ C N e- Radioactive decay In beta decay, a neutron changes into a proton plus an electron. The proton stays in the nucleus and the electron leaves the atom with high energy. The mass number remains unchanged (one neutron lost, one proton gained) but the atomic number increases by one. Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Both examples involved alpha decay. Let’s now look at an example of beta decay 14 14 C N + e- 6 7 -1

+ C N e- Radioactive decay In beta decay, a neutron changes into a proton plus an electron. The proton stays in the nucleus and the electron leaves the atom with high energy. The mass number remains unchanged (one neutron lost, one proton gained) but the atomic number increases by one. Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Both examples involved alpha decay. Let’s now look at an example of beta decay 14 14 C N + e- 6 7 -1 The element nitrogen has been formed from the beta decay of the carbon.

+ I Xe e- Radioactive decay In this example of beta decay, iodine-131 emits a beta particle to become xenon. Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Both examples involved alpha decay. Let’s now look at an example of beta decay 131 131 I Xe + e- 53 54 -1 The mass number remains unchanged, and the proton number (atomic number) increases by 1.

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Some types of nucleus are more unstable than others and decay at a faster rate.

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Some types of nucleus are more unstable than others and decay at a faster rate. 10 Days

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Some types of nucleus are more unstable than others and decay at a faster rate. 10 Days 10 Days

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Some types of nucleus are more unstable than others and decay at a faster rate. 10 Days 10 Days One half-life One half-life

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Some types of nucleus are more unstable than others and decay at a faster rate. 10 Days 10 Days One half-life One half-life HALF-LIFE is the TIME TAKEN for HALF of the radioactive atoms now present to DECAY

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. Some types of nucleus are more unstable than others and decay at a faster rate. Days Nuclei remaining Half-life 64 10 32 1 20 16 2 30 8 3 40 4 50 5

Radioactive decay curve Measurements taken with a GM tube. Don’t forget that you might need to subtract figures for background radiation! Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. 70 60 50 40 30 20 10 x Nuclei remaining Radioactive decay curve x Days Nuclei remaining Half-life 64 10 32 1 20 16 2 30 8 3 40 4 50 5 x x x x 0 10 20 30 40 50 Days

Radioactive decay curve Measurements taken with a GM tube. Don’t forget that you might need to subtract figures for background radiation! Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. 70 60 50 40 30 20 10 x Nuclei remaining Radioactive decay curve x Radioactive isotope Half-life Radon-220 52 secs Iodine-128 25 mins Radon-222 3.8 days Strontium-90 28 years Radium-226 1602 years Carbon-14 5730 years Plutonium-239 24 400 years x x x x 0 10 20 30 40 50 Days

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. In the early hours of 26 April 1986 one of the four reactors at Chernobyl power station exploded. Radioactive isotope Half-life Radon-220 52 secs Iodine-128 25 mins Radon-222 3.8 days Strontium-90 28 years Radium-226 1602 years Carbon-14 5730 years Plutonium-239 24 400 years Because of the long-lived radiation in the region surrounding the former Chernobyl Nuclear Power Plant, the area won't be safe for human habitation for at least 20,000 years.

Radioactive decay Radioactive decay is a random event – The unstable nuclei in some materials will break up, or disintegrate. It is impossible to predict exactly which nuclei will decay. This disintegration of the nuclei is called radioactive decay. In the early hours of 26 April 1986 one of the four reactors at Chernobyl power station exploded. In a radioactive sample, the average number of disintegrations per second is called the activity. The SI unit of activity is the becquerel (Bq). For example, 100Bq = 100 nuclei disintegrating per second. Because of the long-lived radiation in the region surrounding the former Chernobyl Nuclear Power Plant, the area won't be safe for human habitation for at least 20,000 years.

Radioactive decay

Initial count rate = 600 counts per second. Radioactive decay Initial count rate = 600 counts per second.

Count rate falls to 200 counts per second after 25 minutes Radioactive decay Count rate falls to 200 counts per second after 25 minutes

Radioactive decay If the initial count was 600, the half-life is 300 particles, which will be after 16 minutes.

Initial count = 600, one half life = 300, two half lives = 150 Radioactive decay Initial count = 600, one half life = 300, two half lives = 150

Initial count = 600, one half life = 300, two half lives = 150 Radioactive decay Initial count = 600, one half life = 300, two half lives = 150 600 25 16 150

Corrected count rate in Bq Calculate half-life from data or decay curves from which background radiation has not been subtracted Radioactive decay Supplement Every half-minute a teacher records a count rate of a radioactive substance. The background count was 3Bq. Calculate the corrected count rate and draw a graph for these results. Time in minutes Count rate in Bq Corrected count rate in Bq 52 0.5 33 1.0 27 1.5 21 2.0 18 2.5 14 3.0 13 3.5 12 4.0 8 4.5 9

Corrected count rate in Bq Calculate half-life from data or decay curves from which background radiation has not been subtracted Radioactive decay Supplement Every half-minute a teacher records a count rate of a radioactive substance. The background count was 3Bq. Calculate the corrected count rate and draw a graph for these results. Time in minutes Count rate in Bq Corrected count rate in Bq 52 49 0.5 33 30 1.0 27 24 1.5 21 18 2.0 15 2.5 14 11 3.0 13 10 3.5 12 9 4.0 8 5 4.5 6

Corrected count rate in Bq Calculate half-life from data or decay curves from which background radiation has not been subtracted Radioactive decay Supplement Every half-minute a teacher records a count rate of a radioactive substance. The background count was 3Bq. Calculate the corrected count rate and draw a graph for these results. Corrected count rate in Bq 50 45 40 35 30 25 20 15 10 5 x Time in minutes Count rate in Bq Corrected count rate in Bq 52 49 0.5 33 30 1.0 27 24 1.5 21 18 2.0 15 2.5 14 11 3.0 13 10 3.5 12 9 4.0 8 5 4.5 6 x x x x x x x x x 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Time in minutes

Corrected count rate in Bq Calculate half-life from data or decay curves from which background radiation has not been subtracted Radioactive decay Supplement Every half-minute a teacher records a count rate of a radioactive substance. The background count was 3Bq. Calculate the corrected count rate and draw a graph for these results. Use your graph to estimate the half-life of the material Corrected count rate in Bq 50 45 40 35 30 25 20 15 10 5 x Time in minutes Count rate in Bq Corrected count rate in Bq 52 49 0.5 33 30 1.0 27 24 1.5 21 18 2.0 15 2.5 14 11 3.0 13 10 3.5 12 9 4.0 8 5 4.5 6 Original count = 49 x Half of original count = 24.5 x x Half-life = 1 min x x x x x x 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Time in minutes

Ionising Radiation and Living Things

Ionising Radiation and Living Things Alpha, beta and gamma radiation will enter living cells and collide with molecules – these collisions cause ionisation, damaging or destroying the molecules.

Ionising Radiation and Living Things Alpha, beta and gamma radiation will enter living cells and collide with molecules – these collisions cause ionisation, damaging or destroying the molecules. Lower doses cause non-fatal damage to cells, but can cause them to become cancerous, when they divide uncontrollably.

Ionising Radiation and Living Things Alpha, beta and gamma radiation will enter living cells and collide with molecules – these collisions cause ionisation, damaging or destroying the molecules. Higher doses tend to kill cells completely, causing radiation sickness. Lower doses cause non-fatal damage to cells, but can cause them to become cancerous, when they divide uncontrollably.

Ionising Radiation and Living Things Alpha, beta and gamma radiation will enter living cells and collide with molecules – these collisions cause ionisation, damaging or destroying the molecules. Higher doses tend to kill cells completely, causing radiation sickness. Lower doses cause non-fatal damage to cells, but can cause them to become cancerous, when they divide uncontrollably. The extent of the harmful effects depends upon two things.

Ionising Radiation and Living Things Alpha, beta and gamma radiation will enter living cells and collide with molecules – these collisions cause ionisation, damaging or destroying the molecules. Higher doses tend to kill cells completely, causing radiation sickness. Lower doses cause non-fatal damage to cells, but can cause them to become cancerous, when they divide uncontrollably. The extent of the harmful effects depends upon two things. How much exposure there is to the radiation. The energy and penetration of the radiation emitted – some types are more hazardous than others.

Ionising Radiation and Living Things Alpha radiation cannot penetrate through skin, so outside the body beta and gamma radiation are the most dangerous – but both of these are less ionising than alpha and so cause less damage. α β γ

Ionising Radiation and Living Things α Alpha radiation cannot penetrate through skin, so outside the body beta and gamma radiation are the most dangerous – but both of these are less ionising than alpha and so cause less damage. However, if alpha particles get inside the body (ingested, breathed-in) then they can do much more damage in a very localised area because they are so strongly ionising.

Ionising Radiation and Safety

Ionising Radiation and Safety In the school laboratory Handle with tongs, avoid skin contact with a source. Keep source as far away from the body as possible. Avoid looking directly at the source Immediately return source to lead-lined box when not required.

Ionising Radiation and Safety In the school laboratory Handle with tongs, avoid skin contact with a source. Keep source as far away from the body as possible. Avoid looking directly at the source Immediately return source to lead-lined box when not required. In industry Full protective suits prevent inhalation of radioactive dust particles and direct skin contact Use lead-lined suits, lead/concrete barriers, thick lead windows to prevent exposure to gamma radiation. Use of remotely controlled robot arms in highly radioactive areas.

LEARNING OBJECTIVES Core • State the meaning of radioactive decay • State that during α- or β-decay the nucleus changes to that of a different element Use the term half-life in simple calculations, which might involve information in tables or decay curves Recall the effects of ionising radiations on living things Describe how radioactive materials are handled, used and stored in a safe way Supplement Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted Calculate half-life from data or decay curves from which background radiation has not been subtracted

PHYSICS – Radioactive Decay