Radioactivity

Americium-241 is a radioactive isotope used in domestic smoke detectors. Americium-241 has a half-life of 432 years and decays by emitting alpha particles to produce neptunium. Householders are advised to replace the batteries in smoke detectors regularly. Explain whether or not the americium-241 needs to be replaced regularly also.

The Americium will not need to be replaced Americium-241 has a half-life of 432 years i.e. it would take 432 years for half of the Americium-241 to decay into neptunium There is plenty of Americium-241 in the smoke detector to last over a lifetime

What is Carbon-14 dating

The amount of radioactive carbon-14 that has decayed in a dead organism can be measured and the age of the organism can be found. Living organisms contain a constant ratio of carbon 12 to carbon 14 (same as in atmosphere) When the organism dies, the level of radioactive carbon 14 decreases and the C12 to C14 ratio will change The ratio and the half-life of carbon-14 can be used to calculate the age of the organism

Q12: (i) The half-life of a certain radioactive isotope is three years. What fraction of the isotope remains undecayed after: a)Three years b) Six years c) Nine years (ii) The half-life of a certain radioactive isotope is ten years. a) What fraction remains undecayed after forty years? b) What fraction has decayed in this time?

(i) a) Answer = ½ remains b) Answer = ¼ remains c) Answer = 1/8th remains (ii) a) Answer = 1/16th remains b) Answer = 15/16th decayed

Q7: (i) Discuss the properties of the three types of nuclear radiation in terms of: a) Behaviour in an electric field b) Penetrating ability and range

(i) a) Radiation Type - Deflection in Electric field α Particle - Deflects towards negative plate β Particle - Deflects towards positive plate γ ray - No deflection b) Radiation Type - Penetrating Ability - Range α Particle - Thin sheet of paper - Shortest β Particle - Few mm of Aluminium - Longer than α γ ray - Few cm of lead - Longest

Q9: (i) Name and describe three uses of radioactive isotopes (ii) Give two reasons why americium-241 used in smoke alarms is not harmful to people?

(i) 1. Cobalt-60 emits gamma rays that are used to destroy cancer cells 2. Iodine-131 emits beta particles that are used to destroy part of an overactive thyroid gland 3. Americium-241 that emits alpha particles will be absorbed by smoke causing the alarm to sound (ii) 1. the alpha particles emitted only travel a few cm in air 2. The alpha particles cannot penetrate skin

Q3: (i) Describe the nature of alpha particles/what is an alpha particle? (ii) When an alpha particle is emitted what change occurs in the nucleus of the isotope? (iii) Write an equation to represent alpha decay for a radioactive isotope X-4,Z (iv) Ra- 226,88 ~~> Rn- x,y + He- 4,2 What is x and y? (v) Th- 232,90 ~~> A- x,y + e- 0,-1 What is x, y and A? (vi) Write the equation for the decay of uranium-235 when it undergoes alpha emission

(i) An α particle is identical to a helium nucleus (2 protons + 2 neutrons). It has a +2 charge (ii) its mass number decreases by four and atomic number decreases by two (iii) X- A,Z ~~> Y- A-4,Z-2 + He- 4,2 (iv) Answer: x = 222; y = 86 (v) Answer: x = 228; y = 88; A= Ra (Radium) (vi) see image

Q10: (i) What is background radiation? (ii) Give three major sources of background radiation

(i) Background radiation is the radiation naturally present in the environment (ii) 1. Radon gas emitted from the decay of uranium and thorium found in rocks 2. All food eaten (plants absorb radioactive material from the earth) 3. Cosmic rays from the sun

Q5: (i) Describe the nature of gamma ray/what is a gamma ray? (ii) When a gamma is emitted what change occurs in the nucleus of the isotope?

(i) High energy electromagnetic radiation (ii) The structure of the nucleus remains the same, but it loses energy to become more stable

Q11: (i) What is meant by the term half-life? (ii) Explain why the americium-241 in smoke detectors does not need to be replaced despite it being recommended the batteries in the smoke detector are changed regularly

(i) The half-life of an element is the time taken for half of the nuclei in any given sample to decay (ii) It has a half-life of 432 years i.e. it would take 432 years for half of the Americium-241 to decay into neptunium

Q1: (i) What is radioactivity? (ii) What are radioisotopes? (iii) Name the scientist shown that is credited with discovering radioactivity (iv) Name the two scientists shown that won the Nobel prize in physics for their work on radioactivity (v) Outline the contribution of these two scientists (from iv) to the field of physics and chemistry

(i) The spontaneous breaking up of unstable nuclei with the emission of one or more types of nuclear radiation (ii) Radioactive isotopes i.e. isotopes with unstable nuclei and in an attempt to become more stable emit nuclear radiation (iii) Henri Becquerel (iv) Pierre Curie and Marie Curie (v) Isolated and discovered the radioactive elements polonium and radium from an ore of uranium known as pitchblende

Q4: (i) Describe the nature of beta particles/what is a beta particle? (ii) When a beta particle is emitted what change occurs in the nucleus of the isotope? (iii)Write an equation to represent beta decay for a radioactive isotope X- A,Z (iv) C- 12,6 ~~> β + A- x,y What is x, y and A? (v) K- 40,19 ~~> Ca- 40,20 + W What is W? (vi) Ra- 228,80 ~~> A- x,y + e- 0,-1 What is x, y and A? (vii) Write the decay equation for Strontium-90 when it undergoes beta emission

(i) an electron, with a -1 charge (ii) a neutron in the nucleus splits up into a proton and an electron. The proton remains in the nucleus, but the electron is ejected out as a β-particle. The mass number remains the same and the atomic number increases by one (iii) X- A,Z ~~> Y- A,Z+1 + e- 0,-1 (iv) Answer: x = 14; y = 7; A= N (Nitrogen) (v) Answer: W = beta particle (vi) Answer: x = 228; y = 89; A= Ac (Actinium) (vii) see image

Q8: (i) What are the health hazards of nuclear radiation? (ii) Give three precautions that should be taken when working with radioactive materials

(i)Alpha particles, beta particles and gamma rays can cause cancer. Gamma rays are the most dangerous type of nuclear radiation as they have the greatest penetrating ability (ii) 1. Radioactive material should be stored in a lead container 2. Minimise time spent with radioactive material 3. Minimise the distance the radioactive material is from you

The table below shows the mass of a sample of sodium-24 at 10-hour intervals over a 70 hour period. (i) Draw a graph to represent these data (ii) Use the graph to determine the half-life of sodium-24 (iii) Write an equation to represent the beta-decay of a sodium-24 nucleus time (hours) | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | mass (mg) | 400 | 260 | 160 | 100 | 65 | 40 | 25 | 13 |

(ii) 15 hours (iii) 24 24 0 Na --> Mg + β 11 12 -1

Q2: Name the three types of nuclear radiation

1. Alpha particles 2. Beta particles 3. Gamma rays

Give four uses of radioisotopes

1. Medical a) Cobalt-60 emits gamma rays that are used to destroy cancer cells b) Iodine-131 emits beta particles that are used to destroy part of an overactive thyroid gland 2. Archaeology a) Carbon-14 dating 3. Food irradiation Some foods can be treated with gamma rays to destroy any microorganisms and keep the food fresh 4. Smoke Alarms Contain Americium-241 that emits alpha particles will be absorbed by smoke causing the alarm to sound

Outline the health hazards of nuclear radiation

Alpha particles, beta particles and gamma rays can cause cancer Gamma rays are the most dangerous type of nuclear radiation as they have the greatest penetrating ability

Alpha Radiation (α)'s nature

An α particle is identical to a helium nucleus (2 protons + 2 neutrons) It has a +2 charge

Beta Radiation (β)'s nature

An β-particle is an electron It has a -1 charge

What is background radiation and name 3 sources

Background radiation is the radiation naturally present in the environment 1. Radon gas emitted from the decay of uranium and thorium found in rocks 2. All food eaten (plants absorb radioactive material from the earth) 3. Cosmic rays from the sun

How was radioactivity discovered?

Henri Becquerel Discovered radioactivity Noticed that uranium salts wrapped in black paper left an image on a photographic plate they were sitting on i.e. the uranium was emitting some form of radiatioterm-15n Pierre Curie and Marie Curie Isolated and discovered the radioactive elements polonium and radium from an ore of uranium known as pitchblende Henri Becquerel, Pierre Curie and Marie Curie shared the Nobel Prize in physics in 1903. Marie Curie was then awarded the Nobel Prize in chemistry in 1911

Gamma Radiation (γ)'s nature

High energy electromagnetic radiation

Give three differences between a nuclear reaction and a chemical reaction

Nuclear reaction 1. Involves a change in structure of the nucleus 2. New element formed (transmutation) 3. No chemical bonds broken or formed Chemical reaction 1. Involves electrons being transferred or shared 2. No new element formed 3. Chemical bonds broken and formed

Q6: Give three differences between a chemical reaction and a nuclear reaction

Nuclear reaction 1. Involves a change in structure of the nucleus 2. New element formed (transmutation) 3. No chemical bonds broken or formed Chemical reaction 1. Involves electrons being transferred or shared 2. No new element formed 3. Chemical bonds broken and formed

Deflection in electric and magnetic fields

Radiation Type - Deflection in Electric field α Particle - Deflects towards negative plate β Particle - Deflects towards positive plate γ ray - No deflection A beta particle deflects to a greater extent than an alpha particle. As the beta particle is an electron, it's mass is much less than an alpha particle (Helium nucleus)

Penetrating ability and range

Radiation Type - Penetrating Ability - Range α Particle - Thin sheet of paper - Shortest β Particle - Few mm of Aluminium - Longer than α γ ray - Few cm of lead - Longest

What precautions should be taken when working with radioactive material?

Radioactive material should be stored in a lead container Minimise time spent with radioactive material Minimise the distance the radioactive material is from you Use the proper protective clothing e.g. gloves, glasses, coat and use tongs for handling radioactive sources

What is Radioactivity?

Radioactivity is the spontaneous breaking up of unstable nuclei with the emission of one or more types of nuclear radiation

What are radioisotopes?

Radioisotopes are radioactive isotopes i.e. isotopes with unstable nuclei and in an attempt to become more stable emit nuclear radiation

What is meant by half-life?

The half-life of an element is the time taken for half of the nuclei in any given sample to decay

what happens when Gamma Radiation (γ) is emitted

When a nucleus emits γ-radiation the structure of the nucleus remains the same, but it loses energy to become more stable Note: Gamma decay usually accompanies alpha and beta decay

what happens when Beta Radiation (β) is emitted

When an unstable nucleus emits a β particle, a neutron in the nucleus splits up into a proton and an electron The proton remains in the nucleus, but the electron is ejected out as a β-particle The mass number remains the same and the atomic number increases by one

what happens when Alpha Radiation (α) is emitted

When an unstable nucleus emits an α-particle its mass number decreases by four and atomic number decreases by two

What are the three types of radiation

alpha particles, beta particles, gamma rays