1. Chapter 7 - Radioactivity
Science 10 P

2. What is Radiation? Radiation is: Radiation may be in the form of:
anything that radiates away from something.
Radiation may be in the form of:
particles (neutrons, alpha particles, and beta particles), or
waves of pure energy (light, radio waves, X-rays, and gamma rays gamma and X-rays).

3. Where do we find Radiation?
Natural background radiation exists all around us.
Radioactive materials are in many things:
X-rays, radiation therapy and electricity generation are beneficial.
radiation consisting of particles, X-rays, or gamma rays with sufficient energy to cause ionization in the medium through which it passes

4. The Electromagnetic Spectrum
Radiation includes radio waves, microwaves, infrared rays, visible light, and ultraviolet ray. These make up the Electromagnetic Spectrum:

5. Is Radiation Dangerous?
X rays, gamma rays, alpha particles, and beta particles are ionizing radiation.
Ionizing radiation has a lot of energy that gives it the ability to cause changes in atoms—a process called ionization.
Radio and TV signals, microwaves, and laser light are nonionizing types of radiation.

6. Radioactivity - definition
Radioactivity is the release of high energy particles or waves being emitted (released) from the decay (breakdown) of an unstable nucleus of an atom.

7. Radiation: What’s the big deal?
Although there are many beneficial uses of radiation, prolonged exposure to high energy particles and waves can do damage to DNA.
When atoms lose high energy particles and waves, (like in background radiation) they have the potential to interact with an atom and turn it into an ion or even a new atom can be formed.

8. Uses of Radiation in smoke detectors
for sterilising medical instruments
for killing cancer cells
for dating rocks and materials such as archaeological finds
in chemical tracers to help with medical diagnosis
for measuring the thickness of materials in, for example, a paper factory

9. Smoke Detectors
Radiation ionises the air particles inside the smoke detector.
This allows a small electric current to flow.
If there is a fire, smoke particles going into the detector are hit by alpha radiation, reducing the ionisation of the air particles causing the current to drop.
The drop in current is detected by the smoke detector, setting off the alarm.

10. Smoke Detectors
The alpha particles pass between the two charged metal plates, causing air particles to ionise (split into positive and negative ions).
The ions are attracted to the oppositely charged metal plates causing a current to flow.

11. Smoke Detectors
When smoke enters between the plates, some of the alpha particles are absorbed causing less ionisation to take place. This means a smaller than normal current flows so the alarm sounds.

12. Tracers in Medicine
Certain chemicals concentrate in different damaged or diseased parts of the body, and the radiation concentrates with it.
Radiation detectors placed outside the body detect the radiation emitted and, with the aid of computers, build up an image of the inside of the body.
When a radioactive chemical is used in this way it is not normally harmful, because:
it has a short half-life and so decays before it can do much damage
it is not poisonous

13. Tracers in Industry Find leaks or blockages in underground pipes
Find the route of underground pipes
Track the dispersal of waste

14. Monitoring thickness of materials
Radiation is used in industry in detectors that monitor and control the thickness of materials such as paper, plastic and aluminium.
The thicker the material, the more radiation is absorbed and the less radiation reaches the detector.
It then sends signals to the equipment that adjusts the thickness of the material.

15. Monitoring thickness of materials

16. Radiation videos Ted Ed: Is Radiation Dangerous?
Ted Ed: X-rays

18. How was radiation discovered?
In 1895, Wilhelm Roentgen discovered an unknown kind of energy was emitted from certain material when bombarded with electrons. These invisible rays could darken photographic film, just like visible light could. He named them X-rays. “X” for unknown.
Radiation is everywhere, but can be difficult to detect.

19. Henri Becquerel
Roentgen’s work led to the discovery of radioactivity by Henri Becquerel. Becquerel discovered that uranium salts emitted rays that darkened photographic plates. He realized the uranium emitted seemingly invisible energy.

20. Marie Curie named the energy radioactivity
Marie Curie named the energy radioactivity. Using Becquerel’s mineral sample, they isolated the components emitting the rays and concluded the darkening of the photographic plates was due to rays emitted from the uranium atoms in the sample.
Though Henri Becquerel discovered radioactivity, it was Marie Curie who coined the term.
Marie Curie also discovered polonium and radium.
Radium salts, after being placed on a photographic plate, leave behind the dark traces of radiation.

21. Marie Curie
Discoveries and contributions to the field of radioactivity
Crash Course:

22. Check your understanding
In your own words, define radiation.
Where can we find radioactivity
Is all radiation harmful? Explain.
List the role of each scientist that lead to the discovery of radioactivity:
Wilhelm Roentgen
Enri Becquerel
Marie Curie

23. Detecting Radiation
Early discoveries of radiation relied on photographic equipment
Later, more sophisticated devices such as the Geiger-Müller counter were developed to more precisely measure ionizing radioactivity.

24. What is an Isotope?
Isotopes are different atoms of the same element, with a different number of neutrons in the nucleus.
Note they all have same number of protons, just neutrons have changed

25. Isotopes Changing the # of neutrons changes the mass
Remember: mass number = # protons + # neutrons
isotopes still have the same:
element symbol
number of protons (atomic number)

26. Isotopes Isotopes have different neutron numbers.
Why are these isotopes all still grouped together as carbon?

27. Isotopes Stable Atoms Unstable atom Carbon 12 Carbon 13 Carbon 14
6 protons 6 protons 6 protons
6 neutrons 7 neutrons 8 neutrons
Examine the three different carbon atoms right. How are they different from one another?
Why are these isotopes all still grouped together as carbon?

28. Atomic number stays the same as proton number doesn’t change.
Neutron number changes  different atomic mass.

29. Atomic Mass (the decimal #’s)
Atomic mass = average of the mass numbers for all isotopes of an element.
If 19.9% of boron atoms have 5 neutrons, 80.1% have 6 neutrons
19.9% have a mass number of 10, and 80.1% have a mass number of 11
(.199 * 10) + (.801*11) = 10.8
atomic mass of boron = 10.8

30. Representing Isotopes
Isotopes are written using standard atomic notation.
Chemical symbol + atomic number + mass number.
Potassium has three isotopes,

31. Representing Isotopes
Isotopes are written using standard atomic notation.
Chemical symbol + atomic number + mass number.
Potassium has three isotopes,

32. Representing Isotopes
Standard nuclear notation shows the chemical symbol, the mass number and the atomic number of the isotope. Example: the isotopes of carbon. The element is determined by the atomic number 6. Carbon-12 is the common isotope, with carbon-13 as another stable isotope which makes up about 1%.

33. Representing Isotopes.
Potassium has three isotopes,

34. Potassium is found in nature in a certain ratio of isotopes
93.2% is potassium-39
1.0% is potassium-40
6.7% is potassium-41
Atomic mass
= (.932 x 39) + (.001 x 40) + (.067 x 41)
= 39.1

35. Write the standard atomic symbol for the following:
Potassium-39
Potassium-40
Potassium-41

36. Write the standard atomic symbol for the following:
Potassium-39
Potassium-40
Potassium-41

37. Practice Read pages 286-290 Answer Reading Check p291
Practice Problems p291
Worksheet

38. Homework
Acitivity 7-1B page 292

39. Radioactive Decay

40. Radioactive Decay
Scientists have discovered that when atoms of one kind of element emit radiation, they can change into atoms of a NEW element. Why would an atom emit radiation in the first place?

41. Radioactive Decay
Atoms emit radiation because their nuclei are unstable.
Unstable atoms gain stability by losing energy (emitting radiation).
Unlike all previously discovered chemical reactions, radioactivity sometimes results in the formation of completely new atoms.
Radioactivity results from having an unstable nucleus.
When these nuclei lose energy and break apart, decay occurs.
Radioactive decay releases energy from the nucleus as radiation.
Radioactive atoms release energy until they become stable, often as different atoms.
An element may have only certain isotopes that are radioactive. These are called radioisotopes.

42. Radioactive Decay
Radioactive decay is the process by which unstable nuclei lose energy by emitting radiation until they are stable.
Unstable (radioactive) atoms release energy (undergo radioactive decay) until they become stable, often becoming atoms of different elements.
An element may have only certain isotopes that are radioactive. These are called radioisotopes.
Unlike all previously discovered chemical reactions, radioactivity sometimes results in the formation of completely new atoms.
Radioactivity results from having an unstable nucleus.
When these nuclei lose energy and break apart, decay occurs.
Radioactive decay releases energy from the nucleus as radiation.
Radioactive atoms release energy until they become stable, often as different atoms.
An element may have only certain isotopes that are radioactive. These are called radioisotopes.

43. Radioactive Decay
How does the radioisotope Uranium-238 decay?

44. Radioactive Decay
How does the radioisotope Uranium-238 decay? Change Mass #, And Atomic #

45. Types of Radiation

46. Types of Radiation
Radioactive substances give out radiation all the time. There are three types of nuclear radiation - alpha, beta and gamma. Alpha is the least penetrating, while gamma is the most penetrating.
Radiation can be harmful, but it can also be useful. The uses of radiation include smoke detectors, paper-thickness gauges, treating cancer and sterilising medical equipment.

47. Three Types of Radiation
Ernest Rutherford ( ) identified three types of radiation using an electric field.
Rutherford's electromagnetic wave detector consisted of a magnetizing coil with iron wire. (electrical field) In 1899, He also named gamma rays, a form of electromagnetic radiation.
Ernest Rutherford postulated the nuclear structure of the atom, discovered alpha and beta rays, and proposed the laws of radioactive decay. He received the Nobel Prize in Chemistry in 1908.
first person to successfully split an atom using nitrogen and alpha particles.
famed Gold Foil Experiment of 1909 demonstrated that atoms were made up of a charged nucleus orbited by electrons. He published his findings in 1911 with a description of what he called the Rutherford model of the atom. While electrons had been described prior to this experiment, Rutherford was the first person to describe the existence of a small, charged atomic nucleus.
See page 294
(c) McGraw Hill Ryerson 2007

48. Three Types of Radiation
He placed a radioactive source inside a lead block that allowed the radiation to pass out only through a tiny hole.
Rutherford's electromagnetic wave detector consisted of a magnetizing coil with iron wire. (electrical field) In 1899, He also named gamma rays, a form of electromagnetic radiation.
Ernest Rutherford postulated the nuclear structure of the atom, discovered alpha and beta rays, and proposed the laws of radioactive decay. He received the Nobel Prize in Chemistry in 1908.
first person to successfully split an atom using nitrogen and alpha particles.
famed Gold Foil Experiment of 1909 demonstrated that atoms were made up of a charged nucleus orbited by electrons. He published his findings in 1911 with a description of what he called the Rutherford model of the atom. While electrons had been described prior to this experiment, Rutherford was the first person to describe the existence of a small, charged atomic nucleus.
See page 294
(c) McGraw Hill Ryerson 2007

49. Three Types of Radiation
From the hole, the radiation travelled through a slot between electrically charge plates that defected any electrically charged particles.
Rutherford's electromagnetic wave detector consisted of a magnetizing coil with iron wire. (electrical field) In 1899, He also named gamma rays, a form of electromagnetic radiation.
Ernest Rutherford postulated the nuclear structure of the atom, discovered alpha and beta rays, and proposed the laws of radioactive decay. He received the Nobel Prize in Chemistry in 1908.
first person to successfully split an atom using nitrogen and alpha particles.
famed Gold Foil Experiment of 1909 demonstrated that atoms were made up of a charged nucleus orbited by electrons. He published his findings in 1911 with a description of what he called the Rutherford model of the atom. While electrons had been described prior to this experiment, Rutherford was the first person to describe the existence of a small, charged atomic nucleus.
See page 294
(c) McGraw Hill Ryerson 2007

50. Positive alpha particles were attracted to the negative plate.
Negative beta particles were attracted to the positive plate.
Neutral gamma rays had no charge, and therefore did not move towards any plate.

51. Alpha Radiation Alpha radiation is a stream of alpha particles.
What are some characteristics of Alpha particles?
See page
Radium-226 releases an alpha particle and becomes
Radon-222. Radon has two less protons than radium.
(c) McGraw Hill Ryerson 2007

52. Alpha Particles Are positively charged,
Are the most massive of the 3 radiation types
Have same combination of particles as a helium nucleus.
Are slow and penetrate materials much less than the other forms of radiation. A sheet of paper will stop an alpha particle.
Produced during radioactive decay
Represented as either 4 2 a or 4 2 He
Made of 2 protons and 2neutrons
2 protons = 2+ charge
Alpha particles are alos slow and don’t penetrate materials very deeply )piece of paper will stop them)
See page
Radium-226 releases an alpha particle and becomes
Radon-222. Radon has two less protons than radium.
(c) McGraw Hill Ryerson 2007

53. Alpha Particles represented by the symbols
Because it has two protons, it has a charge of 2+.
The release of alpha particles is called alpha decay.
Produced during radioactive decay
Represented as either 4 2 a or 4 2 He
Made of 2 protons and 2neutrons
2 protons = 2+ charge
Alpha particles are also slow and don’t penetrate materials very deeply )piece of paper will stop them)
See page
(c) McGraw Hill Ryerson 2007

54. Alpha Radiation Radium-226 releases an alpha particle and becomes
Note how equation is balanced
Pracitce problems p295
Radium-226 releases an alpha particle and becomes
Radon-222. Radon has two less protons than radium.

55. Practice
Practice Problems p295

56. What is Beta Radiation? A beta particle is an electron represented by:
Electrons are very tiny, so beta particles are assigned a mass of 0.
Since it is only an electron, a beta particle has a charge of 1–
It takes a thin sheet of aluminum foil to stop a beta particle.
Produced during radioactive decay
Representation …
Made of an e so charge is 1-
Produced when a neutron decays into proton and electron (atomic number doesn’t change but atomic mass does. Neutron is retained and e is released.

57. Beta Radiation
What are some characteristics of Beta Particles?

58. How does Beta Radiation occur?
Beta decay occurs when a neutron changes into a proton and an electron.
The proton stays in the nucleus, and the electron is released.
Can be stopped by sheet of aluminum
Is the equation balanced? Yes, atomic number and mass are both equal.
Creation of a proton means the atom produced is changed, but mass is same as a neutron has been replaced by a proton of almost equal mass.
Complete practice problems on p296
See page 296
(c) McGraw Hill Ryerson 2007

59. Beta Radiation A Lithium neutron changes into a proton and electron:
Mass stays the same because an existing neutron changed to a proton.
Atomic number goes up because it has gained a proton

60. Beta Radiation
Iodine-131 releases a beta particle and becomes xenon-131.
A neutron has turned into a proton and the released electron.

61. Practice
Do practice problems p296

62. Gamma Radiation
Gamma radiation is a ray of high-energy, short-wavelength radiation.
Gamma radiation has no charge and no mass, and is represented by:
highest-energy form of electromagnetic radiation.
Highest penetrating power. It takes thick blocks of lead or concrete to stop gamma rays.
Often, other kinds of radioactive decay will also release gamma radiation.
Uranium-238 decays into an alpha particle and also releases gamma rays.
Produced by release of high-energy, short wavelength radiation from a high-enery nucleus (*)
See page 297
(c) McGraw Hill Ryerson 2007

63. Gamma Radiation Highest energy of the 3 types of radiation
Highest penetrating power
Can cause the most damage to a person

64. Gamma Radiation
Because gamma radiation has almost no mass and no charge, the release of gamma radiation does not change the atomic number or the mass number of a nucleus.

65. How does Gamma Radiation occur?
Gamma Radiation results from a redistribution of energy within the nucleus.
A high-energy gamma ray is given off as the isotope falls from a high-energy state to a lower energy state.
Eg. high-energy nickel-60 can decay to nickel-60 by gamma decay:

66. Is the gamma Decay reaction balanced?
Yes, atomic and mass numbers are equal on both sides of arrow.

67. What radiation is present here?

68. Radiation Summary
Nuclear equations are written like chemical equations, but represent changes in the nucleus of atoms.
Chemical equations represent changes in the position of atoms, not changes to the atoms themselves.
The SUM OF THE MASS numbers does not change.
2. The SUM OF THE CHARGES in the nucleus does not change.
See pages
(c) McGraw Hill Ryerson 2007
Take the Section 7.1 Quiz

69. Radiation Summary

70. Radiation Summary

71. Radioactivity Decay Summary

72. Check your progress How is mass number of an element determined?
How do you represent a larger nucleus such as radium-226?
Why does an alpha particle have a positive charge?
How does beta decay result in the production of an element with one more protons than the nucleus started out with?
Since gamma rays are not made of matter, how can they be detected?
Mas number is the umber of paricels in nucleus (sum of protons + nneutorns)
Nucleus was represented by writing down the number of protons and number of neutrons present
2 of the 4 subatomic particles in an alpha particle are protons, each of which contribute a charge of 1+ or a total charge of 2+ on the alpha particle.
In Beta decay, a neutron decays into a proton, which remain in the nucleus and an electron which is emitted from the nucleus as beta radiation.
Gamma rays can be detect by screen coated with zinc sulfide, which glow when struck by gamma rays. Also, a GM counter can detect gamma rays.

73. Find out activity p 299

74. Reading Check
Page 297

75. Isotopes
Examine the three different carbon atoms right. How are they different from one another?
Why are these isotopes all still grouped together as carbon?