6.1 radioactive emissions

Question 1

Q: What is the structure of an atom?

Answer 1

A: Atoms consist of a dense nucleus containing protons and neutrons, surrounded by orbiting electrons.

Question 2

Q: What determines the element of an atom?

Answer 2

A: The number of protons in the nucleus determines the element of an atom.

Question 3

Q: What is the charge of the nucleus?

Answer 3

A: The nucleus has a positive charge due to the presence of protons.

Question 4

Q: What is the relationship between energy levels and electrons in an atom?

Answer 4

A: Electrons orbit the nucleus at specific energy levels, with a maximum number of electrons allowed in each level.

Question 5

What happens to an electron when it absorbs energy?

Answer 5

A: When an electron absorbs energy, it can move to a higher energy level, resulting in excitation.

Question 6

Q: How is ionisation defined?

Answer 6

A: Ionisation occurs when an atom gains or loses an electron from its outer energy level, resulting in the formation of ions.

Question 7

Q: How are positive ions formed?

Answer 7

A: Positive ions are formed when an atom loses electrons from its outer energy level, resulting in a net positive charge.

Question 8

Q: How are negative ions formed?

Answer 8

A: Negative ions are formed when atoms gain electrons in their outer energy level, resulting in a net negative charge.

Question 9

Q: What happens when electrons absorb electromagnetic radiation?

Answer 9

A: Electrons move to higher energy levels when they absorb electromagnetic radiation.

Question 10

Why do dark-colored objects appear dark?

Answer 10

A: Dark-colored objects appear dark because they absorb most of the energy that hits them, rather than reflecting it.

Question 11

What occurs when an electron moves back down to its original energy level after being excited?

Answer 11

A: When an electron moves back down to its original energy level, it emits electromagnetic radiation.

Question 12

How are all the colors in the visible spectrum produced?

Answer 12

A: All the colors in the visible spectrum are produced by electrons moving down energy levels and emitting electromagnetic radiation.

Question 13

Q: What is the total charge within an atom?

Answer 13

A: The total charge within an atom is zero because the number of protons (positively charged) is equal to the number of electrons (negatively charged).

Question 14

Q: What is the atomic number of an element?

Answer 14

A: The atomic number of an element is the number of protons in its nucleus, which also equals the number of electrons in the atom.

Question 15

Q: What is the mass number of an atom?

Answer 15

A: The mass number of an atom is the total number of particles (protons and neutrons) in its nucleus.

Question 16

How can you calculate the number of neutrons in an atom?

Answer 16

A: The number of neutrons in an atom can be calculated by subtracting the atomic number (number of protons) from the mass number.

Question 17

What is nuclear notation?

Answer 17

A: Nuclear notation is a way of representing atoms by writing their atomic symbol with the mass number as the top number and the atomic number as the bottom number.

Question 18

Q: In nuclear notation, what does the top number represent?

Answer 18

A: The top number in nuclear notation represents the mass number, which is the total number of particles (protons and neutrons) in the nucleus.

Question 19

: In nuclear notation, what does the bottom number represent?

Answer 19

A: The bottom number in nuclear notation represents the atomic number, which is the number of protons in the nucleus.

Question 20

Q: How can you determine the number of electrons in an atom?

Answer 20

A: The number of electrons in an atom is equal to the number of protons, which is determined by the atomic number.

Question 21

Q: What are isotopes?

Answer 21

A: Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

Question 22

Do isotopes of an element have the same chemical properties?

Answer 22

A: Yes, isotopes of an element have the same chemical properties because they have the same number of protons and electrons.

Question 23

How does the number of neutrons in an isotope affect its mass?

Answer 23

A: The number of neutrons in an isotope affects its mass, as neutrons have mass but no charge.

Question 24

How does the stability of isotopes relate to the balance of protons and neutrons?

Answer 24

A: Isotopes tend to be more unstable when there is an imbalance of protons and neutrons in their nuclei.

Question 25

Can you explain how to determine the number of protons, neutrons, and electrons in isotopes?

Answer 25

A: The number of protons is determined by the atomic number, the number of neutrons is calculated by subtracting the atomic number from the mass number, and the number of electrons is equal to the number of protons.

Question 26

Q: What is radioactive decay?

Answer 26

A: Radioactive decay is the process by which unstable nuclei emit radiation (particles or waves) to become more stable.

Question 27

Q: What are isotopes?

Answer 27

A: Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

Question 28

How is activity defined in radioactive decay?

Answer 28

A: Activity is the rate at which unstable nuclei from a source of radiation decay, measured in Becquerels (Bq).

Question 29

What is the difference between alpha, beta, and gamma decay?

Answer 29

A: Alpha decay involves the emission of an alpha particle (a helium nucleus), beta decay involves the conversion of a neutron into a proton and the emission of a beta particle (a high-speed electron), and gamma decay involves the emission of gamma rays (high-energy electromagnetic waves).

Question 30

Q: How do alpha, beta, and gamma decay affect the mass number and atomic number of a nucleus?

Answer 30

A: In alpha decay, the mass number decreases by 4 and the atomic number decreases by 2. In beta decay, the mass number remains the same while the atomic number increases by 1. In gamma decay, neither the mass number nor the atomic number of the nucleus changes.

Question 31

Q: How are nuclear radioactive decay equations balanced?

Answer 31

A: Nuclear decay equations are balanced by ensuring that the sum of mass numbers and atomic numbers on both sides of the equation are equal.

Question 32

Q: Describe alpha decay and its effect on the mass number and atomic number.

Answer 32

A: In alpha decay, an alpha particle (helium nucleus) is emitted from the parent nucleus. The mass number decreases by 4, and the atomic number decreases by 2.

Question 33

Q: Explain beta-minus decay and its impact on the mass number and atomic number.

Answer 33

A: Beta-minus decay involves the conversion of a neutron into a proton and the emission of a beta particle (electron). The mass number remains the same, but the atomic number increases by 1.

Question 34

Q: What is gamma decay, and how does it affect the mass number and atomic number?

Answer 34

A: Gamma decay involves the emission of gamma rays from an unstable nucleus. The mass number and atomic number of the daughter nucleus remain the same.

Question 35

Q: How do you balance decay equations?

Answer 35

A: To balance decay equations, ensure that the sum of mass numbers and atomic numbers is equal on both sides of the equation.

Question 36

In the example of alpha decay provided, how are the mass number and atomic number calculated for the daughter nucleus?

Question 37

Q: How do the penetrating powers of alpha, beta, and gamma radiation compare?

Answer 37

A: Alpha radiation is the least penetrating, followed by beta radiation, and gamma radiation is the most penetrating

Question 38

Q: Which type of radiation is stopped by paper?

Answer 38

A: Alpha radiation is stopped by paper.

Question 39

Q: How does ionizing power differ among alpha, beta, and gamma radiation?

Answer 39

A: Alpha radiation is the most ionizing, followed by beta radiation, and gamma radiation is the least ionizing.

Question 40

What is the range of alpha radiation in air?

Answer 40

A: Alpha radiation has a short range in air, typically only a few centimeters.

Question 41

How do the count-rate measurements using different materials help identify the type of radiation emitted by a source?

Answer 41

A: By observing how the count-rate changes when the source is placed behind different materials, one can determine the penetrating power of the radiation. In the provided example, since the count-rate decreased significantly when the source was placed behind aluminum, it indicates that the radiation is likely beta particles.

Question 42

Q: What is half-life in the context of radioactive decay?

Answer 42

A: Half-life is the time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half, or for the activity of a sample to fall to half its original level.

Question 43

How do different isotopes vary in terms of their half-lives?

Answer 43

A: Different isotopes have different half-lives, ranging from fractions of a second to billions of years.

Question 44

How can scientists use half-life to measure the age of objects?

Answer 44

A: By measuring the remaining amount of a radioactive isotope in an object and knowing its half-life, scientists can calculate how long it has been since the object formed or since a specific event occurred.

Question 45

What is the significance of carbon-14’s half-life of 5700 years?

Answer 45

A: The half-life of carbon-14 is used in radiocarbon dating to determine the age of organic materials up to about 50,000 years old.

Question 46

Describe how the amount of a radioactive isotope changes over multiple half-life periods.

Answer 46

A: With each half-life period, the amount of the radioactive isotope remaining decreases by half. For example, after one half-life, there would be 50% remaining; after two half-lives, 25% remaining; after three half-lives, 12.5% remaining, and so on.

Question 47

Q: Explain the procedure for calculating the half-life of a radioactive sample.

Answer 47

A: To calculate the half-life of a sample:

Measure the initial activity, A0, of the sample.
Determine the time it takes for the activity to decrease to half its original value.
The time taken for this decrease is the half-life of the sample.

Question 48

Q: How can the half-life of a radioactive material be determined from a graph?

Answer 48

A: On a graph showing the activity of the sample over time, the half-life can be determined by finding the time it takes for the activity to drop to half of its original value. This is done by drawing lines on the graph to indicate the time intervals corresponding to halving of the activity.

Question 49

Q: What is the significance of the half-life in radioactive decay?

Answer 49

A: The half-life represents the time it takes for the activity of a radioactive sample to decrease to half its original value. It is a characteristic property of each radioactive isotope, providing crucial information for various applications, including medicine, dating techniques, and nuclear physics.

Question 50

Q: How do you calculate the half-life if given the initial and final number of undecayed atoms?

Answer 50

A: If given the initial and final number of undecayed atoms, calculate the number of times the number of undecayed atoms has halved. Then, divide the time period by the number of half-lives to find the half-life of the material.