2A3 Nuclear Processes

Question 1

Define:

Radioactivity

Answer 1

The spontaneous emission of energy or particles (such as alpha particles, beta particles, or gamma rays) from unstable atomic nuclei in an attempt to become more stable.

This process, known as decay, allows the nucleus to become more stable.

Question 2

Define:

Decay series

Answer 2

A sequence of radioactive decays a nucleus undergoes to become stable.

For example, Uranium-238 decays through a series of reactions to form stable Lead-206.

Question 3

When is a nucleus considered unstable?

Answer 3

When nuclear forces cannot overcome electrostatic repulsive forces between protons.

An unstable nucleus undergoes a change that releases energy in the form of a particle or ionizing radiation.

Stability depends on the ratio of neutrons to protons (n/p).

Question 4

Fill in the blanks:

Nuclear reactions conserve both _______ and _______ during any reaction or decay process.

Answer 4

nucleon number; charge

During a nuclear reaction or decay, the nucleon number (total protons and neutrons) and the net charge are always conserved, ensuring no loss or gain in mass or charge.

Question 5

What are the three main types of nuclear processes?

Answer 5

1. Radioactive decay
2. Fission
3. Fusion

These processes release energy by altering atomic nuclei.

Question 6

Define:

half-life

Answer 6

The time it takes for an initial amount of radioactive material to reduce to half its original amount.

The half-life is a constant property for a given radioactive isotope but varies between different elements and isotopes.

Some isotopes have half-lives of fractions of a second, while others (like Uranium-238) can have half-lives of billions of years, affecting their use in dating, medicine, and nuclear energy.

Question 7

How can you determine the half-life of a radioactive substance using a decay graph?

Answer 7

1. Identify the initial amount on the y-axis.
2. Find the y-value that is half of the initial amount.
3. Locate the corresponding x-value (time) where the curve reaches this y-value.
4. The x-value represents the half-life of the substance.

For example, if the initial y-value is 15 g, half-life corresponds to 7.5 g on the y-axis.

Question 8

True or false:

All elements undergo radioactive decay at the same rate.

Answer 8

False

Decay rates vary depending on the isotope’s half-life.

Question 9

What fraction of an original Carbon-14 sample remains after 17,190 years (three half-lives)?

Carbon-14 has a half-life of about 5,730 years.

Answer 9

1/8

The amount of the sample decreases from 1/2 to 1/4 to 1/8 over three half-lives.

Question 10

True or false:

The rate of radioactive decay is affected by external conditions such as temperature or pressure.

Answer 10

False

Radioactive decay is independent of external conditions like temperature or pressure.

Question 11

What type of graph represents radioactive decay?

Answer 11

An exponential decay graph.

The graph is exponential because the decay function involves raising a fraction (1/2) to the power of the number of half-lives elapsed.

The y-value decreases and approaches zero as the x-value increases.

Question 12

Define:

Isotope

Answer 12

Atoms of the same element that have the same number of protons but different numbers of neutrons.

They have the same atomic number but differ in mass number, affecting their stability and behavior in nuclear processes.

Question 13

True or false:

All isotopes of a given element are radioactive.

Answer 13

False

Only certain isotopes, called radioisotopes, are radioactive.

Question 14

What primarily determines the stability of an isotope?

Answer 14

The ratio of neutrons to protons in the nucleus.

Too many or too few neutrons can make a nucleus unstable.

Question 15

Define:

Radioisotope

Answer 15

An isotope with an unstable nucleus that undergoes radioactive decay.

Examples include Uranium-238 and Carbon-14.

Question 16

List the three major types of radioactive decay.

Answer 16

1. Alpha decay
2. Beta decay
3. Gamma decay

Other types include neutron radiation, positron emission (β⁺ decay), and electron capture. These processes are important in nuclear physics, medicine, and energy production.

Question 17

Define:

Alpha particles

Answer 17

They consist of two protons and two neutrons released during alpha decay.

Alpha particles are equivalent to helium nuclei. They tend to be heavy and positively charged, but have low penetration power. They can be stopped by something as thin as a sheet of paper!

Question 18

When does an alpha decay occur?

Answer 18

When a nucleus with too many protons emits an alpha particle (α).

Question 19

List three applications of alpha radiation.

Answer 19

1. Smoke detectors
2. Analysis of rocks and soil composition
3. Cancer treatment

Alpha particle X-ray spectroscopy (APXRS) is used by NASA to study the rocks of Mars.

TAT is a treatment for cancer that targets tumors with alpha radiation.

Question 20

Define:

Beta decay

Answer 20

A type of radioactive decay where a radioisotope emits a beta particle (β), equivalent to an electron.

It increases or decreases the atomic number of a radioisotope by one, but does not change the mass.

Question 21

What are beta particles?

Answer 21

High-speed, high-energy electrons (β⁻) or positrons (β⁺) emitted during beta decay.

These particles are produced when a proton is broken into a smaller particle. They have moderate penetration power, but can be stopped by aluminum.

Question 22

Define:

Gamma decay

Answer 22

It is the release of high-energy photons from an unstable nucleus without changing its composition.

Gamma rays are electromagnetic waves with high energy but no mass. They can be dangerous to humans and can be stopped by thick lead.

Question 23

How is gamma decay used in the medical field?

Answer 23

• Radiation therapy for cancer.
• Sterilizing equipment.
• Diagnostic imaging tracers.

Gamma rays can pass through human tissue, which allows for diagnostics and therapeutic uses. However, they must be used carefully because they have the potential to damage human tissue and DNA.

Question 24

Compare the penetration power of alpha, beta, and gamma radiation.

Answer 24

• Alpha: low, stopped by paper.
• Beta: moderate, stopped by aluminum.
• Gamma: high, stopped by thick lead.

The penetration depends on the type of radiation and can determine the level of danger of that kind of radiation to humans.

Gamma rays can penetrate and ionize tissues, create free radicals, and cause cancers.

Question 25

What is a **nuclear reaction**?

Answer 25

A process involving the **transformation of atomic nuclei**. ## Footnote Two examples include fission and fusion.

Question 26

# Define: Nuclear fission

Answer 26

A large nucleus **splits** into two or more smaller nuclei. ## Footnote To create this kind of reaction, unstable heavy atoms are hit with neutrons. The additional neutrons lead to more instability, which then leads to the split of the nucleus into smaller atoms or neutrons.

Question 27

# Define: Nuclear fusion

Answer 27

Two light nuclei **combine** to form a heavier nuclei. ## Footnote When this happens, the final resultant atom is lighter than the two individual pieces. Since mass was lost in the reaction, a large amount of energy is released.

Question 28

# Define: Nuclear transmutation

Answer 28

The **conversion of one element into another** by changing the number of protons in an atom’s nucleus. ## Footnote This often occurs through bombardment or decay. For example, the natural decay of potassium-40 into argon-40 occurs spontaneously when potassium-40 emits a beta particle.

Question 29

What **material** is commonly used as fuel in nuclear fission reactors?

Answer 29

Uranium-235 ## Footnote Uranium-235 is ideal for its ability to sustain a chain reaction.

Question 30

What is one major **safety concern** associated with **nuclear fission**?

Answer 30

The potential for **radioactive leaks or meltdowns** in nuclear reactors. ## Footnote Events like Chernobyl highlight the importance of safety measures.

Question 31

# True or false: Neutrons play **no role** in radioactive decay.

Answer 31

False ## Footnote Neutrons can convert into protons or trigger decay processes.

Question 32

What is the **difference** between nuclear fusion and nuclear fission?

Answer 32

* Fusion: **two light nuclei combine** to form a heavier nucleus. * Fission: **large nucleus splits** into two or more smaller nuclei. ## Footnote One reaction represents the combination of nuclei, while the other represents the split of a large nuclei. Both produce energy, but we are only able to easily harness the energy created from fission.

Question 33

Why is **helium** not radioactive when it is formed in fusion reactions?

Answer 33

Helium is a **stable element with a balanced ratio** of protons and neutrons. ## Footnote It does not undergo radioactive decay.

Question 34

# Fill in the blanks: In nuclear fission, a heavy **nucleus splits into** \_\_\_\_\_\_\_\_ and \_\_\_\_\_\_\_.

Answer 34

smaller nuclei; neutrons ## Footnote Energy is also released in the process. This process is the basis for nuclear power generation.

Question 35

When does a **chain reaction** occur in nuclear fission?

Answer 35

When **neutrons released** from a fission reaction **initiate further fission reactions**, sustaining the reaction. ## Footnote This is responsible for the continuous energy production in nuclear reactors.

Question 36

What is the primary product of **fusion in stars**?

Answer 36

Helium ## Footnote Fusion combines hydrogen nuclei forming helium, releasing energy in the process.

Question 37

What is the **significance** of mass defect in nuclear reactions?

Answer 37

It shows that **mass converts into energy (E = mc²)** in nuclear reactions. ## Footnote This goes against past thinking that mass and energy could not be converted into one another. Mass defect is crucial in understanding energy production in nuclear power plants and stars.

Question 38

What is the **relationship** between mass defect and nuclear binding energy?

Answer 38

* They are **directly related**. * Nuclear binding energy is the energy **obtained by the loss of mass**. ## Footnote Binding energy is the energy required to break a nucleus into its component nucleons. The relationship is explained by Einstein's equation E=mc², where E is energy, m is the absolute mass defect in kg, and c is the speed of light.

Question 39

# True or false: The **mass defect** of a nucleus is always zero.

Answer 39

False ## Footnote There is always a small mass defect due to binding energy.

Question 40

# Define: Nuclear equations

Answer 40

Symbolic **representations of nuclear reactions** written with reactants and products separated by an arrow. ## Footnote Example format: Reactants ⟶ Products.

Question 41

Why is it important to **balance** nuclear equations?

Answer 41

To **ensure conservation** of mass and atomic numbers. ## Footnote Balancing verifies the reaction's validity. The sum of the mass numbers and atomic numbers of reactants must equal those of products.

Question 42

# Define: Nuclear chemistry

Answer 42

A field of chemistry that deals with the **use of radioactive isotopes** and other nuclear reactions. ## Footnote It is used daily in our lives for: * Diagnosing diseases * Treating medical conditions * Determining the age of artifacts * Energy production

Question 43

How do radioactive isotopes help in **radiation therapy**?

Answer 43

They **target and kill dangerous cells** while protecting surrounding tissues. ## Footnote They emit radiation that travels only over a short distance.

Question 44

What is a **radioactive tracer**?

Answer 44

A radioactive isotope used to **track chemical pathways** or **locate abnormalities** in the body. ## Footnote Stable atoms in the body are replaced by radioactive atoms, which help in diagnosing diseases.

Question 45

# Define: Carbon dating

Answer 45

A method that uses the **decay of carbon-14** to determine the age of artifacts. ## Footnote It relies on measuring the ratio of carbon-14 to carbon-12 in once-living materials. The half-life of carbon-14 is approximately *5,730 years*. Every 5,730 years, half of the carbon-14 in an artifact decays into nitrogen through a beta decay.