2A3 Nuclear Processes Flashcards
Explain the characteristics and effects of nuclear processes such as radioactive decay, fission, and fusion.
Define:
Radioactivity
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.
Define:
Decay series
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.
When is a nucleus considered unstable?
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).
Fill in the blanks:
Nuclear reactions conserve both _______ and _______ during any reaction or decay process.
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.
What are the three main types of nuclear processes?
- Radioactive decay
- Fission
- Fusion
These processes release energy by altering atomic nuclei.
Define:
half-life
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.
How can you determine the half-life of a radioactive substance using a decay graph?
- Identify the initial amount on the y-axis.
- Find the y-value that is half of the initial amount.
- Locate the corresponding x-value (time) where the curve reaches this y-value.
- 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.
True or false:
All elements undergo radioactive decay at the same rate.
False
Decay rates vary depending on the isotope’s half-life.
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.
1/8
The amount of the sample decreases from 1/2 to 1/4 to 1/8 over three half-lives.
True or false:
The rate of radioactive decay is affected by external conditions such as temperature or pressure.
False
Radioactive decay is independent of external conditions like temperature or pressure.
What type of graph represents radioactive decay?
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.
Define:
Isotope
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.
True or false:
All isotopes of a given element are radioactive.
False
Only certain isotopes, called radioisotopes, are radioactive.
What primarily determines the stability of an isotope?
The ratio of neutrons to protons in the nucleus.
Too many or too few neutrons can make a nucleus unstable.
Define:
Radioisotope
An isotope with an unstable nucleus that undergoes radioactive decay.
Examples include Uranium-238 and Carbon-14.
List the three major types of radioactive decay.
- Alpha decay
- Beta decay
- 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.
Define:
Alpha particles
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!
When does an alpha decay occur?
When a nucleus with too many protons emits an alpha particle (α).
List three applications of alpha radiation.
- Smoke detectors
- Analysis of rocks and soil composition
- 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.
Define:
Beta decay
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.
What are beta particles?
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.
Define:
Gamma deca
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.
How is gamma decay used in the medical field?
- 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.
Compare the penetration power of alpha, beta, and gamma radiation.
- 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.
What is a nuclear reaction?
A process involving the transformation of atomic nuclei.
Two examples include fission and fusion.
Define:
Nuclear fission
A large nucleus splits into two or more smaller nuclei.
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.
Define:
Nuclear fusion
Two light nuclei combine to form a heavier nuclei.
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.
Define:
Nuclear transmutation
The conversion of one element into another by changing the number of protons in an atom’s nucleus.
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.
What material is commonly used as fuel in nuclear fission reactors?
Uranium-235
Uranium-235 is ideal for its ability to sustain a chain reaction.
What is one major safety concern associated with nuclear fission?
The potential for radioactive leaks or meltdowns in nuclear reactors.
Events like Chernobyl highlight the importance of safety measures.
True or false:
Neutrons play no role in radioactive decay.
False
Neutrons can convert into protons or trigger decay processes.
What is the difference between nuclear fusion and nuclear fission?
- Fusion: two light nuclei combine to form a heavier nucleus.
- Fission: large nucleus splits into two or more smaller nuclei.
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.
Why is helium not radioactive when it is formed in fusion reactions?
Helium is a stable element with a balanced ratio of protons and neutrons.
It does not undergo radioactive decay.
Fill in the blanks:
In nuclear fission, a heavy nucleus splits into ________ and _______.
smaller nuclei; neutrons
Energy is also released in the process.
This process is the basis for nuclear power generation.
When does a chain reaction occur in nuclear fission?
When neutrons released from a fission reaction initiate further fission reactions, sustaining the reaction.
This is responsible for the continuous energy production in nuclear reactors.
What is the primary product of fusion in stars?
Helium
Fusion combines hydrogen nuclei forming helium, releasing energy in the process.
What is the significance of mass defect in nuclear reactions?
It shows that mass converts into energy (E = mc²) in nuclear reactions.
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.
What is the relationship between mass defect and nuclear binding energy?
- They are directly related.
- Nuclear binding energy is the energy obtained by the loss of mass.
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.
True or false:
The mass defect of a nucleus is always zero.
False
There is always a small mass defect due to binding energy.
Define:
Nuclear equations
Symbolic representations of nuclear reactions written with reactants and products separated by an arrow.
Example format: Reactants ⟶ Products.
Why is it important to balance nuclear equations?
To ensure conservation of mass and atomic numbers.
Balancing verifies the reaction’s validity.
The sum of the mass numbers and atomic numbers of reactants must equal those of products.
Define:
Nuclear chemistry
A field of chemistry that deals with the use of radioactive isotopes and other nuclear reactions.
It is used daily in our lives for:
- Diagnosing diseases
- Treating medical conditions
- Determining the age of artifacts
- Energy production
How do radioactive isotopes help in radiation therapy?
They target and kill dangerous cells while protecting surrounding tissues.
They emit radiation that travels only over a short distance.
What is a radioactive tracer?
A radioactive isotope used to track chemical pathways or locate abnormalities in the body.
Stable atoms in the body are replaced by radioactive atoms, which help in diagnosing diseases.
Define:
Carbon dating
A method that uses the decay of carbon-14 to determine the age of artifacts.
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.
