2A4 Radioactivity Flashcards
Describe the characteristics of different kinds of radiation, decay, fission, and fusion reactions.
Define:
radioactive decay
A spontaneous process where unstable nuclei emit radiation to become stable.
This process continues until a stable nucleus is formed.
It can involve a change in the number of protons and/or neutrons.
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).
List the three major types of radioactive decay.
- Alpha decay
- Beta decay
- Gamma decay
Neutron radiation is also another type.
Define:
beta decay
A type of radioactive decay where a radioisotope emits a beta particle (β), equivalent to an electron.
It increases or decresases the atomic number of a radioisotope by one, but does not change the mass.
What are beta particles?
High-speed electrons or positrons released in a beta decay.
A positron is a subatomic particle that has a similar mass to an electron, but with a positive charge. These particles are produced when a proton is broken into a smaller particle. They have moderate penetration power, but can be stopped by aluminum.
When does an alpha decay occur?
When a nucleus with too many protons emits an alpha particle (α).
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!
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:
gamma decay
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.
Define:
nuclear transmutation
The transformation of one element into another due to changes in the number of protons and electrons during nuclear decay.
This often occurs through bombardment or decay.
An example is the decay of uranium-238 into plutonium-239.
What is nuclear notation?
A way to denote changes in the nuclear structure using the elemental symbol, atomic number, and atomic mass.
Example: Uranium can be written as 238/92 U.
Define:
half-life
The amount of time it takes for half of the nucleus of an element to break down.
It is a measure of the rate at which radioactive decay occurs.
It can range from seconds to years.
How do you calculate the number of half-lives that have passed?
n = t / T
Where t is the time that has passed and T is the length of the half-life.
What does the equation N=No(1/2)^n represent?
It calculates the remaining amount of an element after a set number of half-lives.
where:
- N is the remaining amount
- No is the initial amount
- n is the number of half-lives that have elapsed
What is the remaining amount of cobalt-60 after one half-life if the initial amount is 10.0 mg?
5 mg
This is half of the initial amount of cobalt-60.
The amount that remains after two and three half-lives is 2.5 and 1.25 mg respectively.
What percentage of a substance remains after four half-lives if the starting sample is 100%?
6.25%
This is determined by halving the amount for each half-life.
- After 1 half life, 50% remians
- After 2 half lives, 25% remains
- After 3 half lives, 12.5% remains
- After 4 halflives, 6.25% remains
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.
How can you determine half-lives from a decay graph?
By finding the x-value corresponding to the y-value that is half of the initial amount.
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.
True or False:
Neutrons play no role in radioactive decay.
False
Neutrons can convert into protons or trigger decay processes.
What is a nuclear reaction?
A process involving the transformation of atomic nuclei.
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.
What is the difference between nuclear fusion from 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.
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.
Energy is also released in the process.
Define:
mass defect
The difference between the total mass of a nucleus and the sum of its individual nucleons.
Mass defect accounts for the energy binding the nucleus together.
What is the formula for calculating mass defect?
Nuclear Mass Defect = ma - (Z⋅mp + N⋅mn)
where:
- ma is the actual mass of the nucleus
- Z is the number of protons
- mp is the mass of a proton
- N is the number of neutrons
- mn is the mass of a neutron
What is the significance of mass defect in nuclear reactions?
It disproves the belief that mass and energy cannot be converted into each other.
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.
Describe the purpose of balancing 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 in daily our lives for:
- Diagnosing diseases
- Treating medical conditions
- Determining the age of artifacts
- Energy production
What is the role of radioactive isotopes 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.
