1. Earth’s Materials and Processes-Part 4 Radioactive Decay and Absolute Dating

2. An unstable nucleus releases energy to become more stable
Radioactive Decay
Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.
There are numerous types of radioactive decay. The general idea:
An unstable nucleus releases energy to become more stable

3. Chemistry Terms! (They’re Back!)
The Atomic Number: the Number of Protons in the nucleus of an Atom.
Nucleus: It’s where the Protons and Neutrons are located in an Atom.
Protons: Positively Charged Particles in the Nucleus of the atom. Mass = (approx) 1 AMU
Neutrons: Neutrally charged particles in the nucleus of an atom Mass = (approx) 1 AMU
Mass Number of an atom: Number of Protons + Number of Neutrons in the nucleus of an atom.

4. Alpha Decay
Type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or ‘decays’ into an atom with a mass number that is reduced by four and an atomic number that is reduced by two.

5. Example

6. Beta Decay
Type of radioactive decay in which a beta ray (fast energetic electron or positron) and a neutrino are emitted from an atomic nucleus.

7. Example

8. Gamma Decay
Type of radioactivity in which some unstable atomic nuclei dissipate excess energy by a spontaneous electromagnetic process.

9. Alpha particles cannot escape a sheet of paper.
Beta particles cannot escape a sheet of aluminum.
Gamma particles can only be reduced by a much larger object, such as a piece of lead.

10. Types of Radioactive Decay

11. Sources of Radioactivity
Primordial - from before the creation of the Earth
Cosmogenic - formed as a result of cosmic ray interactions
Human produced - enhanced or formed due to human actions (minor amounts compared to natural)

12. Sources of Radioactivity
Naturally Occurring Sources:
Radon from the decay of Uranium and Thorium
Potassium -40 – found in minerals and in plants
Carbon 14 – Found in Plants and Animal tissue
Manmade Sources:
Medical use of Radioactive Isotopes
Certain Consumer products –(eg Smoke detectors)
Fallout from nuclear testing
Emissions from Nuclear Power plants

13. Radiation Sources

14. The Alpha, Beta and Gamma particles all add energy to the body’s tissues. The effect is called the Ionizing Energy. It can alter DNA.
Even though Alpha particles are not very penetrative if the decaying atom is already in the body (inhalation, ingestion) they can cause trouble.

15. Radioactive Decay: Summed Up
During radioactive decay, a “parent” atom releases energy and particles as it changes to a new kind of atom, a “daughter” atom.

16. Radioactive Decay
Radioactive elements happen naturally in igneous rocks
Scientists use the rate of decay to calculate the rock’s age
As the radioactive element in the rock decays it changes into another element
Composition changes slowly over time
Amount of radioactive element goes down and amount of new element goes up

17. Half-Life of Radioactive Atoms
The time it takes for one half of the radioactive atoms to decay.

18. Half-Life Example
Rate of decay is constant for each radioactive element
Scientists can measure the rate of decay experimentally

19. Radiometric Dating
Table lists several common radioactive elements and their half-lives.
Carbon-14 has a half-life of 5,730 years and is useful in dating plants and animals that lived up to about 50,000 years ago. (It has a short half-life…)
Potassium-40 decays to a stable argon-40 and has a half-life of 1.3 billion years. It is useful in dating most ancient rocks because of its long half-life.

20. In radioactive dating first measure the amount of radioactive element in a rock (“parent” element)
Then measure the amount of stable element that the unstable radioactive element decays into (“daughter” element)
By calculating the ratio of radioactive element to the stable element you can determine the age of the rock

21. Earth’s Age…Estimated
Earth’s ever changing processes makes it difficult for scientists to determine Earth’s absolute age
Radioactive dating shows that the oldest rocks found on Earth are about 4.0 billion years old
The oldest fossils of living things are about 3.5 billion years