1. Chapter 10 Nuclear Changes

2. What is Radioactivity?
Certain isotopes of many elements undergo a process called radioactive decay
During radioactive decay, the unstable nuclei of these isotopes emit particles, or release energy, to become stable isotopes
The released energy and matter is referred to as nuclear radiation
After radioactive decay, the element changes into a different isotope of the same element or into an entirely different element

3. What is Radioactivity?
Recall that isotopes of an element are atoms that have the same number of protons but different numbers of neutrons in their nuclei
Different elements are distinguished by having different numbers of protons

4. What is Radioactivity? Four types of nuclear radiation Alpha particles
Beta particles
Gamma rays
Neutrons

5. What is Radioactivity?

6. What is Radioactivity?

7. What is Radioactivity? Alpha particles
Made of 2 protons and two neutrons
Same as the helium nuclei
Positively charged
More massive than any other type of nuclear radiation
Do not travel far through materials
Barely pass through a sheet of paper
Can ionize other atoms thus losing energy

8. What is Radioactivity? Beta particles
Often fast-moving electrons but may also be positively charged particles called positrons
Positrons have the same mass as electrons
Neutrons, which are not charged, decay to form a proton and an electron
The electron, which has a very small mass, is then ejected at a high speed from the nucleus as a beta particle
Pass through a piece of paper , but most are stopped by 3 mm of aluminum or 10 mm of wood
Not as massive as alpha particles
Can ionize other atoms thus losing energy

9. What is Radioactivity? Gamma rays
Not made up of matter and do not have an electric charge
Form of electromagnetic energy
Consist of energy packets called photons
Like light and X-rays
Have more energy than light or X-rays
Can ionize and cause damage in matter
Can penetrate up to 60 cm of aluminum or 7 cm of lead
Greater damage to health

10. What is Radioactivity? Neutron radiation No charge
Therefore, do not ionize matter
Therefore, they are able to travel farther through matter than alpha and beta particles
A block of lead about 15 cm thick is required to stop most fast neutrons

11. What is Radioactivity?
Anytime that an unstable nucleus emits alpha or beta particles, the number of protons and neutrons change
Example: radium-226 (an isotope of radium with the mass number 226)changess to radon-222 by emitting an alpha particle

12. What is Radioactivity? Gamma decay changes the energy of the nucleus
No change in the atomic number of the element

13. What is Radioactivity? Beta Decay: Loses electron
Atomic number changes (increase of one)
Mass number before and after the decay does not change
The atomic number of the product nucleus increases by one (neutron changes into a proton)
Example: carbon-14 changes into nitrogen-14

14. What is Radioactivity? Alpha Decay:
Loses 2 protons and 2 neutrons (helium nuclei)
Both atomic mass and number change’

15. What is Radioactivity?

16. What is Radioactivity? What do the colors mean?
Zone 1 counties have a predicted average indoor radon screening level greater than 4 pCi/L (picocuries per liter) (red zones)Highest Potential
Zone 2 counties have a predicted average indoor radon screening level between 2 and 4 pCi/L (orange zones)Moderate Potential
Zone 3 counties have a predicted average indoor radon screening level less than 2 pCi/L (yellow zones)Low Potential

17. PHILADELPHIA COUNTY

18. MONTGOMERY COUNTY

19. BUCKS COUNTY

20. RADON

21. RADON

22. RADON

23. What is Radioactivity? Radioactive Decay Rates
Half-Life: time in which half of a radioactive substance decays
Last from a nanosecond to billions of years
Used to diagnose medical problems
Detector follows the element as it moves through the patient’s body
Predict the age of fossils/rocks

24. What is Radioactivity?

25. What is Radioactivity?

26. What is Radioactivity?
Radium-226 has a half-life of 1,599 years. How long will 7/8 of a sample of radium-226 take o decay?
Fraction remaining 1/8
Amount of sample remaining after 3 half-lives
½ x ½ x ½ = 1/8
3 half-lives X 1,599 years/half-life = 4,797 years

27. What is Radioactivity? Radioactive decay is exponential decay
Example: Carbon-14

28. What is Radioactivity?

29. Nuclear Change

30. Nuclear Change
The stability of a nucleus depends on the nuclear forces that hold the nucleus together.
These forces act between the protons and the neutrons
Like charges repel, so how can so many positively charged protons fit into an atomic nucleus without flying apart?
Strong nuclear forces cause neutrons and protons to attract one another—this attraction is much stronger than the electric repulsion between protons

31. Nuclear Change Nuclei with more than 83 protons are always unstable
These nuclei will always decay and, in the process, release large amounts of energy and nuclear radiation

32. Nuclear Change
Nuclear fission: process of splitting heavier nuclei into lighter nuclei
Neutrons and energy are released
Some mass will be changed into energy
The equivalence of mass and energy is explained by the Theory of Relativity (Einstein)
Energy= mass X (speed of light)2 = mc2
Under ordinary conditions this change does not happen spontaneously

33. Nuclear Change
Neutrons released by fission can start a chain reaction (one reaction triggers another and so on)
Continuous series of nuclear fission reactions

34. Nuclear Change
Critical mass: the minimum mass of a fissionable isotope that provides the number of neutrons needed to sustain a chain reaction
In nature the concentration is low
Chain reactions can be controlled to be used to generate electricity
Control rods regulate fission by slowing the chain reaction

35. Nuclear Change

36. Nuclear Change
Nuclear Fusion: energy can be obtained when very light nuclei are combined to form heavier nuclei
Example:
Sun: energy is formed primarily when hydrogen nuclei combine releasing energy
Large amount of energy is needed to start a fusion reaction
Reason is that all nuclei are positively charged and repel one another with electric force
Energy needed to overcome this force (Stars: the extreme temperature overcomes this force)

37. Nuclear Change

38. Nuclear Radiation Today
We are continually exposed to radiation from natural sources (sun, soil, rocks, plants)(80%)
Human-made sources (computer monitors, smoke detectors, X-rays, etc.)(20%)
Measured in units called rems (1rem = 1,000 millirems)
Dental X-ray= 1 millirem
Safe limit for workers is about 5,000 rems per year

39. Nuclear Radiation Today
Exposure varies from location to location, activities (jobs/recreational), habits (smoking), home to home (smoke detectors: emit alpha particles)