1. 2.3: Detecting Radioactivity, Nuclear Reactions
2/1/17
SPS3. Students will distinguish the characteristics and components of radioactivity.
a. Differentiate among alpha and beta particles and gamma radiation. b. Differentiate between fission and fusion. c. Explain the process half-life as related to radioactive decay. d. Describe nuclear energy, its practical application as an alternative energy source, and its potential problems.

2. Part I: Detecting Radioactivity
because you can’t see or feel radiation (alpha or beta particles or gamma rays), you must use special instruments to detect them.
each of these tools detects the ions produced by the radioactive particles as they collide with matter, not the radiation itself.
cloud chamber = a small glass box full of tiny droplets of water vapor (like fog).
A radioactive source placed inside the box will produce ions in the air as the isotopes knock electrons off the air molecules.
Water condenses around these ions, forming trails of droplets that indicate radioactivity.

3. https://www.youtube.com/watch?v=e3fi6uyyrEs cloud chamber
cloud chamber = a small glass box full of tiny droplets of water vapor (like fog).
A radioactive source placed inside the box will produce ions in the air as the isotopes knock electrons off the air molecules.
Water condenses around these ions, forming trails of droplets that indicate radioactivity.
alpha particles leave a short, thick trail in a cloud chamber
beta particles leave a long, thin trail
bubble chamber = similar to the cloud chamber, only filled with superheated liquid instead. Ions cause small bubbles to form in the liquid as it boils, leaving trails of bubbles behind.
cloud chamber

4. bubble chamber = similar to the cloud chamber, only filled with superheated liquid instead. Ions cause small bubbles to form in the liquid as it boils, leaving trails of bubbles behind.
Geiger counter = a device the size of a microphone filled with gas and connected to a meter. Ions stripped from the gas are picked up by a wire, converted to electrical current, and then converted to audible clicks. The speed at which the counter clicks indicates the amount of radiation present.
Geiger sound

5. Self Check
Questions!

6. (so you can see the trails)
In the cloud chamber video, what was the material that looked like white tubes placed under the chamber? _______ Why was it there?
dry ice
to cool down the vapor
(so you can see the trails)

7. Describe what a Geiger counter sounds like:
a series of audible clicks (more clicks =
more radiation present)

8. bubble chamber = similar to the cloud chamber, only filled with superheated liquid instead. Ions cause small bubbles to form in the liquid as it boils, leaving trails of bubbles behind.
Geiger counter = a device the size of a microphone filled with gas and connected to a meter. Ions stripped from the gas are picked up by a wire, converted to electrical current, and then converted to audible clicks. The speed at which the counter clicks indicates the amount of radiation present.

9. Part II: Sources of Radiation
background radiation = low-level radiation emitted by naturally occurring isotopes in the rocks, soil, water, and the atmosphere, as well as building materials (bricks, concrete, wood).
as a result, all plants and animals contain some small amounts of these isotopes (such as 14C).
largest source of background rad. is radon gas (Rn):
comes from the natural decay of 238U in Earth’s crust
Rn itself emits alpha particles as it decays
Rn seeps into houses through basement walls in contact with soil

12. Rn seeps into houses through basement walls in contact with soil
cosmic rays produce radioactive isotopes when they hit molecules in the upper levels of the atmosphere. Lower levels absorb most of this radiation.
exposure to background rad. varies with a person’s location, the materials their house is constructed from, and the altitude at which they live.

13. Self Check
Questions!

14. What is the largest source of background radiation for most people?
radon gas (Rn)

15. What protects us from most radiation from cosmic rays?
the atmosphere

16. Rn seeps into houses through basement walls in contact with soil
cosmic rays produce radioactive isotopes when they hit molecules in the upper levels of the atmosphere. Lower levels absorb most of this radiation.
exposure to background rad. varies with a person’s location, the materials their house is constructed from, and the altitude at which they live.
Part III: Nuclear Reactions
there are two basic types of nuclear reactions: fission and fusion.
fission = the process of splitting a nucleus into several smaller nuclei.

17. Part III: Nuclear Reactions
there are two basic types of nuclear reactions: fission and fusion.
fission = the process of splitting a nucleus into several smaller nuclei.
when a neutron is fired at a 235U nucleus, it absorbs the neutron, becomes unstable, and splits, producing 2 new nuclei and several more neutrons in the process, as well as a tremendous amount of energy.
the energy produced comes from a slight loss of mass during the reaction.
the mass is converted to energy through Einstein’s famous equation:
inside nuclear reactor

18. the mass is converted to energy through Einstein’s famous equation:
E = energy (measured in joules)
m = mass (measured in kilograms)
c = the speed of light (3.0 x 108 m/s)
100 trillion joules of energy can be produced from 1 gram of mass!
the neutrons released in a fission reaction can trigger chain reactions.
E = mc2

19. chain reaction = series of repeated fission reactions caused by the release of neutrons in each reaction.
uncontrolled chain reactions can be very destructive, releasing enormous amounts of energy in an instant.
controlled chain reactions use materials to absorb the extra neutrons so that the reaction takes place at a constant rate.
critical mass = amount of material required so that each fission reaction produces approx. 1 more fission reaction.

20. temps like this can be found in the center of stars, such as our Sun.
critical mass = amount of material required so that each fission reaction produces approx. 1 more fission reaction.
fusion = nuclear reaction involving 2 nuclei with low masses combining to form one nucleus of larger mass.
fusion can only take place at extremely high temp eratures (millions of C), since the particles must be moving extremely fast to be able to react.
temps like this can be found in the center of stars, such as our Sun.

21. temps like this can be found in the center of stars, such as our Sun.
fusion can only take place at extremely high temp eratures (millions of C), since the particles must be moving extremely fast to be able to react.
temps like this can be found in the center of stars, such as our Sun.
fusion reactors have not yet been built yet on Earth.
fusion reactions also release a tremendous amount of energy (E = mc2).
fusion in the sun
Nuclear energy basics, issues

22. Self Check
Questions!

23. The nuclear reaction that splits large nuclei into 2 smaller nuclei is
(fission, fusion).

24. (Controlled, Uncontrolled) nuclear reactions take place in nuclear reactors in power plants.

25. Metaphor for a chain reaction:
spreading secrets (your friend tells 2 people, they each tell 2 people, etc.)

26. temps like this can be found in the center of stars, such as our Sun.
fusion can only take place at extremely high temp eratures (millions of C), since the particles must be moving extremely fast to be able to react.
temps like this can be found in the center of stars, such as our Sun.
fusion reactors have not yet been built yet on Earth.
fusion reactions also release a tremendous amount of energy (E = mc2).
fusion in the sun
Nuclear energy basics, issues