POGIL Activity: Types of Radiation

Ionization

You have learned about atomic structure. You know that the atomic nucleus is positively charged and it is orbited by negatively charged electrons. When atoms gain electrons they are a type of ion called an anion (AN-eye-on). Anions have a negative charge. When atoms lose electrons they are a type of ion called a cation (CAT-eye-on). Cations have a positive charge.

	Before				After
1	Na	+	energy		Na+	+	e–
2	Cl	+	e–		Cl–	+	energy
3	Fe	+	energy		Fe+	+	e–
4	I	+	e–		I–	+	energy

1. Use Model 1, above, to fill in the following table:

   	Name & Symbol of Element	Charge before	Number of Protons	Number of Electrons before	Charge after	Cation or Anion?	Number of Electrons after
   1
   2
   3
   4

2. Each row in Model 1 is depicting a process. Describe what happens to the atom in the first row.
3. Describe what happens to the atom in the second row.
4. What is the difference between what happens in each of those two rows?
5. Which rows in the table show an event which requires an input of energy?

When an atom loses an electron it must absorb some energy in order to pull the negative electron away from the positive nucleus because opposite charges attract. Ionization is the name for the process when an atom absorbs some energy and loses an electron as a result.

6. Which of the rows in Model 1 are showing an atom being ionized? Justify your answer.
7. What form of energy do you think could cause ionization of actual atoms?

Types of Radiation

Radiation is the emission of energy or particles that move outward along rays. There are two basic types of radiation. The first type of radiation is harmless to living things unless it is extremely intense. This type is generally known as non-ionizing radiation. The second can cause ionization and is called ionizing radiation. Ionization is when an atom or molecule loses an electron and becomes positively charged.

Light is a form of radiation. Radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays and gamma rays are just different names for the same thing: electromagnetic radiation. These different names reflect differences in energy. The microwaves used to heat your food in a microwave oven are the same as the microwaves used to transmit your cell-phone calls. Microwave radiation is a form of low-energy electromagnetic radiation. Radio waves, microwaves, infrared light and visible light are all too low in energy to cause any damage to living things. These are the only types of non-ionizing radiation.

Non-ionizing Radiation
Type	Type of Particle	Mass	Speed	Picture	Facts
Radio Waves	Photon	0 amu	3 × 108 m/s		Many types of matter are transparent to radio waves. Used for communication.
Microwaves	Photon	0 amu	3 × 108 m/s		Passes through most materials but can cause warming in others. Used for communication and cell phones and cooking.
Infrared Light	Photon	0 amu	3 × 108 m/s		Also called ‘heat radiation’ because all objects with a temperature radiate light in the infrared. Used in remote controls and for night vision.
Visible Light	Photon	0 amu	3 × 108 m/s		A narrow range of wavelengths which can be perceived by the human eye. This type of light can excite electrons in atoms and molecules.

Answer the following questions using Model 2.

8. What does the phrase ‘non-ionizing radiation’ mean?
9. What do all forms of non-ionizing radiation have in common according to the facts in the table?
10. If radiation is going to cause a cancer-causing mutation it must damage DNA by ionizing atoms that are part of the DNA molecule. Are any of the types of radiation in Model 2 capable of causing cancer?
11. Energy per photon is inversely proportional to wavelength. Using the pictures as a guide, which of the forms of non-ionizing radiation has the most energy per photon? Which has the least?
12. Most of the energy we receive from the Sun is in the form of visible light. Even though visible light photons cannot cause ionization you should not look directly at the Sun. Why not?

Of the types of electromagnetic radiation, only ultraviolet rays, x-rays and gamma rays can directly cause atoms or molecules to become ionized. Ultraviolet rays can cause sun burns and exposure over time can lead to the development of cancer. They do this by breaking chemical bonds between atoms in molecules. X-rays and gamma rays mostly pass right through living things but if they hit an atom or molecule they can also break chemical bonds and knock electrons loose.

There are two other forms of radiation that can cause ionization and they are fundamentally different from electro-magnetic radiation (or light). Light can be understood to be made of little packets of pure energy called photons, which have no mass. Alpha particles are massive particles with a +2 positive charge. An alpha particle is a high-speed helium-4 (⁴₂He) nucleus which is ejected by the nucleus of a large, unstable atomic nucleus. Because of its positive charge and large mass and incredible speed an alpha particle (also written α-particle) can cause a large number of atoms to become ionized.

Beta-rays (also written β-rays) are high-speed electrons ejected by an unstable atomic nucleus. They come from a neutron in the nucleus which is transformed into a proton. In the process the electron flies out of the nucleus. Even though it has a small mass a β-particle is strongly ionizing because of its very large speed and because of its –1 electric charge.

Ionizing Radiation
Type	Type of Particle	Mass	Speed	Picture	Facts
Ultraviolet	Photon	0 amu	3 × 108 m/s		Single photons are capable of breaking chemical bonds and separating electrons from atoms, also known as ionization.
X-rays	Photon	0 amu	3 × 108 m/s		Passes through most materials but can cause damage if it does not. When a photon strikes an atom or molecule it is likely to cause ionization.
Gamma Rays (γ-rays)	Photon	0 amu	3 × 108 m/s		Passes through most materials but can cause damage if it does not. When a photon strikes an atom or molecule it is likely to cause ionization. Gamma ray photons originate in the nucleus of an atom.
Alpha Rays (α-rays)	Alpha Particle	4 amu	1.5 × 107 m/s		An alpha-particle is a high-speed helium-4 nucleus (+2 charge) ejected by an unstable atomic nucleus. Very strongly ionizing.
Beta Rays (β-rays)	Beta Particle	5.49 × 10–4 amu	3 × 107 m/s	e–	A beta-particle is a high-speed electron (–1 charge) ejected by an unstable atomic nucleus. Very strongly ionizing.

Answer the following questions using Model 3.

13. What does the phrase ‘ionizing radiation’ mean?
14. There are two basic types of ionizing radiation according to Model 3. Define and describe these two types.
15. In order for a mutation to occur a cell’s DNA must be damaged, for example by ionization. Which types of radiation in Model 3 are capable of causing damage to DNA?
16. Sun burns and tans are caused by exposure to damaging light from the Sun. Which part of the Sun’s light spectrum causes the damage that results in the production of a tan or the pain of a sunburn?
17. Once it slows down and becomes neutralized by gaining two electrons what does an alpha-particle become?
18. Only a few types of radiation are called nuclear radiation. Using Model 3 define this phrase.
19. Is nuclear radiation the only type of dangerous radiation? Why or why not?

20. In the space below create an outline that contains all of the main points that you believe you were meant to learn by doing this activity. Do it with bullets or with headings and sub-headings (A., B., 1., 2., etc.) Work with your group on this part and consult with your teacher before moving on to the next part of the activity.
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
21. In the space below use your outline to write a short paragraph that summarizes all of the main points you wrote above. Do this part completely independently but share your work with your group members after you are finished. Make any changes or additions you find necessary to make a final draft of this information. Type up this draft to turn in as the recorder’s report.