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9th Grade Physical Science
Unit 6 The Power of the Nucleus
#5A The Unstable Nucleus
#5A
To Begin
Radioactive decay is the process by which an unstable atom emits particles from its atomic nucleus.
Because every atomic nucleus experiences a conflict between the two strongest forces in nature (the strong
force and the electrostatic (electromagnetic) force), it is not surprising that there are many elements which
are unstable and emit some kind of radiation (high energy particles).
Purpose
• Students will understand that radioactive decay always results in a new element.
• Students will be able to explain the process of both alpha decay and beta decay.
• Students will be able to identify an alpha particle and beta particles.
Process
What is Radioactive Decay?
1. The diagrams show two of the most common
types of radiation, alpha and beta radiation. An
alpha particle is made of 2 _________ and 2
_________. The alpha particle is similar to the
nucleus of which element? __________________.
When the unstable atom undergoes alpha decay it
emits an alpha particle…this is alpha radiation.
parent nucleus
daughter nucleus
2. Beta-minus decay involves both an _______________ and an ____________ being emitted from the
nucleus. A neutron (neutral particle) actually is transformed into a proton (+ charge) by the emission of
these negative particles.
3. Both alpha and beta radiation emit particles that cause a change in the number of protons in the atom.
Once the number of protons is changed, the atom is transformed into a different _____________.
4. When an atomic nucleus starts out with 20 protons and 22 neutrons and undergoes alpha decay, how
many protons does the daughter nucleus have? _________. How many neutrons? ________. Is it the same
element or a different element? ___________. Does it have the same mass or a different mass? __________
5. When an atomic nucleus starts out with 20 protons and 20 neutrons and undergoes beta-minus decay,
how many protons does the daughter nucleus have? __________. How many neutrons? ________. Is it the
same element or a different element? ____________. Does it have the same mass?__________.
What Makes an Element Radioactive
6. To understand radioactivity, we need to think about the structure of an atomic nucleus and what
conditions might make that nucleus be unstable. Every nucleus contains neutrons as well as protons.
Neutrons have ______ charge and protons have a _________charge.
7. Are protons attracted to other protons, or are they repelled? ___________. What tis the name of the
force that is responsible for attraction/repulsion of charged particles?____________________________
8. What is the name of the force that actually holds the protons together in the nucleus?
______________________
9. The positively charged protons in the nucleus want to _________each other due to electrostatic forces!
The Strong Nuclear Force is the ____________ force between the protons that holds them together. In the
nucleus, there is a constant battle between the electrostatic force that wants to push protons apart and the
attractive strong nuclear force “gluing” the protons to each other.
10. This Strong Nuclear force is stronger than the electromagnetic force (electrostatic force). But, unlike the
electromagnetic force that can work over very long distances, the range of the Strong force is extremely
small and limited to size of the nucleus! Because of limitations of distance, atoms with large nuclei often
have an unstable outcome between these two competing forces.
11. Neutrons probably act as a buffer to help minimize the repulsion between protons. If the neutron to
proton ratio is not just right, then protons are emitted or transformed in order to regain stability between the
strong force and the electrostatic force.
12. In a large nucleus like that of Uranium, which has 92 protons, the electrostatic repulsive force becomes
too much for the strong nuclear force to contain. Subsequently, the nucleus is very unstable and radioactive
decay occurs. Uranium decays through a series of steps into a more stable element. Radioactivity is the
principle on which nuclear energy and nuclear weapons are based!
13. Draw a labeled diagram of a nucleus with 9 protons
electrostatic and the strong force at work (be creative!).
and 10 neutrons
where you show both the