Transcript Chapter 19

Chapter 19
Radioactivity
Chapter 19:1
Fun Fact: If the nucleus of the hydrogen atom
was a ping pong ball, the electron in the 1s
orbital would be 0.3 mile away and have a
mass of 2.5 billion tons.
The energies involved in nuclear processes are
typically millions of times larger than those
associated with normal chemical reactions.
Chapter 19:1
Nucleons: particles of neutrons and protons.
Atomic #: # of protons.
Mass #: # of protons + neutrons.
Atoms that have identical atomic # but different
mass numbers are called isotopes.
Nuclide: applied to each unique atom
Chapter 19:1
Carbon
12C
13C
6
6
14C
6
Many nuclei are radioactive: they
spontaneously decompose.
14C
14N + 0e
where e, represents an
6
7
-1
electron, which is called a beta b particle.
Both the atomic number and the mass number
must be equal.
19.1: Types of Radioactive Decay


Alpha (a) particle: a helium nucleus 4He
2
A very common mode of decay for heavy
radioactive nuclides.
Radium-222 to give Radon-218.
222Ra 4He + 218Rn
88
2
86
230Th
90
4He+ 226Ra
2
88
19.1: Types of Radioactive Decay
-1
Beta (b) particle: 0e
-1
 The net effect of b-particle production is to
change a neutron to a proton.
 Results in no change in mass number and an
increase in 1 in atomic number
234Th
234Pa + 0e
90
91
-1

131I
53
131Xe
54
+ -10e
19.1: Types of Radioactive Decay
-1


Gamma ray(g): high-energy photon of light.
Zero charge and zero mass number.
238U
92
234Th
90
+ 4He+ 20g
2
0`
19.1: Types of Radioactive Decay

Positron: particle w/ same mass as the
electron but the opposite charge. 0e
+1
19.1: Types of Radioactive Decay

Electron capture: a process by which one of
the inner-orbital electrons is captured by the
nucleus.
201Hg + 0e
80
-1
201Au
79
+ 00`
g
19.3: Detection of Radioactivity and
Concept of Half-life.


Objectives: To learn about radiation
detection instruments.
To understand half-life.
Figure 19.2: A representation of a
Geiger-Müller counter (Geiger).
Ar(g)
Ar+(g) + e-
Argon doesn’t conduct a current, “pulse”
19.3: Detection of Radioactivity and
Concept of Half-life.

Scintillation counter: uses sodium iodide
(gives off light) when struck by a high-energy
particle. Detector senses the flashes of light
and counts the decay events.

Half-life: time required for half of the original
sample of nuclei to decay.
Uses of Radioactivity
19.4: Dating by Radioactivity.

Objectives: To learn how objects can be
dated by radioactivity

Carbon-14 dating: can be used to date wood
and cloth artifacts. Reacts with oxygen to
form carbon dioxide.
Half-life of 5730 years.

Uses of Radioactivity
19.5: Medical Applications of
Radioactivity.







Objectives: To discuss the use of radiotracers in
medicine.
Radiotracers-radioactive nuclides that can be
introduced into organisms in food or drugs.
Examples:
Iodine-131: illnesses of the thyroid.
Thallium-201 damage to the heart muscle after a
heart attack.
Technetium-99 similar.
Table 19-4 p. 619
Uses of Radioactivity
19-6: Nuclear Energy


Fusion: combining 2 light nuclei to form a
heavier nucleus.
Fission: splitting a heavy nucleus into 2
nuclei
Figure 19.4: Unstable nucleus.
fission process.
Figure 19.6: Diagram of a nuclear
power plant.
Figure 19.7: Schematic of the
reactor core.
Figure 19.8: Radioactive
particles and rays vary greatly
in penetrating power.
1.
2.
3.
4.
The Energy of the radiation
The penetrating ability of the radiation
Ionizing ability of the radiation
Chemical properties of the radiation.
Total amount of mRem 125/year
Human activities: 67 mrem