The Atom and Radiation
Nuclear Radiation and an
Introduction to Electromagnetic
Radiation
Goals: To answer the following
questions



What is radiation?
Where is radiation found?
What is radiation used for?
Complete the survey on page 410. You
should copy each statement in your
notebook and indicate whether you feel
the statement is true or false. We will
revisit these at the end of the unit.
The Discovery of Radioactivity



The German physicist W.K. Roentgen
“accidentally” discovers a mysterious source of
radiant energy that can pass through low density
shields (like card board). He calls this
mysterious energy X-rays.
Further research showed that X-rays cannot
pass through everything, particularly high
density materials like lead and bone.
Roentgen takes the first X-rays of his wife’s
hand to present to his colleagues.
The Discovery of Radioactivity



The French physicist Henri Becquerel takes interest in
Roentgen's X-rays. He investigated whether certain
minerals could emit X-rays. He experiments with
Uranium and a photographic plate (develops upon
exposure to light).
Another accident happens…Becquerel becomes
frustrated with his research, wraps the photographic
plate in black paper (to prevent light exposure), throws it
in his desk drawer with a piece of Uranium on top and
closes it up.
What do you know??? A few days later, Becquerel
discovers that the photographic plate has been exposed
while sitting in his dark drawer.
The Discovery of Radioactivity
What Becquerel inadvertently discovered
was radioactivity, the spontaneous
emission of nuclear radiation.
 Soon after, Becquerel's colleagues, Marie
Curie and her husband Pierre discover two
other radioactive elements: polonium and
radium.

What is Radioactivity?


Radioactivity: the spontaneous emission of
nuclear radiation.
We now know that there are two categories of
radiation:

Non-ionizing radiation – low-energy radiation that
transfers energy to matter


usually only harmful in large amounts
Ionizing radiation – high-energy radiation that can
eject electrons from atoms/molecules to form highly
reactive ions and can cause serious cell damage

exposure should be limited.
Concerns…..

But radiation is all around us…the
question is, should we be concerned about
our safety?? Are we in danger of serious
exposure to radiation?
Forms of Radiation

Radiation comes in several forms as shown in
the electromagnetic spectrum below; but not all
forms are represented here
Types of Radiation
 Three
main types (from the 2 categories) :
1. Non-ionizing electromagnetic radiation
 Radio
 Micro
 Infrared
 Visible
 low energy UV
2. Ionizing electromagnetic radiation
High UV
 X-rays
 Gamma rays

3. Ionizing atomic particle radiation

radioactive elements
Why are some elements radioactive? To
answer this question, you must
understand a little about atomic structure.
 All matter can be broken down into atoms:


1.
2.
3.
An atom is
composed of three
parts:
Protons
Neutrons
Electrons
Parts of the Atom
A proton is a positively charged particle
that is located in the center of an atom. All
atoms of an element have the SAME
number of protons
 A neutron is a particle with no charge and
is also located in the center of an atom.
 An electron is a negatively charged
particle that orbits around the protons and
neutrons.

Parts of the Atom

The center of the atom where the protons and
neutrons are located is called the nucleus.
Name
Proton
Electron
Neutron
Location
Nucleus
Outside
Nucleus
Nucleus
Charge
+1
-1
0
• The Number of Protons is the Atomic Number (found on
the periodic table)
• Mass of an atom is the number of Neutrons plus number
of Protons
• Mass Atom = Protons + Neutrons
• Notation
number p + number n
number p
A
E
Z
Symbol of element
E.g.
Mass #
Atomic #
12
C
6
Symbol of element
Element Protons Neutrons Mass #
Symbol
39
K
19
20
39
Nitrogen
7
7
14
14
Al
13
14
27
27
He
2
2
4
4
Lithium
3
11
4
12
7
20
Ne
20
10
23
40
10
20
Zinc
30
35
65
S
16
16
32
Sodium
Ca
19
7
N
Al
13
2
K
He
7
Li
3
23
11
40
20
20
10
Na
Ca
Ne
65
30
32
16
Zn
S
Isotopes


While all atoms of the same element must have
the same number of protons, they do not all
have to have the same number of neutrons.
This makes some atoms of the same element
heavier than others. These are referred to as
isotopes:
Isotope – Atom of the same element (same #
protons) but with different Mass Number due to
varying numbers of neutrons
Element Protons Neutrons Mass #
Li
3
4
Symbol
7
7
8
8
3
Li
3
5
C
6
6
12
12
C
6
7
13
13
C
6
8
14
14
B
5
4
9
9
B
5
6
11
11
H
1
0
1
1
H
H
1
1
2
2
3
1
3
6
6
6
5
5
1
2
1
3
1
Li
Li
C
C
C
B
B
H
H
H
Isotopes (cont.)






Some isotopes are stable and others are
unstable. This is where radioactivity comes in.
A stable isotope is not radioactive, but an
unstable isotope is!
Ex. 12C is stable
13C is stable
14C is radioactive
Radioactive elements will emit radiation until
they become a stable isotope.
Emitted radiation
This emitted radiation can be one of three
types:
 Alpha ( 42 α or 42 He )– heavy particle
radiation (easily blocked because its so
big).
0 β or 0 e )– particle radiation smaller
 Beta ( -1
-1
than alpha
 Gamma ( 0 γ )– high energy radiation
0

Emitted radiation


Alpha and Beta cause radioactive elements to
change to a new element.
Gamma causes no change in the radioactive
element.


Every Element has Isotopes – the amount of
each isotope is fixed
Ex. Uranium
Mass
238
235
234


Abundance
99.28%
0.71%
0.0054%
Which isotope of Uranium is used to make an
atomic bomb?
Complete the Assignment in your notebook:
Pg. 426-427 #2, 4, 17, 18, 21 and 24
Radiation Exposure
Naturally occurring radioisotopes provide a
constant small dose of radiation
 Radioactive isotopes constantly decay,
releasing alpha, beta and/or gamma
radiation.
 This constant, inescapable radiation is
called background radiation.


Natural background radiation:
- Outer space

All forms of electromagnetic radiation
- Ground water, rocks, soil

contain Uranium and Thorium
- Atmosphere

contains radon
- Food and Environment

like C-14 and potassium




Manmade background radiation:
Fallout (nuclear weapons testing)
Airplane flights
Released from




burning fossil fuels
nuclear power plants
mining
making



cement
concrete
sheet rock

Two units are used to measure radiation:
Rad measures the absorbed dose of
radiation
 Rem measures the ionizing effect of the
radiation

Average U.S. individual receives 0.360
rem per year.
 About 0.300 rem of this is from natural
sources
 U.S. limit for background radiation in a
given area is 0.500 rem.
 U.S. safe exposure in the work
environment is 5.000 rem.




How much is safe?
Ionizing radiation breaks bonds in molecules
within the body. At low exposure levels,
your body can fix the minimal damage.
Higher exposure levels that your body
cannot fix will lead to damaged DNA, causing
mutations (tumors and birth defects)
Copy the dosage chart on page 433 into your
notebook
Alpha
Radioactive isotopes decay until a stable
nucleus can be formed. What happens
when radioactive isotopes decay?
 Many elements release alpha radiation:

226
Ra
88
(radium)

4
2
He +
(alpha particle)
222
86
Rn
(Radon)
As these radioactive isotopes decay, an
alpha particle is released and a new
element is formed.
Beta
Many elements release beta radiation:
222
86
Rn
(radon)
 As
0
-1
e +
(beta particle)
222
87
Fr
(Francium)
these radioactive isotopes decay, a
beta particle is released and a new
element is formed.
Gamma

In addition to releasing a radiation particle
(alpha or beta), most radioactive decay is
accompanied by the release of gamma
radiation too. Remember, gamma
radiation is just energy; it is not a particle,
so it does not cause the element to
change its identity.
How do you determine the new
element made after radioactive decay?
1.
2.
3.
4.
5.
Identify the starting element and write the
symbol.
Identify the type of radiation released.
Subtract the two upper left numbers to find the
mass of the new element formed.
Subtract the two lower left numbers to find the
atomic number of the new element formed.
Look up the new atomic number on the
periodic table to find the new element made.
Radon




Produced as Uranium in the soil decays.
Uranium decays to produce radon gas:
When this gas is inhaled, it further decays in
your lungs into Polonium, Bismuth and Lead
(these heavy metals cannot be exhaled).
The alpha radiation is being released into your
body, causing cell damage.
Complete the Assignment in your notebook:
Pg. 446-447 # 1, 2, 4, 5, 8, 13, 23 and 24
Half-Life



Radioactive isotopes change
what they are as they decay and
release radiation.
Scientists call the amount of
time it takes for half of a
radioactive sample to decay a
half life.
14C has a half life of 5,730
6
years.

This means that if we started
with 100 grams of 146 C, only 50
grams of 146C would remain after
5,730 years have passed. The
other 50 grams will have turned
into 14
N as a beta particle is
7
released.
How long does it take for a
radioactive sample to decay?


Although it is not possible to predict
when any individual isotope will
decay, this question can be
answered for an entire radioactive
sample by the half-life of each
radioisotope.
The half-life of radioisotopes varies
greatly, but is constant for a
particular radioisotope. So constant
and reliable, it could be used to keep
time.
How long does it take for a
radioactive sample to decay?


Why would anyone want to know
this?
It’ very useful to know how long a
radioisotope used in medicine will
remain radioactive within the body,
to plan how long hazardous nuclear
wastes must be stored and to
estimate the age of ancient
organisms, cavitations or rocks
(fossils).
Radioisotopes and Medicine
1. Diagnostic: help to understand what is
happening inside the body
 Tracer Studies


Study a specific part of the body
Radioactive isotopes behave the same way
as non-radioactive ones
Can be “seen” moving through the body
 Can “see” where they accumulate
 Show how body processes that chemical
(copy top chart on p 455)

Used as Tracers
Radioisotopes Half-Life
Use
Technetium-99 6.01 h
Measure Cardiac output; locate
strokes, brain and bone tumors.
Gallium-67
78.3 h
Diagnosis of Hodgkin’s disease
Iron-59
44.5 d
Determine the rate of red blood cell
formation (these contain iron); anemia
assessment
Chromium-51
27.7 d
Determine blood volume and lifespan
of red blood cells
Hydrogen-3
12.3 y
Determine volume of body’s water;
assess vitamin D usage in body
Thallium-201
72.9 h
Cardiac arrest
Iodine-123
13.3 h
Thyroid function diagnosis
2. Therapeutic: Treats the disease
Used for Irradiation Therapy
Radioisotopes Half-Life
Use
30.1 y
Treat shallow tumors (external source)
Phosphorus-32 14.3 d
Treat leukemia a bone cancer affecting
white blood cells (internal source)
Iodine-131
8.0 d
Treat thyroid cancer (external source)
Cobalt-60
5.3 y
Treat shallow tumors (external source)
Yttrium-90
64.1 h
Treat pituitary gland cancer internally
with ceramic beads
Cesium-137

Suitable or Unsuitable
Must have a short half life
 Cannot emit alpha radiation
 Cannot be poisonous to the patient


Diagnostic Scans
1. X-ray:
 Wave
that’s part of EMS
 Not an atom/element
 High energy
2. MRI:
 uses
hydrogen protons and radio waves
 *NOT RADIOACTIVE!*

Scans (cont.)
3. CAT scan:
 X-ray
that produces cross section images of your
body that rather than the overlapping images
 the X-ray unit rotates around your body then a
powerful computer creates cross-sectional images,
like slices, of the inside of your body.
4. PET scan:
 uses
positions (positively charged antimatter)
attached to sugars
 Collect/gather where cells grow quickly
Cancer and Radiation

Cancer cells



Contain mutated DNA
Multiply at abnormally fast rates (tumor formation)
Radiation in cancer treatment


Ionizing radiation kills all kinds of cells
Use to target cancer cells
Answer the following questions on pg. 462-463
# 8-11, #13
Nuclear Forces
Nuclear fission: The splitting of the atom
into smaller atoms, often resulting in the
release of tremendous amounts of energy
 How much??? The fission of Uranium-235
produces 26 million times more energy
than the combustion of methane.

How does nuclear fission work???
 1n
0

93Kr + 140Ba + 3 1n + ENERGY
+ 235
U
—>
92
36
0
56
Bombarding a uranium atom with one neutron produces
two smaller atoms and two more neutrons, free to collide
with other uranium atoms. This causes a chain
reaction to occur.
Animation
Animation 2


Since not all of the neutrons produced will hit
and split a uranium nucleus, a minimum amount
of uranium is necessary. The more uranium
present, the more likely the produced neutrons
will hit and split another uranium nucleus.
This minimum amount of uranium is called its
critical mass. It is the minimum amount of
fissionable material required to sustain a chain
reaction.
Uranium
Mined from the ground as Uranium Oxide
U3O8
 Two isotopes

1. Uranium-235
- natural abundance = 0.720%
- used for fission in nuclear reactions and
weapons
2. Uranium-238
- most abundant = 99.275%
Enrichment
Must have between 1 to 3% U-235 for
fission
 2 ways to enrich U-235

1. Change U3O8 into UF6 gas
- needs to be done about 1200 times
- get 4% u-235
2. Use lasers
- excite electrons of lighter isotope (U-235)
- collected using magnetic fields
- works in 1 try
Nuclear Weapons

Fission Bomb (a.k.a. Atom Bomb)
1. 2 non-critical masses
portions of U-235 are propelled into each other –
make 1 critical mass
 1 neutron then starts fission, then…BOOM!
2
2. 1 critical mass
 Usually
Plutonium
 Compressed to get explosion
Nuclear Weapons

Fusion Bomb (a.k.a. H-Bomb)

Uses Lithium Hydride
 High
temperatures create fusion
 Fusion: 2 different isotopes fuse together
 Releases more energy (100x)
Nuclear Power


There are many benefits in using nuclear
technology to create electricity, but this must be
carefully regulated. If the reactor reaches
temperatures that are too high, the danger of a
meltdown occurs.
A nuclear meltdown can occur when
temperatures inside the reactor reach levels that
are too high. The materials used to construct
the reactor actually melt. If this happens, the
chain reaction is no longer contained and
dangerous radioactive material can be expelled
into the environment.
Animation
Animation 2
Cooling System
How does it work?
When the steam from
the generator is
cooled by water from
When
the steam
from
nearby
water sources
the generator is
cooled by water from
nearby water sources
Cooling Tower
Nuclear Power Plants in US
Nuclear Power has reached
dangerous conditions twice.
Three Mile Island
Chernobyl
1979, Pennsylvania
1986, Russia
the reactor reached dangerous
temperatures, but no meltdown
occurred
the reactor reached temperatures
high enough to cause the core to
melt
caused by both equipment failure
and human error
caused by both poor plant design
and improper operation
while some radioactive material
was expelled into the atmosphere,
no damage sustained by people or
environment
radiation spewed into the
atmosphere and spread over the
entire Northern Hemisphere
caused government to create
stricter regulations over nuclear
power plants
an estimated 75 million people
exposed

The Chernobyl
incident
happened April
26, 1986 in
Ukraine.

The Chernobyl
accident was a
result of a flawed
reactor design that
was operated with
inadequately
trained personnel
and without proper
regard for safety.

When the operator
went to shut down the
reactor from it’s
unstable condition
arising from previous
errors, a peculiarity of
design caused a
dramatic power surge.

3 mile island is
located in Harrisburg
PA

The 3 mile island is a
nuclear generating
station
What Happened?

Occurred on 4:00 a.m. March 28, 1979

Problem in secondary, non-nuclear section of the plant

The main water pump failed and prevented steam
generators from removing heat that the radioactive
material was producing

The pressure in the primary system (nuclear part of
plant) increased
What Happened?



The relief valve on top of
the pressurizer did not
close when the pressure
decreased
Workers reduced the flow
of coolant which made
the fuel overheat
Half of the long metal
tubes which held the
nuclear fuel pellets
ruptured and the pellets
started to melt
Future Technology…

Nuclear Fusion - the joining of two smaller nuclei
to create a large nucleus and tremendous energy
release.



Produces more energy per atom than fission
Requires tremendous heat and pressure!
Technology does not yet exist that allows more energy
to be produced than must be put in.
Answer the following questions on pg. 481-482
#1,2,8,9,16,18,19,20