This document summarizes key concepts in nuclear chemistry including: 1) The discovery of radioactivity by scientists like Roentgen, Becquerel, and the Curies who observed emissions from uranium that could pass through matter and expose photographic plates. 2) Types of nuclear radiation including alpha, beta, gamma and their properties. 3) The concept of radioactive decay and half-life and how radioactive isotopes decay into more stable elements. 4) Nuclear reactions including fission which is used in nuclear power plants and weapons, and fusion which powers the sun.

1. Radioactivity
Chapter 25

2. • Nuclear chemistry
• study of the structure of atomic nuclei
• changes they undergo.
Nuclear Radiation

3. • Wilhelm Roentgen (1845–1923)
• 1895-invisible rays were emitted when
electrons bombarded the surface of
certain materials.
The Discovery of Radioactivity
• caused photographic plates to darken.
• named the invisible high-energy
emissions X rays.

4. • Henri Becquerel (1852–1908) was
studying phosphorescence
• minerals that emit light after being
exposed to sunlight
The Discovery of Radioactivity
•phosphorescent
uranium salts
produced
spontaneous
emissions that
darkened
photographic plates.

5. • Marie Curie (1867–1934)
and her husband Pierre
(1859–1906) took
Becquerel’s mineral
sample (called
pitchblende) and isolated
the components emitting
the rays.
The Discovery of Radioactivity
• darkening of the photographic plates was
due to rays emitted specifically from the
uranium atoms present in the mineral
sample.

6. The Discovery of Radioactivity
• Marie Curie named the process by
which materials give off such rays
radioactivity
• the rays and particles emitted by a
radioactive source are called
radiation.

7. • isotopes are atoms of the same
element that have different numbers of
neutrons.
Types of Radiation
• Isotopes of atoms with unstable nuclei
are called radioisotopes
• emit radiation to attain more stable
atomic configurations in a process
called radioactive decay
• lose energy by emitting one of several
types of radiation.

8. Why do some atoms decay?
• The nucleus contains tightly packed
protons and neutrons (nucleons)
• The strong nuclear force keeps the
nucleons packed together even though
protons want to push each other away
• Stable atoms have a neutron to proton
ratio of about 1:1

9. • As atomic number increases, more
neutrons are required to have enough of a
strong force to keep the protons pushed
together
• The neutron to proton ratio for stable
atoms increases to 1.5:1

10. Band of Stability
• When the number of
protons and neutrons are
plotted, the stable nuclei
are found within the “band
of stability”
• Radioactive isotopes are
outside the band of
stability
– They will undergo nuclear
reactions to become more
stable
– All elements higher than
atomic# 83 are radioactive

12. Basic Assessment Questions
Question 3
Topic
26
Calculate the neutron-to-proton ratio for .

13. Types of Nuclear Radiation
• Alpha
• Beta
• Gamma

14. Alpha Radiation
• Release of 2 protons and 2 neutrons
– Equivalent to a He nucleus
– Charge of 2+
– Mass = 4 amu
• Largest and slowest
– Least penetrating  can be stopped by paper
• Changes to a different element with a lower
atomic mass and lower atomic number
• Example: Polonium-212 (atomic# 84) is
converted to Lead-208 (atomic# 82)

16. Beta Radiation
• Decay of a neutron into a proton and
electron
– Electron is emitted, proton stays
– Forms a new element b/c of addition of proton
• Decay of the proton into a neutron and
positron (like a positive electron)
– The positron is emitted as a beta particle
• Faster than alpha particles  can be
stopped by aluminum foil

18. Gamma Radiation
• Not a particle
• Electromagnetic wave with short
wavelength and high frequency & energy
• No mass, no charge
• Very fast  speed of light
• Stronger than X-ray
• Stopped by several centimeters of lead

21. • Transmutation: changing one element into
another through radioactive decay
– Adding or removing a proton changes the
atomic number, resulting in a different element
• Half-Life: amount of time for half of a
sample of a radioactive element to decay
into something else
– Can range from a fraction of a second to
billions of years
– Amount remaining=initial amount(1/2)t/T
• t=total time
• T=half-life

23. Half-life
n
i
f m
m )
(2
1

mf: final mass
mi: initial mass
n: # of half-lives

24. Half-life
• Fluorine-21 has a half-life of 5.0 seconds. If you
start with 25 g of fluorine-21, how many grams
would remain after 60.0 s?

25. Nuclear Decay
• Alpha Emission
He
Th
U 4
2
234
90
238
92 

parent
nuclide
daughter
nuclide
alpha
particle
Numbers must balance!!

26. Nuclear Decay
• Beta Emission
e
Xe
I 0
-1
131
54
131
53 

electron
• Positron Emission
e
Ar
K 0
1
38
18
38
19 


positron

27. Nuclear Decay
• Electron Capture
Pd
e
Ag 106
46
0
-1
106
47 

electron
• Gamma Emission
– Usually follows other types of decay.

28. Types of Transmutation
• Induced transmutation
– Nucleus of an unstable isotope (radionuclide)
is struck with a high velocity charged particle
• Particle accelerator
• Need lots of energy and unstable nucleus
– Elements atomic 93 and higher (transuranium
elements)
• Natural transmutation
– Occurs naturally as a radioisotope decays to
become more stable

29. Basic Assessment Questions
Question 1
Topic
26
What element is formed when polonium-214
( ) radioisotope undergoes alpha decay?
Give the atomic number and mass number of
the element.

30. Basic Assessment Questions
Question 2
Topic
26
What element is formed when undergoes
beta decay? Give the atomic number and mass
number of the element.

31. Basic Assessment Questions
Question 4
Write a balanced nuclear equation for the
beta decay of the following radioisotope.
Topic
26

32. Nuclear Fission
• Fission = divide
• Neutron hits an unstable atom
• Nucleus splits into two fragments of about
the same mass
– Some single neutrons are released (energy)
– These neutrons can smash into other atoms
• Causes a chain reaction

33. Fission Reaction

35. Nuclear reactors
• Nuclear power plants use
the process of nuclear
fission to produce heat in
nuclear reactors.
• The heat is used to
generate steam, which is
then used to drive turbines
that produce electricity.

36. Atomic Bomb- uncontrolled fission reactions

37. • Little Boy: $2billion in research; made of
Uranium-235; equal to 20,000 tons of TNT;
140,000 people died; 2/3 of the city destroyed
• Fat Man: Plutonium-239; 70,000 people died;
40% of the city destroyed

38. Hydrogen Bomb
• 1000 times more powerful than atomic
bomb
• March 1, 1954; Bikini Atoll in Pacific
– Never in war
• Fission reaction triggers fusion of
Hydrogen isotopes

39. Nuclear Fusion
• Opposite of fission
• Two nuclei fuse together to form one
nucleus with a larger mass
– Not simple sum of masses
– Some mass lost as energy
• Requires high temperature:
Thermonuclear reaction
• Occurs in the sun and stars
– 4 H combine to form one He, 2e- and energy

40. Nuclear Fusion

41. Solar Flare

42. Radiation Detectors
• Cloud Chamber
– supersaturated water or ethanol
– radioactive particle flows through
and knocks e- off
– vapor condenses showing path
– alpha: short/thick trails; beta:
long/thin
• Bubble Chamber
– superheated liquid
– e- knocked off again
– bubbles are formed

43. Measuring Radiation
• Geiger Counter
– produces electric
current when near
radiation
– Results in clicks or a
digital reading

44. Using Nuclear Reactions in
Medicine
• Tracers: monitor body
processes
– Iodine-131
• emits beta particles
• used to detect tumors in
thyroid gland
– also used: Carbon-11
and Sodium -24

45. • Cancer Treatment
• damage cancer cells
• Gold -198 or Iridium -192 -- implanted in or
near tumor
• Cobalt-60
– outside body
– emits gamma rays

46. • Positron Emission
Tomography (PET)
– Fluorine-18 attached to
molecules that go to brain
– positrons are emitted and collide
with electrons forming 2 gamma
rays
– the gamma rays are detected
and indicate brain activity

47. • http://www.hpwt.de/Kern2e.htm
• http://www.colorado.edu/physics/2000/isot
opes/radioactive_decay3.html
• http://www.msd.k12.or.us/schools/mhs/proj
ects/Fission/frames.html
• http://www.cnn.com/SPECIALS/cold.war/e
xperience/the.bomb/history.science/