1. What is so dangerous about nuclear energy?
Journal 14
 What is so dangerous about nuclear energy?

2. Nuclear Chemistry
Nuclear Chemistry
Bravo – 15,000 kilotons

3. Chapter 21
Atomic nuclei are made of protons and neutrons. Collectively known as nucleons.
An atom of an element (or an isotope) is called a nuclide and can be represented by the nuclear symbol or the hyphenated symbol.
Example: Radium

4. Mass Defect
Because an atom is made of protons, neutrons and electrons, you would expect the mass to be the sum of the masses of those particles.
BUT the actual mass of an atom of an element is less!!!!!! Why?
This difference in mass is called the MASS DEFECT.

5. What causes loss in mass?
Einstein said
E = mc2
Mass can be converted to energy
Some of the mass of the atom has been used as energy to hold the nucleus together.
This is called nuclear binding energy.

6. Nuclear Stability
Nuclear binding energy is a measure of nuclear stability.
We measure it in binding energy per nucleon.
Binding energy per nucleon = binding energy
# of nucleons
Elements that have intermediate sized nuclei have the greatest binding energies and therefore are the most stable.

7. Nuclear Binding Energies

8. Elements that are larger or smaller have unstable nuclei.
In order to become stable they must either lose or gain mass by ejecting particles
This is known as radiation!

9. Nuclear Stability and Decay
Unstable isotopes will undergo decay to achieve a more stable ratio of neutrons to protons
The type of decay depends on the ratio of neutrons to protons
Too many neutrons, turn neutrons to protons
Too many protons, capture electrons and turn protons to neutrons, this emits a positron

10. Nuclear Stability Isotopes with low atomic numbers
fig 28.6
Isotopes with low atomic numbers
The stable ratio is 1 neutron to 1 proton
Isotopes with high atomic numbers
The stable ratio is 1.5 neutrons to 1 proton
This creates the band of stability

11. Nuclear Stability Isotopes in Region A Isotopes in Region B
Region C
Alpha decay
fig 28.6
Isotopes in Region A
Have too many n, use beta decay to turn neutrons  protons
Isotopes in Region B
Have too many p+, use positrons to turn p+  neutrons
Isotopes in Region C
Have too many p+ & n use alpha decay to reduce the numbers
Region A
beta decay
Region B
positron

12. Radioactive decay
All nuclei with atomic numbers greater than 83 are radioactive
These nuclei have too many neutrons and too many protons to be stable
So most undergo decay
losing energy by emitting radiation

13. CA Standards
Students know the three most common forms of radioactive decay (alpha, beta, and gamma) and know how the nucleus changes in each type of decay.
Students know alpha, beta, and gamma radiation produce different amounts and kinds of damage in matter and have different penetrations.
Students know some naturally occurring isotopes of elements are radioactive, as are isotopes formed in nuclear reactions.

14. Types of Radiation Radiation Alpha particles Beta Positron Gamma
When we are looking at any type of radiation or radioactive decay we must remember that matter is conserved!

15. Nuclear Symbols Element Mass number symbol (p+ + no) Atomic number
(number of p+)

16. Alpha Particle Emission Beta Particle Emission
Gamma Ray Emission
Symbol or
Mass
Heavy
Light
No Mass
How it changes the nucleus
Decreases the mass number by 4
Decreases the atomic number by 2
Contains 2 protons and 2 neutrons
Converts a neutron into a proton
Send off a fast moving e- (β)
Increases atomic number by 1
-High energy radiation –just energy! (gamma rays)
-No change to the nucleus
-emitted with alpha & beta radiation
Penetration
Low
Medium
High
Protection provided by…
Paper, clothing
Cardboard, wood
Lead
Danger
Low, slow moving
Medium, fast

17. Types of Radioactive Decay
alpha production (a, He): helium nucleus
beta production (b, e):
gamma ray production (g):

18. Alpha Radiation
Alpha decay is limited to VERY large, nuclei such as those in heavy metals.
(a, He): helium nucleus

19. Alpha particles in a reaction
Alpha radiation is emitted from U-238
23892U →23490Th + 42He
Is matter conserved?
Yes!
Now you try!
Alpha radiation is emitted from Rn-222
22286Rn →
Yes
21884Po+ 42He

20. Gamma particles in a reaction
23090Th→22688Ra + 42He + γ
When the alpha particle is released a huge amount of energy is also released (the gamma particle)!

21. Beta Radiation
Beta decay converts a neutron into a proton and an e- (β) is released

22. Beta particles in a reaction
C-14 is a beta emitter, show the decay process
146C →147N + 0-1β
What Happened?
np+; so atomic mass is still 14
a new p+= atomic number of 7 (now N)
A β-particle flies out of the atom
0-1 β is the same as 0-1 e

23. Now you try What Happened? np+; so atomic mass is still 40
4019K →
4020Ca β
What Happened?
np+; so atomic mass is still 40
a new p+= atomic number of 20 (Ca)
A β-particle flies out of the atom
0-1 β is the same as 0-1 e

24. Positron Particle Same mass as an electron
Neutrons can be formed by protons that emit a positron
They have a negligible mass
Consequently they are more penetrating than alpha particles
They have a charge of +1

25. Positrons in a reaction
Potassium-38 will emit a positron, show the decay.
3819K → 3818Ar + 0+1β
What Happened?
p+  n; atomic mass is still 38
p+  n; atomic number decrease by 1; 18 (Ar)
A positron flies out of the nucleus
Now you try
137N →
136C + 0+1β

26. CA Standards
Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome the electromagnetic repulsion between the protons.
Students know the energy release per gram of material is much larger in nuclear fusion or fission reactions than in chemical reactions. The change in mass (calculated by E = mc2) is small but significant in nuclear reactions.

27. Fission- big to small
Fission - Splitting a heavy nucleus into two nuclei with smaller mass numbers.

28. Fusion Reaction- small to big Example:Deuterium – Tritium
Fusion - Combining two light nuclei to form a heavier, more stable nucleus.

29. Energy and Mass
Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein’s equation: DE = Dmc2 Dm = mass defect DE = change in energy c = speed of light
Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.

31. A Fission Reactor

32. Practice band of stability p 703 # 9 & 10

33. Discovery of Radiation
Wilhelm Conrad Roentgen
had discovered X rays
Pierre & Marie Curie
Discovery of several radioactive elements
Coined “Radioactive”
Nobel Laureates
Brainpop- marie curie