1. Nuclear Changes Objectives: Students will:
Use the symbols for alpha, beta, and gamma radiation, and compare the penetrating ability.
Write and analyze nuclear equations to balance and solve for unknowns.

2. Radioactivity

3. Radioactive Atoms
There are about 2000 different isotopes that are known.
Of this number, only 279 are stable-they do not change over time.
All other isotopes are called radioisotopes, because the nucleus will decay (change) over time and release radiation-energy or particles.
This change is spontaneous-occurs without action/intervention.
Humans have learned to capitalize/manipulate nuclear changes and have developed many tools incorporating radioisotopes.

4. Discovery Antoine Henri Becquerel- Accidental observation
fogging on photographic film plates in the presence of Uranium.
Paul & Marie Curie were able to show that it was the radioactive rays emitted by the Uranium atoms that caused the fogging.
We still use film badges to detect radiation.

5. Nuclear Equations describe Nuclear Change
Mass # A
Nuclear equations use isotopic symbols. X
On either side of the arrow, mass numbers and atomic numbers must equal. (Conservation of mass)
This will help you determine any missing particles. Z
Atomic #
Sum of Mass Numbers (A) = 14
= 14
Sum of Atomic Numbers (z) = 6
= 6

6. Types of Radioactive Decay: Alpha
Alpha (α) Particles, which is a Helium nucleus, are commonly emitted by heavy nuclides, and can be written in two ways:
Alpha particles have a charge of +2.
Ex:
Write the equation for when Thorium-230 undergoes alpha decay.
Parent Nuclide  Radiation + Daughter Nuclide

7. Types of Decay: Beta
A beta (β) particle is a negatively charged electron that formed when a neutron splits into a proton and an electron, and the electron is ejected from the nucleus.
It can be written two ways:
Remember, the mass of an electron is so
small that it gets assigned a mass number of 0, so the net effect of β-particle production is to change a neutron to a proton:
Write the equation for Actinium-227 decay, a beta particle producer.

8. Types of Radiation: Gamma
A gamma (γ) ray is a high energy photon (packet) of electromagnetic radiation with no mass and no charge.
It can be written two ways:
Visible light is also composed of photons of electromagnetic radiation, but those photons contain significantly less energy than gamma photons.

9. Penetrating ability of Radiation

10. Other useful nuclear particles/info
Proton:
Neutron:
If you see a number in front of a particle, it is a coefficient, which means multiple of that particle.
Distribute the coefficient to A and Z to solve.

11. Other useful information
Emission vs. Capture
Emission(Emit/Emitted): Indicates the particle is being released, and should be on the _______________ side of the arrow in the equation.
Capture/Bombardment: Indicates the particle is being absorbed, and should be on the _______________ side of the arrow in the equation.
Right
Left

12. Why Radioactive?
Since over 85% of isotopes are radioactive, it is helpful to identify some similarities.
All atoms over atomic # 83 are radioactive
There are simply too many protons/neutrons to be held together by the nuclear force, which holds particles together at extremely short distances.
Will undergo decay, sometimes many cycles,
until they get to a smaller atom.
Ex: Uranium-238
eventually decays to Pb-206

13. Why Radioactive?
The radioactivity of smaller atoms can be predicted based on the neutron to proton ratio in the nucleus.
Atomic Numbers 1-20, a 1:1 ratio is stable.
Atomic Numbers 21-83, the band of stability approaches 1.5:1
This is because the function of the neutron is to buffer the repulsion of the positive protons.
More protons = more neutrons necessary

15. Nuclear Transformutations & Applications

16. History of Nuclear Transmutations:
The first nuclear transmutation, or change of one element into another, was observed in 1911 when Lord Rutherford bombarded Nitrogen-14 with an alpha particle to produce Oxygen-17 and a proton.
Write the equation for this transmutation.
The bombarding particle here is an alpha particle which is positively charged.
So that the alpha particle isn’t repelled by the nucleus, the bombarding particle must move at high speeds.

17. Particle Accelerators allow the particles to achieve high speeds
Through neutron, proton, and alpha particle bombardment, scientist have been able to extend the periodic table.
Prior to 1940, the heaviest element known was Uranium.
In 1940, Neptunium-239 was produced by neutron bombardment of Uranium-238.
Since then, elements #93 & beyond have been synthesized. These are called the transuranium elements.

18. Alpha, Beta, and Gamma are ionizing radiation (so are other Electromagnetic waves)
Ionizing radiation carries enough energy to knock electrons off of atoms when they travel through matter, creating positive ions and lose electrons.
The familiar instrument for detecting radiation is a Geiger Counter.
Contains Argon Gas
Connected to a speaker which clicks every time a high speed particle knocks an electron off an Argon atom.
A scintillation counter uses a substance that gives off light when struck by a high-energy particle, and the detector senses the flashes of light.

19. Geiger Counter
Scintillation Counter

20. Scintillation Counters are used to detect decay events…
An important characteristic of a radioisotope is its half-life, or the time required for half the original sample to decay.
For example, if a certain radioactive sample contains nuclei at a given time, and 500 nuclei 7.5 days later, then the half-life of that isotope is 7.5 days.
There is a broad spectrum of half-life times from milliseconds to millions or billions of years.
The length of the half-life, and the type of radiation released determines the usage.

21. Sample Problem #1
Silicon-31 has a half-life of approximately 2.5 hours. If we begin with a sample containing mg of Si-31, what is the amount remaining after 10 hours?

22. Sample Problem #2
Carbon-14 emits beta radiation and decays with a half-life of years. Assume you begin with 2.00 x g of C-14.
Write the equation for the beta decay of Carbon-14
How long is three half lives?
How many grams are left at the end of years?

23. Sample Problem #3
A mg sample of Hydrogen-3 was collected. After years, mg remains.
What is the half life of Hydrogen-3?