Radioactivity and Nuclear EnergyChapter 19

http://www.youtube.com/watch?v=PEHcHcneFFc&feature=related

Chemical vs. Nuclear

Chemical Reactions

• Break and form bonds

• Created with valence electrons

• Type of elements do not change during the reaction

• Small energy changes

Nuclear Reactions• Involve nuclei

changes• Can involve e-, p+,

and no

• Convert 1 element to another element

• LARGE energy changes

Facts about the Nucleus

•The nucleus is composed of nucleons:

–Neutrons and protons

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Isotopes and Nuclides

•Isotopes: atoms that have identical atomic numbers but different mass numbers

CCC 146

136

126

How are they similar? How are they different?

Radioactivity

• Radioactivity – the result of the spontaneous decomposition of an unstable nucleus. – Includes the production of high energy

particles that make the nucleus more stable.

e N C 01-

147

146

Radioactive Isotopes

•85% of the 2000 known isotopes are radioactive.

–279 of those 2000 are not radioactive

•Percent abundance of isotopes is much smaller.

–Not radioactive: C-12 – 99% of all C–Radioactive: C-14 < 0.1%

85%

15%

How do we know if a nucleus is stable?

– Protons and neutrons are nucleons

– Held together by strong nuclear force

Nuclear Stability•How can you tell if an element is stable?

–Look at proton to neutron ratio (p:n)

–Atomic number less than 20:• Want p:n = 1:1

–Above atomic number 20 have more neutrons than protons, which increases the ratio

ON, C, 168

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126

Where are the stable nuclei found?

•Band of Stability shows where the stable nuclei can be found

– Depends on the proton to neutron ratio

– Location determines the type of decay for the isotope

How can I become a stable nucleus?1. Alpha Radiation

–Helium nuclei are emitted from a radioactive source

•Called alpha particles–Contain two protons and two neutrons

»Overall positive charge

U

Th

He

He42

How can I become a stable nucleus?

2. Beta Radiation–Fast-moving electrons created by the break-down of a neutron in an atom

•Called beta particles

e01-

C

N

e-

How can I become a stable nucleus?

3. Gamma Radiation–High-energy electromagnetic radiation given off by a radioisotope

•Often given-off along with alpha or beta radiation

–Have no mass or charge

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How can I become a stable nucleus?4. positron emission

–Positron :•has same mass as an electron but the opposite charge

•Created when a proton breaks apart to create a neutron and positron

e01

B

Be

e+

How can I become a stable nucleus?5. Electron capture

•Capture an inner electron and turn it into a proton

•“Hand of God”

Practice time

• Practice WS with isotopic notation and what ratio you have for Neutron to proton and types of decay – due tomorrow!!!