Nuclear Force

Radioactivity

• The breakdown or decay of unstable nuclei in an attempt to form more stable nuclei.

• Isotopes are radioactive when, for whatever reason, the attraction b/w p+ & no is insufficient to hold the nucleus together in its existing state.

• Isotopes that are radioactive are called radioisotopes. Isotopes that are not radioactive are called stable isotopes.

3 types of radioactive decay

• : 2p+s & 2nos – a He nucleus• : e- lost from a no

• : gamma rays – very high energy light

3 types of radioactivity

1. : 2p+s & 2nos – a He nucleus

2. : e- lost from a no

3. : gamma rays – very high energy light

3 contributing factors to radioactivity

1. Nuclear size lim Fn

2. Ratio of no/p+

3. Instability of nuclear E levels

Nuclear E levels

• What evidence is there for nuclear E levels?• Hint: E conservation• Do you know what the evidence for atomic E

levels is?

238U decay series

• What does the word “series” mean?• Ultimate product of U-238 series is Pb-206.• Pb-206 is the only stable product in the U-238

decay series.• There are many intermediate products in the

U-238 decay series.

Half-life

• The time it takes for half of a radioactive sample to decay.

• Radioactive decay is an exponential function.

Exponential decay formula

• an = ao ekt

• an = final # of moles or atoms• ao = initial # moles or atoms• e = natural log• ekt = .5, since we are dealing with “half”-life• k = a constant that varies w/ the half-life of the

radioisotope.• t = half-life of the radioisotope in question or • t = the time of decay

Writing nuclear equations

• ex. From U-238 decay series• Note notation of a no & e- ( particle)

3 types of nuclear reactions

1. Radioactivity2. Nuclear fission (p.811 text)

3. Nuclear fusion (paper in text p. 811)

Types of nuclear reactors

1. Light-water : U-2352. Breeder : U-238 (paper in Concepts)

Radioactive dating

• U-238: used for dating rocks How it is done. • C-14: used for dating fossils How it is done.