# AP Physics V.B Nuclear Physics. 31.1 Nuclear Structure.

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AP Physics V.B Nuclear Physics

31.1 Nuclear Structure

Rutherford’s Scattering Experiment

Mass and charge of... Protons Neutrons

Symbolically... Atomic mass number (protons and neutrons) Atomic number (protons) Chemical symbol A = N + Z

“OK, let’s just drop Z”

Isotopes

Atomic mass units

Conversion of atomic mass units to energy

31.2 The Strong Nuclear Force and Binding Energy

Take carbon-12 for instance

The total mass of a stable nucleus is always less than the sum of the masses of its protons and neutrons. Or, philosophically, “The sum of the parts is greater than the whole.”

So where is the extra mass?

Note: binding energy is not something a nucleus has. It is something is lacks. Binding energy is much larger than the energy required to eject an electron.

Ex. Calculate the total binding energy for iron-56.

Ex. Calculate the total binding energy for helium.

Keeping it all together

The strong nuclear force Approximately one-million times e-m forces Attractive between all nucleons Currently, there is no mathematical description Short range – falls to zero beyond the diameter of the nucleus

Fig. 31.2 Note: up to approximately 30-40 protons N = Z. Beyond this stable nuclei contain more protons than neutrons. Why?

For nuclei with more than 83 protons...

p. 972: 10-13, 14, 07B7 10.9.279 EE -27 kg 12.225.1 MeV 14.1622 MeV 07B7 a.0.0232u b.3.46 EE -12 J c.8.66 EE 31 d.8.69 EE 9 kg

Henri (you can call him “Henry”) Bequerel

The Curies

Three types of radioactivity

1. Alpha decay – emits a He nucleus

General form of alpha decay

Converted energy of alpha decay Kinetic energy of the alpha particle Recoiling energy of the parent nucleus

Ex. Find the energy released when uranium-232 decays to thorium 228.

2. Beta Decay – the emission of an electron (not an orbital electron)

“Whoa, dudes, how does that happen?”

More complications – add the neutrino (and its evil cousin the anti-neutrino)

Neon to fluorine and the positron

General form for beta decay

3. Gamma Decay – emission of a gamma ray because of a change in energy level in the nucleus

General form for gamma decay *Indicates excited state

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