Symbolically... Atomic mass number (protons and neutrons) Atomic number (protons) Chemical symbol A = N + Z
“OK, let’s just drop Z”
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 Note: up to approximately 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, 07B EE -27 kg MeV MeV 07B7 a u b.3.46 EE -12 J c.8.66 EE 31 d.8.69 EE 9 kg
Henri (you can call him “Henry”) Bequerel
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