NUCLEAR PHYSICS AND RADIOACTVITY
I.
Nuclear structure
A. Nucleons
1. neutron: charge = 0 C; 1.008665 amu
2. proton: charge = +1.60 x 10-19 C; 1.007276 amu
B. Electrons: charge = -1.60 x 10-19 C; 0.000548 amu
C. Atomic number Z = number of protons; N = number of neutrons
D. Atomic mass number A = number of protons + number of neutrons
1. A = Z + N
2. u = amu =1.6605 x 10-27 kg
3. A also called nucleon number; examples: AXz, 1H1, 1n0, 0e-1
E. Isotope – nuclei that contains same number of protons but different number of neutrons.
1. Examples: 1H1, 2H1, 3H1
II.
Strong Nuclear Force – one of the 4 fundamental forces
A. Independent of electric charge
B. Range is very short
C. Hold the nucleus in atoms together
III.
Mass Defect of the Nucleus and Nuclear Binding Energy
A. Binding energy – the energy required to break a nucleus apart.
1. Binding energy = (Mass defect) c2
E = m c2
2. Energy = J = Nm
3. 1 eV = 1.6 x 10-19 J
1u = 931.5 MeV
IV.
Radioactivity - , , and ; particles and electromagnetic radiation
A. Disintegration must obey the following conservation laws:
1. Mass/energy
2. Electric charge
3. Linear and angular momentum
4. Nucleon number
B. Alpha decay 4He2 particle with a +2e charge A = 4 which is stable
1. Example: 238U92  234Th90 + 4He2
2. General equation: APZ  A-4DZ-2 + 4He2
3. Calculations example: 238U92  234Th90 + 4He2
238.0508 u  234.0436 u + 4.0026 u = 238.0462 u
m in amu = 238.0508 u – 2380462 u = 0.0047 u if 1 u = 931.5 MeV then
0.0046 amu = 4.3 MeV
m in kg if 1 u = 1.6605 x 10-27 kg then 0.0046 u = 7.6383 x 10-30 kg
Using E = mc2 (7.6383 x 10-30 kg)( 3.0 x 108 m/s)2 = 6.8648 x 10-13
C.  decay; particles - or 0e-1
1. General formula: APZ  ADZ=1 + 0e-1
2. Example: : 234Th90  234Pa91 + 0e-1
234.04359 u  234.04330 u = 0.0026 u = 2.4 MeV
3. Neutron decay: 1n0  1p1 + 0e-1
4. + decay yields a positron or a positive electron (antimatter)
D.  decay results from a nucleus that is in an excited state which goes to a lower energy level and a
gamma ray or photon is emitted.
1. APZ * ADZ + 
V.
Neutrino – results from a beta decay; symbol  and it is associated with the weak nuclear force
VI.
Radioactive decay and Activity
A. N = number of parent nuclei
B. Half life = T1/2 at t=0 then N = N original (No) if t= T1/2 then N = ½ No; at t= 2T1/2 then N =
1/4No
C. The activity of a radioactive sample is the number of disintegrations that occur per second. N/t;
Bq is a Becquerel = 1 disintegration/second
VII.
Radioactive Dating -T1/2 is the time for one half life
A. Example is the half life of C – 14. T1/2 is approximately 5700 years.
VIII.
Radioactive Decay series
A. 238U92  234Th90 + 4He2
  234Pa91 + 0e-1

226
Ra88  222Rn86  218Po84  214Pb82
Detectors – Geiger-Mueller tube, can detect: , , and ; uses ionization which produces a current
Photographic emulsion – photographs; Photomultiplier tubes.
IX.
IONIZING RADIATION, NUCLEAR ENERGY AND ELEMENTARY PARTICLES
I.
Biological effects of ionizing radiation
A. Ionizing radiation – photons with enough energy can knock an electron out of an atom or
molecule.
1. Usually an x-ray or gamma ray, but alpha and beta particles can when they are in close
proximity.
2. Alters the structure of the molecules in a cell.
3. Exposure measured in Roentgens (R) = charge of the ions (q)/mass of the air
a. R = q/m = C/kg 1 R = 2.58 x 10-4 C/kg
4. Absorbed dose measured in a Gray 1 G = 1J/kg
5. Rad = radiation absorbed dose 1 rad = 0.01 G
6. RBE – relative biological effectiveness is used to compare damage caused
by different types of radiation.
B. The effects of ionizing radiation on humans:
1. Short-term: radiation sickness, nausea, fever, diarrhea, loss of hair
2. Long term: hair loss, eye cataracts, cancers, genetic defects
II. Induced nuclear reactions – change elements 4He2 + 14N7  17O8 + 1H1
III. Nuclear fission: 1n0 + 235U92  236U92  141Ba56 + 92Kr36 + 31n0 ; chain reactions
IV.
Nuclear fusion: 1H1, + 3H1,  4He2 + 1n0
V.
Elementary particles
A. Neutrinos – no electric charge, very small mass, travels at or near the speed of light.
B. Positrons – (positive electron, antimatter) They have the same mass as a n electron, but with a
positive charge. When an electron and a positron come in contact, annihilation occurs and
electromagnetic radiation in the form of gamma rays results.
C. Muons and Pions – weak nuclear force.
D. Quarks – up, down, strange, and three more. They have fractional charges. Quarks cannot exist
independently. Baryons – protons and neutrons are made up of three quarks.
E. Standard model: Atoms are composed of a nucleus (which composed of protons and neurons
which are composed of quarks, which are composed of ?) surrounded by a cloud of electrons.