Nuclear Force

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Nuclear Force




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Nuclear Force




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Fundamental forces in Nature

• Gravitational force Mass objects
• Electromagnetic Charged objects
• Nuclear Force Acts between nucleons

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• Nuclear force has both an attractive and
  repulsive nature.

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Nuclear Force

• At large seperation distances the nuclear force
  between nucleons has a similar behaviour as the
  electrical force

mutual repulsion


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Nuclear Force

• At large seperation distances the nuclear force
  between nucleons has a similar behaviour as the
  electrical force

No force

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Nuclear Force

• Over short distances the attractive part of the
  nuclear force dominates, thus stabilizing the
  nucleus

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Binding energy per nucleon

• Increase in atomic number -gt Increase repulsion
  between protons.
• No repulsion between neutrons and other particles
  (Only attraction at short range)
• Repulsion increases within the nucleus as more
  protons are added -gtmore neutron are requiered

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Binding energy / nucleon
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• Light nuclei with mass number lt that of 56Fe
  would increase their binding energy and become
  more stable by fusing with other light nuclei.
• Heavy nuclei such as 235U would rather split
  (fission) to increase their binding energy.

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Nuclear Stability and Radioactive Decay

• Most nuclei in nature are unstable.
• Nuclei stabilize themselves by emitting particles
  / photons (radioactivity).
• Forms of radiation emitted from nuclei include a,
  b, and g rays.

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Alpha radiation

• Nuclei are not frozen objects.
• Through collective motion of the nuclei helium
  clusters (alpha particle) could be knocked out of
  the nucleus

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• Alpha decay results in a reduction of 4 in the
  atomic mass of the original element and a
  decrease of 2 in its atomic number.

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Beta decay

• There are two types of b decay
• b Proton converts into a neutron and in the
  process a high energy positron is created
• b- Neutron converts into a proton and a high
  energy electron is created

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• Beta decay does not change the atomic mass number
  of a nucleus.
• It does however change the atomic number of the
  element!!!

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Gamma Radiation

• Similar to the electrons inside an atom, the
  nucleons in a nucleus have kinetic energy which
  is quantized.
• When a nucleon undergo an energy transition a
  high energy photon (g-rays) is emitted.

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Notes

• Test 3 tomorrow _at_ 10 am in the Physics 1st year
  lab.
• Revision on Modern Physics on Tuesday 31 May _at_
  10am in Lecture Room D.
• PHY124F Exam 20 June _at_ 9am Venue SC1 (3 hour
  paper)

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Activities and Half-Life
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Activities and Half-Life
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Activities and Half-Life
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Activities and Half-Life
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Activities and Half-Life
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Activities and Half-Life
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Activities and Half-Life
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Activities and Half-Life
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Activity of a Nuclear Species

• The decay rate of decay (Activity) a sample of
  radioactive nuclei is directly proportional to
  the number of species at a particular time.

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• Hence

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• Hence

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• Hence

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• Hence

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• Hence

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Half-Life of a radioactive species

• The half-life of a radioactive species is the
  time it takes the original number of radioactive
  species to be halved.

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• We wish to find the time it takes N0 species of
  nuclei to reduce to N0 / 2

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Exercise

• The radioactive isotope 57Co has a half-life of
  272 days.
• Find its decay constant
• IF your source has an activity of 2.00 mCi,
  how many radioactive nuclei does it contain?
• What is the activity of your source after one
  year?