Nuclear physics

• Explain why, when a particle and antiparticle annihilate each other, each gamma photon produced must carry at least the rest mass energy of one of the initial particles.

  • The energy carried away by the gamma photons must equal the total energy of the particles to begin with (kinetic energy + rest mass energy).
  • The energy is split evenly between the two gamma photons.
  • So each gamma photon must carry away at least the rest mass energy of one particle.
• explain the orgin of the B- particle the is emitted from the nucleus during beta decay

  neutrons decay into a proton and an electron
• why is there deflection in the gold foil expriment greater than 90 degrees

  the nucleus is charged and the majority of the mass of an atom is in the nucleus
• state what is meant by the decay constant of a radioactive isotope

  it is the probality of decay per unit time
• what is meant by radioactive decay?

  it is the random and spontaneous decay of an unstable nuclei relatively stable nuclei by emission of alpha,beta and gamma.
• what does mass defect mean?

  difference between the mass of the nucleusand the constituents when nucleons are separted to infinity
• state what is meant by binding energy?

  Amount of energy required to separate the nucleons in nucleus to take them to infinity
• random


  cannot predict when a nucleus will decay
• spontaneous


  decay is not affected by external enviroment
• decay constant


  probability of a nucleus to decay per unit time
• why count rate less when placed near a detector?

  • sample emits radiation in all directions
  • some radiation absorbed by air
  • self absorption within the source
  • inefficiency of detector
• what is fission

  large single unstable nuclei divided into two smaller identical nuclei causing neutrons to be released
• energetically possible fission reaction are if products binding energy is more than reactants binding energy