International University,
Vietnam National University, HCMC
Physics for Biology
Tran Nguyen Lan, Ph.D
Department of Physics, HCMIU-VNU
Email: lantrann@gmail.com
Room: A1.503
Week 13
Content
Part II
- Chapter 5 Mechanical and Sound waves
- Chapter 6 Electricity
- Chapter 7 Optics
- Chapter 8 Nuclear Physics
Chapter 8: NUCLEAR PHYSICS
8.1. Properties of Nuclei
8.2. Nuclear Binding and Nuclear Structure
8.3. Nuclear Reactions
8.4. Radioactivity
8. 1 Properties of Nuclei
• Every atom contains at its center an extremely
dense, positively charged nucleus, which is
much smaller than the overall size of the atom
but contains most of its total mass.
• Model : a nucleus is a sphere with a radius R
that depends on the total number of nucleons
(neutrons and protons):
Nucleon number A (mass number).
8.2.
8.3.
8.5. Radiobiology
• Is the study of the action of radiations on living
things.
• Principles of Radiation Biology: The biological
effects of ionizing radiations are the
manifestations of the energy absorption within a
living system.
Deposition of radiation energy
Ionization and excitation are the results of energy
deposition in a biological system.
• Excitation (non-ionization) - the raising of an electron in
an atom or molecule to a higher level without actual
ejection of the electron is called excitation.
• Ionization - if the radiation has sufficient energy to
eject one or more orbital electrons from the atom of
molecule, the process is called ionization, and that
radiation is said to be ionizing radiation.
Types of ionizing radiations
• Particulate: all charged particles and uncharged
particles (protons, alpha and beta particles, heavy:
ions, Neutrons, Negative piamesons)
• Electromagnetic: x- and gamma rays (photons)
Alpha particles (α) are positively
charged and made up of two protons
and two neutrons from the atom’s
nucleus (24He). Alpha particles come
from the decay of the heaviest
radioactive elements, such
as uranium, radium and polonium. Even
though alpha particles are very
energetic.
Beta particles (β) are small, fast-moving
particles with a negative electrical
charge that are emitted from an atom’s
nucleus during radioactive decay. These
particles are emitted by certain unstable
atoms such as hydrogen-3 (tritium),
carbon-14 and strontium-90.
Gamma rays (γ) are weightless packets of energy
called photons. Unlike alpha and beta particles,
which have both energy and mass, gamma rays
are pure energy. Gamma rays are similar to
visible light, but have much higher energy.
Gamma rays are often emitted along with alpha or
beta particles during radioactive decay.
X-rays are similar to gamma rays in that
they are photons of pure energy. X-rays
and gamma rays have the same basic
properties but come from different parts
of the atom. X-rays are emitted from
processes outside the nucleus, but
gamma rays originate inside the nucleus
Ionizing radiation
• Directly ionizing: individual particles have sufficient
kinetic energy, they can directly disrupt the atomic
structure of the absorber through which they pass and
produce chemical and biological changes. eg charged
particles.
• Indirectly ionizing: they produce chemical and
biological damage themselves, but when they are
absorbed in the material through which they pass they
give up their energy to produce fast moving charged
particles. eg x and gamma rays.
DNA damage due to radiation ionization
