Test 1: Milestones in Physics and Biology

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Milestones in Physics and Biology:

1. The following scientists made important contributions to the understanding of radiation. You should know their contribution and the year it was made. Which of the following scientists discovered X-ray radiation?

Einstein
Becquerel
Curie
Roentgen
Rutherford

2. How many years after the discovery of X-rays did the first report of the medical use of X-rays appear in a medical journal?

1
10
25
50

The Physics and Chemistry of Radiation Absorption

3. Types of ionizing radiations

Electrons can be accelerated to near the speed of light by linear accelerators
The mass of a proton is approximately equal to eight (8) electrons
An alpha particle consists of two protons and two neutrons
Neutrons and protons are approximately the same size

4. Wave and particle properties

An electron's behavior has wave like properties.
Protons have properties of waves and particles
Alpha particles do not exhibit wave properties.
The wavelength of X-rays is 1000 times larger than that of visible light.
The speed of light through different materials is always the same, 3x10E8m/s or 186,000 miles/h.

5. Directly and indirectly ionizing radiation and direct and indirect action of radiation

Charged particles are directly ionizing
Uncharged particles are indirectly ionizing
Directly ionizing radiation can interact with matter via the direct action
Directly ionizing radiation can interact with matter via the indirect action
Indirectly ionizing radiation cannot interact with matter via the direct action

6. Absorption of X-rays

Photoelectric effect, Compton process and pair production are processes by which a specific indirectly ionizing radiation interacts with tissue.
Lower x-ray energies are used for TBI prior to bone marrow transplants since photoelectric effect dominates at lower
energies, bone will absorb more of the dose than muscle, and the mass absorption coefficient for photoelectric absorption varies with the atomic number cubed.
The Compton process always interacts via the indirect action of radiation, not the direct action of radiation.
Almost all of the energy of the incoming X-ray is eventually absorbed by the tissue regardless of whether the X-ray interacts via the photoelectric effect or the Compton process.

7. Absorption of X-rays (continued)

There is an approximately 80% chance that radiation will interact with water since 80% of the cell is water and radiation absorption is a stochastic process.
It is much more likely that radiation damage modification (as can occur with changes in oxygen concentration) occuring during the time of radiation exposure is a result of interactions with DNA via the direct action of radiation than via the indirect action of radiation.
The hydroxyl radical interacts with DNA via the direct action of radiation.
The consequence of DNA damage from X-rays is manifest within 48 hours, post irradiation.

8. Absorption of Neutrons

Neutrons is a misnomer since they are charged particles with a charge of +1
Neutrons are indirectly ionizing radiation
When a neutron interacts with tissue by the process of elastic scattering, a neutron of lesser kinetic energy results whereas with inelastic scattering, often no neutron of lesser energy results.
An example of spallation products are the three alpha-particles that result from a neutron interacting with a carbon nuclei.