NM Rad Bio 2016

Question 1

Alpha Particles

1. Physical characteristics
2. Range
3. Shielding
4. Biological Hazard

Answer 1

1. Large mass (A = 4), 2 protons & 2 neutrons (+2 charge), ionizes atoms by stripping electrons as it passes by
2. Range: deposits large amount of energy in short distance
3. Shield: Stopped by a few cm of air, sheet of paper or outer layer of skin
4. If inhaled or ingested = internal exposure

Question 2

Electrons (beta particles) and positrons

1. Physical characteristics
2. Range
3. Shielding
4. Biological Hazard

Answer 2

Emitted by unstable nucleus (= beta particles), produced by photon interaction with matter, at the end of path, positron + electron = 2 gamma photons
1. ~8000 times less massive than alpha particle, causes ionization by electrical interactions with electrons in material, readily scattered –> zig zag paths, not as effective at causing ionization (as alpha)
2: range: in air, ~10 ft. in tissue = a few cm
3. thin layers of plastic, glass, Al, or wood
4. high exposures = damage to skin,
mostly internal hazard (beta emission)

Question 3

Neutrons

1. Physical characteristics
2. Range
3. Shielding
4. Biological Hazard

Answer 3

When neutron slows down–> captured by a neucleus = radioactive
1. more massive than electrons, less massive than alpha particles. interact with charged particles by colliding with them. (no electrostatic forces)
2. no electrostatic forces = high penetrating ability, difficult to stop. Range hard to define
3. Moderate to low E = materials with high hydrogen content (water, polyethylene plastic)
High E = steel or lead
4. external whole body hazard d/t high penetrating ability

Question 4

Protons

1. Physical characteristics
2. Range
3. Shielding
4. Biological Hazard

Answer 4

high energy protons created in particle accelerators

protons are more penetrating than alpha particles due to having half the charge & scattered less b/c greater mass.

Question 5

X-rays and gamma rays

1. Physical characteristics
2. Range
3. Shielding
4. Biological Hazard

Answer 5

1. Have no mass or charge, travel at speed of light, ionize matter as a result of direct interactions with orbital electrons
2. very high penetrating power (low probability of interacting w/ matter) d/t no mass or charge
3. very dense materials (lead, concrete, steel)
4. can result in radiation exposure to whole body.

Question 6

Types of radioactive decay (6)

Answer 6

1. Alpha emission
2. Beta emission
3. Positron emission
4. Electron capture
5. Gamma emission
6. Spontaneous fission

Question 7

Units used for:

Activity of a source

Answer 7

Curie

Becquerel (SI unit)

Question 8

Units used for:

Absorbed dose

Answer 8

Rad

Gray (SI)

Question 9

Units used for:

Biologically effective dose

Answer 9

Rem

Sievert (SI)

Question 10

Units used for:

Intensity

Answer 10

Roentgen

C/kg (SI)

Question 11

Mechanisms of energy loss, charged particles (2):

Answer 11

1. Electrostatic interactions

2. Radiative emission

Question 12

Types of charged particle emission (3):

Answer 12

1. Excitation
2. Ionization
3. Bremsstrahlung

Question 13

Net result of the photoelectric effect:

Answer 13

Complete absorption of X-Ray and ejection of photoelectron

Question 14

Net result of the Compton scatter:

Answer 14

Recoil electron and a scattered photon

Both capable of further ionization

Question 15

Net result of Pair Production

Answer 15

Emission of positron & electron, each with rest mass of 0.511 MeV

Question 16

Photodisinegration

Answer 16

Nuclear binding energy is overcome (>= tens of MeV) absorbed
Nucleus is split into fragments
Above DXI & RT range

Question 17

What is a survival curve?

Answer 17

A semi-log plot of cell survival fraction vs increasing dose.

Question 18

Each point on a cell survival curve corresponds to what?

Answer 18

A single dose of radiation