Unit 1 Exam

Exam 05/20

Radiation Biology

The study of the effects of ionizing radiation on biological tissue  

At what level of organization does radiation interact at?

Atomic

When do early effects of radiation occur?

Within minutes or days

Early effects of radiation

Radiation sickness, GI or CNS syndome, hematologic syndrome

When does late effects of radiation occur?

Within months or years

Late effects of radiation

Cancers, skin damage, cataracts

Fetal effects of radiation

Prenatal death, neonatal death, congenital malformation, childhood malformation, diminished growth and development

What is exposure measured in?

Coulomb/kG

What is air kerma and absorbed dose measured in?

Gy

Air Kerma

Kinetic energy released in matter

Absorbed Dose

Amount of energy (radiation) absorbed per unit mass (patient tissue) of an irradiated object

What is equivalent and effective dose measured in?

Sv

Equivalent dose

Measures biologic harm; average absorbed dose in human tissue or organs by different types of radiation

Effective Dose

Defined as the sum of the tissue-equivalent doses weighted by the ICRP organ (tissue) weighting factors (W_t); best measure of radiologic harm

Occupational cumulative dose limit

Age x 10 mSv

Occupational annual dose limit

50 mSv

Occupational eye dose limit

150 mSv

Occupational skin/extremity dose limit

500 mSv

Occupational 1 month fetus dose limit

0.5 mSv

Occupational fetus gestation dose limit

5 mSv

What NCRP report discusses dose limits?

116

Public annual frequent radiation dose limit

1 mSv

Public annual infrequent radiation dose limit

5 mSv

Public eye and skin/extremity dose limit

50 mSv

Nucleus

Center of atom composed of protons and neutrons

What is the energy needed to remove an electron from an atom?

Binding energy

Energy shells

Orbit nucleus occupied by electrons

What orbital shell is closest to the nucleus?

K

What orbital shell has the highest binding energy?

Shell closest to the nucleus

What orbital shell would have more # of electrons?

Outer shells of an atom can hold more electrons, specifically the valence shells.

How do you determine the max # of electrons per shell?

2n²

Valence electrons

Electrons in the outermost shell of an atom

Octet Rule

Electrons in outermost shell can have no more than 8 electrons

Ionization

Adding or removing an orbital electron from an atom

Binding energy of carbon

.3 keV

Binding energy of barium

37 keV B

Binding energy of tungsten

70 keV

Molecules

Combination of atoms formed by ionic and covalent bonding

Ionic Bonding

Attraction, giving of an electron (two oppositely charged particles (ions))  

What is an example of ionic bonding?

NaCl

Covalent Bonding

Sharing of electrons

What is an example of covalent bonding?

h2o

Atomic Number

Z number; number of protons

Atomic Mass Number

A number; number of protons + number of neutrons in nucleus

Isotopes

Atoms of the same element that have the same atomic number but different atomic mass numbers

What is an example of an isotope?

Barium (Z# 56, A# 138)

Radioisotopes

Combination of protons and neutrons that lead to an unstable nucleus

Coherent (classical) scattering  

X-ray interacts with an atom and excites it, the photon scatters when it is released and does not change direction (same energy, same wavelength); occurs at very low energy levels (typically 10 kV)  

Coherent (classical) scattering

Compton scattering

Ionization of an outer shell electron; outer shell electron is ejected and the incoming x-ray photon scatters in a different direction; the scattered photon has less energy, longer wavelength and lower frequency 

What interaction causes occupational exposure?

Compton scattering

Compton scattering

Photoelectric absorption

X-ray photon absorbed; ionization of inner shell electron, electron is ejected causing an unstable atom because an inner shell electron is missing (inner shell vacancy is filled by outer shell electrons – characteristic cascade)  

What interaction results in a major part of image production and contrast?

Photoelectric absorption

Photoelectric absorption

Pair production

X-ray or gamma ray has strong energy that may escape interaction with electrons coming close enough to nucleus and be influenced by its strong electric field; x-ray disappears and positron (+) and negatron (-) appear in its place  

What energy level does pair production occur?

1.02 MeV

What imaging uses pair production?

PET scans

Pair production

What occurs when a positron unites with an electron?

2 gamma rays are created