Radiation

radiation

energy traveling through space as electromagnetic waves or particulate matter

• natural and human-made sources

• avoidable and small doses are manageable

common exposures of radiation

• radon gas in homes/buildings

• cosmic rays (sun)

• medical procedures (x-rays, CT scans, nuclear)

• consumer products

• industrial application

• our own bodies have radioactive elements

electromagnetic spectrum

R → M → I → V → U → X → G

Wilhelm Rontgen

discovered X-rays while experimenting on accident

• could penetrate soft tissue but not bone

• first clinical X-ray taken of his wife

• award the first-ever Nobel Prize

• refused to patent the discovery

  • believed that science should benefit all humanity

Henri Becquerel

left uranium salts on a plate in the dark expecting no reaction

discovered plate was exposed anyways

• uranium emits radiation even without light

named it uranic rays (later termed radioactivity by Curie)

Becquerel shared the Nobel Prize in Physics

with Pierre and Marie Curie

SI unit of radioactivity is the

Becquerel (Bq) named in his honor

1 Bq =

1 nuclear disintegration per second

Pierre and Marie Curie

coined “radioactivity”

• proved radiation is an atomic property not a chemical one

• identified 2 elements

  • polonium and radium

• isotope isolation

  • developed methods to isolate radioactive isotopes

Marie Curie won 2 noble prizes

Physics

Chemistry

ionizing radiation

energy is enough to eject electrons from atoms

• damages DNA in cells

• radiation sickness, cancer, genetic damage

• risk is determined by dose, duration, and tissue type

source of ionizing radiation

X rays

Gamma rays

alpha/beta particles

cosmic rays

ionizing radiation has

no safe threshold at cellular level

non-ionizing radiation

enough energy to vibrate or move atoms, not ionize them

• cause thermal effects

• minor annoyance to serious injury

sources of non-ionizing radiation

• UV (closer to ionizing at higher frequencies)

• visible light

• infrared

• microwave

risk depends on intensity and duration

ionizing radiation damages living cells

1. ionization

2. free radicals

3. DNA strand break

4. repair or fail

1. ionization

radiation ejects electrons from atoms within tissue, creating reactive ion pairs

2. free radicals

ionized water molecules (H2O) produce highly reactive hydroxyl radicals (-OH)

3. DNA strand break

hydroxyl radicals attack the DNA causing single or double-strand breaks

• double-strand breaks are more lethal

• if repair fails then genomic instability and malignant transformation

4. repair or fail

cells attempt DNA repair

uncorrected errors lead to mutation, cell death, or cancer

natural sources of ionizing radiation

• cosmic rays

• radon gas

• terrestrial radiation

• internal radionuclides

cosmic rays

high energy particles from space, exposure doubles per 2000m of altitude

• airline crews receive 3x more dose annually

radon gas

naturally occurring, odorless from uranium decay in soil and rock, accumulates in basements, #2 cause of lung cancer

~50% of US radiation exposure from radon

terrestrial radiation

radioactive elements (uranium, thorium, radium) in rock and soil that emit gamma radiation

internal radionuclides

K-40 in bananas and potatoes

Ra-226 in Brazil nuts

C-14 in all living tissue

normal (not a health concern)

radon is an invisible hazard

• colorless

• odorless

• tasteless

from radioactive decay of uranium in soil, rock, water

• enters cracks in foundations and porous walls

• lodge in lung tissue

• associated with lung cancer death

• 2nd leading cause of lung cancer after smoking

sub-basement depressurizing systems

can reduce radon levels by more than 50%

trivial radioactivity in everyday food

• bananas

• potatoes

• brazil nuts

• red meat

medical procedures

• X-rays

• CT scans

• nuclear medicine

• radiation therapy

consumer products

• tanning beds

• smoke detectors

• building materials (granite countertops)

industrial and nuclear

• nuclear power plant operations and radioactive waste management

• oil and gas exploration equipment

• industrial radiography

• food irradiation

• product sterilization

four factors that govern radiation exposure

• time (length of exposure)

• shielding (dense materials absorb radiation to protect)

• distance (closer to source, higher the exposure)

• activity (rate of energy emission of a source)

Sievert (Sv)

unit that represents the health risk of ionizing radiation

• probability of causing radiation-induced cancer and genetic damage

radiation that we are typically exposed to on a daily basis

is low (usually in mSv)

doses in perspective

eating 1 banana < dental x-ray < flight < chest x-ray < mammogram < annual US background < CT scan < occupational limit

<0.25 Sv

no detectable clinical effects in most individuals

0.25 - 1 Sv

mild radiation sickness

• nausea

• fatigue

• temporary drop in WBC

1-2 Sv

moderate sickness

• vomiting

• hair loss

• immune suppression

• 2-6 week latency period

2-6 Sv

severe

• hemorrhage

• bone marrow failure

• 3-4 Sv without medical treatment

> 6 Sv

extreme

• GI tract & CNS damage

• near-certain death without immediate medical intervention

acute radiation syndrome (ARS)

requires whole-body exposure to > 1 Sv received over a short period of time

• bone marrow transfusion and supportive care needed