Radiation

Tuesday, Sept 27

Atom – basic building block of matter

Atoms contain 3 types of particles – protons (+); neutrons (no charge), and electrons (-). Electrons are in orbit around the nucleus.

All matter is made up of elements – fundamental substances that cannot be broken down by chemical means.

Radiation – light energy that travels and spreads out as it goes

- energy in transit in the form of particles and electromagnetic waves

Electromagnetic radiation – all the wavelengths of light energy that make up visible light, radio and TV waves, ultraviolet waves, microwaves, and ionizing radiation

Visible light, radio and TV waves, ultraviolet waves, microwaves – do not carry enough energy to separate molecules or remove electrons from atoms

Ionizing radiation – radiation with enough energy to remove tightly bound electrons from their orbits, causing the atom to become charged or ionized (electrically charged ions formed)

Can destroy chemical bonds in tissue and in DNA.

Sources of ionizing radiation: sun, rocks, soil, past nuclear weapons,

radioactive medical and industrial wastes, nuclear and coal power plants; security check devices

Exposed to higher amounts at high altitudes, in certain jobs, certain medical treatments

Categories of origin:1. Cosmic radiation from sun and space

More at high altitudes – atmosphere (ozone layer) helps protect earth. Denver > LA or Boston

2. Radioactive materials in earth’s crust – soils, rocks, sands. Radioactive gases escape from these (Radon) and enter air and water.

3. Manmade – for industrial, medical (Xrays and labeled drugs) and dental, and consumer use; Nuclear weapons; nuclear power plants

Radon gas is considered “an enhanced natural source” – concentrates in houses and mine shafts, etc due to human actions

Estimated that 82% of our exposure is from natural and enhanced “natural” sources. Harm relates to type and exposure pathway.

4 types of ionizing radiation:

Alpha particles; beta particles; gamma rays, x-rays

Differ by particle source, energy and speed, penetrability, and consequent ability to do harm.

Gamma and x-rays are worst.

1. Alpha particles - fast moving bits of atoms that are given off by a radioactive

substance (fragments contain 2 protons and 2 neutrons)- Velocity is 1/20th the speed of light (slow)- Natural elements can be alpha emitters – uranium-238;

thorium-232; radium-226; radon-222; polonium-210: found in rocks , soils, and water

- Useful in some medical and industrial processes Radium-226 used to treat cancer by putting it into the tumor

to kill the cells; Polonium-210 used as a static eliminator in paper mills (alpha particles attract loose electrons and reduce static charge); Americium-241used to create a current in smoke detectors. Smoke breaks the current and sets off alarm.

- Released during some mining operations- For most, greatest exposure is radon gas or smokingHealth Effects: lack energy to penetrate skin; problem if inhaled

or ingested; or if enter blood through a wound.Lung and other cancer risks.

2. Beta Particles-Fragments of atoms that originate from nucleus and become like electrons- A little smaller than alpha particles- Speed varies over a wide range- technetium-99; phosphorus-31; tritium H-3; carbon-14, strontium-90; cobalt-60; iodine-129 and 131- used in medical diagnosis, imaging, and treatment; luminous dials on gauges, and wrist watches; carbon-14 used to date matter up to 30,000 years of age; other industrial measuring instruments

Health effects: can burn skin; travel further into tissues than alpha particles; ingestion and inhalation a worse problem than for alphas

Don’t play with instruments or devices that are marked with radioactive sign.

3. Gamma rays- very short wavelengths; fastest in natural spectrum- travel at speed of light- easily pass through many materials – lead shield needed- differ from X rays in that gamma rays come from the nucleus and x-rays come form the electron field surrounding the nucleus- most widely used radiation source- cesium-137; cobalt-60; technetium-99m (shorter half-life)

Cesium-137 – cancer trt; investigate deep in earth for oil wells; measure soil density at construction sites; quality control of fill levels in food and drug packaging

Cobalt-60 – sterilization of medical equipment; pasteurization of foods and spices; gauge metal thickness in steel manufacturing; cancer trt

Technetium -99m – common radioactive isotope in medicine

- Gamma ray trts also improve durability of wood and plastics

3. Gamma rays (cont)-Used to check seals on welds; to inspect jet engine blades and parts

Common sources of exposure: natural occurrence in potassium in soil, water, bananas, meats; nuclear medicine for bone, thyroid, lung scans.

Medical trts; discarded medical or industrial devices.

External exposure; inhalation; ingestion – all a problem.

Penetrate tissue more deeply – can cause radiation sickness at high doses (possibly lethal); lower doses – cancer and neural damage, etc.

4. X rays – manmade source

Most exposure through diagnostic medical and dental x-rays.

Penetrate deeply.

Like Gamma, but different source.

Routes

1. Inhalation

- chief concerns are contaminated dust, smoke, or gases (like Radon)

- mostly alpha and beta particles

- particles can lodge in lungs and remain for a long time

- if particles decay slowly, exposure continues over a long time

The amount of time it takes to decay one half of the radioactive atoms in a group to another form is called half-life.

2. Ingestion- Alpha and beta are of most concern- energy released directly to tissue (digestive; kidney, and bone)

Routes

3. External exposure- little concern about alpha particles; more about Beta; most

about Gamma and xray.Gamma and x ray can penetrate the entire body.(should be shielded by lead apron or container; soil covering

buried contaminations)

Health Effects

Amount and duration of exposure determines health effects.

I. Acute effects – short term effects from high doses

Radiation sickness – nausea, vomiting, weakness, hair loss, skin burns, diminished organ function

Health Effects

II. Chronic – long term, low level

Cancer is a primary health effect

1910 – understood that radiation causes skin cancer

Best studies of chronic effects are on Japanese atomic bomb survivors; natives of Marshall Islands (where bomb testing was done); and uranium miners.

Radiation changes DNA – mutationa caused.

Exposure (rem)

Health Effect Time to Onset 

5-10   changes in blood chemistry  

50   nausea  hours

55   fatigue

70   vomiting  

75   hair loss   2-3 weeks

90  diarrhea   

100  hemorrhage  

400 death from fatal doses  within 2 months

1,000   destruction of intestinal lining 

  internal bleeding  

death   1-2 weeks

2,000   damage to central nervous system    

loss of consciousness   minutes

  death  hours to days