Med Apps Nuclear Science

Uses, Medical Applications, and the

Environment

Radiation

Radiation is split into two categories: ionizing and non-ionizing.

Non-Ionizing Radiation

Radiation that has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons, is referred to as "non-ionizing radiation." Examples of this kind of radiation are sound waves, visible light, and microwaves.

Passage of Radiation Through Matter

When we speak of radiation, we include alpha, beta, gamma and x-rays, as well as protons, neutrons, and other particles such as pions (elementary particles).These charged particles can ionize the atoms or molecules that they pass through, so they are referred to as ionizing radiation.This ionization can cause damage to materials, particularly to biological tissue.

Alpha and Beta Radiation

Charged particles (alpha and beta) cause ionization because of the electric force; they can attract or repel electrons, removing them from the atoms of the material.With their energies, a single alpha or beta particle can cause thousands of ionizations.

Neutral Particles

X-rays and gamma rays can knock out electrons (and ionize the atom) by passing through the material.These charged particles can then ionize other particles.Neutrons are large enough to cause the nucleus of a particle to break apart when it hits, altering the molecule; this particle can then ionize other particles.

Damage to Materials

Radiation passing through matter can cause considerable destruction:

Metal becomes brittle after being exposed to intense radiation (nuclear power plants, space shuttle with cosmic radiation) Cells become damaged - Ions or radicals are produced that are highly reactive and take part in chemical reactions that interfere with the normal operation of the cell.

Damage to Materials

When cells are altered, it may not perform its normal function, or may perform a harmful function.Radiation can kill/alter more cells than can be replaced (or in the time others can be replaced)Either too many cells die, or the ones that are altered replicate themselves, to the detriment of the organism.Radiation can cause cancer - the rapid production of defective cells.

Damage to Biological Organisms

Radiation damage to biological organisms are separated into two categories, dependent on its location in the body: somatic and geneticSomatic refers to any part except the reproductive organs - it causes cancer and (at high doses) radiation sickness or even deathGenetic refers to damage to reproductive cells that affects an individual’s offspring. This damage is known as a mutation; the mutations can be transferred to the offspring’s offspring.

Dosimetry

Although the passage of radiation through the body can cause damage, radiation can also be used to treat certain diseases, including cancer, often by directing beams of radiation at the tumor to destroy it. It is important to be able to quantify the amount, or dose, of radiation (known as dosimetry).

Units of Radiation

The strength of a source can be specified at a given time by stating the source activity, or how many disintegrations per second occur.

The traditional unit is the Curie (Ci) 1 Ci = 3.70 x 10 10 disintegrations per second

This number comes from the activity of 1 gram of radium.

Units for Radiation

The proper unit (SI) for source activity is the bequerel (Bq)1 Bq = 1 disintegration per second

Absorbed Dose

Absorbed dose is the effect that radiation has on the absorbing materialThe earliest unit of dosage was the roentgen (R ), which was defined in terms of the amount of ionization produced by the radiation.Today, 1 R is defined as the amount of X-ray or gamma radiation that deposits 0.878 x 10-2 J of energy per kilogram of air.

Absorbed Dose

Normally, the rad is used.1 rad is the amount of radiation which deposits energy at a rate of 1 x 10-2 J/kg in any absorbing materialThe SI unit for absorbed dose is the Gray (Gy)1 Gy = 100 rad

Absorbed Dose

The absorbed dose depends not only on the strength of the radiation, but also the absorbing material.Example: Bone is more dense than flesh, so it absorbs more of the radiation passing through the body

Taking into account all of the variables with radiation (amount, measured units, etc.) there needs to be a more meaningful units for the comparison of biological damage. The Relative Biological Effectiveness (RBE) or Quality Factor (QF) of a type of radiation is defined as the number of rads of x-ray or gamma radiation that produces the same biological damage as 1 rad of the given radiation.

Quality Factor

TYPE QFX- and gama rays 1Beta (electrons) 1Fast protons 1Slow neutrons 3Fast neutrons up to 10Alpha particles and

heavy ions up to 20

Effective Dose

The effective dose can be given as the product of the dose in rads and the QF, and this unit is known as the rem (rad equivalent man).

Effective dose (in rem) = dose (in rad) x QF

Effective Dose

The rem is being replaced by the sievert (Sv)Effective dose (Sv) = dose(Gray) x QF1 seivert = 100 remBy this definition, 1 rem of any radiation does about the same amount of biological damage.

Effects of Doses of Radiation

10 Sv (1000 rem)- Risk of death within days or weeks1 Sv (100 rem) - Risk of cancer later in life (5 in 100)100 mSv (10 rem)- Risk of cancer later in life (5 in 1000)50 mSv (5 rem)- Threshold Limit Value (TLV) for annual dose for radiation workers in one year20 mSv (2 rem)- Threshold Limit Value (TLV) for annual average doses, averaged over 5 years

Background Radiation

Radiation is present in our everyday lives: cosmic radiation, naturally occurring radiation in rocks and soil, and naturally occurring radioactive isotopes in our foodThe natural radioactive background averages about 0.36 rem per year per person.It is recommended that the general population does not exceed 0.5 rem per year, exclusive of natural resources.

Radiation at Work

Individuals who work at nuclear plants, hospitals, and research are exposed to more than the general public. For that reason, the level of exposure is increased to 5 rem/yr whole body dose.To protect themselves and to keep track of how much radiation they are exposed to, these individuals wear a dosimeter, typically a radiation film badge, which is a piece of film wrapped in light-tight material. Ionizing radiation passes through this material and darkens the film. The more exposure to radiation, the more exposed the film is.

Large doses of radiation can cause reddening of the skin and a drop in white blood cell count, as well as nausea, fatigue, and loss of body hair. These effects are known as radiation sickness.Larger doses spread over a long period of time are not as dangerous as small doses in a short amount of time.