Sources of Radiation

1
Sources of Radiation

• Natural background radiation is everywhere
• There are terrestrial and cosmic sources as well
  as those all over our planet.
• The level is variable by location.
• The largest single source is radon. Radon is a
  radioactive gas that can accumulate in homes and
  in the workplace. The levels vary by location but
  the national average is 200 mrem/year.

2
Typical natural background levels are 60 mrem in
NE, E, W, and Central United States.45 mrem in
Atlantic and Gulf Coastal states and 120 mrem in
the Colorado Plateau. The amount of radiation
the typical radiation worker is exposed to is
about the same order of magnitude as an average
abdominal radiograph or a years background
exposure.
3
Units of Activity in U.S.

• In the United States, exposure is commonly
  measured in units of mrem, or 1/1000 of a Rem. In
  other countries the unit of measure is typically
  the millisievert. This is defined later.
• In this exercise we are only concerned with
  ionizing radiation because it contains sufficient
  energy to break chemical bonds by removing an
  electron from an atom or molecular substance.
• Breaking of bonds in biological systems can cause
  the system to malfunction.

4
Kinds of Radiation at Union College

• At Union College the radiation sources are
  sources of Alpha particle, Beta particle, gamma
  radiation, X-rays, and in some instances
  neutrons.
• Alpha particles lose their energy in short
  distances, as within 2 inches of air or the
  surface of skin thus generally it is not
  dangerous. Its danger is if it enters the body
  internally where its lifetime and energy can be
  very harmful.
• i.e., Alpha emitters mostly come from long lived
  isotopes like uranium so emit for a long time.

5
Most Common Radiation at Union College

• Beta emitters are the most common isotopes dealt
  with at Union College.
• They can typically penetrate into the skin
  one/half inch, through a few feet of air but
  might be blocked by a plastic shield. A problem
  with a shield made from dense material is that
  the Beta particle can generate other radiation
  which is detected beyond the expected penetration
  depth. Often this radiation is gamma.
• Beta emitting isotopes life times vary over a
  large range.

6
Non-particulate Radiation

• Gamma radiation is not a particle like first two.
  It penetrates many shields and normally requires
  several inches of lead to stop it. Its source
  might be from isotopes undergoing decay and can
  come from beta particles striking certain
  materials. Their energy levels vary considerably
  and so exposure to them is not recommended. They
  find use in medical imaging.

7
The Third Particle

• Neutrons are particles and being neutral in
  charge typically penetrate most materials without
  interaction. Their danger depends on the energy
  of the neutron. Typically Union Colleges only
  connection with them is their use for
  activating materials for analysis by the
  Geologists via neutron activation done at Oregon
  State University.

8
Quantity of Radiation Terminology

• Dose This is a generic term for the quantity of
  absorbed radiation per unit mass. Dose
  equivalent is the term for quantity of absorbed
  dose in tissue modified by certain risk factors
  dependent upon the type of radiation to which one
  is exposed.
• Dose rate Is the absorbed dose delivered per
  unit of time

9
More Radiation Terminology

• Rad Is the absorbed radiation dose, the unit
  of dose (or energy absorbed) per unit mass in
  materials, including tissue. The international
  unit is the Gray ( 1 Gy 100 rad)

10
What is a Roentgen?

• It is the unit to measure ionization in air as a
  result of exposure to X-Rays or gamma-radiation
  there is no international equivalent term.
• Curie A unit of activity of radioactive
  substances (decaying at the rate of 3.7 E10
  disintegrations per second per curie) The
  international unit for activity is the becquerel
  ( 1 disintegration per second). It is abbreviated
  Bq. 3.7E10 Bq is one curie

11
Even More Radiation Terminology

• Rem This is most commonly the term used by the
  Radiation Safety Officer. It is the Roentgen
  Equivalent in Man versus air, i.e., it is unit
  of effective dose that corrects absorbed dose for
  the risk for high energy particle radiation which
  do more damage to tissue than an equivalent
  absorbed dose of X- or Gamma-rays. International
  unit is sievert (1 Sv 100 rem)

12
An Important term relating the strength of your
sample

• Curie The unit of activity of radioactive
  substances (decaying at the rate of 3.3 E10
  disintegrations per second is a curie. The number
  comes from the activity of uranium. At Union
  College we deal mostly with mCi or uCi. The
  international unit of activity is the becqueral
  (1 disintegration per second) abbreviated Bq.

13
How do we describe or discuss the life or
stability of an isotope?

• This is measured by a term called half-life.
  The larger this number the more stable and longer
  lived is that isotope. It represents the amount
  of time for half of the quantity of the isotope
  to undergo decay, i.e., changed into a different
  isotope or isotopes.
• The t1/2 for tritium is small compared to that of
  uranium U-238 is about 4E9 years while tritium
  is about 12 years. Any given quantity of H3
  disappears in about 120 years, about ten
  half-lives.

14
Less commonly used term

• Sometimes we are concerned with the radiation
  near the surface.
• The Half Value Layer is the thickness of a given
  substance required to cut exposure from a beam of
  radiation in half. Such a layer might be 20 to 80
  percent of total radiation being emitted.
• Leak Test Is a test of the surface of a sealed
  source to determine whether the seal is still in
  tact.

15
Man-made sources of exposure

• Typically an individual might encounter sources
  of radiation in
• diagnostic radiology
• Nuclear medicine
• Radiation therapy
• During medical X-ray analysis
• In a Laboratory

16
Most Common Sources

• But the most common sources of radiation are in
  water (even bottled water), soil, and the air.
  Radiation received from the sun and natural
  radioactive material (ores) are often a greater
  source of radiation exposure than the radiation
  found in the workplace. In the United States,
  Colorado has about the highest level in soil.

17
What are the undesirable effects from higher
exposures

• Although low when adhering to safe radiation
  standards undesirable effects from higher
  exposures are
• Cancer
• Genetic mutations
• Effects on an embryo/fetus

18
Effects from various exposure levels

• Even though radiation can be of great benefit,
  too much exposure, like from the sun can be
  dangerous. Two types of effects are
• 1. Effects that will occur when given a certain
  minimum exposure (or threshold effects)
• 2. Effects that have a higher chance of occurring
  with higher levels of exposure.

19
Effects from Threshold Levels of radiation
exposure

• Cataracts in the eyes
• Skin erythema (skin reddening)
• Hair loss
• Precancerous skin conditions

20
Given these effects what are normal levels of
radiation in a procedure?

• Radiation Oncology 5K rad (tumor treatment)
• CT of Pelvis 1 rad. or CT of Head 3 rad
• Chest X-ray 15 mrad
• Dental exam 300 mrad
• Mammogram 150 mrad glandular dose

21
Chances of Getting Cancer

• However, the reality is that risks from natural
  and most medical levels of radiation are quite
  low. The chance of getting cancer from 10 mrem of
  radiation is equivalent to the change of winning
  the lottery when you bought only one lottery
  ticket

22
What are the Occupational Dose Limits?

• Effective dose 2E3 mRem per year
• To the lens of the eye 15E3 mRem
• To the skin 50E3 mRem
• To the hands, feet, knees, elbows 50E3 mRem
• Those expected to receive 10 of the limit level
  must wear dosimeters.

23
How do we minimize exposure?What are Safe
Practices

• The ALARA (as low as reasonably achievable)
  philosophy and its guidelines are what help to
  keep the risk or radiation down. The ALARA
  guidelines are limits established to ensure that
  safety is maintained. We know the lower doses
  carry lower risk, and this concept helps to
  maintain cost effective safety.

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ALARA

• Time Less exposure time means lower exposure
  level
• Distance The radiation level falls off at a rate
  of inverse square of the distance. So stay as far
  from the sample as possible
• Shielding As indicated earlier, various shields
  can diminish or block the radiation

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Key Safety Tips

• Be able to recognize radiation signage and which
  packages might contain radioactive materials.
  Apply the ALARA practice to them.
• Do not consume anything or put items like
  cosmetics on your face where there are
  radioactive material or might have been from
  contamination. Wear gloves, wash hands.
• If radioactive materials are spilled, restrict
  access to the area and contact the Radiation
  Safety Officer

26
Who should be specially cautions?

• Individuals close to their exposure limits
• Females who are pregnant or might become pregnant
• Young children or infants
• Old frail individuals
• Those who have cancer or similar diseases
• Women might want to declare they are pregnant
  because exposure limits are lower for them thus
  protecting the fetus.

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So what do you do in a Radiation Emergency?

• Follow the letters in the word RACE
• R rescue or evacuate anyone in the area of a
  spill or condition of high exposure
• A alarm, sound one if appropriate
• C call the Radiation Safety Officer (RSO)
• E exit the area but be close enough to
  communicate with the RSO information

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Contact Numbers

• Campus Safety 388-6911 This is a good first
  number as they can contact the RSO via radio or
  by using one of several phone numbers
• RSO 388-6911 (office number) or [phone]
  (cell phone which is normally carried at all
  times by the RSO)
• Please complete the following Quiz and submit to
  the RSO

29
QUIZ

• Quiz questions for Radiation Program
• Where besides a laboratory with radioactive
  materials might you find ionizing radiation? Give
  three examples
• Which state in the United States has the highest
  natural background levels of radiation?
• What ionizing radiation material are you using or
  will be using in your research?
• Which ionizing radiation particle could be most
  harmful to you but also has a short distance of
  travel in air?
• What is one potential problem with assuming that
  beta particle radiation can be stopped with a
  high density material and there would be no other
  radiation in the area.
• Which generic term applies to the quantity of
  absorbed radiation per unit mass?
• What is described as a unit of activity of
  radioactive substance whose international unit is
  the becquerel?
• REM ?
• What term might be used to describe the stability
  of an isotope?
• Name a two potentially undesirable effects of
  high exposures to radiation.
• What is ALARA a mnemonic of ?
• What are the three terms most associated with the
  philosophy ALARA?
• Is it reasonable to put anything in your mouth
  which might have been exposed to radioactive
  material?
• In case of a spill, who always must be contacted
  (not necessarily the first person though)?
• Why are young children more susceptible to
  radiation damage than very old people?
• When an emergency arises, what do the letters
  RACE stand for?
• Should a spill of radioactive material or some
  other emergency related to radiation, what is the
  most sure fire phone number to call?