Radiation Safety Training: Fundamentals

University of Alaska Fairbanks

September 2013

Training Contents1) Radiation safety fundamentals

• Types of radiation

• Terms and definitions

2) The principle of ALARA

• Shielding

• Detection of radiation and contamination

• Principles of radiation protection

3) Properties of common radioactive materials used in UAF research labs

Radiation Safety Fundamentals

Radioactivity is a natural and spontaneous process by which unstable radioactive atoms decay to a different state and emit excess energy in the form of radiation.

Radioactive decay is a random process.

The type of radiation emitted by radioactive isotopes is known as ionizing radiation.

Ionizing radiation has the ability to change the physical state of atoms it interacts with, causing them to become electrically charged or IONIZED.

Radiation Safety Fundamentals (cont.)

There are four main types of ionizing radiation.

o Alpha emission/alpha particleso Beta emission/beta particleso Gamma emission/gamma rays or X-rayso Neutrons

Some isotopes decay by a process known as electron capture. For example, in 55Fe, the nucleus absorbs an electron from the inner orbital. The hole left in the inner orbital is filled by an electron from an outer shell, resulting in an energy loss. The energy loss is manifested in the emission of auger electrons and x-rays.

Alpha emission 4alpha particles During alpha emission, a helium nucleus is ejected from an atom

Occurs when the neutron to proton ratio is too low in a particular atom.

The alpha particle is relatively large, slow-moving, and has no charge.

Beta emission 4 beta particles During beta emission, a neutron is converted into a proton, releasing an electron (the beta particle).

Occurs when neutron to proton ratio is too high in a particular atom.

Beta particles can travel greater distances than alpha particles and can penetrate some objects to at least some degree.

Gamma rays are emitted from the nucleus during radioactive decay of some elements.

X-rays are produced when electrons are removed from atoms or the atom is rearranged.

Gamma rays and x-rays have both electric and magnetic properties (electromagnetic radiation).

Gamma rays and x-rays can travel great distances, and can readily penetrate the body.

Gamma emission 4gamma rays

Neutrons Neutrons are heavy, uncharged particles that cause the atoms that they strike to become ionized.

Typical sources are nuclear reactors or cyclotrons, but neutrons can also generated from alpha emitters mixed with beryllium (e.g., Radium-beryllium sources).

Neutrons are dangerous mainly because they create unstable atoms when they strike materials, ionizing the atoms in the material (thus creating radioactive isotopes in the material).

The Radioactive Games Parlor One way to think about the relative danger of radioactive materials is to think of them as being bowling balls, pin balls, or lasers.

The Radioactive Games ParlorAlpha particles are like bowling balls.

o They crash into objects and are easily stopped by the atoms in the object (e.g., the bowling pins).

o External to the body, this is not a problem, as the outer layer of skin is dead. They can be stopped by a piece of paper.

o Internally, alpha particles are very dangerous. When they bombard an atom in a cell, they can dislodge electrons, thereby ionizing the atom in the cell.

The Radioactive Games ParlorBeta particles are like pin balls.o They are smaller than bowling balls, and may

make it past some atoms in the object before finally striking an atom.

o Some lower-energy beta particles (14C, 3H) cannot penetrate very far into the dead skin layer, and thus do not pose much of an external hazard. Internally, they can cause damage.

o Higher-energy beta particles (32P), can penetrate into the living skin layer, and can cause a great deal of damage internally.

The Radioactive Games ParlorGamma rays are like lasers.

o Gamma rays (and x-rays) are not particles. They are wave energy, and can travel great distances in air (much like a laser or other light beam).

o They may pass completely through an object without striking a single atom.

o If they do strike an atom, their high energy will dislodge an electron, thus ionizing the atom.

o Gamma emitters can readily cause damage both externally and internally.

Radiation Terms and Definitions

Activity:

The curie is the unit of activity most often used in the United States and expresses the rate of radioactive disintegrations per unit time, based on the following:One curie (Ci) :

3.7 x 1010 dps (disintegrations per second)

One millicurie (mCi) :3.7 x 107 dps = 1 x 10-3 Ci

One microcurie (µCi):3.7 x 104 dps or 2.22 106 dpm (1 x 10-6 Ci)

(dpm is disintegrations per minute)

Radiation Terms and Definitions (cont.)

Half-life (T½) is the amount of time required for radioactivity to decrease by one half.

Each radioisotope has a unique half-life.

14C: 5,730 years3H: 12.3 years32P: 14.28 days

Half-life is a FIXED number. It does not increase with temperature or pressure, and cannot be changed.

Radiation Terms and Definitions (cont.)

Radiation Exposure:

The Roentgen is the unit of radiation exposure in air and is expressed as the amount of ionization per unit mass of air due to X-ray or gamma radiation.

Absorbed Dose:

Radiation absorbed dose (rad) represents the amount of energy deposited per unit mass of absorbing material.

Radiation Terms and Definitions (cont.)

Dose Equivalent:The measure of the biological effect of radiation requires a variable called the quality factor (QF). Units are in rem or millirem (mrem).

The quality factor takes into account the different degrees of biological damage produced by equal doses of different types of radiation.

The QF for beta, gamma, and x-ray radiation is 1.

The QF for neutron radiation is 10.

The QF for alpha radiation is 20.

Thus, alpha radiation is considered 20x more harmful than beta or gamma radiation with regard to biological damage.

Radiation Terms and Definitions (cont.)

Damage from radiation depends on several factors such as whether the exposure was from internal or external sources.

External Exposure comes from a source outside the body, such as a medical x-ray. To do harm, the radiation must have enough energy to penetrate the body.

If it does, three factors affect the radiation dose that the individual will receive:

The amount of time the individual was exposed

The distance from the source of radiation

The amount of shielding between the individual and the source of radiation.

Radiation Terms and Definitions (cont.)Internal Exposure can occur when a radioisotope enters the body by inhalation, ingestion, absorption through skin, or through an open wound.

If this happens, any kind of radiation can directly harm living cells.

Radioactive material inside human body will cause an internal dose.

Radiation Terms and Definitions (cont.)After internal exposure occurs, the damage caused by the radiation depends on the following factors:

The amount of radioactive material deposited into the body The type of radiation emitted The physical characteristics of the element The half-life of the radioisotope The length of time in the body

The Principle of ALARAUAF is committed to the As Low As Reasonably Achievable (ALARA) concept for working with ionizing radiation.

Keeping exposures ALARA helps ensure that work with ionizing radiation presents a very low risk to faculty, staff, students and the general public.

The key components of ALARA are:1. Minimizing and limiting use of ionizing radiation.2. Shielding sources that emit radiation3. Keeping work areas clean and free of

contamination by practicing good lab hygiene.

Radiation Protection: Shielding

Placing material between the source of radiation and people working nearby is considered SHIELDING.

Radiation Protection: Shielding (cont.)

The following shielding guidelines can be used:

Alpha particles (α) stopped by paper

Beta particles (β) stopped by wood or Plexiglas

Gamma (γ) and X-rays (X) stopped by lead or concrete

NOTE: do not use lead as shielding for 32P. When the emitted beta particle strikes a high density material such as lead, an x-ray is generated.

Neutrons (η) are absorbed by hydrogen-rich materials (i.e. concrete, water, wax)

Detection of radiation and radioactive contamination: using a Ludlum Geiger counter

1. Turn switch to “BAT”. Needle should go into “BAT TEST” area.

2. Turn switch to the lowest scale and turn on audio switch.

3. Make sure switch is set to “fast” response mode (F) rather than “slow” (S).

4. Note meter “background” reading in a location away from radiation source.

Detection of radiation and radioactive contamination: using a Ludlum Geiger counter (cont.)4. Place probe (window face down) about ½ inch

from surface being surveyed. Do not let probe touch surfaces being checked, as this can result in contamination of the probe.

5. Survey work area by slowly moving probe over surfaces, listen to audible “clicks” from survey meter speaker.

6. Look for areas of contamination (higher than background readings).

7. NOTE: the exposure limit for the general public is 2 mrem/hour.

NOTE: Geiger counters can be used for 32P and 125I. They will NOT detect 3H, 14C, or 35S.

Radiation Protection: External Exposures to Gamma Rays and X-raysExternal exposure to gamma and x-ray radiation is controlled by the following three factors:

Time:

Minimize exposure time by careful experimental design and planning.

Do a “cold” run without isotopes in order to streamline your protocol and become familiar with the steps involved.

Distance: Radiation intensity decreases as a the distance from the source increases. Doubling the distance decreases the radiation intensity by four-fold (inverse square law).

Shielding: Use lead as shielding material.

Radiation Protection: External Exposures to Beta Radiation

The main concern with beta radiation is skin exposure, as some beta particles can penetrate the epidermis and reach the live cell layer.

Time and distance methods of exposure reduction for x-rays and gamma rays listed above also apply to beta radiation.

Shielding: use >½” thick Plexiglas. Do not use lead. Some beta radiation produces x-rays (Bremsstrahlung or “braking radiation”) when interacting with lead.

Radiation Protection: Internal Exposures to RadiationRoutes of internal exposure

1. Absorption

2. Inhalation

3. Ingestion

4. Injection

If you every suspect that you may have internal contamination with radioactive materials, contact the UAF Radiation Safety Officer immediately (474-6771).

Radiation Protection: Internal Exposures to Radiation (cont.)Prevent absorption :

1.Change gloves frequently.

2.Avoid touching your eyes, nose or mouth while conducting experiments.

3.Monitor your work area with survey meter or regular wipe testing.

4.Wash your hands after removing gloves and before leaving the lab. If appropriate, check your hands and lab coat with a survey meter (for 32P or 125I only).

Radiation Protection: Internal Exposures to Radiation (cont.)Prevent inhalation:

1.Use fume hood when you are using any volatile sources of radioactivity.

Prevent ingestion:

2.Never eat or drink in the laboratory.

3.Never store food in refrigerators or freezers or other areas designated for chemical or radioactive material storage.

Radiation Protection: Internal Exposures to Radiation (cont.)Prevent injection:

1.Practice safe sharps handling. Do not recap needles and dispose of sharps in a sharps container (labeled with “Caution, Radioactive Materials” label or tape.

2.Be careful handling glass that is contaminated with radioactive materials. Use plastic lab ware whenever possible.

Radioactive materials used at UAFCarbon-14 (C-14, 14C)

Half-life: 5730 yearsType of emission: pure beta Energy (average/maximum): 0.049/0.156 MeVMax range in air: 24 cm Max range in H2O: 0.28 mm Hazard: InternalDetection method: Wipe tests & Liquid Scintillation Counting (LSC)(98% efficient); NO Geiger counter!

Radioactive materials used at UAF (cont.)Hydrogen-3 (3H, tritium)

Half-life: 12.28 yearsType of emission: pure betaEnergy (average/maximum): 5.7/18.6 keVMax range in H2O: 6x10-3nmHazard: InternalDetection: Wipe tests & LSC(60-65% efficient); NO Geiger counter!

Radioactive materials used at UAF (cont.)Sulfur - 35 (35S)

Half-life: 87.44 daysType of emission: pure betaEnergy (average/maximum): 0.049/0.167 MeVMax range in air: 26 cmMax range in H2O: 0.32 nmHazard: InternalDetection: Wipe tests & LSC (97% efficient); NO Geiger counter!

Radioactive materials used at UAF (cont.)Iron- 55 (55Fe)

Half-life: 2.7 yearsType of emission: X-rays, auger

electronsEnergy (gamma/electrons): 6 keV/5.2 keVMax range in air: 0.15 cmMax range in tissue: 0 cmHazard: Internal (blood)

Detection: Wipe tests & LSC (0-400) (35% efficient); NO Geiger counter!

Radioactive materials used at UAF (cont.)Phosphorus -32 (32P)

Half-life: 14.28 daysType of emission: pure beta (but may generate x-rays if lead is used as shielding)Energy (average/maximum): 0.695/1.71 MeVMax range in air: 790 cm

Max range in H2O: 0.76 cmHazard: External skin,

internalDetection:Survey meter, wipe tests & LSC (100% efficient); Geiger counter is very useful.

Radioactive materials used at UAF (cont.)Iodine -125 (125I)

Half-life: 60.14 daysType of emission: low-energy gamma, x-raysEnergy (average/maximum): MeVMax range in air: cmMax range in H2O: cmHazard: External, internal

(thyroid)Detection:Survey meter, wipe tests & gamma counter; Geiger counter can be useful if it has a gamma probe.

Radioactive materials used at UAFRelative toxicity ranking of radioisotopes is based upon internal uptake through ingestion, inhalation, or absorption of radioisotopes.High toxicity Medium-high

toxicityLow-medium

toxicityLow toxicity

None 125I (gamma)137Cs (gamma)

32P (beta)35S (beta)14C (beta)

3H (beta)55Fe (x-rays, auger electrons)

Thank you!