Lesson 6 Radiological Hazards

Fixed Contamination

Fixed contamination is not easily transferred from one place to another. It usually becomes fixed by physical or chemical absorption or by entrapment in physical irregularities of the surface material.

Acute Dose

Acute doses have a greater effect on us because the body does not have time to repair or replace the damaged body cells. An acute dose of 10,000-25,000 mrem could cause slight blood changes, but a normal individual would not be otherwise affected. An acute dose greater than 100,000 mrem causes half of the exposed population to experience nausea (due to damage to the intestinal lining). This is common in radiation therapy patients. Acute doses greater than 500,000 mrem may cause so much body damage that the body cannot recover. For example, the firefighters at Chernobyl are estimated to have received doses in excess of 800,000 mrem. This, compounded with the burns they received, caused them to succumb to the effects of their injuries.

Acute Radiation Exposure

Acute radiation exposure is the result of a large dose in a short period of time. An acute exposure, where recovery is probable, includes the following possible effects: Lowering of the white blood cell count Nausea Bacterial infections Vomiting Loss of appetite Reddening of the skin Diarrhea Fatigue, hair loss, and possible sterility A more severe exposure can cause: Fever Abdominal pains Explosive diarrhea Internal bleeding Infection Shock Convulsions, coma, and ultimately death Acute exposure is usually considered to be 25 rem over 24 hours.

Chronic Dose

Chronic doses are small amounts of radiation over a long period of time, such as our normal daily exposures over our lifetimes. We know that the body is able to tolerate a chronic dose better than an acute dose.

Chronic Radiation Exposure

Chronic radiation exposure involves low levels of ionizing radiation over a long period of time. Among the possible effects of chronic exposure are the increased risk of developing cancer and cataracts. In addition, research indicates possible genetic effects in humans from radiation damage to sperm and egg cells. Genetic damage can result in birth defects; furthermore, an exposed worker's genetic effects can be passed to future generations. The potential for chronic exposure to ionizing radiation is measured in mrem over many days. OSHA's ionizing radiation standard is in 29 CFR 1910.96.

Dose Limits

Dose limits represent the maximum permissible radiation dose equivalent that an individual is allowed to receive. They should never be considered desirable dose equivalent levels. EPA has established a recommended action limit of 1 mrem/hr. EPA states that investigation and monitoring may continue as readings increase above background radiation levels. However, at the action level of 1 mrem, the area should be vacated, the boundary clearly marked, and a health physicist employed. Department of Energy (DOE) limits are the same as those established for all federal agencies by the Environmental Protection Agency.

Radiation Protection

Humans cannot sense radiation. Radiation must be detected and measured using radiation monitoring instruments. It is vitally important that each drum, container, and area be checked for ionizing radiation. Containers must also be checked as they are opened. Remember that on a waste site, containers can be unmarked or improperly marked. Whenever radiation is detected on any marked or unmarked container or inside a container when it is opened, the Nuclear Regulatory Commission (NRC) must be contacted for advice. Some states have a radiation safety agency, which should be contacted. In the event that radioactive material is found, a basic understanding of protection against the radiation is needed. A worker who comes into contact with radioactive material can be radioactively contaminated. This means that the radioactive material has become attached to the person's body, clothing, or equipment, or has entered the body through openings in the skin, inhalation, ingestion, absorption, or injection. Assistance by a qualified health physicist technician is highly recommended. The best protection against radiation is prevention of contamination and keeping exposures as low as possible. ALARA is an acronym that stands for reducing exposure to ionizing radiation to a level, which is As Low As Reasonably Achievable. The ALARA concept requires tasks that are to be performed in a radiologically contaminated area to be reviewed to ensure all pertinent controls are applied. This concept is integrated into all site activities involving radioactive materials and is the responsibility of all individuals involved.

Ionizing Radiation

Ionizing radiation has many uses (e.g. measuring soil density and food pasteurization). The three types of ionizing radiation are: Alpha Beta Gamma

Time

Obviously, the less time spent exposed to a radioactive source, the less exposure there is. Keep in mind that exposures to radiation are additive in their effect. Federal limits for radiation exposure are expressed as the total dose received in a given unit of time.

Sources of Radiation Exposure

On a daily basis, the human body must deal with these exposures. At a properly monitored worksite, the occupational exposure that workers could receive is but a small portion of the exposure with which the body is already successfully dealing. Any release of radioactive material is a potential source of radiation exposure to the population. In addition to exposure from external sources, radiation exposure can occur internally by ingesting, inhaling, injecting, or absorbing radioactive materials. Both external and internal sources can irradiate the whole body or a portion of the body. The amount of radiation exposure is usually expressed in a unit called the millirem (mrem). In the United States, the average person is exposed to an effective dose equivalent of approximately 360 mrem (whole-body exposure) per year from all sources (NCRP Report No. 93).

Radioactive Decay

One source of radiation is the nuclei of unstable atoms. For these radioactive atoms (also referred to as radionuclides or radioisotopes) to become more stable, the nuclei eject or emit subatomic particles and high-energy photons (gamma rays). Unstable isotopes of radium, radon, uranium, and thorium, for example, exist naturally. Others are continually being made naturally or by human activities such as the splitting of atoms in a nuclear reactor. Either way, they release ionizing radiation. This decaying is caused by instability within the nucleus of the material.

Radiation Dosage and Units

Radiation doses are measured using standard radiation units. These units are: the Roentgen (R), rad (Radiation Absorbed Dose), and rem (Roentgen Equivalent Man). The Roentgen is defined only in terms of the ionizing effect on air and applies only to X-rays and gamma rays. It does not relate to the effect of radiation on the human body. The rad measures the absorbed dose (i.e., the amount of ionizing radiation (any type) absorbed into a material). The rad does not take into account the potential effects that different types of radiation have on the body. The rem is the most commonly used unit of measure and is used for dose equivalence. It takes into account the difference in the potential human biological effects produced by different types of radiation.

Radiation Types

Radiation is categorized as either ionizing or non-ionizing. Both are energy waves (ionizing radiation can also exist as particles); nevertheless, non-ionizing radiation contains less energy. The major types of radiation emitted as a result of spontaneous decay are alpha and beta particles, and gamma rays. X-rays, another major type of radiation, arise from processes outside of the nucleus.

Dose Rates

Radiation units include a time factor, and are commonly referred to as dose rates. These can be expressed as follows: R/hr or mR/hr (mR/hr is 1/1000th of the unit R/hr) Rad/hr or mrad/hr Rem/hr or mrem/hr

Radioactive Contamination

Radioactive contamination can be in the form of any of the three states of matter: Solid Liquid Gas Solid contamination is usually in the form of very small particles such as dirt or dust. These are most commonly found on the floor, ground, and other surfaces. Liquids can be contaminated with suspended or dissolved radioactive solids. Radioactive gases produced in some processes have the potential for leaking via ruptures or failures in containment systems and storage vessels. Radioactive contamination may be fixed or transferable/smearable.

Radiation Exposure

Radiosensitivity explains how a given cell is sensitive to radiation damage. Scientists have found that the faster a cell reproduces the more sensitive it is to radiation. The following cells are considered to be the most radiosensitive because of their reproductive rate: Blood and blood-producing organs Reproductive cells (sperm/egg) Cells of the unborn child Immature white blood cells Digestive tract cells Nerve, muscle and bone cells reproduce slowly and are considered the least radiosensitive. Of course, radiation affects each person differently depending on such factors as age, medical history, and physical and mental condition. As with chemical exposure, the effect of radiation exposure may be acute or chronic.

Shielding

Shielding places protective materials between the worker and the source, for example, walls, barriers, or protective clothing. Recall that no protective clothing shields against gamma radiation. The protective clothing discussed later in this course is for protection against chemicals - not radiation. Note: Neutron particles are less common than Alpha and Beta particles and are stopped most effectively by materials rich in Hydrogen, such as water, though concrete can be used

Beta Particles

Stopped by a layer of clothing or by a few millimeters of a substance such as aluminum. radiation presents a health hazard to human skin, eyes, and internal organs if ingested or inhaled. The cornea of the eye is especially vulnerable.

Gamma Rays

Stopped by several feet of concrete or a few inches of lead. Most dangerous

Distance

The distance can greatly reduce the amount of exposure. The farther from the source, the exposure will be less. Staying away from a radiation source, even a number of feet, will greatly reduce worker exposure.

Comparison of Radiation Health Risk

The following table compares the estimated loss of life expectancy due to radiation as compared to other health risks.

Non-Ionizing Radiation

This includes radiant heat, radio waves, ultraviolet radiation, and light. Waste site sources of non-ionizing radiation (Microwaves) include welding (which emits strong visible light and ultraviolet radiation) and laser instruments (which are used for measuring and leveling). Radiation emitting equipment should be used with proper precautions. Ionizing radiation has sufficient energy to remove electrons from atoms. In this lesson, it will simply be referred to as radiation.

Transferable/Smerable

Transferable/smearable contamination, on the other hand, is easily removed; any object that makes contact with it will in turn become contaminated. Clean-up activities where radioactive dust or dirt is present can lead to airborne contamination due to the mechanical action of sweeping or bagging activities. Examples of transferable contamination include: Surface contamination, which can be spread by contact Airborne contamination, which can be spread by grinding or burning, by air currents, and by evaporation Hot particles, which are small pieces of radioactive material with a very high radioactivity level. Hot particles can be especially hazardous to the skin or the extremities due to their short range and the intensity of the radiation emitted.

Introduction

Unlike many of the other hazards present on a hazardous waste site, detection of radiation is solely dependent on monitoring by instrument. Although not commonly considered the primary hazard on most waste sites, radioactive materials may be present in drums, including lab packs (pre-packaged materials that are being exposed of in a larger container), in either solid or liquid form. Waste from hospitals and research facilities in particular, should be suspected of containing ionizing radiation. In order to avoid exposure, it is important that workers realize the precautions that must be taken when dealing with radiological waste or sources.

Radiation Dosage

When we talk in terms of dosage in radiation, we use the same terms found in toxicology i.e. amount of exposure times the duration of exposure (quantity x time). We also classify radiation doses as acute or chronic.

Alpha Particles

stopped by a sheet of paper