PROTECTION AGAINST SEALED

SOURCES

SEALED SOURCE RADIOACTIVE MATERIAL Sealed sources are radioactive

materials encased or "sealed" inside metal or plastic and can take many different forms, sizes and shapes. All forms share some type of encapsulation that prevents their radioactive contents from leaking or dispersing, barring tampering or a severe accident. In some forms, the radioactive material is an inherent part of the source and cannot be separated.

Almost all "sealed sources" can be handled without concern that the radioactive material will rub-off or be dispersed onto hands or clothing. There is, however, reason to be concerned about exposure to the radiation emitted from the sealed source. Sealed sources are not a significant contamination hazard under normal conditions; however, they may present an external exposure hazard.

SEALED SOURCE FORMS INCLUDE:

Plated sources In this form, the radioactive

material coats a disk or planchette. This coating may be covered, depending upon the type of radiation, by mylar, aluminum, steel,

or plastic.

CapsulesIn this form, a capsule usually made of metal surrounds the radioactive material. These sources are often placed onto the end of metal or plastic handling rods. Another example of a capsule is when a mixture of radioactive compounds is placed into a container and welded or sealed closed.

Activated metal In this form, a metal wire or foil has

been exposed to a neutron flux to irradiate the metal and create a radioactive isotope from the original material. This form of sealed source may have a plastic or epoxy coating to protect the activated metal. In some instances, however, the metal is not protected.

Many commonly used laboratory devices also contain sealed sources, such as gas chromatographs with electron capture detectors, liquid scintillation detectors, and static eliminators.

SAFE USE OF SEALED SOURCES Sealed sources present an external radiation

hazard as opposed to a contamination hazard. Sealed sources can emit any type of ionizing radiation, including alpha particles, beta particles, gamma rays, x-rays, or neutrons.

1. Do not touch electroplated sources, as this may result in the removal of the active material.

2. Wear gloves when working with a plated or deposited source.

3. Monitor hands and fingers after handling a plated or deposited source.

4. Do not use handling tools in such a way as to penetrate the surface of the source.

5. Storage containers should not have material that abrades the surface of the electroplated sources.

6. Sealed Sources shall not be opened under any circumstances!

7. Only authorized individuals shall perform the repair and cleaning of sources. The safety and handling precautions furnished by the manufacturer shall be maintained in a location that is readily available to all workers and followed.

8. Storage containers must be properly labeled.

EQUIPMENT CONTAINING SEALED RADIOACTIVE SOURCES The equipment which may contain

sources of interest in this publication varies widely in construction and application. Descriptions of some of the main types of equipment are provided below

1 .MEDICAL APPLICATIONS

1.1. Brachytheraphy (therapy at a short distance) is a term that is used to describe the interstitial application of radioactive sources by placing them directly in the tumour (e.g. breast, prostate), in moulds (e.g. skin, rectum) or in special applicators (e.g. vagina, cervix). Originally, brachytherapy techniques involved the use of individual needles or manual afterloading. Relatively low activity sources were used in these applications. Historically, 226Ra encapsulated in platinum in either needles or tubes of a few mm in diameter and up to 5 cm in length was used (Fig).

226RA APPLICATOR.

Emission of alpha particles (helium nucleus) leads to pressure buildup in a sealed capsule. A buildup of pressure may eventually damage the encapsulation, resulting in a release of radioactivity. Remote afterloading techniques were developed in the 1970s. 226Ra was replaced mainly by 137Cs and 60Co and more recently by 192Ir and 252Cf. These techniques involve the use of machines which can contain a large number of relatively low activity sources, but which taken together represent a significant inventory stored in a single, relatively transportable container. An example of brachytherapy equipment is shown in Fig. 3. This type of equipment typically contains activities of up to 185 GBq (usually of 137Cs). Remote afterloading equipment is used to arrange sources into an appropriate configuration and to transfer them either pneumatically or on the end of a cable into the patient applicator.

FIG. 3. TYPICAL BRACHYTHERAPY MACHINE

1.2 .TELETHERAPY The other principal medical application of

sealed sources is teletherapy, where a large source (typically 60Co but possibly 137Cs) of several hundred TBq is used, external to the body, to irradiate a tumour. 60Co teletherapy heads can contain up to 500 TBq of activity.. An example of a 60Co unit is shown in Fig. 4.

FIG. 4. TYPICAL TELETHERAPY MACHINE

1.3 .OTHER MEDICAL APPLICATIONS Sealed radioactive sources are also used

in medicine for bone densitometry (241Am, 153Gd and 125I), for whole blood irradiation (137Co, 60Co) and as gamma radiosurgery knives (60Co).

2 .INDUSTRIAL APPLICATIONS In heavy industries such as steel

foundries or fabrication, portable, mobile or fixed radiographic equipment incorporating various radionuclides may be installed in purpose built enclosures. Mobile or fixed installations incorporate heavier shielding than portable source housing

Typical industrial applications with their main isotopes are shown below:

(a) Industrial radiography: 6oCo, 192Ir, 75Se, 170Tm, 169Yb, 137Cs (historical); 241Am/Be, 252Cf (neutron radio-graphy);

(b) Moisture detectors: 241Am/Be, 137Cs, 226Ra/Be, 252Cf;

(c) Well logging: 241Am/Be, 137Cs; (d) Gauges: 137Cs, 6oCo, 241Am, 85Kr,

90Sr(+90Y), 32P, 147Pm;

(e) Static eliminators: 241Am, 210Po, 226Ra;

(f) Lightning rods: 241Am, 85Kr, 226Ra (historical); (g) Dredgers: 60Co

(h) X ray fluorescence analysis: 55Fe, 109Cd, 238Pu, 241Am, 57Co;

(i) Calibration: 60Co, 137Cs; (j) Smoke detectors: 241Am, 239Pu.

RADIOGRAPHY Radiography is the use of ionizing

electromagnetic radiation such as X-rays to view objects. Although not technically radiographic techniques, imaging modalities such as PET and MRI are sometimes grouped in radiography because the radiology department of hospitals handle all forms of imaging. Treatment using radiation is known as radiotherapy.

MRI

(POSITRON EMISSION TOMOGRAPHY )PET

RADIOGRAPHY OF KNEE IN MODERN X-RAY MACHINE

X-RAY RADIOGRAPHS

HISTORY Radiography started in 1895 with the

discovery of X-rays , a type of electromagnetic radiation. Soon these found various applications, from helping to find shoes that fit, to the more lasting medical uses.

X-rays were put to diagnostic use very early, before the dangers of ionizing radiation were discovered. Initially, many groups of staff conducted radiography in hospitals, including physicists, photographers, doctors, nurses, and engineers. The medical specialty of radiology grew up around the new technology, and this lasted many years. When new diagnostic tests involving X-rays were developed, it was natural for the radiographers to be trained and adopt this new technology. This happened first with fluoroscopy, computed tomography (1960s), and mammography

Ultrasound (1970s) and magnetic resonance imaging (1980s) was added to the list of skills used by radiographers because they are also medical imaging, but these disciplines do not use ionizing radiation or X-rays.

DIAGNOSTIC RADIOGRAPHY

Diagnostic radiography involves the use of both ionizing radiation and non-ionizing radiation to create images for medical diagnoses. The predominant test is still the X-ray. X-rays are the second most commonly used medical tests, after laboratory tests. This application is known as diagnostic radiography.

Since the body is made up of various substances with differing densities, X-rays can be used to reveal the internal structure of the body on film by highlighting these differences using attenuation, or the absorption of X-ray photons by the denser substances (like calcium-rich bones). Medical diagnostic radiography is undertaken by a specially trained professional called a diagnostic radiographer in the UK, or a radiologic technologist in the USA.

PROJECTION RADIOGRAPHY The creation of images by exposing an object to X-

rays or other high-energy forms of electromagnetic radiation and capturing the resulting remnant beam (or "shadow") as a latent image is known as "projection radiography." The "shadow" may be converted to light using a fluorescent screen, which is then captured on photographic film, it may be captured by a phosphor screen to be "read" later by a laser (CR), or it may directly activate a matrix of solid-state detectors. Bone and some organs (such as lungs) especially lend themselves to projection radiography. It is a relatively low-cost investigation with a high diagnostic yield.

Projection radiography uses X-rays in different amounts and strengths depending on what body part is being imaged:

Hard tissues such as bone require a relatively high energy photon source, and typically a tungsten anode is used with a high voltage (50-150 kVp) on a 3-phase or high-frequency machine to generate braking radiation. Bony tissue and metals are denser than the surrounding tissue, and thus by absorbing more of the X-ray photons they prevent the film from getting exposed as much. Wherever dense tissue absorbs or stops the X-rays, the resulting X-ray film is unexposed, and appears translucent blue, whereas the black parts of the film represent lower-density tissues such as fat, skin, and internal organs, which could not stop the X-rays. This is usually used to see bony fractures, foreign objects (such as ingested coins), and used for finding bony pathology such as osteoarthritis, infection (osteomyelitis), cancer (osteosarcoma), as well as growth studies (leg length, achondroplasia, scoliosis, etc.).

Soft tissues are seen with the same machine as for hard tissues, but a "softer" or less-penetrating X-ray beam is used. Tissues commonly imaged include the lungs and heart shadow in a chest X-ray, the air pattern of the bowel in abdominal X-rays, the soft tissues of the neck, the orbits by a skull X-ray before an MRI to check for radiopaque foreign bodies (especially metal), and of course the soft tissue shadows in X-rays of bony injuries are looked at by the radiologist for signs of hidden trauma (for example, the famous "fat pad" sign on a fractured elbow).

Dental radiography uses a small radiation dose with high penetration to view teeth, which are relatively dense. A dentist may examine a painful tooth and gum using X-ray equipment. The machines used are typically single-phase pulsating DC, the oldest and simplest sort. Dental technicians or the dentist may run these machines—radiologic technologists are not required by law to be present.

Mammography is an X-ray examination of breasts and other soft tissues. This has been used mostly on women to screen for breast cancer, but is also used to view male breasts, and used in conjunction with a radiologist or a surgeon to localise suspicious tissues before a biopsy or a lumpectomy. Breast implants designed to enlarge the breasts reduce the viewing ability of mammography, and require more time for imaging as more views need to be taken. This is because the material used in the implant is very dense compared to breast tissue, and looks white (clear) on the film. The radiation used for mammography tends to be softer (has a lower photon energy) than that used for the harder tissues. Often a tube with a molybdenum anode is used with about 30 000 volts (30 kV), giving a range of X-ray energies of about 15-30 keV. Many of these photons are "characteristic radiation" of a specific energy determined by the atomic structure of the target material (Mo-K radiation).

Other modalities are used in radiography when traditional projection X-ray cannot image what doctors want to see. Below are other modalities included within radiography; they are only summaries and more specific information can be viewed by going to their individual pages

FLUOROSCOPY