DOE-HDBK-1141-2001 Module 8-12, Radiological Assessor Training - Student's Guide Module 8-12

Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–1 I. Introduction The guidance in DOE-STD-1128-98, Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities, should be reviewed in detail prior to conducting an assessment of plutonium facilities. The following is a brief overview of the radiological aspects of plutonium. II. Background Plutonium was first synthesized in the winter of 1940- 41 by a team of scientists at the University of California. Its potential use in weapons was quickly identified, and much of the effort of the Manhattan Project was in the production of sizable quantities of plutonium. Other uses for plutonium include use as: • Reactor fuel • Heat sources in thermoelectric generators to power satellites • Components in portable neutron sources Plutonium is a silvery-white metal that readily oxidizes to a dull gray color. It can be found in a variety of physical and chemical forms. Several of the chemical forms (including the pure metal) are pyrophoric, so care must be exercised in handling the material. Because of the pyrophoric nature of plutonium and its alloys, the preferred form for storing, shipping, and handling is as plutonium oxide. III. Radiological properties of plutonium A. Isotopes There are 15 isotopes of plutonium, all radioactive, beginning with Plutonium-232 and ending with Plutonium-246. The radioisotopes of primary interest are Plutonium-238, Plutonium- 239, and Plutonium-240, all of which are primarily alpha-emitters. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–2 1. Plutonium-238 (half-life = 87.7 yrs) is most commonly used as a heat source in thermoelectric generators. Because of its heat production, care must be taken in handling gram or larger quantities, as it could melt plastic or ignite other materials. 2. Plutonium-239 (half-life = 24,000 yrs) is the primary component of plutonium reactor fuel (>85%) and weapons grade plutonium (>90%), with Plutonium-240 (half-life = 6,560 yrs) constituting most of the remainder in both cases. 3. Plutonium radioisotopes emit relatively few high-energy gamma rays, so kilogram quantities can often be processed without serious gamma dose problems. However, small amounts of some radioisotopes or decay products can increase external dose. For example, Plutonium-241 decays by beta emission to Americium-241, which emits a 60- keV gamma ray. This can be a significant source of dose to hands in glove boxes. 4. Neutron dose rates from spontaneous fission and from alpha-neutron reactions with light elements may be significant (e.g., 1 kg of Pu-F4 (Pu-238) would have a contact neutron dose equivalent rate of 4800 rem/hr). B. Biological effects of internally deposited plutonium The primary hazards from the most common chemical form of plutonium (PuO2) are inhalation and ingestion. This chemical form is relatively insoluble. Therefore, uptake through the gastroin- testinal (GI) system following an ingestion is small. Inhaled plutonium can remain in the lungs for a considerable time before being removed through the lymph system. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–3 Plutonium is difficult to remove from the body. The primary method is through the administration of chelating agents as soon after the intake as possible. Trained medical personnel are needed to administer chelating agents.

The plutonium that enters the systemic system is mostly translocated to the liver and the bone (as is discussed in the following section). Accordingly, development of cancer in these organs and in the lungs are of particular interest in evaluating long-term effects from intakes of plutonium. C. Survey techniques A radiation protection program in a plutonium facility shall ensure the detection of all types of radiation (i.e., alpha, beta, gamma, x-ray, and neutron) over large energy ranges. Alpha- sensitive instruments are necessary for most contamination control surveys. Continuous air monitors (CAMs), sample extraction lines that go to CAMs, and continuous radiation dose monitors should be placed outside the glove boxes and hoods. Neutron surveys become important when processing tens of grams of Plutonium-238 or hundreds of grams of mixed isotopes of plutonium, particularly compounds (i.e., PuO2, PuF4). The neutron survey is important in instances where photon shields, such as leaded glass, are used. Such shields normally stop all of the charged particles, most of the low-energy photons, and essentially none of the neutrons. Under these circumstances, neutron radiation is likely to be the major contributor to whole body dose. Exposure rate surveys are normally conducted with photon-sensitive instruments with known Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–4 energy responses for photons with energies ≥ 10 keV. Monitoring practices include, but are not limited to, the following: • Contamination surveys of the workplace • Release surveys • External exposure rate surveys • Airborne radioactivity surveys (both real time (CAMs) and historical (fixed air head)) • Routine surveillance by a Radiological Control Technician All workplaces shall be monitored for contamination levels on a regularly scheduled basis. The frequency of such surveys will depend on the potential for dispensability of the radioactive material. As a minimum, all gloves, work surfaces, floors, and equipment within the workplace should be surveyed. Airborne radioactivity surveys should be performed for: • Prompt detection of airborne contaminants for worker protection • Personnel dose assessment • Monitoring of trends within the workplace • Special studies Intakes In most plutonium facilities, the primary radiological hazard is the potential for internal intakes of plutonium. This hazard must be controlled by appropriate facility and equipment Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–5 design, contamination control procedures, and protective clothing/equipment. Plutonium transferred from the initial entry site is assumed to be translocated to the liver (45%) and the bone (45). Retention half-life in the liver is 20 yrs and in the bone is 50 yrs, according to International Commission on Radiological Protection (ICRP) Publication 30. Control must be verified by a bioassay program. Urinalysis is the most common technique, but fecal analysis and in vivo monitoring may also be appropriate. DOE-STD-1121-99, Internal Dosimetry, provides technical guidance on internal dosimetry programs, including enhanced workplace monitoring for instances where there is a technology shortfall, such as for plutonium. This standard should be reviewed prior to conducting assessments of internal dosimetry programs. The standard also discusses appropriate

evaluation of bioassay results. D. Monitoring instruments Portable instruments should be calibrated in accordance with DOE G441.1-7, Portable Monitoring Instrument Calibration. DOE-STD- 1128-98 has additional guidance on monitoring instrumentation. Facilities that deal with unencapsulated plutonium should have continuously operating effluent monitors to determine whether or not plutonium is being released to the environment. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–6 Criticality alarm systems (gamma or neutron) should be provided in each area where an accidental criticality is possible. E. Sources of external dose External dose control for plutonium is primarily concerned with photon dose rates from handling plutonium in a glove box and from the neutron dose rate from some mixtures of plutonium. While significant high-energy penetrating photons are not commonly associated with plutonium, low- energy photons (x- and gamma-rays) can create significant dose rate problems to extremities. This is particularly a concern when large amounts of Plutonium-238, Plutonium-241, or Americium-241 (from the decay of Plutonium-241) are present. Neutrons can also represent a potentially significant dose due to spontaneous fission (alpha, neutron) reactions or neutron induced fission. The neutron dose is largely determined by the radioisotope and other materials near the source. F. Control of external dose External dose control is accomplished with traditional dose reduction techniques: • Time (minimize) • Distance (maximize) • Shielding (use as needed) Other work practices, including good housekeeping and specialized tool and equipment design, can reduce external dose, as well. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–7 G. Techniques for internal dose control The confinement system is a series of physical barriers that, together with a ventilation system, minimizes the potential for release of radioactive material into work areas and the environment under normal and abnormal conditions, thereby minimizing internal dose. Generally, three confinement systems are used to achieve the confinement system objectives at plutonium handling facilities. They consist of the following: • Primary confinement is provided by piping, tanks, glove boxes, encapsulating material, and the like, and any off-gas system that controls effluent from within the primary confinement. It provides confinement of the area immediately surrounding the hazardous material. • Secondary confinement is provided by the walls, floor, roof, and associated ventilation exhaust systems of the cell or enclosure surrounding the process material or equipment. Except in the case of glove box operations, the area inside this barrier is usually unoccupied; it provides protection for operating personnel. • Tertiary confinement is provided by the walls, floor, roof, and associated ventilation exhaust system of the facility. It provides a final barrier against release of hazardous material to the environment. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–8 Different devices may be used to confine and control radioactive material. The selection of the appropriate device will depend on the quantity of material, its form, and the operations to be performed. Fume hoods may be used for some operations

with plutonium, depending on the quantity and dispersability of the material. In general, plutonium fume hood operations shall be limited to wet chemistry processes and less than 100 mg of plutonium. Higher levels of plutonium are generally handled in glove boxes. Care should be taken in the design of the glove box to ensure confinement of the material and any fire. Ventilation may also be employed to confine plutonium, although it usually is used in conjunction with other measures. H. Personnel protection Workers in plutonium facilities need to be appropriately trained on the hazards. DOE has developed DOE/EH-0425, Plutonium Facilities Training. This document provides DOE's guidance on expectations for training of plutonium workers. The use of personal air sampling programs should be considered to monitor individual workers for exposure to airborne plutonium. Section 4.4.4 of DOE-STD-1121-98, Internal Dosimetry, discusses use of breathing zone or personal air monitoring when there is a technology shortfall (i.e., the derived investigation level is less than the minimum detectable activity). Technology shortfalls are common for routine plutonium bioassay programs. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–9 In addition, DOE has issued guidance on use of air monitoring results when there is a technology shortfall in Radiological Control Technical Position (RCTP) 2001-01, Questions and Answers Concerning Acceptable Approaches to Implementing Bioassay Program Requirements. In part, RCTP 2001-01 states that, when there is a technology shortfall for bioassay and air monitoring results indicate exposures greater than 100 millirem in a year are likely, one should assess dose based on the air monitoring results. As a minimum, personnel who perform operations in controlled areas should wear coveralls and shoe covers. For inspections or visits, lab coats and shoe covers may be permissible. When contaminated wet areas are to be entered, water- repellent (plastic or rubber) clothing shall be worn. No personal outer clothing should be permitted under coveralls. Hands should be protected by a minimum of two barriers; for example, at least one pair of surgeon’s gloves and one pair of rubber gloves should be worn. Protective clothing should be removed at the step- off pad, and personnel monitoring for contamination shall be performed. Respiratory protection equipment shall be readily available. Respiratory protection equipment should be used for all bag-out operations, bag and glove changes, and any situation involving a potential or actual breach of confinement. Protection, in the form of air-purifying or atmosphere-supplying respirators, shall be used whenever concentrations of radionuclides in the air are likely to exceed the applicable DACs. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 8–10 I. Inventory control and accountability requirements Real-time or near real-time accountability systems should be incorporated if possible. J. Criticality safety considerations Criticality alarm systems (gamma or neutron) shall be provided in each area where an accidental criticality is possible. Criticality safety requirements may include: ANSI/ANS 8.3-1986, Criticality Accident Alarm Systems; ANSI/ANS 8.1-1983, Nuclear Criticality Safety in Operations with Fissionable Materials Outside Reactors; and ANSI/ANS 8.19-1984, ANS Administrative Procedures for Nuclear Criticality.

It is important to review site requirements documents prior to conducting the assessment. All DOE facilities that possess sufficient quantities and kinds of fissile material to potentially constitute a critical mass shall provide nuclear accident dosimetry. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 9–1 I. Introduction 10 CFR Part 835.501(d) requires written authorizations to control entry and perform work in radiological areas, commensurate with the radiological hazards. DOE-STD-1098-99, Radiological Control, July 1999, Chapter 3, Part 2, provides guidance on DOE's expectations for such written authorizations. These written authorizations may take a variety of forms tailored to the work processes involved. Often, the form will be that of a Radiological Work Permit (RWP), discussed in detail below. II. Radiological Work Permits (RWPs) A. Purpose The RWP is designed to document the radiological conditions and associated controls in a work area. The RWP should be integrated with other work authorizations that address safety and health issues, such as those for industrial safety and hygiene, welding, and confined space entry. Articles 311 and 312 of DOE-STD-1098-99 provide guidance on preparing work control procedures consistent with the principles of Integrated Safety Management. This includes use of multidiciplinary teams to prepare work control procedures for tasks involving significant types of hazards and referring to DOE Order 440.1A, Worker Protection Management for DOE Federal and Contractor Employees. B. Typical RWP process 1. Requester submits an RWP request form. 2. Radiological Control Supervisor accepts form, collects additional job information as necessary, and assures that completion of Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 9–2 appropriate radiological surveys to be performed in the work area. 3. Radiological Control Technicians, or other appropriately trained and authorized personnel, perform surveys, analyze samples, and report results. 4. RWP controls are established based on the results of the surveys. 5. Radiological Control personnel, in consultation with relevant technical staff, complete, distribute and implement the RWP. 6. Radiological Workers and Radiological Control personnel review completed RWP, prior to start of job, during pre-job briefs, and/or ALARA reviews. 5. Radiological Worker/Supervisor advises Radiological Control personnel when job is complete (so RWP can be terminated). 8. Radiological Control personnel maintain surveys and RWP documentation. C. Types of RWPs There are two basic types of Radiological Work Permits: • Job-specific RWP • General RWP The job-specific permit is used for jobs which present a greater potential for significant radiation dose, airborne radioactivity, or spread of contamination, and which involve “hands on” work. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 9–3 Examples of jobs that would likely require job- specific RWPs include those where work is: • Performed with detailed, specific, written work procedures, approved in advance by Radiological Control personnel • “Hands-on” work performed infrequently on radiological systems (e.g., valve replacement in process buildings) • Performed in areas in which the radiological conditions have no history of remaining stable

The general RWP typically is used for jobs with less potential for health physics concerns and for routine, repetitive jobs that do not involve “hands on” work. Examples of jobs that may be worked under a general RWP include: • Routine tours, inspections, inventories, valve lineups, equipment tagouts, surveys, and equipment operation. • Work routinely performed on nonradiological systems (e.g., fire protection systems in shut- down process buildings). • Routine operations involving radioactive material for which the radiological conditions have a history of remaining stable. Keep in mind that there may be a need for other (nonradiological) permits or authorizations to safely perform these jobs. For example permits may be needed to address nonradiological hazards, such as: electrical, confined space, asbestos, hazardous materials, respiratory protection, fire, heavy equipment and scaffolding. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 9–4 D. Time limits The job-specific RWP usually remains in effect only for the duration of the job (typically less than 30 days). The general RWP typically is approved for a period of time of one year or less. E. Elements of an RWP include: • Description of work (detailed) • Radiological conditions (contamination, airborne, radiation levels) in the work area • Dosimetry (TLD badge, self-reading dosimetry, special dosimetry) requirements • Requirements for a pre-job briefing, if necessary • Radiological Control Technician coverage (start of job, continuous, intermittent) • Training requirements to work in the area • Protective clothing requirements • Respiratory protection equipment requirements • Stay time requirements • Radiological conditions that may limit work or void the RWP • Special dose reduction (ALARA) or contamination reducing measures to be considered • Special personnel contamination monitoring requirements Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 9–5 • Work document number (if used) • Unique RWP identification number • Date of permit issue and expiration date • Signatures of Radiological Worker and supervisor (attesting to their understanding of RWP requirements and agreement to follow) and Radiological Control staff F. RWP Elements for Radiological Assessment The following are RWP program elements which may be reviewed as part of a radiological assessment: • RWPs appropriately required for activities and areas • Completeness of information on RWPs • Adequacy of radiological surveys to support RWP • Worker adherence to RWP requirements • RWP appropriately reviewed and approved • Adequacy of worker monitoring (TLDs, bioassay, air monitoring RCT coverage) specified on RWP • ALARA considerations included in RWP • RWP program implemented in accordance with written procedures Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Module 9–6 This page intentionally left blank. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 10–1 I. Introduction 10 CFR Part 835, Occupational Radiation Protection, specifies contamination control requirements in Subpart L. DOE G441.1-9, Radioactive Contamination Control Guide, provides guidance on meeting the requirements. Chapters 3 and 4 of DOE-STD-1098-99, Radiological Control, also provide guidance on meeting the requirements and additional information for implementing an effective contamination control program. All of these documents should be reviewed prior to conducting an assessment.

II. Contamination containment and temporary control measures Minimization of internal dose The minimization and control of internal dose should be conducted in accordance with the following hierarchy of controls: 1. Engineered controls, including containment of radioactive material at the source wherever applicable, should be the primary method of minimizing airborne radioactivity and internal dose to workers. Engineered controls are devices such as glove boxes, glove bags, portable filtration units, and containment tents. They should be used to prevent worker inhalation of radionuclides. Portable and fixed/permanent shielding using dense materials (lead) or portable plastic interlocking fluid filled containers are also engineered features, used to minimize external radiation dose. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 10–2 The use of these devices reduces the spread of contamination, cleanup time, and decontamination costs. These measures help maintain doses ALARA. In addition, they can reduce the need for respirators and the impact on work in nearby areas. Engineered controls should be used in accordance with technical instructions, proper training, and effective administrative controls Site-specific manuals should contain generic instructions on the design, controls, training, and use of engineered controls. 2. Administrative controls, including access restrictions and the use of specific work practices designed to minimize airborne contamination, should be used as the secondary method to minimize worker internal dose. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 10–3 3. Only when engineered and administrative controls have been applied and the potential for airborne radioactivity still exists, should personnel protective equipment, including use of respiratory protection, be considered. Chapter 3 of DOE-STD-1098-99 discusses: Access controls for Contamination Areas Controlling the spread of contamination Monitoring for contamination. Appendix 3 C, Contamination Control Practices, includes recommended selection of protective clothing, and a recommended sequence for donning and doffing. Use of respiratory protection should be considered under the following conditions: • Entry into posted Airborne Radioactivity Areas • During breach of contaminated systems or components • Work in areas or on equipment with removable contamination levels greater than 100 times the values in Table 2-2 of DOE-STD-1098-99 • During work on contaminated or activated surfaces with the potential to generate airborne radioactivity The selection of respiratory protection equipment should include consideration of worker safety, comfort, and efficiency. The use of positive pressure respiratory protection devices is recommended wherever practicable to alleviate fatigue and increase comfort. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 10–4 Respirators can provide adequate protection for workers in an airborne radioactivity environment, but engineered controls may be more practical. By using engineered controls instead of respirators, the worker is not subjected to the stresses created by wearing a respirator. It is more difficult to breath and communicate when wearing a respirator. Vision is impaired, and the respirator is not comfortable. Productivity can therefore be improved by using engineered features instead of respirators.

To minimize intakes of radioactive material by personnel, smoking, eating, or chewing shall not be permitted in Contamination, High Contamination, Airborne Radioactivity Areas, or Radiological Buffer Areas established for contamination control purposes. Contamination should be contained at its source. The principle is to prevent contamination spread from occurring. The most effective methods based on sound ALARA principles should be used. All controls should be documented and clearly controlled by RWPs. Respirators may be appropriate for simple, straightforward jobs. In specific situations the use of respiratory protection may be contraindicated due to physical limitations or the potential for significantly increased external dose. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 10–5 In such situations, written authorization should be obtained from the line organization manager and the Radiological Control Manager prior to incurring internal dose. Specific justification of the need to accept the dose, including a description of measures taken to mitigate the intake of airborne radioactivity, should be documented as part of the radiological work documentation. The use of personal air sampling programs should be considered to monitor individual workers for exposure to airborne radioactive material, especially when the use of respiratory protection is contraindicated. This is particularly important when there is a bioassay program technology shortfall (i.e., the derived investigation level is less than the minimum detectable activity). Section 4.4.4 of DOE-STD-1121-98, Internal Dosimetry, discusses use of breathing zone or personal air monitoring. In addition, DOE has issued guidance on use of air monitoring results when there is a technology shortfall in Radiological Control Technical Position (RCTP) 2001-01, Questions and Answers Concerning Acceptable Approaches to Implementing Bioassay Program Requirements. In part, RCTP 2001-01 states that, when there is a technology shortfall for bioassay and air monitoring results indicate exposures greater than 100 millirem in a year are likely, one should assess dose based on the air monitoring results. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Module 10–6 This page intentionally left blank. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Module 11-1 Radiological Work Site Mockup Demonstration Checklist for Module 11 The exercise is a mock-up demonstration that is performed by the instructors to give the participants an opportunity to assess and identify poor radiological work practices. You will be instructed to identify and make notes of the poor radiological practices during the demonstration. Observe the demonstration and watch for poor radiological work practices. Write down poor work practices in your student’s guide for discussion after demonstration. After the demonstration: • Identify poor radiological practices • Make recommendations for improvement Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Module 11-2 Notes Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–1 I. Introduction 10 CFR Part 835, Occupational Radiation Protection, includes provisions for exposure to ionizing radiation from DOE activities. Included in the 10 CFR 835 definition of a radiological worker is "operation of radiation producing devices". 10 CFR 835 also specifies requirements for sealed radioactive sources.

II. DOE Guidance DOE G441.1-5, Radiation-Generating Devices Guide, provides guidance on DOE's expectations for controlling exposure from radiation generating devices (RGD). The IG includes a definition of a RGD as "a collective term for devices which produce ionizing radiation including, certain sealed radioactive sources, small particle accelerators used for single purpose applications which produce ionizing radiation (e.g., radiography), and electron generating devices that produce x-rays incidentally." For sealed radioactive sources, refer to DOE G441.1-13, Sealed Radioactive Source Accountability and Control Guide. Article 365 of DOE-STD-1098-99, Radiological Control, provides additional guidance, including the use of ANSI N43.3, ANSI N43.2, and 10 CFR Part 34 for meeting its requirements covering RGDs. DOE HDBK-1109-97, Radiological Safety Training for Radiation-Producing (X-Ray) Devices, provides guidance on DOE's expectations for radiation safety training for individuals using RGDs. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–2 III. X-ray machines A. Components X-ray devices have been in existence for about 100 years. Although there are many different designs of x-ray machines, they all have the same basic components. These include a source of electrons, an electrical potential difference to accelerate the electrons, and an anode, or target for the accelerated electrons to strike. Usually, the source of electrons in an x-ray machine is a thin wire filament from which electrons are emitted when it is heated by a large electrical current. Controlling the current through the filament, then, becomes a way to control the number of electrons available for acceleration. The electrical potential difference between the cathode (filament) and the anode (or target) is the force that accelerates the electrons. The larger the potential difference, the more kinetic energy the electrons will acquire. The potential difference is measured in units of kilovolts (kV). The energy of the electrons is measured in units of kilo electron volts (keV), with one electron volt being the amount of energy required to move one electron through a potential difference of one volt. The accelerated electrons then strike the anode (or target). The target may consist of various materials, depending on the purpose and design of the x-ray tube. X-ray production is most efficient in high atomic number targets, like tungsten. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–3 When electrons strike and excite target atoms, the kinetic energy of the electrons is deposited in the target as heat. When electrons ionize target atoms, characteristic x-rays will be emitted as electrons from outer shells fill vacancies created by ejected electrons. B. X-ray energy spectrum The energy of the x-ray photons coming out of the x-ray machine is of interest to the users of the machine. The typical energy spectrum from an x-ray machine consists of the characteristic x- rays from the target, which have discrete energies, and the bremsstrahlung photons which have a whole range of energies, the maximum energy depending on the potential difference across the tube. For a typical x-ray machine, the bremsstrahlung photons far outnumber the characteristic x-rays. C. Design features

The cathode and anode of the x-ray tube are enclosed in an evacuated glass tube or envelope. The vacuum is necessary to ensure that the accelerated electrons will interact in the target, and not with gas molecules. The x-rays are produced in all directions in the target. However, only x-rays directed toward the exit port, or window, will comprise the useful beam. Several devices are used to control the size of the useful x-ray beam. A lead diaphragm is a sheet of lead with a hole in it. It is placed near the exit port, and restricts the size of the useful beam by absorbing x-rays that don't pass through the hole. The size of the beam is not adjustable with this type of device unless another diaphragm with a different-size opening is used. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–4 For some operations, the size of the useful beam must be adjusted by the operator. An adjustable collimator is essentially a set of movable lead sheets. Two sheets restrict the width of the beam, and two sheets restrict the length of the beam. The operator can then adjust the size of the beam to any desired combination of length and width. Often, the lowest energy x-rays are not desired in the beam. The low energy x-rays can be filtered out by placing absorbing material (called filters) in the path of the beam. Aluminum or copper is commonly used, depending on the energy of the machine. The addition of filters increases the average energy of the beam, since the lower energy x-rays are removed from the beam when they are absorbed by the filters. D. Common uses and hazards X-ray machines are most commonly used for radiography, or the examination or inspection of the structure of materials by non-destructive means. X-ray machines used in medicine are fairly standardized in appearance, and in the way they are installed. That is not true of x-ray machines used for industrial applications. X-ray machines may be fixed installations, mobile units, or completely enclosed cabinet systems. The cabinet x-ray systems are commonly used for security applications (e.g., baggage inspection units). The major hazard from x-ray machines is the external dose hazard to machine operators and other people in the vicinity. No one should ever be exposed to the primary (or useful) beam. Exposure to leakage radiation (from the housing) and scatter radiation should be reduced by appropriate controls. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–5 IV. Analytical x-ray machines A. Fluorescence analysis Characteristic x-rays that result from ionization of atoms can be used to identify atoms, since the characteristic x-rays will have energies that are unique to that element. This forms the basis for x-ray fluorescence spectroscopy. A sample to be analyzed is irradiated by a beam of high- intensity x-rays. The x-rays ionize atoms in the sample, which emit characteristic x-rays when the electron shell vacancies created by ionization are filled. The characteristic x-rays can be analyzed by determining their energy, or by determining their wavelength. Either way, the result leads to information about the elemental composition of the sample. These instruments are usually completely enclosed. Access doors are provided for changing samples, and the doors are equipped with interlocks to prevent access to the x-ray beam. The hazard is primarily an external dose hazard

to scattered radiation from the components and the sample, and is typically fairly low. B. X-ray diffraction When x-rays are scattered by a crystalline solid, they are scattered from the different atoms, but only in certain directions. This technique is used for crystal structure research. The primary beam and the diffracted beams are very small and well collimated. In some types of diffraction equipment, the sample cannot be enclosed in a structure. The primary beam is controlled by a shutter that opens and closes. The major hazard associated with diffraction Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–6 units is intense, localized exposure from the primary beam to the hands or eyes that can occur during sample changing or beam alignment procedures with the shutter inadvertently open. The primary beam is very small, but may have an intensity of up to 40,000 R/min. At this exposure rate, even short exposures of the hands and fingers could result in severe injury, and potential loss of fingers. V. Sealed gamma ray sources Sealed gamma ray sources are used for a variety of applications in industry. Gamma ray sources are the most common sealed source encountered, although others are used and are discussed later. Radiography is probably the most common use, and may be performed with the gamma rays from sealed sources of Cobalt-60, Cesium-137, or Iridium-192. Other uses of sealed gamma ray sources are thickness gauges (e.g., to determine the thickness of sheet metal), level gauges (e.g., to determine a fluid level in a container), and density gauges (e.g., to measure the geologic formation porosity during oil and mineral logging). The hazard from these sources is primarily an external dose hazard. The most common cause of overexposure incidents with gamma radiography sources results from radiographers failing to perform radiation surveys to verify that the gamma source is back in the shielded position. Also, if mechanical damage to the source encapsulation occurs, radioactive material contamination will be a hazard as well. VI. Other sealed sources Sealed sources of beta particles may be used as thickness gauges (e.g., measurement of dust on filter paper, or gauging thickness of thinner plastics). . Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–7 Neutron sources have a variety of applications and are commonly used in moisture gauges (e.g., determining moisture content in raw materials such as gravel, wood chips, etc.). The fast neutrons emitted by the source are moderated by the hydrogen atoms in the material being measured, and can then be detected with a neutron detector. Of course, the more moisture contained in the material, the more hydrogen atoms will be present. Neutron sources are also used to some extent for radiography of very dense materials like lead or steel, which otherwise would require very high energy photons to radiograph. Californium-252 emits neutrons after undergoing spontaneous fission, and therefore serves as a neutron source. Neutrons can also be produced fairly easily by nuclear reactions in certain materials such as beryllium. The primary hazard from beta and neutron sources is from the external radiation fields they generate. These sources would only become an internal hazard should the source rupture or leak and radioactive material subsequently is inhaled or ingested. An additional hazard of neutron activation exists around neutron sources.

10 CFR 835 Subpart M "Sealed Radioactive Source Control" establishes requirements for accountable sealed radioactive sources. Requirements include provisions for (at intervals not to exceed 6 months): inventory posting leak testing Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–8 VII. Other radiation-generating devices Other radiation-generating devices (RGDs) that may be encountered are small particle accelerators (<10 MeV) used for radiography, ion implantation, or the production of incidental photons or particles (neutron generators). Some RGDs produce radiation incidental to their primary purpose. Examples of devices that produce radiation incidentally are electron beam welders, electron microscopes, and pulse generators. VIII. Categorizing RGD installations The ANSI standards referenced earlier categorize RGD installations into the following categories for radiation safety purposes. A. Exempt shielded installations The RGD and all objects exposed to the source of radiation shall be within a permanent enclosure that, under all circumstances of use, possesses sufficient inherent shielding and prevents inadvertent entry to any part of the body. The exposure at any accessible region 5 cm from the outside surface of the enclosure shall not exceed 0.5 mrem in any one hour. B. Shielded installation The RGD and all objects exposed to the source are within a permanent enclosure from which persons are excluded during the irradiation. Some of the requirements for shielded installations include mandatory interlocks, audible and visual warning devices, a "crash" button, and posting of warning signs. Skyshine is the term used to describe radiation emerging more or less vertically from a shielded enclosure, which then scatters from air molecules to produce radiation at some distance from the source. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Notes Module 12–9 C. Unattended installation The RGD is installed in a single-purpose shielded enclosure, and the design shall ensure that individuals are not exposed to doses exceeding 100 mrem in a year. D. Open installation Open installations must be conspicuously posted, and have a conspicuously defined perimeter. The perimeter must delimit the area in which the exposure can exceed 5 mrem in any one hour. The operational staff shall provide constant surveillance. Other requirements include use of survey meters, personnel dosimetry, and temporary shielding. Radiological Assessor Training DOE-HDBK-1141-2001 Student’s Guide Module 12–10 This page intentionally left blank. Part 4 - Student's Guide