Radiation monitoring, personal

BS3664 Film badges for personal radiation monitoring. 

Why would someone working around radioactive waste in a landfill use a radiation monitor instead of a watch to determine when the workday is over At what point would that person decide to stop working ... 

Silicon semiconductor detectors for nuclear radiation monitors of neutron rays have been developed by Kitaguchi et al. (1995,1996). These are diffused p-n junction-type devices with low leakage current coated on the surface of the B-containing sensor element. Neutrons were detected as recoil protons by interaction of the proton radiator and a-particles generated by the nuclear reaction °B (n, a) Li. The energy response of this radiation detector meets the standard recommendations and is suited as an area monitor and a personal dosimeter as well. 

Nuclear medicine facihties also represent a special hazard. Normally, nuclear injections use a short-hved isotope Tc with a halfhfe of a little over 6 hours. If the injection is in a large animal, such as a horse, the personnel exposure level can be substantial and workers should be provided with personal radiation monitors. Collection of the feces and urine may be required. In addition, the animal may not be released to a member of the pubhc until the exposure levels fall below the legal limits for unmonitored persons (more on this later). X-rays of animals also represent a special hazard since one cannot simply teU an animal to hold still. Often taking of x-rays will require a person to hold the animal stiU. Holders wUl often receive substantial levels of scattered x-ray radiation so this duty should be spread among a number of individuals. 

Figure 5.10 Film badge for personal radiation monitoring. The various areas shown on the front of the badge provide for information to be obtained about the radiation reaching the frlm. The open " area may be covered with a a very thin mylar film which will allow betas to be detected in that aaea. 

The TL dosimeters are mainly used for the measurement of low doses, thus these systems are mostly used in radiation therapy, personal dosimetry (Christensen et al. 1982), and environmental monitoring (Deplanque and Gesell 1982). The use of thermoluminescent dosimetry in radiation processing (ISO/ASTM 2002g) where the doses are high is of limited importance due to supralinearity, saturation effects, and radiation damage. Calcium fluoride... 

At all stages of medical care, the treatment of highly contaminated individuals will require special facilities or isolated facilities with the specif procedures that limit the spread of contamination and disposal of contaminated waste. For the deteetion of radioaetive eontam-ination, radiation equipment should be available, such as specialized radiation monitoring instruments, whole body counter, and iodine thyroid counter. Usually a radiation protection officer or health physicist performs the measurements. For the purpose of dose reeonstraction, different instruments and methods can be used, such as electronic paramagnetic resonance (EPR) spectrometry and cytogenetic dosimetry. Because of this, collection of various tissues (blood, hair, and teeth) and clothes of exposed persons should be organized. Provisions (plastic bags, labels, etc.) should be made in advance. 

Assistance may be provided in various ways. For some minor Incidents, only advice by telephone may be necessary. In some cases the Re onat Coordinating Office may arrange for assistance to be provided at the scene of the incident by knowledgeable persons who are located nearby. If the circumstances warrant, a radiological assistance team will be dispatched by the Regional Coordinating Office to the scene of the incident. For most incidents in which a team is dispatched, the response may be made by one or two individuals. However, for larger or more complex incidents the team may consist of several specialists. Teams may include Team Leader, Radiation Monitors, Medical Officer, Public Information Officer, and other specialists as required. 

Hi) Film dosimeter. This is perhaps the most widely used type of dosimeter. It uses the blackening of photographic film induced by ionizing radiations as its principle (see section on photographic methods). This dosimeter is mostly used for monitoring personal exj osure by... 

All radiation monitors and contamination monitors, both permanently installed and hand held, as well as personal dosimetry systems, should be periodically calibrated, tested and maintained according to a quality assurance programme in respect of ... 

In Chapter 5.4, optical ultraviolet radiation sensors are described, including UV-enhanced silicon-based pn diodes, detectors made from other wide band gap materials in crystalline or polycrystalline form, the latter being a new, less costly alternative. Other domestic applications are personal UV exposure dosimetry, surveillance of sun beds, flame scanning in gas and oil burners, fire alarm monitors and water sterilization equipment surveillance. 

Section 1 of the Report presents the quantities Hz and E and the relationship of each quantity to its corresponding radiation protection system. Section 2 describes the use of personal monitors for workers in the United States, including their calibration and how they are worn on individuals in various occupational settings. Section 3 discusses practical ways to use one or two personal monitors to obtain estimates of Hz and E. Section 4 provides the NCRP s... 

As a second example, consider a case in which the front of the body is irradiated by a nonuniform field of scattered radiation, the trunk is shielded by a protective apron on the front of the body, and the personal monitor value and tissue doses are as given in Table 1.3. The resulting values for He and E are 0.12 mSv and 0.05 mSv, respectively. In this case, the difference is caused primarily by the manner in which the remainder contribution is calculated (see Tables 1.1 and 1.2). Note also that a personal monitor located on the front at the neck outside and above the protective apron would have indicated a value of 1 mSv (see Table 1.3), which is a large overestimate of either He or . 

It is not practical in the work environment to measure the absorbed doses in the various organs and tissues necessary to compute He or E directly. Therefore, a number of quantitative relationships between He or E and various field or operational quantities have been developed and are available in the literature. The operational quantity named personal dose equivalent, HJ d), has been developed for the purpose of personal monitoring (ICRU, 1992), where d is the depth below a specified point on the body. For strongly-penetrating radiation, a depth of 10 mm is employed and the quantity is then specified as H iVS). The relationship between He or E and /fp(lO) is the most practical for use in determining He or E to workers for external exposure to low-LET radiation. 

The distance between the radiation source and the PMMA slab surface is large enough so that the radiation field approximates an aligned and expanded field (ICRU, 1992). An anterior to posterior radiation condition is simulated. The central ray of the radiation field is perpendicular to the center of the PMMA slab. Multiple personal monitors are irradiated to obtain information on accuracy and precision. Irradiation of the personal monitors using fields incident at nonperpendicular angles is used to examine differences from the response to the perpendicular irradiation. 

The calibration procedure provides a body of data about how the personal monitor responds to the various irradiation conditions. These data are converted into formulas or algorithms that generate a value for Hp(lO) for the irradiation conditions assumed in the workplace. The formulas or algorithms apply to the personal monitor system calibrated, and do not change unless there is a modification in the design or types of radiation detectors used in the personal monitor. An example of such a body of data for a particular monitoring device is provided by Ehrlich and Soodprasert (1994). 

Complete calibration of the personal monitors using the NIST secondary standards for all irradiation conditions is not done routinely. More often, the physical response of the components of the personal monitor is compared to the response of other calibrated radiation detection instruments to assess whether the personal monitor components respond the same as during complete calibration. This comparative calibration usually involves fewer radiation fields. 

The distance between the backscatter medium or body and the radiation detector elements in the holder of a personal monitor can also influence the response of the personal monitors. The backscatter fluence and resultant air kerma at the surface of a backscatter medium can decrease by a factor of two at a separation distance of 1 cm. Therefore, significant uncertainties can arise when the separation between personal monitor and the body surface varies during irradiation or differs from that used... 

Current federal regulations limit the deep dose equivalent based on that part of the body likely to receive the highest exposure. If personal monitor results are not available or the personal monitor was not located at the position of highest exposure, the regulations allow the substitution of surveys and other radiation measurements (NRC, 1991). These requirements strongly influence the current practices in the United States for the number and location of personal monitors on individuals. 

In addition, multiple personal monitors are often used for situations in which a worker is exposed to a nonuniform radiation field, in an attempt to assess the region of the body receiving the highest deep dose equivalent. Approaches to the use of multiple personal monitors vary widely, and the number used and their locations depend on the particular work activity. For example, during work inside a steam generator, where the radiation fields are potentially isotropic, a total of 12 to 14 personal monitors may be placed at specific locations on both the front and the back of the body, and on top of the head. In other work situations, when the radiation field may be relatively directional but variable (e.g., during control-rod drive maintenance in a boiling-water reactor) the individual may wear all of the personal monitors at locations on the front of the body. 

Use of Personal Dose Equivalent for a Strongly-Penetrating Radiation Value Determined with One Personal Monitor as a Sxurogate for Effective Dose Equivalent or Effective Dose... 

The Conference of Radiation Control Program Directors (CRCPD) recognized this need to convert personal monitor readings to He... 

Derivation of Effective Dose Equivalent and Effective Dose from Personal Monitor Values of Personal Dose Equivalent for Strongly-Penetrating Radiation... 

USE OF PERSONAL MONITORS TO ESTIMATE EFFECTIVE DOSE EQUIVALENT AND EFFECTIVE DOSE TO WORKERS FOR EXTERNAL EXPOSURE TO LOW-LET RADIATION... 

Use of personal monitors to estimate effective dose equivalent and effective dose to workers for external exposure to low-LET radiation, p. cm.—(NCRP report no. 122)... 

This Report is one of the series developed under the auspices of Scientific Committee 46, a scientific program area committee of the National Council on Radiation Protection and Measurements (NCRP) concerned with operational radiation safety. The Report provides practical recommendations on the use of personal monitors to estimate effective dose equivalent (Hg) and effective dose (E) for occupationally-exposed individuals. The Report is limited to external exposures to low-LET radiation. Recent additions to the radiation protection literature have made the recommendations possible. In order to avoid delay in utilizing the recommendations in the United States, the quantity as well as E, has been included until such time as the federal radiation protection guidance and associated implementing regulations are revised to express dose limits in E as recommended by the NCRP. 

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