Applications of New Technology: External Dosimetry (softcover)
Author: Jack F. HigginbothamISBN: 9780944838693 ISBN10: 0944838693
Published: 1996 | 464 pp | Softcover
OUT OF PRINT
Medical Physics | December 1996
Medical Physics, December 1996
Reviewer: Govinda Rajan, Bhabha Atomic Research Centre, Bombay, India
"This book contains 19 chapters contributed by various experts in the field. It was initially prepared for student use at the 1996 Health Physics Society Summer School, held at the University of Washington. This school was sponsored by the Health Physics Society and these proceedings are now made available to the practicing health physicists and others involved in radiation protection. The book, as the title suggests, is concerned with only external exposures of radiation workers, especially in a nuclear industry, to beta gamma and neturons, the personal monitoring of doses received from these radiations and the risks involved in such exposures. The book is of particular importance today, when adverse publicity and unfounded fears of radiation and radiation waste management are halting the building of nuclear power plants in the U.S., while other countries are committed to nuclear power to meet the demands of the future. Any compromise on radiation safety on the part of health physicists could further worsen this situation.
"The book contains 19 contributed chapters. The first chapter deals with the historical development of radiation dosimetric quantities (tolerance dose, roentgen, roentgen equivalent physical, roentgen equivalent man, absorbed dose, dose equivalent and effective dose) and the various dosimetric systems that are currently in use for monitoring external doses (film, TLD, pocket chamber, nuclear track detector, etc.). While the monitoring of skin exposures using a film or TLD badge is well established today, much work is in progress to define the radiation fields and measuring the radiation doses to different body organs to estimate the effective dose received by the radiation worker and the associated risks involved. These points are dealt with in more detail in the later chapters.
"The second chapter considers the health risks associated with low doses of ionizing radiation as estimated from the exposures encountered in medical and occupational exposures and in atomic bomb survivors, nuclear fallout, etc.
"The third chapter, 'Basics of External Dosimetry', explains how the interaction of radiation with matter leads to dose (or energy deposition) in the medium and how these doses can be computed or measured. Chapter four deals exclusively with beta ray dosimetry or the computation of dose from beta ray exposures.
"The chapters 5 to 8 deal with the various types of dosimetric systems in use namely the films, TLDs, electronic dosimeters and optically stimulated luminescence dosimeters for the purposes of personnel monitoring and the performance specifications of these dosimeters.
"Chapter 9 discusses the basic principles of neutron dosimetry. Unlike the dosimetry of photons or electrons, there is no charge - hence no charged particle interactions - or no electromagnetic fields - hence no photon type interactions - associated with neutrons and hence their interactions are only with the nucleus. This chapter mentions the important types of neutron interactions (elastic collisions, inelastic collisions, radiative capture, neutron or charged particle emission, etc.) and how these interactions lead to energy deposition in matter and can be used for monitoring neutron doses.
"While the dosimeters can be used for personal monitoring, radiation levels in rooms can be monitored using protection survey instruments. Chapter 10 on 'Advances in Portable Survey Instrumentation' reviews the various types of portable radiation detectors available (ionization chamber, proportional counter or gas flow proportional counter, GM counter, scintillators and semiconductors), including the recent ones which are microprocessor controlled.
"Chapter 11 on 'Laboratory Accreditation Program - Dosimetry' deals with a very important concept in radiation measurements. To ensure the accuracy of any radiation measurement the dosimeter must satisfy well defined performance specifications, must be calibrated from an accredited calibration laboratory to make measurements traceable, directly or indirectly, to the Primary Standards Laboratory (NIST in the U.S.). Various bodies are involved in achieving this goal and they are known by different names. ANSI, for instance, has evolved standard criteria for the testing of personal dosimeters, which must be followed by all the laboratories that estimate the personal monitoring doses.
"The National Voluntary Laboratory Accreditation Program (NVLAP) is the agency that tests the dose evaluating laboratory in question for its competence in providing personal monitoring services before issuing accreditation to the laboratory. These aspects are explained in some detail in this chapter.
"Chapter 12 deals with cost analysis of external radiation protection dosimetry. Personal monitoring services cost money and the expenditure involved will depend on the sophistication of the monitoring and decisions regarding who should be monitored and at what levels of dose. These decisions do not only involve radiation protection principles, in which case recommendations like ICRP can be used as guidelines, but other social factors as well, like the image of nuclear power following the Three Mile Island accident, consequences of litigation involving radiation workers, the economy of the industry and several other related factors. This chapter discusses some of these factors in some detail. Chapter 13 discusses a new, sturdy electronic personal dosimeter developed in Japan for the monitoring of nuclear workers.
"Chapter 14 is regarding the monitoring of occupation exposures in the medical applications of radiation. This chapter discusses the ICRP 26 recommendations on dose limits, the reduction in the dose limits as per the more recent ICRP 60 recommendations and its effect on room shielding and personal monitoring. It also discusses the age old problem of 'appropriate position for wearing the personal monitoring badge' in a diagnostic department and the estimation of effective dose in fluoroscopy. There is no mention of the desirable characteristics of survey instruments for surveying the areas around the linac facilities, which would have been very useful to the Radiation Safety Officers of therapy installations. GM type survey meters are not quite suitable for surveying pulsed radiations, as in the case of medical linacs. When these accelerators are in the energy range that can cause neutron production, the radiation survey around such facilities require much more complex instrumentation.
"Chapter 15 deals exclusively with the skin dose assessment for beta sources. In places where beta sources are encountered, skin contamination and skin doses are the two important parameters to be monitored. Response of skin to radiation, skin dose limits as per ICRP 60 and computation of skin doses using TLDs, dichromic film or extrapolation chambers are some of the important points discussed in this chapter.
"Chapters 16 and 18 deal with the important and more difficult problem of computing effective dose received by the radiation worker from his dosimeter reading. This requires the proper characterization of the radiation field and the computation of conversion factors which are the 'dose quantities per unit photon fluence.' Thus 'air kerma per unit fluence', 'effective dose per unit fluence', etc. can be computed for different photon energies or neutron energies. These theoretical conversion factors can be coupled with proper calibration techniques for the personal monitor to determine doses of interest, in the field of radiation protection. Unfortunately, this chapter makes use of ICRP 26 definitions and organ weightage factors, when many users have already made a change to ICRP 60.
"Chapter 17 on 'Public Dose Assessment' is of general nature and discusses the problem of environmental monitoring to gain public confidence even though the levels involved may be very low and monitoring would involve unnecessary expenses.
"Chapter 19, 'External Dosimetry in Litigation', deals with problems that arise during litigation. Personal dose records become very important in such cases. The accurate estimates of the actual duration of occupational exposures and non occupational exposures and the internal and external dose contributions to the effective dose received by the litigant are essential for defending the institute's case. The chapter stresses the importance of having uniformity in regulatory limits among federal agencies so that it will reduce inconsistencies in court judgements. As professionals in the field, we know that exceeding the limits do not mean injury to the litigant and we are in fact dealing at dose levels at which we have so far no proof of positive injury to the radiation worker and the limits are only conservative limits to err on the safer side. This knowledge has to be passed on to the general public as well as to the other professionals so that there will be less litigation and better rational judgements. This chapter mentions some of the judgements passed by the court in litigations.
"Considering the fact that there are very few books on health physics or radiation safety in the field, this book is a welcome addition to the new literature on the subject. It covers all the essential aspects of personal monitoring and environmental survey and will help the readers to gain a good understanding of radiation protection in cases of external exposures. It is particularly recommended for medical physicists and health physicists involved in radiation safety work or in personal monitoring of radiation workers."