Radiation Detection And Measurement Knoll
Vanya Lamunyon
Over the decade that has passed since the publication of the 3rd edition, technical developments continue to enhance the instruments and techniques available for the detection and spectroscopy of ionizing radiation. The Fourth Edition of this invaluable resource incorporates the latest developments and cutting-edge technologies to make this the most up-to-date guide to the field available:
GLENN FREDERICK KNOLL is Professor of Nuclear Engineering and Radiological Sciences in the College of Engineering at the University of Michigan. Following his undergraduate education at Case Institute of Technology, he earned a Master's degree from Stanford University and a doctorate in Nuclear Engineering from the University of Michigan. During his graduate work, he held national fellowships from the Atomic Energy Commission and the National Science Foundation.
He joined the Michigan faculty in 1962, and served as Chairman of the Department of Nuclear Engineering from 1979 to 1990 and as Interim Dean of the College of Engineering from 1995-96. He held appointments as Visiting Scientist at the Nuclear Research Center in Karlsruhe, Germany and as Senior Fellow in the Department of Physics at the University of Surrey, U.K. His research interest have centered on radiation measurements, nuclear instrumentation, and radiation imaging. He is author or co-author of over 140 technical publications, 8 patents, and 2 textbooks.
He has been elected a Fellow of the American Institute for Medical and Biological Engineering, the American Nuclear Society, and the Institute of Electrical and Electronics Engineers. He has been selected to receive three national awards given annually to a single recipient for achievements in engineering and education: the 1979 Glenn Murphy Award from the American Society for Engineering Education, the 1991 Arthur Holly Compton Award of the American Nuclear Society, and the 1996 Merit Award of the IEEE/Nuclear and Plasma Sciences Society. He is one of five receiving editors of Nuclear Instruments and Methods in Physics Research, Part A, and a past or present member of the Editorial Boards for Nuclear Science and Engineering, IEEE Transaction on Medical Imaging, and Physica Medica. In 1999, he was elected to membership in the National Academy of Engineering. He has served as consultant to 25 industrial and government organizations in technical areas related to radiation measurements, and is a Registered Professional Engineer in the State of Michigan.
There are seven basic methods used in the institutional setting for measuring ionizing radiation. The method selected depends on the type and amount of radiation to be measured, the requisite sensitivity, the time available for the measurement, and equipment cost.
One of the oldest methods of measuring ionizing radiation is the gas detector. A simple design would be comprised of no more than an anode and cathode that define a volume in space, a voltage supply, and an ammeter. See Figure 1.7.
Gas detectors demonstrate a characteristic curve of signal strength as a function of applied voltage; see Figure 1.8. In all cases the signal is initiated when a photon or charged particle ionizes a gas molecule in the detector volume.
If the applied voltage is just sufficient to collect all the released electrons on the anode, and provide replacement electrons from the cathode, we observe a current that is proportional to the exposure rate. A gas detector operated in this mode is called an ionization chamber. Refer to Knoll ch. 5.
Small, electrically charged pocket ionization chambers are used to measure whole body dose for individuals who occasionally work in a radiation area, or who may be exposed to a high dose rate while performing a special task.
If the applied voltage is increased, rather than collecting an electrical current, each individual ionizing particle can cause a cascade of secondary ionizing events that are detected as an electrical pulse. The process is called gas multiplication. The magnitude of the electrical pulse is proportional to the energy of the particle that initiated the signal. Thus, for a fixed applied voltage, the signal from a 4.9 MeV 241Am alpha particle will be almost three times larger than the signal from a 1.8 MeV 32P beta particle. See Knoll ch. 6.
If the voltage in the gas detector were increased further, the positive charge on the anode would pull electrons off the cathode and there would be a continuous signal whether ionizing radiation were present or not. This is referred to as continuous discharge. A detector operating in this region cannot be used as a measuring tool.
TLDs can be used to measure patient dose in diagnostic radiology and radiation therapy. They are also used as extremity dosimeters to measure finger dose for individuals handling small, high activity sources or as a personal monitor.
To measure samples with gamma emitters such as 125I or 99mTc, the sample can be placed beside a NaI(Tl) crystal that is optically coupled to a PMT; the entire assembly is enclosed in an aluminum envelope to keep out room light and humidity. The energy of the incident gamma ray is converted to a flash of light in the crystal. The PMT detects the individual scintillation events and their relative intensities.
We regret the passing of a leader, mentor, and friend, Glenn Frederick Knoll, professor emeritus of nuclear engineering and radiological sciences at the University of Michigan. Glenn was born to the Reverend Oswald and Clara Bernthal Knoll on 3 August 1935 and died 20 April 2014 in his winter home in Santa Rosa, California.
After earning an undergraduate degree from Case Institute of Technology in 1957 and a master's from Stanford University in 1958, Glenn received his PhD at the University of Michigan in 1963. He then joined the university faculty, where he initiated the new research field of room-temperature semiconductor radiation detectors. While his true calling was teaching and research, Glenn also served as chairman of the Department of Nuclear Engineering and interim dean of engineering. He retired from the University of Michigan in 2011.
A gifted teacher and brilliant researcher, Glenn served as a mentor and role model for generations of students. Colleagues claimed they made careers out of his innovative ideas by applying them to nuclear medicine, radiography, oil-well exploration, nuclear physics, environmental stewardship, and homeland security.
Glenn's contributions have been recognized widely. He was inducted as a fellow of the Institute of Electrical and Electronics Engineers (IEEE), the Institute of Medical and Biological Engineering, and the American Nuclear Society (ANS). He was also honored with the ANS Glenn Murphy Award for Education, the ANS Arthur Holly Compton Award, the IEEE Career Outstanding Achievement Award, and the IEEE Third Millennium Medal. He was a member of the National Academy of Engineering (NAE), contributing after 9/11 to the NAE book Making the Nation Safer. A member of the Health Physics Society (HPS) from 1991 to 2001, Glenn presented at many HPS meetings (most recently in 2011).
Glenn enjoyed the technical fraternity of colleagues and collaborated internationally. He served as an International Atomic Energy Agency program reviewer and taught his radiation detection course on every continent but one. As a journal editor, he was well known and respected. His textbook, Radiation Detection and Measurement, remains the standard reference after four decades and translation into multiple languages.
On the day of his death, Glenn was still as active as ever. He was reviewing proposals and writing white papers to meet imminent deadlines. He sent final ideas for the upcoming Symposium on Radiation Measurements and Applications (SORMA), the international conference that he fathered nearly 50 years ago and that still gathers in Ann Arbor. With his death, we have lost a legendary friend and colleague.
Alan M. Jackson, CHP
I had the pleasure of taking Glenn Knoll's class in graduate school. It was a challenging class and the lab was one of the best I ever had. He was an excellent lecturer and his book is, of course, great. Later in my career I became the health physicist responsible for the engineering campus. Even though I was a former student and he was interim dean and buddy of the University of Michigan president (James Duderstadt), he always treated me as a peer. He always took safety seriously and responded to my concerns responsibly. One day he noticed I had the old version of his book and told me to come to his office to get a new one. I was too embarrassed to come and he later stopped me in the hall and gave me a signed copy of his book with a wonderful note. That book is one of my most treasured possessions.
Dennis A. Palmieri, MPH, JD
I would have liked to begin by not having to begin at all. I wish we were still blessed with the presence of this giant in the field of radiation detection, nuclear engineering, and health physics. I came to know Professor Glenn Knoll when I was a student in his radiation instrumentation class back in 1978. The class had the reputation of being daunting to those of us with biology degrees. We quickly learned, though, that Dr. Knoll had the rare ability to talk clearly at our level without being patronizing. When most professors barely knew a student, Dr. Knoll always greeted us by our first names with a smile and a joke. I left that class withf a more comprehensive and practical understanding of the class material than I'd ever had from any course. Later, when I worked for the University of Michigan Radiation Control Service, Dr. Knoll sat on the University's Radiation Policy Committee and provided wise and unbiased counsel. He was a conscientious researcher who put the principles of safe use and ALARA into his everyday research. There are few instructors who can reach out and leave a mark on everyone they've taught or collaborated with. Glenn Knoll was one of those people. I congratulate you, Glenn, on a life well-lived, a life of achievement and accomplishment, and for showing me your gracious kindness and wisdom. You'll live on within us and forever remain a giant in our field. Rest in peace.