Practical Gamma-ray Spectrometry E-Book

Gordon Gilmore

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 1108

Veröffentlichungsjahr: 2011

Beschreibung

The Second Edition of Practical Gamma-Ray Spectrometry has been completely revised and updated, providing comprehensive coverage of the whole gamma-ray detection and spectrum analysis processes. Drawn on many years of teaching experience to produce this uniquely practical volume, issues discussed include the origin of gamma-rays and the issue of quality assurance in gamma-ray spectrometry. This new edition also covers the analysis of decommissioned nuclear plants, computer modelling systems for calibration, uncertainty measurements in QA, and many more topics.

Leseprobe

Contents

Preface to the First Edition

Preface to the Second Edition

Internet Resources within the Book

1: Radioactive Decay and the Origin of Gamma and X-Radiation

1.1 INTRODUCTION

1.2 BETA DECAY

1.3 ALPHA DECAY

1.4 SPONTANEOUS FISSION (SF)

1.5 MINOR DECAY MODES

1.6 GAMMA EMISSION

1.7 OTHER SOURCES OF PHOTONS

1.8 THE MATHEMATICS OF DECAY AND GROWTH OF RADIOACTIVITY

1.9 THE CHART OF THE NUCLIDES

2: Interactions of Gamma Radiation with Matter

2.1 INTRODUCTION

2.2 MECHANISMS OF INTERACTION

2.3 TOTAL ATTENUATION COEFFICIENTS

2.4 INTERACTIONS WITHIN THE DETECTOR

2.5 INTERACTIONS WITHIN THE SHIELDING

2.6 BREMSSTRAHLUNG

2.7 ATTENUATION OF GAMMA RADIATION

2.8 THE DESIGN OF DETECTOR SHIELDING

3: Semiconductor Detectors for Gamma-Ray Spectrometry

3.1 INTRODUCTION

3.2 SEMICONDUCTORS AND GAMMA-RAY DETECTION

3.3 THE NATURE OF SEMICONDUCTORS

3.4 THE MANUFACTURE OF GERMANIUM DETECTORS

3.5 DETECTOR CAPACITANCE

3.6 CHARGE COLLECTION IN DETECTORS

3.7 PACKAGING OF DETECTORS

4: Electronics for Gamma-Ray Spectrometry

4.1 THE GENERAL ELECTRONIC SYSTEM

4.2 DETECTOR BIAS SUPPLIES

4.3 PREAMPLIFIERS

4.4 AMPLIFIERS AND PULSE PROCESSORS

4.5 RESOLUTION ENHANCEMENT

4.6 MULTICHANNEL ANALYSERS AND THEIR ANALOGUE-TO-DIGITAL CONVERTERS

4.7 LIVE TIME CORRECTION AND LOSS-FREE COUNTING

4.8 SPECTRUM STABILIZATION

4.9 COINCIDENCE AND ANTICOINCIDENCE GATING

4.10 MULTIPLEXING AND MULTISCALING

4.11 DIGITAL PULSE PROCESSING SYSTEMS

5: Statistics of Counting

5.1 INTRODUCTION

5.2 COUNTING DISTRIBUTIONS

5.3 SAMPLING STATISTICS

5.4 PEAK AREA MEASUREMENT

5.5 OPTIMIZING COUNTING CONDITIONS

5.6 COUNTING DECISION LIMITS

5.7 SPECIAL COUNTING SITUATIONS

5.8 UNCERTAINTY BUDGETS

6: Resolution: Origins and Control

6.1 INTRODUCTION

6.2 CHARGE PRODUCTION – ωP

6.3 CHARGE COLLECTION - ωC

6.4 ELECTRONIC NOISE - ωE

6.5 RESOLVING THE PEAK WIDTH CALIBRATION

7: Spectrometer Calibration

7.1 INTRODUCTION

7.2 REFERENCE DATA FOR CALIBRATION

7.3 SOURCES FOR CALIBRATION

7.4 ENERGY CALIBRATION

7.5 PEAK WIDTH CALIBRATION

7.6 EFFICIENCY CALIBRATION

7.7 MATHEMATICAL EFFICIENCY CALIBRATION

8: True Coincidence Summing

8.1 INTRODUCTION

8.2 THE ORIGIN OF SUMMING

8.3 SUMMING AND SOLID ANGLE

8.4 SPECTRAL EVIDENCE OF SUMMING

8.5 VALIDITY OF CLOSE GEOMETRY CALIBRATIONS

8.6 SUMMARY

8.7 SUMMING IN ENVIRONMENTAL MEASUREMENTS

8.8 ACHIEVING VALID CLOSE GEOMETRY EFFICIENCY CALIBRATIONS

8.9 TCS, GEOMETRY AND COMPOSITION

8.10 ACHIEVING ‘SUMMING-FREE’ MEASUREMENTS

8.11 MATHEMATICAL SUMMING CORRECTIONS

8.12 SOFTWARE FOR CORRECTION OF TCS

9: Computer Analysis of Gamma-Ray Spectra

9.1 INTRODUCTION

9.2 METHODS OF LOCATING PEAKS IN THE SPECTRUM

9.3 LIBRARY DIRECTED PEAK SEARCHES

9.4 ENERGY CALIBRATION

9.5 ESTIMATION OF THE PEAK CENTROID

9.6 PEAK WIDTH CALIBRATION

9.7 DETERMINATION OF THE PEAK LIMITS

9.8 MEASUREMENTS OF PEAK AREA

9.9 FULL ENERGY PEAK EFFICIENCY CALIBRATION

9.10 MULTIPLET PEAK RESOLUTION BY DECONVOLUTION

9.11 PEAK STRIPPING AS A MEANS OF AVOIDING DECONVOLUTION

9.12 THE ANALYSIS OF THE SAMPLE SPECTRUM

9.13 NUCLIDE IDENTIFICATION

9.14 THE FINAL REPORT

9.15 SETTING UP NUCLIDE AND GAMMA-RAY LIBRARIES

9.16 BUYING SPECTRUM ANALYSIS SOFTWARE

9.17 THE SPECTRUM ANALYSIS PROGRAMS REFERRED TO IN THE TEXT

10: Scintillation Spectrometry

10.1 INTRODUCTION

10.2 THE SCINTILLATION PROCESS

10.3 SCINTILLATION ACTIVATORS

10.4 LIFETIME OF EXCITED STATES

10.5 TEMPERATURE VARIATION OF THE SCINTILLATOR RESPONSE

10.6 SCINTILLATOR DETECTOR MATERIALS

10.7 PHOTOMULTIPLIER TUBES

10.8 THE PHOTOCATHODE

10.9 THE DYNODE ELECTRON MULTIPLIER CHAIN

10.10 PHOTODIODE SCINTILLATION DETECTORS

10.11 CONSTRUCTION OF THE COMPLETE DETECTOR

10.12 THE RESOLUTION OF SCINTILLATION SYSTEMS

10.13 ELECTRONICS FOR SCINTILLATION SYSTEMS

10.14 COMPARISON OF SODIUM IODIDE AND GERMANIUM DETECTORS

11: Choosing and Setting up a Detector, and Checking its Specifications

11.1 INTRODUCTION

11.2 SETTING UP A GERMANIUM DETECTOR SYSTEM

11.3 OPTIMIZING THE ELECTRONIC SYSTEM

11.4 CHECKING THE MANUFACTURER’S SPECIFICATION

12: Troubleshooting

12.1 FAULT-FINDING

12.2 PREAMPLIFIER TEST POINT AND LEAKAGE CURRENT

12.3 THERMAL CYCLING OF THE DETECTOR

12.4 GROUND LOOPS, PICK-UP AND MICROPHONICS

13: Low Count Rate Systems

13.1 INTRODUCTION

13.2 COUNTING WITH HIGH EFFICIENCY

13.3 THE EFFECT OF DETECTOR SHAPE

13.4 LOW BACKGROUND SYSTEMS

13.5 ACTIVE BACKGROUND REDUCTION

13.6 ULTRA-LOW-LEVEL SYSTEMS

14: High Count Rate Systems

14.1 INTRODUCTION

14.2 DETECTOR THROUGHPUT

14.3 PREAMPLIFIERS FOR HIGH COUNT RATE

14.4 AMPLIFIERS

14.5 DIGITAL PULSE PROCESSING

14.6 THE ADC AND MCA

14.7 DEAD TIMES AND THROUGHPUT

14.8 SYSTEM CHECKS

15: Ensuring Quality in Gamma-Ray Spectrometry

15.1 INTRODUCTION

15.2 NUCLEAR DATA

15.3 RADIONUCLIDE STANDARDS

15.4 MAINTAINING CONFIDENCE IN THE EQUIPMENT

15.5 GAINING CONFIDENCE IN THE SPECTRUM ANALYSIS

15.6 MAINTAINING RECORDS

15.7 ACCREDITATION

16: Gamma Spectrometry of Naturally Occurring Radioactive Materials (NORM)

16.1 INTRODUCTION

16.2 THE NORM DECAY SERIES

16.3 GAMMA SPECTROMETRY OF THE NORM NUCLIDES

16.4 NUCLEAR DATA OF THE NORM NUCLIDES

16.5 MEASUREMENT OF CHEMICALLY MODIFIED NORM

17: Applications

17.1 GAMMA SPECTROMETRY AND THE CTBT

17.2 GAMMA SPECTROMETRY OF NUCLEAR INDUSTRY WASTES

17.3 SAFEGUARDS

17.4 PINS – PORTABLE ISOTOPIC NEUTRON SPECTROMETRY

Appendix A: Sources of Information

A.1 INTRODUCTION

A.2 NUCLEAR DATA

A.3 INTERNET SOURCES OF OTHER NUCLEAR DATA

A.4 CHEMICAL INFORMATION

A.5 MISCELLANEOUS INFORMATION

A.6 OTHER PUBLICATIONS IN PRINT

Appendix B: Gamma- and X-Ray Standards for Detector Calibration

Appendix C: X-Rays Routinely Found in Gamma Spectra

Appendix D: Gamma-Ray Energies in the Detector Background and the Environment

Appendix E: Chemical Names, Symbols and Relative Atomic Masses of the Elements

Glossary

Index

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Library of Congress Cataloging in Publication Data

Gilmore, Gordon.

Practical gamma-ray spectrometry. — 2nd ed./Gordon Gilmore.

p. cm.

Includes bibliographical references and index.

ISBN 978-0-470-86196-7 (cloth: alk. paper)

1. Gamma ray spectrometry—Handbooks, manuals, etc. I. Title.

QC793.5.G327G55 2008

537.5′352—dc22

2007046837

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 978-0-470-86196-7

Dedication

To my friends and family who, I suspect, never really believed I would get this finished, and to the publishers who patiently tolerated many delays before I did so

Preface to the First Edition

This book was conceived during one of the Gamma Spectrometry courses then being run at the Universities’ Research Reactor at Risley. At that time, we had been ‘peddling’ our home-spun wisdom for seven or eight years, and transforming the lecture notes into something more substantial for the benefit of course participants seemed an obvious development.

Our intention is to provide more of a workshop manual than an academic treatise. In this spirit, each chapter ends with a ‘Practical Points’ section. This is not a summary as such but a reminder of the more important practical features discussed within the chapter. We have attempted, not always successfully, it must be admitted, to keep the mathematics to a minimum. In most cases, equations are presented as faites accomplis and are not derived.

One practical process that can have a major influence on the reliability of the results obtained by users of gammaspectrometric equipment is that of sampling. It was after much discussion and with some regret that we decided to omit this topic. This is because it is peripheral to our main concern of describing the best use of instrumentation, because we suspect that another book would be necessary to do justice to the subject, and because we do not know much about it. What is clear is that an analyst must be aware that uncertainties introduced by taking disparate samples from an inhomogeneous mass can far outweigh uncertainties in the individual measurements themselves. This is a particular problem when sampling such a diverse and complex mass as the natural environment.

No previous knowledge of nuclear matters or instrumentation is assumed, and we hope the text can be used by complete beginners. There is even a list of names and symbols of the elements; while chemists may smile at this, in our experience not every otherwise scientifically literate person can name Sb and Sn, or distinguish Tb and Yb.

In a practical book, we think it useful to mention particular items of commercial equipment to illustrate particular points. We must make the usual disclaimer that these are not necessarily the best, nor the worst, and in most cases are certainly not the only items available. In general, the manufacturers do a fine job, and choosing one product rather than another is often an invidious task. We can only recommend that the user (1) decides at an early stage what capabilities are required, (2) reads and compares specifications (this text should explain these), (3) is not seduced by the latest ‘whizz-bang device’, yet (4) bears in mind that more recent products are better than older ones, not just in ‘bald’ specification but also in manufacturing technology, and should consequently show greater reliability.

Readers may notice the absence of certain terms in common use. The exclusion of some such terms is a deliberate choice. For example, instead of ‘photopeak’ we prefer ‘full-energy peak’; we have avoided the statisticians’ use of ‘error’ to mean uncertainty and reserve that word to indicate bias or error in the sense of ‘mistake’. ‘Branching ratio’ we avoid altogether. This is often used ambiguously and without definition. In other texts, it may mean the relative proportions of different decay modes, or the proportions of different beta-particle transitions, or the ratio of ‘de-excitation’ routes from a nuclear-energy level. Furthermore, it sometimes appears as a synonym for ‘gamma-ray emission probability’, where it is not always clear whether or not internal conversion has been taken into account.

We hope sensitive readers are not upset by our use of the word ‘program’. This ‘Americanized’ version is well on its way to being accepted as meaning specifically ‘computer program’, and enables a nice distinction to be made with the more general (and more elegant-looking) ‘programme’.

We have raided unashamedly the manufacturers’ literature for information, and our thanks are due particularly to Canberra and Ortec (in alphabetical order) for their cooperation and support in this. The book is not a survey of the latest research nor a historical study, and there are very few specific references in the text. Such that do exist are put at the end of each chapter, where there will also be found a more general short-list of ‘Further Reading’.

We also acknowledge our continuing debt to two books: Radiation Detection and Measurement, by G.F. Knoll, John Wiley & Sons, Ltd (1979, 1989) and Gammaand X-ray Spectrometry with Semiconductor Detectors, by K. Debertin and R.G. Helmer, North-Holland (1988). These can be thoroughly recommended.

So why write another book? Fine as these works are, we felt that there was a place for a ‘plain-man’s’ guide to gamma spectrometry, a book that would concentrate on day-to-day operations. In short, the sort of book that we wish had been available when we began work with this splendid technique.

Gordon R. Gilmore and John D. Hemingway

Preface to the Second Edition

During 2005, while this second edition was being prepared, I was totally unprepared to receive a telephone call that my co-author on the first edition, John Hemingway, was seriously ill after suffering a brainhaemorrhage. Only a few days later, on 5th September, he passed away. My original, and obvious, intent was to update the sections allocated to John and myself and publish this second edition as ‘Gilmore and Hemingway’. That intent was frustrated by contractual difficulties with John’s estate. It became necessary for me to rewrite those sections completely and remove John’s name from the second edition. I deeply regret that that was necessary. It has deprived us all of John’s often elegant prose and has meant that some topics that John had particular interest in introducing to the new edition have had to be omitted.

Earlier in that year, another reminder of the inexorable passage of time came with the death of someone whose name had been familiar to me throughout my career in gamma spectrometry. On 16th January, Richard Helmer passed away at the age of 70 years. His co-authored work, the justly famous Gamma and X-Ray Spectrometry with Semiconductor Detectors, was one of the books that introduced John and myself to the complexities of gamma spectrometry and one which we consistently recommended to others. His influence as an author and in many other roles, such as an evaluator of nuclear data, has left all of us in his debt, whether we all realize it or not.

On a lighter note, during the year 2005 the very title of this book was called into question. The radiochemical mailing list, RADCH-L, agonized, in general terms, over which is the correct term – ‘spectrometry’ or ‘spectroscopy’. Of course, the suffix ‘-metry’ means to measure and ‘-scopy’ means to visualize – and so the discussion went on, to and fro. Eventually, the 1997 IUPAC ‘Golden Book’, Compendium of Chemical Terminology, was quoted: ‘SPECTROMETRY is the measurement of such [electromagnetic] radiations as a means of obtaining information about the system and their components’. That seemed to be the ‘clincher’. The prime objective of our activities is to measure gamma radiation, not just to create a spectrum, and so spectrometry’ it is, performed by ‘gamma spectrometrists’!

Before a second edition is approved, the publishers canvass the opinion of people in the field as to whether a new edition is justified and ask them for suggestions for inclusion. I have taken all of the suggestions offered seriously but, in the event, have had to disappoint some of the reviewers. For example, X-ray spectrometry is such a wide field with a different emphasis to gamma spectrometry and the space available within this new edition so limited, that merely exposing a little more of the ‘iceberg’ seemed pointless. In other cases, my ignorance of certain specific matters was sufficient to preclude inclusion. I can only offer my apologies to those who may feel let down.

Since the first edition (1995), there have been a number of significant advances in gamma spectrometry. Indeed, some of those advances were taking place while I was writing, meaning re-writes even to the update! In particular, I have included digital pulse processing and I have explained the changes in the way that nuclear data are being kept up to date. On statistics, I have introduced the matter of uncertainty budgets as being of increasing importance now that more laboratories seek accreditation. I have had to re-assess the ideas I espoused in the first edition on peak width and now have a much more comfortable mathematical justification for fitting peakwidth calibrations.

Throughout, I have tried to keep to the principles John and I declared in the Preface to the first edition – an emphasis on the practical application of gamma spectrometry at the expense of, if possible, the mathematics. That being the case, I have reproduced most of the Preface to the first edition below. The first edition was very well received. I can only hope that I have done enough to ensure that popular opinion is as supportive of this second edition.

Gordon R. Gilmore

Internet Resources within the Book

Throughout this book, I list sources of information of value to gamma spectrometrists. The reality of life in 2007 is that, for very many people, the Internet is the first ‘port-of-call’ for information. Because of this, I have leaned heavily on Internet sources and quoted links to them as standard URLs – Uniform Resource Locators, i.e. Internet addresses, to suitable websites. URLs are usually not ‘case-sensitive’. However, that depends on the type of server used to host the website. It is better to type the URL as given here, i.e. preserving upper/lowercase characters.

A word of caution is necessary. The Internet can be a source of the most up-to-date information and can be far more convenient than waiting for books and articles to be delivered, or a trip to a distant library. However, I feel duty bound to remind readers that, as well as holding the upto-date information, the Internet is also a vast repository of ancient, irrelevant, inaccurate and out-of date information. It is up to the user to check the pedigree, and date, of all downloaded material. I believe the links that I have quoted to be reliable. Because the Internet is essentially an ephemeral entity, reorganization of a website can result in URLs becoming inactive. Usually, however, the information will still be available on the ‘parent site’ somewhere, but will need looking for.

As a convenience for readers of this book, I have created a website, http://www.gammaspectrometry.co.uk, hosted by Nuclear Training Services Ltd, which holds links to all of the URLs referred to throughout the book, organized by chapter. The site also carries a number of other resources that readers might find useful:

All the links quoted in Appendix A – Sources of information.The data reproduced in Appendices B-E.Some of the test spectra referred to in Chapter 15 and a test-spectrum generator.Spreadsheet tools to illustrate certain points in the text, including some used to generate figures within the text.A number of useful spectra to illustrate points in the text.Links to relevant organizations and manufacturers.A set of ‘taster’ modules from the Online Gamma Spectrometry course.

This website will also be used to ‘post-up’ corrections to the text, should any be needed, before they are able to appear in future reprints, which I hope will be useful. In due course, I also intend to create a ‘blog’ to allow reader feedback and discussion of issues raised.