These titles were compiled from the list of References at the end of Chapter 9. They are brought together here for easy access. The first ten entries are textbooks, followed by references to three publications in peer-reviewed journals.

Cember H. (1996) Introduction to Health Physics, 3rd edn. McGraw-Hill, New York, USA.

IAEA (1986) Radiation Protection Glossary, IAEA Safety Series No.76, International Atomic Energy Agency, Vienna, Austria.

IAEA (1996a) Basic Safety Standards for Protection Against Ionising Radiation and for the Safety of Radioactive Sources, IAEA Safety Series No.115, International Atomic Energy Agency, Vienna, Austria.

ICRP (1991) Publication 60, 1990 Recommendations of the International Commission on Radiological Protection, Vol 21, pp. 1–3, Pergamon Press, Oxford, UK.

ICRU (1993) Quantities and Units in Radiation Protection Dosimetry, ICRU Report 51, International Commission on Radiation Units and Measurements, Bethesda, Maryland, USA.

Martin A. and Harbison S.A. (1996) An Introduction to Radiation Protection, 4th edn, Chapman and Hall, London, UK.

Simmons J.A. and Watt D.E. (1999) Radiation Protection: A Radical Reappraisal, Medical Physics Publishing, Madison, Wisconsin, USA.

Shapiro J. (1981) Radiation Protection, A Guide for Scientists and Physicians, 2nd edn, Harvard University Press, Cambridge, Mass, USA.

Shleien B. (Ed) (1992) The Health Physics and Radiological Health Handbook, Revised Edition, (Scinta Inc, Silver Spring MD 20902, USA). See also Shleien, B, Slaback, L.A. Jr. and Birky, B. (Eds), (1997), 3rd Edition, William and Wilkins, POB 23291, Baltimore, MD 21298-9533, USA.

Turner J.E. (1986) Atoms, Radiations and Radiation Protection, Pergamon Press, New York, USA.

Clarke R.H. (1991) The Causes and Consequences of Human Exposure to Ionising Radiations, Radiation Protection Dosimetry, 36, 73–77.

This glossary lists terms in common use in the nuclear sciences. Fifteen terms used in radiation protection are listed in Table 2.2 and properties of nuclear particles are summarised in Table 1.2.

Absorption (1) The retention, in a material, of energy removed from radiation passing through it. (2) The process whereby neutrons (or other elementary particles) are captured by nuclei.

Activation analysis A method of analysis based on the identification and measurement of characteristic radiation from radio nuclides formed by neutron irradiation in a sample of the irradiated material.

Activity (of a substance) Short for radioactivity. The number of disintegrations per unit time taking place in a radioactive material. The unit of activity is the becquerel (Bq), one disintegration per second.

Alpha particles Energetic helium nuclei (4He) emitted from the nuclei of higher Z number atoms (Z > 60) during alpha particle decays.

Annihilation radiation The electromagnetic radiation resulting from the mutual annihilation of the mass of negatively charged electrons (negatrons) and positrons (β− − β+). The annihilation radiation consists of two photons, each 0.51 MeV, emitted in opposite directions.

Atomic mass unit One-twelfth of the mass of a carbon-12 atom and approximately equal to the mass of a single proton or neutron. It is abbreviated amu.

Atomic number The number (Z) of protons in the nuclei of the atoms of an element, indicating the position of that element in the periodic table.

Atomic weight For a given specimen of an element, the mean weight of its atoms, expressed in either atomic mass units (physical scale) or atomic weight units (chemical scale).

Radiation detectors, a summary

Ionising radiations as normally used cannot be observed by the unaided human senses. They were discovered thanks to photographic emulsions which remain important detectors to this day, particularly in the biological sciences. There are many designs of detectors developed to respond to specific characteristics of the different types of ionising radiations discussed in earlier chapters and notably in Section 4.3.3.

Sections 5.2 and 5.3 will deal with ionisation detectors used for β and γ radiations, Section 5.4 will deal with liquid scintillation (LS) counting, adding to the material presented in Section 4.2.4. This will be followed by a description of microcalorimetry, an efficient detection method when working with high activities of many β and γ ray emitters. Section 5.4 will also cover the detection of neutrons at low and high intensities. Section 5.5 will deal with semiconductor detectors, which have long been indispensable for photon as well as for charged particle spectrometry.

Readers who seek details about specialist applications in any branch of radioactivity measurements are referred to the work of Knoll (1989), who deals with the scientific principles underlying these procedures over a broader range than other currently available textbooks.

Characteristics of ionisation detectors

Saturation currents and gas multiplication

A long established method for measuring the intensity of nuclear radiations uses their ability to ionise air or other gases such as argon or methane. Instruments that use an electric field to collect the ions and serve to measure the resultant ionisation current are known as ionisation chambers, but ionisation detectors can also be operated as pulse counters.

Introduction

The last chapter of our book will describe the use of radioisotopes for assessing the impact of human activities on the environment. The range of opportunities is very extensive as seen by the list of applications in Table 9.1 which is by no means complete. Emphasis will be placed on assessing such impacts using two methods, described here as the mathematical modelling approach and the archival approach.

1. The modelling approach. Due to recent vast increases in the power of computers, applications of mathematical modelling techniques to environmental science are now very widespread and underpin much of our detailed understanding of processes in the oceans, the atmosphere and coastal and terrestrial ecosystems. Since increasing use is being made of numerical models for scientific prediction and environmental management, there is a growing need for independent verification of the model predictions. Tracer techniques are a powerful tool for model validation, as will be demonstrated in several examples.

2. The archival approach. This approach to the study of environmental processes involves using evidence from the past to understand the present and to assess the future. The approach is implemented in two stages. The first stage involves the systematic dating of material which has accumulated layer by layer often over long periods of time. Cores extracted from sediments, ice sheets, old growth trees or massive corals are commonly used. From knowledge of the dates of the samples and their locations in the core, it is possible to calculate the average rate of growth or accumulation.

Radionuclides and the emitted radiations have long been applied routinely throughout all branches of engineering and the technologies to obtain useful results, many of which could not have been obtained by other means.

As with the application of any other tool or technique, problems can be encountered. Practitioners working with radioactivity face health risks but long-standing records show that, overall, risks in the nuclear industries have been consistently smaller than those faced by workers in most other industries. This is so not least thanks to easily followed, legally backed precautions, developed over the decades to ensure safe operating conditions during all nuclear radiation applications carried out within the common sense rules devised for that purpose.

This book was written for workers and students as yet largely unfamiliar with the nuclear sciences and with the advantages in numerous fields which quickly become apparent on employing nuclear radiations. The potential of nuclear science and engineering for enhancing, e.g. the effectiveness of nuclear power production and of radioactive tracers is far from exhausted. Today's beginners could have a highly rewarding way ahead of them.

A useful overview of the contents can be readily obtained by scanning the chapter and section headings in the table of Contents. The bibliography contains over 120 references to assist practitioners looking for more detailed and/or more specialised information than could be included here. The latest information about nuclear data and specialist techniques is available via the Internet, with web sites and other comments listed in Appendix 3.

Introduction

A change of emphasis

Beginning with this chapter, the emphasis of this book will shift from discussing the science and technology of radioactivity and ionising radiations to considering how they are employed to advance scientific, technological and social objectives. The present chapter will concentrate on industrial applications of X and γ rays, charged particles and neutrons, and also on the applications of high-intensity radiations for chemical processing. Chapter 8 will discuss industrial radiotracing and Chapter 9 the contribution of nuclear techniques to understanding and protecting the environment.

An overview of industrial applications

Summary

The goal of modern manufacturing is to produce quality products as economically as possible using processes designed to minimise adverse impacts on the environment. The processes should result in the maximum efficiency in the use of energy and materials and the minimum generation of waste products.

Nuclear techniques contribute to this goal when applied to:

• optimising the efficiency of industrial processes;

• diagnosing problems in plant operations;

• examining industrial components using non-destructive methods;

• analysing the composition and structure of materials;

• treating materials with high-energy radiation for the purposes of sterilisation or modification of their properties;

• assessing the impact of industrial and urban development on the environment and designing remedial action.

The scope of these applications is outlined below.

Optimisation and control of processes in industrial plant

Optimisation and control of industrial processes depend first and foremost on the measurement of key parameters. In modern industrial plant, these data are often interpreted with the aid of sophisticated mathematical models designed to monitor the processes and to diagnose operational problems.

Introduction

The purpose of this discussion is to introduce readers to basic principles that underpin the applications of tracer techniques to fluid flow investigations.

The general concept of the tracer experiment is illustrated in Figure 8.1. It involves a three-stage process: (a) injecting the tracer T at A; (b) observing the response of the detector to the tracer at B; and (c) using the data to enhance knowledge of the ‘system’. As indicated in Section 8.2.1, the term ‘system’ may be interpreted in a very broad way. However, this discussion will be restricted to water flowing along a pipeline or through a rapidly stirred tank (Figure 8.6(b)).

Let it be assumed that the tracer T is injected into the bulk flow as a short pulse and traverses the cross section B in the time interval between t0 and (t0 + dt). A simple expression will be developed for the average transit time or residence time for water particles between the point of injection of the tracer A, and the sampling cross section at B. This expression will be used as the basis for:

• determining the mean residence time and residence time distribution of the tracer ‘particles’ between A and B;

• establishing the criterion for complete mixing of the tracer with the bulk flow of the water;

• measuring the flow rate of water at B assuming complete mixing has been achieved.

Residence time distributions of tracer particles between the points of injection and sampling

Suppose NT ‘particles’ of the tracer t are injected as an instantaneous pulse at A, are diluted and dispersed within the system (Figure 8.1) and monitored at B.

The penetrating power of nuclear radiations

Chapter 3 dealt with selected properties of ionising radiations emitted by radionuclides with emphasis on the properties of X and γ rays and this emphasis will continue in the present chapter.

Gamma rays are useful for applications because of their high penetrating power (Section 1.3.5). Other applications utilise the short or very short ranges in matter of α or β particles, e.g. for the manufacture of paper or plastic materials to be discussed in Section 7.3.2. The large majority of industrial applications require radiations that are capable of transmitting information to a detector after travelling through a few centimetres of a metal or equivalent thicknesses of other materials, which is most effectively done by sufficiently energetic γ rays, about 0.5 MeV or higher.

Electrically uncharged neutrons also have high penetrating powers, although they are strongly absorbed by some elements (Section 1.3.6). Being equal in mass to protons, their interactions with matter are subject to different rules than that of massless γ rays (Table 1.2) Additional information about neutrons will be given in Section 5.4.4 in preparation for the numerous important applications to follow in Section 7.4.

It is again emphasised that radionuclides and the emitted radiations should only be used if one is sufficiently familiar with their characteristics (see below). Familiarity is also required with methods for the preparation of radioactive sources, with the success or failure of a project often depending on how well this has been done.

Introduction

Radiotracers come on the scene

The first use of radiotracers happened almost by accident. In 1912, two Austrian-Hungarian chemists G. de Hevesey and F.A. Paneth, research students at Professor Rutherford's Manchester laboratory, were challenged by Rutherford to demonstrate their chemical skills by separating minute traces of radium-D, as it was then known, from the lead with which it was associated and which had been derived from uranium deposits. They worked hard for two years but had to conclude that radium-D and lead must belong to a group of ‘practically inseparable substances’ later known as isotopes.

De Hevesey, a future Nobel Laureate, then conceived the idea of adding radium-D (subsequently identified as 210Pb, a β particle emitting isotope of lead), to bulk lead and use the emitted β particles to trace sparingly soluble lead salts. It worked ‘like a charm’ and was the first example of radio-tracing. Applications to many aspects of chemistry, biology and agriculture soon followed. Through the 1920s, progress was limited by the fact that the only radiotracers available were those separated from naturally radio- active materials. This was to change dramatically in the following years with:

• the discovery of artificial radioactivity by Frederick Joliot and Irene Joliot-Curie (early in1933);

• the construction in 1932 of the first cyclotron designed to produce radionuclides by M. S. Livingston and E. O. Lawrence;

• the discovery of neutron activation by Enrico Fermi in the mid-1930s (Section 1.3.3); and

• the construction in 1942 of the Chicago pile (nuclear fission reactor), by a team also led by Enrico Fermi, which opened the doors for the large scale production of radiotracers (Section 1.3.3).

Introduction

Chapter 1 introduced basic properties of radioactivity, including radio-activation processes and criteria for nuclear stability. Two other subjects necessary when applying radioactivity will be introduced in this chapter: units and standards employed for radioactivity measurements and radiation do simetry, and an introduction to rules and procedures developed to permit radiation applications to be carried out safely and efficiently with adequate protection from potentially harmful effects due to ionising radiations.

Appendix 2 at the end of this book lists publications carrying comprehensive information on health physics and radiation protection; these could be consulted if and when in doubt about safe operating conditions. The comments in this chapter and elsewhere in this book can cover no more than a small part of a large subject.

Units and standards of radioactivity

A summary of their characteristics

The consistency of results of physical measurements made in different locations depends on the consistency of the units employed for this purpose. All industrialised countries have passed laws accepting an international system of metric units for physical measurements known as Système International (SI) (BIPM, 1985) along with provisions for monitoring the coherence of these units by standards established in national and international standards laboratories. These laboratories cooperate around the globe to ensure that the units employed in their respective countries (see Section 2.3.2 below) are identical in size with those used in other countries, an essential activity because units for physical measurements have high industrial and commercial as well as scientific importance.

I welcome the publication of the book Practical Applications of Radioactivity and Nuclear Radiations – An introductory text for engineers, scientists, teachers and students by Drs Gerhart Lowenthal and Peter Airey.

This book aims to provide readily accessible information on the applications of nuclear science and technology to industry, the environment and scientific research. It is tailored to students and non-specialists who seek to be informed, and may eventually wish to contribute to this world-wide endeavour. Emphasis is placed on the science underpinning the applications.

An objective of international bodies such as the Forum for Nuclear Cooperation in Asia (FNCA) and the International Atomic Energy Agency (IAEA) is to extend the benefits of nuclear related technologies across national boundaries. One of the authors (P.A.) was involved for a number of years in this endeavour through the IAEA.

I am pleased to endorse this book as a further step in this on-going quest.

The discovery of X rays and radioactivity in the 1890s had a profound effect on the century which was to follow. After more than one hundred years of endeavour which has been both marred by conflict and enriched by high achievement, we enter the new millennium with a more mature understanding of the benefits that nuclear technology can bring to mankind.

I review the two main aspects of convection modeling important for the stellar structure: i) the determination of the temperature gradient in the stellar interior, and in particular in the superadiabatic part of the envelope, which plays a key role for the determination of the stellar Teff; ii) the description of chemical mixing –mainly in the presence of nuclear burning. I discuss these two aspects in general, and their importance for low and very low mass stars and brown dwarfs structures.

In particular, I discuss the uncertainty (of ∼ 200K) in the Teff of masses M ≲ 0.1 M⊙ in the phase of Deuterium burning, and the role of mixing in the problem of Lithium burning in very low masses. For this latter problem, I show that the relation between the age of a cluster and the luminosity of the lithium depletion edge is not only independent of the mixing timescale, but also independent of the metallicity, in the population I range, so that the Lithium test can be safely used as an age indicator.

Modeling convection: MLT and FST models

A convection model for general use in stellar structure relies on the computation of two main quantities: the fluxes and the scale length ∧. As the models presently available are all local, one can not expect that the description be unique, so there will be also one or more tuning parameters.