Progress in Nuclear Physics (eBook)

O. R. Frisch (Herausgeber)

eBook Download: EPUB

2013 | 1. Auflage
316 Seiten
Elsevier Science (Verlag)
978-1-4831-6470-0 (ISBN)

Infos

Progress in Nuclear Physics, Volume 9 is a collection of six papers dealing with nuclear physics. The monograph discusses the significance of visual techniques in the development of high energy physics; the development of solid semiconductor detectors; theoretical techniques of high-energy beam design; and the structure analysis of collision amplitudes. The book explains that the spark technique is preferred over the bubble chamber when used in experiments with continuous sources of radiation. The use of germanium and silicon semiconductor detectors has enabled advances in studies on protons, alphas, and heavy ions, through fast response time, ease of construction, and simple power requirements. The problems encountered in beam design and effective uses of large accelerators are discussed extensively. For example, the book explains that inefficient beam practice can diminish intensity factors in the accelerator, so different beam designs such as the quadruple and the separated beam design as well as the pulsed high-field magnets are considered. The link between theory and experiment of collision amplitudes is reviewed, including structure analysis in the physics of elementary particles. The resulting processes after strange particles such as K-mesons interact with nuclei, instead of reacting with individual nucleons, are briefly noted. The text also includes discussion on the essential electromagnetic properties of the muon and the different research by Crowe, Charpak et al., and Hughes et al. about this subject. This collection of papers will prove useful for nuclear physicists, scientists, and academicians in the field of nuclear physics.

Textauszug

2

SEMICONDUCTOR COUNTERS

G. Dearnaley

Publisher Summary

Semiconductor junction detectors have many advantages for applications in low-energy nuclear physics, and no experiment with charged particles should in future be designed without full consideration of the possibilities of the new detectors. The design of amplifiers has already been influenced by the requirements of semiconductor counters, but there are still many problems in handling and storing the wealth of data that can be obtained with a number of detectors operated simultaneously. Conduction counters are at present at an earlier stage of development, but in many ways are simpler to understand than junction counters. This chapter discusses the applications of semiconductor counters in nuclear physics. The study of semiconductor detectors and their response to nuclear radiation provides a valuable new method of investigating the solid-state physics of semiconductors. There are many possible experiments in this field if only those who practise these two branches of physics can be brought together. Advances in the physics of semiconductors and in the technology of their preparation will make new developments in radiation detectors possible.

CONTENTS

1 INTRODUCTION

2 INSULATORS AND SEMICONDUCTORS

(a). An outline of the theory and nomenclature

(b). Semiconductor junctions

3 CONDUCTION COUNTERS

(a). The requirements and advantages of solid counters

(b). Methods of preparation and performance

4 SEMICONDUCTOR JUNCTION DETECTORS

(a). The use of junctions in particle detection

(b). Preparation of junction detectors

(i). Diffused junctions

(ii). Surface-barrier detectors

(iii). Lithium-drifted detectors

(c). Characteristics of junction detectors

(d). Comparison of diffused-junction and surface-barrier counters

5 PULSE AMPLIFIERS FOR SEMICONDUCTOR DETECTORS

6 APPLICATION OF SEMICONDUCTOR COUNTERS IN NUCLEAR PHYSICS

(a). General applications

(b). Silicon dE/dx detector

(c). Detector for polarization studies

(d). Multiple detectors

(e). Semiconductor fast-neutron detectors

7 CONCLUSIONS

REFERENCES

1 INTRODUCTION

THE recent development of solid semiconductor detectors, first of germanium and then of silicon, has revolutionized the study of charged nuclear particles such as protons, alphas and heavy ions in low-energy nuclear physics. Detectors consisting of a p – n junction in one of these materials have excellent energy resolution and linearity of response. They give a fast signal and are relatively insensitive to gamma-rays and neutrons. They also have the advantages of a very compact size, ease of construction and simple power supply requirements. Their simplicity allows them to be adapted to a variety of applications.

The basis of their operation is the collection, by a strong electric field, of the electrons released by ionization along the path of the charged particle. In this respect they are similar to the solid conduction counters or crystal counters of such insulators as diamond, silver halides, sodium chloride and cadmium sulphide. The properties and limitations of conduction counters were described in an earlier article in this series by CHAMPION (1953). The sensitive volume of a semiconductor junction detector is limited in thickness to a few millimetres whereas the conduction counter is sensitive throughout the volume of the crystal. For the study of betas, gammas and high-energy particles, therefore, the conduction counter has much greater possibilities. The availability of large silicon crystals of high purity and crystalline perfection has contributed much to the development of junction detectors. A simple introductory treatment of the behaviour of a semiconductor p – n junction will be given in Section 2. It has also been possible to make significant improvements in the performance of conduction counters by the use of silicon crystals, while other semiconductors such as gallium arsenide seem promising for this field in the future.

CHAMPION (1953) described how, in the conduction counter, a small crystal of insulator may be operated as a solid ionization chamber, the electric field being applied between plane electrodes. Owing to crystalline imperfections and the presence of impurity atoms the performance of these counters was very variable; only about one diamond in a thousand, for example, showed counting properties. The energy resolution achieved with these counters was rather poor and their properties changed with time owing to polarization effects. As a result they were used only rarely in nuclear physics.

Modem semiconducting materials can be prepared with uniform and controllable properties, and if by some means the conductivity of the crystal can be reduced sufficiently a conduction counter can be produced. The mobility of electrons in such pure crystals is generally much greater than in the substances earlier employed. Such conduction counters have been prepared by VAN PUTTEN and VAN DER VELDE (1961) with gold-doped silicon at 140°K, by GIBBONS and NORTHROP (1960) with “thermally-compensated” silicon at 78°K, and by HARDING, HILSUM, MONCASTER, NORTHROP and SIMPSON (1960) with oxygen-compensated gallium arsenide at room temperature. GIBBONS and NORTHROP (1962) have obtained about 10% energy resolution for 1·3 MeV gamma-rays in a 6 mm cube detector and conclude that inhomogeneities in material were the principal cause of line-broadening. These types of semiconductor detector will be considered in more detail in Section 3. It seems quite feasible that larger volume conduction counters will eventually be prepared which are suitable for high-resolution gamma-ray spectroscopy.

As early as 1949, K. G. MCKAY at Bell Telephone Laboratories had shown that a p – n junction in the semiconductor germanium would detect alpha particles. The arrangement he employed is shown in Fig. 1. The absence of trapping or recombination enabled a counting efficiency close to 100% to be achieved and there was no polarization, both factors indicating a distinct improvement over the performance of conduction counters at that time. Since the junction was a simple point contact only a small area about 10−3 cm in a diameter was sensitive to charged particles in this counter. Work ten years ago at Purdue University under LARK-HOROWITZ on germanium photovoltaic cells and on radiation damage in semiconductors by charged particles paved the way for the development of the first useful semiconductor detectors. In 1957, MAYER and GOSSICK at Purdue showed that in a gold-coated germanium detector in which the p – n junction is very close to the crystal surface, as in a photovoltaic cell, the whole area of the junction could be made sensitive to alpha-particles. In the same year in the U.S.S.R. AIRAPETIANTS and RYVKIN (1957) showed that the performance was improved by cooling the germanium. The first application of germanium detectors was made by WALTERS, DABBS, ROBERTS and WRIGHT (1958) in measurements on the alpha emission of nuclei oriented at low temperatures. They obtained 4% energy resolution for alphas of 5 MeV in a 1 cm2 detector, the design of which is shown in Fig. 2.

FIG. 1 Arrangement used by MCKAY for the first p–n junction counter (MCKAY, 1949).

FIG. 2 Structure of the germanium counter of WALTER, DABBS, ROBERTS and WRIGHT (1958).

Early in 1959 groups at Chalk River, Harwell, R.C.A. Victor (Montreal) and Hughes Aircraft Co. (Los Angeles) began to experiment with junction counters of silicon, suitable for use at room temperature. The great practical advantage of this has caused germanium to be almost completely superseded by silicon for detector preparation today. The two principal methods of forming a p – n junction are by diffusion and by what is termed the surface-barrier technique. These processes and a comparison of the two forms of junction counter will be given in Section 4.

The high electric field strength combined with low current in the...

Produkt-Details

• Erscheint lt. Verlag: 22.10.2013
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Quantenphysik
• Themenwelt: Technik
• ISBN-10: 1-4831-6470-5 / 1483164705
• ISBN-13: 978-1-4831-6470-0 / 9781483164700