Cosmic Rays at Earth

P.K.F. Grieder

• Publisher: Elsevier Science
• Year: 2001
• ISBN:
  9780080530055
• Topic: Physical Sciences
• Subtopic: Astronomy & Astrophysics

In 1912 Victor Franz Hess made the revolutionary discovery that ionizing radiation is incident upon the Earth from outer space. He showed with ground-based and balloon-borne detectors that the intensity of the radiation did not change significantly between day and night. Consequently, the sun could not be regarded as the sources of this radiation and the question of its origin remained unanswered. Today, almost one hundred years later the question of the origin of the cosmic radiation still remains a mystery.Hess' discovery has given an enormous impetus to large areas of science, in particular to physics, and has played a major role in the formation of our current understanding of universal evolution. For example, the development of new fields of research such as elementary particle physics, modern astrophysics and cosmology are direct consequences of this discovery. Over the years the field of cosmic ray research has evolved in various directions: Firstly, the field of particle physics that was initiated by the discovery of many so-called elementary particles in the cosmic radiation. There is a strong trend from the accelerator physics community to reenter the field of cosmic ray physics, now under the name of astroparticle physics. Secondly, an important branch of cosmic ray physics that has rapidly evolved in conjunction with space exploration concerns the low energy portion of the cosmic ray spectrum. Thirdly, the branch of research that is concerned with the origin, acceleration and propagation of the cosmic radiation represents a great challenge for astrophysics, astronomy and cosmology. Presently very popular fields of research have rapidly evolved, such as high-energy gamma ray and neutrino astronomy. In addition, high-energy neutrino astronomy may soon initiate as a likely spin-off neutrino tomography of the Earth and thus open a unique new branch of geophysical research of the interior of the Earth. Finally, of considerable interest are the biological and medical aspects of the cosmic radiation because of it ionizing character and the inevitable irradiation to which we are exposed.

This book is a reference manual for researchers and students of cosmic ray physics and associated fields and phenomena. It is not intended to be a tutorial. However, the book contains an adequate amount of background materials that its content should be useful to a broad community of scientists and professionals. The present book contains chiefly a data collection in compact form that covers the cosmic radiation in the vicinity of the Earth, in the Earth's atmosphere, at sea level and underground. Included are predominantly experimental but also theoretical data. In addition the book contains related data, definitions and important relations. The aim of this book is to offer the reader in a single volume a readily available comprehensive set of data that will save him the need of frequent time consuming literature searches.

Chapter 1

Cosmic Ray Properties, Relations and Definitions

1.1 Introduction

1.1.1 General Comments

This chapter contains a very rudimentary description of the relevant processes that govern the gross features of cosmic ray phenomena in the vicinity of the Earth, in the atmosphere and underground, and summarizes the mathematical relations that describe them. It also contains definitions of various concepts and frequently used quantities, and data of the atmosphere. It is not intended to be a tutorial for newcomers to the field.

Cosmic ray physics covers a wide range of disciplines ranging from particle physics to astrophysics and astronomy. Those who want to enter the field should consult appropriate text books that deal with the particular topics of interest (For an introduction see e.g. Sandström, 1965; Allkofer, 1975; for more specific topics such as extensive air showers see Galbraith, 1958; Khristiansen, 1980; Sokolsky, 1989; for high energy interactions, etc., see Gaisser, 1990).

The purpose of this chapter is twofold. For the researcher who is familiar with the field and is using the data in the subsequent chapters for his work, relations, definitions and cosmic ray related data that may not be readily available are placed at his finger tips. On the other hand, for those workers that are not particularly interested in cosmic ray research but need the data that are presented in the following chapters for their work, such as biologists, health physicists and others, it serves as an overview and brief introduction to cosmic ray physics.

1.1.2 Heliospheric Effects and Solar Modulation

The primary cosmic radiation which consists predominantly of protons, alpha particles and heavier nuclei is influenced by the galactic, the interplanetary, the magnetospheric and the geomagnetic magnetic fields while approaching the Earth. The interplanetary magnetic field (IMF) amounts to about 5 nanotesla [nT] (or 50 μG) at the Earth’s orbit. The magnetospheric field is the sum of the current fields within the space bound by the magnetopause and is subject to significant variability, while the geomagnetic field is generated by sources inside the Earth and undergoes secular changes. The combined fields are typically 30 to 60 μT (0.3 – 0.6 G) at the Earth’s surface, depending on the location. Time dependent variations are on the order of one percent. The electrically charged secondary cosmic ray component produced in the atmosphere is also subject to geomagnetic effects. Further details concerning these subjects are discussed in Section 1.8.

The cosmic ray flux is modulated by solar activity. It manifests an 11 year cycle and for certain effects also a 22 year cycle, and other solar influences. It should be remembered that the solar minimum and maximum cycle is 11 years and that the solar magnetic dipole flips polarity every solar maximum, thus imposing a 22 year cycle as well. Both cycles cause various effects on the galactic cosmic radiation in the heliosphere. The modulation effects decrease with increasing energy and become insignificant for particles with rigidities in excess of ∼10 GV. Solar modulation effects and terminology are summarized in Chapter 6.

1.2 Propagation of the Hadronic Component in the Atmosphere

1.2.1 Strong Interactions

Upon entering the atmosphere the primary cosmic radiation is subject to interactions with the electrons and nuclei of atoms and molecules that constitute the air. As a result the composition of the radiation changes as it propagates through the atmosphere. All particles suffer energy losses through hadronic and/or electromagnetic processes.

Incident hadrons are subject to strong interactions when colliding with atmospheric nuclei, such as nitrogen and oxygen. Above an energy of a few GeV, local penetrating particle showers are produced, resulting from the creation of mesons and other secondary particles in the collisions. Energetic primaries and in case of heavy primaries their spallation fragments continue to propagate in the atmosphere and interact successively, producing more particles a...

Table of contents

• Cover image
• Title page
• Table of Contents
• Cover
• Copyright
• Dedication
• Preface
• Comments for Reader
• Acknowledgements
• Chapter 1: Cosmic Ray Properties, Relations and Definitions
• Chapter 2: Cosmic Rays in the Atmosphere
• Chapter 3: Cosmic Rays at Sea Level
• Chapter 4: Cosmic Rays Underground, Underwater and Under Ice
• Chapter 5: Primary Cosmic Radiation
• Chapter 6: Heliospheric Phenomena
• Chapter 7: Miscellaneous Topics
• Appendix A: Miscellaneous Data: Tables
• Appendix B: Miscellaneous Data: Figures
• Appendix C: Cosmic Ray Experiments of Past and Present
• Appendix D: Miscellany
• Index