Technical Reports Series No. 409 Dosimetry for Food Irradiation INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 2002 DOSIMETRY FOR FOOD IRRADIATION The following States are Members of the International Atomic Energy Agency: AFGHANISTAN GHANA PANAMA ALBANIA GREECE PARAGUAY ALGERIA GUATEMALA PERU ANGOLA HAITI PHILIPPINES ARGENTINA HOLY SEE POLAND ARMENIA HUNGARY PORTUGAL AUSTRALIA ICELAND QATAR AUSTRIA INDIA REPUBLIC OF MOLDOVA AZERBAIJAN INDONESIA ROMANIA BANGLADESH IRAN, ISLAMIC REPUBLIC OF RUSSIAN FEDERATION BELARUS IRAQ SAUDI ARABIA BELGIUM IRELAND SENEGAL BENIN ISRAEL SIERRA LEONE BOLIVIA ITALY SINGAPORE BOSNIA AND HERZEGOVINA JAMAICA SLOVAKIA BOTSWANA JAPAN SLOVENIA BRAZIL JORDAN SOUTH AFRICA BULGARIA KAZAKHSTAN SPAIN BURKINA FASO KENYA SRI LANKA CAMBODIA KOREA, REPUBLIC OF SUDAN CAMEROON KUWAIT SWEDEN CANADA LATVIA SWITZERLAND CENTRAL AFRICAN LEBANON SYRIAN ARAB REPUBLIC REPUBLIC LIBERIA TAJIKISTAN CHILE LIBYAN ARAB JAMAHIRIYA THAILAND CHINA LIECHTENSTEIN THE FORMER YUGOSLAV COLOMBIA LITHUANIA REPUBLIC OF MACEDONIA COSTA RICA LUXEMBOURG TUNISIA CÔTE D’IVOIRE MADAGASCAR TURKEY CROATIA MALAYSIA UGANDA CUBA MALI UKRAINE CYPRUS MALTA UNITED ARAB EMIRATES CZECH REPUBLIC MARSHALL ISLANDS UNITED KINGDOM OF DEMOCRATIC REPUBLIC MAURITIUS GREAT BRITAIN AND OF THE CONGO MEXICO NORTHERN IRELAND DENMARK MONACO UNITED REPUBLIC DOMINICAN REPUBLIC MONGOLIA OF TANZANIA ECUADOR MOROCCO UNITED STATES OF AMERICA EGYPT MYANMAR URUGUAY EL SALVADOR NAMIBIA UZBEKISTAN ESTONIA NETHERLANDS VENEZUELA ETHIOPIA NEW ZEALAND VIET NAM FINLAND NICARAGUA YEMEN FRANCE NIGER YUGOSLAVIA, GABON NIGERIA FEDERAL REPUBLIC OF GEORGIA NORWAY ZAMBIA GERMANY PAKISTAN ZIMBABWE The Agency’s Statute was approved on 23 October 1956 by the Conference on the Statute of the IAEA held at United Nations Headquarters, New York; it entered into force on 29 July 1957. The Headquarters of the Agency are situated in Vienna. Its principal objective is “to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world’’. © IAEA, 2002 Permission to reproduce or translate the information contained in this publication may be obtained by writing to the International Atomic Energy Agency, Wagramer Strasse 5, P.O. Box 100, A-1400 Vienna, Austria. Printed by the IAEA in Austria October 2002 STI/DOC/010/409 TECHNICAL REPORTS SERIES No. 409 DOSIMETRY FOR FOOD IRRADIATION INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 2002 VIC Library Cataloguing in Publication Data Dosimetry for food irradiation. — Vienna : International Atomic Energy Agency, 2002. p. ; 24 cm. — (Technical report series, ISSN 0074–1914 ; no. 409) STI/DOC/010/409 ISBN 92–0–115502–6 Includes bibliographical references. 1. Food — Preservation. 2. Ionizing radiation. 3. Radiation preservation of food. 4. Radiation dosimetry. I. International Atomic Energy Agency. II. Series: Technical reports series (International Atomic Energy Agency) ; 409. VICL 02–00294 FOREWORD A Manual of Food Irradiation Dosimetry was published in 1977 under the auspices of the IAEA as Technical Reports Series No. 178. It was the first monograph of its kind and served as a reference in the field of radiation processing and in the development of standards. While the essential information about radiation dosimetry in this publication has not become obsolete, other publications on radiation dosimetry have become available which have provided useful information for incorporation in this updated version. There is already a Codex General Standard for Irradiated Foods and an associated Code of Practice for Operation of Irradiation Facilities used for Treatment of Food, issued in 1984 by the Codex Alimentarius Commission of the FAO/WHO Food Standard Programme. The Codex Standard contains provisions on irradiation facilities and process control which include, among other requirements, that control of the processes within facilities shall include the keeping of adequate records including quantitative dosimetry. Appendix A of the Standard provides an explanation of process control and dosimetric requirements in compliance with the Codex Standard. By 1999, over 40 countries had implemented national regulations or issued specific approval for certain irradiated food items/classes of food based on the principles of the Codex Standard and its Code of Practice. Food irradiation is thus expanding, as over 30 countries are now actually applying this process for the treatment of one or more food products for commercial purposes. Irradiated foods are being marketed at retail level in several countries. With the increasing recognition and application of irradiation as a sanitary and phytosanitary treatment of food based on the provisions of the Agreement on the Application of Sanitary and Phytosanitary Measures of the World Trade Organization, international trade in irradiated food is expected to expand during the next decade. It is therefore essential that proper dosimetry systems are used to ensure the compliance of trade in irradiated food with national and international standards. In view of the foregoing, FAO and the IAEA, through their Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Vienna, considered it timely to revise the Manual of Food Irradiation Dosimetry. A Consultants’ Meeting was convened in Vienna from 27 to 30 October 1998 to revise the Manual. It was attended by R. Chu, MDS Nordion, Kanata, Canada; I. de Bruyn, Atomic Energy Corporation of South Africa Ltd, Pretoria; D.A.E. Ehlermann, Federal Research Centre for Nutrition, Karlsruhe, Germany; W.L. McLaughlin, National Institute of Science and Technology, Gaithersburg, Maryland, USA; P. Thomas, Bhabha Atomic Research Centre, Mumbai, India. Subsequently, D.A.E. Ehlermann incorporated contributions from the other participants and from IAEA staff members, and finally K. Mehta revised and edited the document. EDITORIAL NOTE Although great care has been taken to maintain the accuracy of information contained in this publication, neither the IAEA nor its Member States assume any responsibility for consequences which may arise from its use. The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA. An appendix, when included, is considered to form an integral part of the standard and to have the same status as the main text. Annexes, footnotes and bibliographies, if included, are used to provide additional information or practical examples that might be helpful to the user. CONTENTS 1. GENERAL ASPECTS OF FOOD IRRADIATION . 1 1.1. Introduction . 1 1.2. Codex Alimentarius provisions . 2 1.3. International trade aspects . 3 1.4. Advisory technological dose limits . 4 1.4.1. Applications at low dose levels (10 Gy–1 kGy) . 6 1.4.2. Applications at medium dose levels (1–10 kGy) . 6 1.4.3. Applications at high dose levels (10–100 kGy) . 7 1.5. Need for dosimetry . 7 1.6. Objectives . 8 1.7. Scope . 8 2. FUNDAMENTALS OF DOSIMETRY . 9 2.1. Introduction . 9 2.2. Absorbed dose . 10 2.3. Interaction of radiation with matter . 12 2.3.1. Physical aspects of radiation absorption . 12 2.3.2. Depth–dose distribution . 14 2.3.3. Electron equilibrium . 18 2.4. Dosimetry systems . 21 2.4.1. Classes of dosimeter . 21 2.4.2. Characterization of dosimetry systems . 22 2.4.2.1. Calibration . 23 2.4.2.2. Traceability . 24 2.4.2.3. Batch homogeneity . 27 2.4.2.4. Uncertainty in dose measurement . 27 2.4.2.5. Influence quantities . 27 2.5. Selection criteria for routine dosimeters . 28 2.6. Uncertainty in dosimetry . 28 2.7. Use of dosimeters . 31 3. IRRADIATOR DESIGN CONCEPTS . 32 3.1. Introduction . 32 3.2. Criteria for irradiator design . 33 3.3. Selection of radiation source . 36 3.3.1. Gamma rays . 36 3.3.2. Electrons . 37 3.3.3. Bremsstrahlung (X rays) . 38 3.3.4. Dose distribution in the product . 40 3.4. Specific irradiator designs . 41 3.4.1. Radionuclide source irradiators . 42 3.4.1.1. Stationary irradiators . 43 3.4.1.2. One direction multipass irradiators . 43 3.4.1.3. Two direction multipass irradiators (product overlap irradiators) . 44 3.4.1.4. Other irradiator concepts . 47 3.4.2. Accelerator irradiators . 49 3.4.2.1. Stationary type accelerator irradiators . 50 3.4.2.2. One direction one pass irradiators . 50 3.4.2.3. Two direction two pass irradiators . 51 3.4.2.4. Beam scanning and dose uniformity . 52 4. PROCESS VALIDATION . 53 4.1. General . 53 4.2. Product qualification . 54 4.3. Facility qualification . 54 4.3.1. General . 54 4.3.2. Characterization of the facility . 55 4.3.2.1. Radionuclide source irradiators . 55 4.3.2.2. Accelerator irradiators . 57 4.3.2.3. Dosimetry systems . 59 4.3.3. Reference dose mapping . 59 4.3.3.1. Radionuclide source irradiators . 60 4.3.3.2. Accelerator irradiators . 61 4.3.4. System variability . 63 4.4. Process qualification . 65 4.4.1. Objectives . 65 4.4.2. Product dose mapping . 66 4.4.2.1. Special process loads . 67 4.4.3. Verification process . 68 4.4.4. Process parameters . 69 4.4.5. Reference dosimetry location . 72 4.5. Documentation and certification . 72 5. FACILITY OPERATION AND PROCESS CONTROL . 73 5.1. General . 73 5.2. Facility operation . 74 5.3. Process control . 76 5.3.1. Process parameters . 77 5.3.2. Routine product dosimetry . 78 5.3.3. Product control . 80 5.3.4. Process interruption . ..