A COMPARATIVE CALCULATION OF DOSE RATE USING RAD PRO CALCULATOR FOR SHIELDING REQUIREMENTS OF COBALT-60 AND CESIUM-137 SOURCES AT CERT.

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A COMPARATIVE CALCULATION OF DOSE RATE USING RAD PRO CALCULATOR FOR SHIELDING REQUIREMENTS OF COBALT-60 AND CESIUM-137 SOURCES AT CERT.

 

CHAPTER ONE

1.0 INTRODUCTION

1.1 General Background

The term shielding implies the deliberate introduction of material between the radiation and an object to reduce radiation intensity and damage to the object. This is preferred method of controlling radiation because it results in intrinsic safe working conditions (Martin and Harbison, 1980). The type of shielding used and the thickness require depend on the type of radiation, its energy, the flux and the dimension of the source (Esien-umo, 2007).

1.1.1 Shielding of x-ray generators:

The hazards of x rays were recognized within months of Roentgen’s 1895 discovery, but dose limitation by time, distance, and shielding was at the discretion of the individual practitioner until about 1913. Only then were there organized professional efforts to establish guides for radiation protection, and not until about 1925 were there instruments available to quantify radiation exposure. In his monumental survey of organization for radiation protection, Taylor (1979) begins with British and German efforts at establishing guidance for x-ray shielding. In 1913, the German Radiological Society on X-Ray Protection Measures issued recommendations that 2 mm of lead shielding was needed, regardless of generator voltage, workload, or filtration. In Britain, the Roentgen Society addressed radiation protection, stressing operator protection, the need for beam collimation, and the importance of scattered X rays. No explicit recommendations on shielding requirements were issued.

1.1.2 Shielding of Radium sources:

In 1927, the International Committee on X-Ray and Radium Protection issued the following recommendations for storage of radium sources. Tubes and applicators should have at least 5 cm of lead shielding per 100 mg of radium. Radium solutions required lead shielding ranging from 15 cm for a 0.5 g source to 30 cm for a 2g source. NCRP Report 2 (1934) specified a 3-m protective zone around stored Ra sources, and recommended exhaust fans or hoods for removal of radon and decay products escaping from unsealed sources. Shielding of stored sources was revised to 4 cm of lead for 100 mg to 6 cm for 300 mg. NCRP Report 4 (1938) addressed dosimetry for gamma rays emitted from radium sources. It was not until 1941 that there was established a tolerance dose for radium, expressed in terms of a maximum permissible body burden of 0.1 Ci. This was done largely in consideration of the experiences of early “radium-dial” painters and the need for standards on safe handling of radioactive luminous compounds (NCRP, 1941).

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A COMPARATIVE CALCULATION OF DOSE RATE USING RAD PRO CALCULATOR FOR SHIELDING REQUIREMENTS OF COBALT-60 AND CESIUM-137 SOURCES AT CERT.