【国外标准】 Standard Guide for Dosimetry In Radiation Processing of Fluidized Beds and Fluid Streams (Withdrawn 2016)

Dosimetric Techniques—The processes addressed here utilize a variety of techniques for the dynamic presentation of the product to the radiation source. This may involve gravitational flow or simple pneumatic transport about or past the radiation source. In the case of fluidized beds, the product may be presented to the radiation source while supported in a gaseous or liquid stream moving at relatively high velocities. This document provides a guide to the dosimetric techniques suitable for these processes. Food Products—Food products may be treated with ionizing radiation, such as energetic electrons from accelerators or gamma rays from 60Co or 137Cs sources, or X-rays, for numerous purposes, including control of parasites and pathogenic microorganisms, insect disinfestation, growth and maturation inhibition, and shelf-life extension. Note 1—Food irradiation specifications usually include upper and lower limits of absorbed dose: a minimum to ensure the intended beneficial effect and a maximum to avoid product degradation. For a given application, one or both of these values may be prescribed by regulations that have been established on the basis of available scientific data. Therefore, it is necessary to determine the capability of an irradiation facility to process within these absorbed-dose limits prior to the irradiation of the food product. Once this capability is established, it may be necessary to monitor and record the dose range delivered to the product during each production run to verify compliance with the process specifications within a predetermined level of confidence. Randomized Flow—In a stream of randomized flow; i.e. turbulent instead of laminar, variations occur which lead to a dose distribution for the particles entrained in the stream. The “idealized” maximum and minimum doses possible can be calculated based upon knowledge of the applied dose rate, the product dwell time in the irradiation cell and the product or bed thickness. The experimentally determined maximum and minimum doses delivered to each particle, should not be confused with these idealized dose limits. Treatment range—The location of the product (or of the dosimeter) in the fluidized bed or stream will determine its absorbed dose during passage through the radiation field. The experimental dose measurements in the fluidized bed or stream will define the range of product dose. The desired effect imparted to the product by irradiation will then be based upon this range of product dose and not upon maximum or minimum dose. Note 2—In situations where a randomized mixing within the fluidized bed occurs with the intention that the particles or fluid elements pass through several radiation zones and accumulate a total dose with different dose rates, maximum and minimum dose values are difficult to determine and must be based on the results for the experimental dosimetry irradiated with the product . In the case of fluids, stirring after processing results only in effective treatment at a mean dose; no max and min dose measurement. For example, lethality curves will be determined as a function of this range of product treatment to the product in the fluidized bed or stream as determined by dosimetric techniques.1.1 This guide describes several dosimetry systems and methods suitable for the documentation of the irradiation of product transported as fluid or in a fluidized bed. 1.2 The sources of penetrating ionizing radiation included in this guide are electron beams, X-rays (bremsstrahlung) and gamma rays. 1.3 Absorbed doses from 10 to 100,000 gray are considered, including applications such as disinfestation, disinfection, bioburden reduction, sterilization, crosslinking and graft modification of products, particularly powders and aggregates. 1.4 This guide does not purport to address the safety concerns, if any, associated with the use of fluidized beds and streams incorporating sources of ionizing radiation. It is the responsibility of the user of this guide to establish appropriate safety and health practices and to determine compliance with regulatory limitations prior to use.