The penetrability of X-rays produced from 3 -Mev„ accelerated electrons is 

 almost identical to that of gamma rays produced from cobalt 60 o Therefore, in 

 this study we consider 3-Mev. X-rays and gamma rays from cobalt 60 to be equally 

 effective for use in food irradiation, 



For a given target, the conversion efficiency of accelerated electrons to X-rays 

 depends on the electron kinetic energy expressed in Mev D For tungsten, these 

 calculated forward X~ray production efficiencies apply (9): 



Forward X-ray production 

 Electron kinetic energy efficiency 



Mev. Percent 



1 2.0 



2 „ 4.1 



3 6.2 



5 11.0 



10 18.7 



These data show that X-ray production efficiency can be improved by increasing the 

 energy of the accelerated electrons from which the X-rays are producedo 



Facility Output 



The potential volume of produce that can be radiation-pasteurized by a radiation 

 facility is directly related to these factors: 



1. The size of the radiation source . The facility sizes considered in this study 

 are, for cobalt 60, 1 and 3 kilowatts, and for X-ray machine, 3 kilowatts,, 



2. The radiation dose . As referred to in this discussion, applied radiation is the 

 radiation striking the surface of a package being irradiated, as distinguished from 

 radiation absorbed by it. Absorbed radiation dosage varies by location in the 3- 

 dimensional space of an irradiated package. The acceptable rule-of-thumb for 

 computing absorbed dosage variation within an irradiated product is represented by 

 the minimum to maximum ratio 1:1.25. 



Technical research on radiation-pasteurization of fresh strawberries indicates 

 that (1) 175 kilorads are required as a rninirnurn absorbed radiation dosage for good 

 results, (2) 200 kilorads are optimum, and (3) 225 kilorads are a permissible maxi- 

 mum. According to the 1:1.25 rule°of-thumb, an absorbed dosage of 218.75 kilorads 

 is needed to assure that the minimum of 175 kilorads will be met (175 kilorads 

 multiplied by 1.25 = 218.75 kilorads). Therefore, an application dosage level of 220 

 kilorads is considered in this study. 



3. The net utilization efficiency of the radiation source. This refers to the 

 percentage of total radiation emanation absorbed by the material being irradiated. 

 The net utilization efficiency of an ionizing radiation source is the product of (a) 

 the percentage of area efficiency, and (b) the percentage of thickness efficiency of 

 absorption. In this analysis, the area efficiency of irradiation refers to the dis- 

 tribution or dispersion of ionizing energy in the form of gamma rays or X-rays over 

 the product surface area. Similarly, the thickness efficiency of absorption refers to 

 the percentage of ionizing energy absorbed through the third dimension of the product. 

 This can be significantly influenced by the geometry (physical location) of the source 

 in relation to the package to be irradiated, the thickness of the package, and the 

 specific gravity of the product contained in it. 



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