ENGINEERING RESEARCH INSTITUTE THE UNIVERSITY OF MICHIGAN ANN ARBOR HIGH RADIOPASTEURIZATION AS A "NEW" FOOD PROCESS L. E. Brownell S. N.u-rohit Project 194 -7 U.S. ATOMIC ENERGY COMMISSION CONTRACT NO. AT(ll-)-162 October 1955

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TABLE OF CONTENTS Page LIST OF TABLES iii LIST OF FIGURES iv I. THE PROCESS OF HIGH RADIOPASTEURIZATION 1.1 A. REVIEW OF RADIATION-DOSE RANGES PROPOSED FOR FOODS 1.1 B. PRELIMINARY STUDIES OF HIGH RADIOPASTEURIZATION 1.2 C. THE WHOLESOMENESS OF HIGH-RADIOPASTEURIZED: FOODS 1.6 II. DESIGN OF A RADIATION FACILITY FOR HIGH RADIOPASTEURIZATION 1.13 A. DESIGN OF A RADIATION CHAMBER 1.14 B. RADIATION SOURCE 1.17 C. ISODOSE CURVES 1.21 D. INTEGRAL DOSE CURVE 1.26 E. CAPACITY CALCULATION 1.26 F. CAPACITY COMPARISONS 1.30 G. COST ESTIMATES 1.31 H. UNIT COSTS 1.32 I. SHIELDING CALCULATIONS 1.32 J. DISCUSSION AND SUMMARY 1.34 REFERENCES 1.36 ii

LIST OF TABLES Table Page I RECENT HISTORY OF OUTBREAKS OF BOTULISM, 1931-1941 1.7 II HEAT RESISTANCE OF TYPES A AND B CLOSTRIDIUM BOTULINUM 1.8 III HEAT RESITANCE OF TOXINS OF CLOSTRIDIUM BOTULINUM 1.9 IV SUMMARY OF CHARACTERISTICS OF FOOD POISONING CAUSED BY BACTERIA OR THEIR PRODUCTS 1.12 V CAPACITY COMPARISONS 1.30 VI UNIT COSTS 1.32 iii

LIST CF FIGURES Figure Page 1 Samples of irradiated and nonirradiated smoked salmon after removal from sealed polyethylene bags 1.3 2 Data on irradiated smoked salmon stored at room temperature (750-850F) 1.4 3 Irradiated broiled breast of chicken stored for two weeks at room temperature (75~-850F) 1.5 4 Control broiled breast of chicken stored for two weeks at room temperature (75~-85~F) 1.5 5 Elevation view of high-radiopasteurization chamber 1.15 6 Plan view of high-radiopasteurization chamber 1.16 7 Plan view showing spacing of one half of fuel elements for irradiation facility 1.18 8 Source elements, elevation view 1.18 9 H function vs distance from one fuel element (dose rate normalized to 105 r/hr at 3 feet from one fuel element) 1.20 10 Vertical distance vs dose rate for different values of x 1.22 11 Dose rate vs lateral distance from ~ of source for different values of z 1.23 12 Dose rate vs horizontal distance for different values of x 1.24 13 Isodose curves in vertial planeperpendicular to source at center line for one quadrant of radiation chamber 1.25 14 Absorption-corrected isodose curves 1.27 15 Absorption-corrected dose vs vertical distance 1.28 16 Integral dose curve for half cycle (44') 1.29 17 Extrapolated curve for shielding calculations 1.53 iv

LIST OF FIGURES (concluded) Figure Page 14 Absorption-corrected isodose curves 1.27 15 Absorption-corrected dose vs vertical distance 1.28 16 Integral dose curve for half cycle (44') 1.29 17 Extrapolated curve for shielding calculations 1.33 v

HIGH RADIOPASTEURIZA ION AS A "NEW" FOOD PROCESS I. THE PROCESS OF HIGH RADIOPASTEURIZATION A. REVIEW OF RADIATION-DOSE RANGES PROPOSED FOR FOODS 1. Radiosterilization.-A great many studies are presently in process in various laboratories using various doses of ionizing radiation for food preservation. The initial studies were in most cases directed toward the use of sterilizing doses in the range of 2-4 megarep. Preliminary studies at The University of Michigan and elsewhere have indicated that sterilizing doses of radiation produce undesirable changes in most foods, particularly in the odor and flavor of meats and dairy products. At present, no completely satisfactory method for preventing these undesirable changes is known. Many investigators in various laboratories are studying the problem and satisfactory solutions may be found for certain food items. Thus, radiosterilization which would permit long-term storage at room temperature is the ultimate goal of much research being conducted in this field. However, it presents more problems than the use of lesser dosages of radiation which would not completely sterilize. 2. Radiopasteurization.-A dose of radiation less than that required for sterilization and in the range of about 100,000 rep might be termed a radiopasteurization dose in that, like thermopasteurization, most but not all of the microorganisms are destroyed. Radiopasteurizating doses equal to 2-5% of sterilizing doses can be used to reduce the population of microorganisms 90-99+% without producing undesirable changes in the food. Such a radiopasteurization treatment could be used to extend the refrigerator shelf-life of perishable foods which might make possible new methods of handling. A new method of wholesaling fresh meat has been proposed l2 for consideration by some of the larger packing houses and some of the larger retailers of fiesh meat. This proposed new method consists of preparing packaged standard cuts of fresh meat, packaged fresh ground meat, packages of cut chicken, etc., in retail-size portions at the packing house rather than at the retail meat market, and of radiopasteurizing the packaged meat at the packing house by using a dose of about 100,000 rep prior to shipping to the retailer. The extension of the refrigerator shelf-life of fresh meat by radiopasteurization should make this new method feasible. A number of advantages might be realized by the consumer, the retailer, and the packing house as a result of using this new method of wholesaling meat and radiopasteurization. 1.1

3. Low Radiopasteurization. -A still lesser dosage of radiation of 10,000-25,000 rep termed low radiopasteurization might be used for some other types of food processing. Such low-radiopasteurization doses will not destroy a sufficient quantity of the population of vegetative microorganisms found in fresh foods, such as meat, to affect appreciably the storage life at either refrigerator or room temperatures. This range of radiation, however, has the least influence on flavor and color and would be the most economical to employ because of the high radiation capacities possible at such low dosages. Such a dosage might be used for the treatment of potatoes and onions for sprout inhibition,' for grain and cereal products for insect control,' to break the cycle of trichinosis in pork,' to control tapeworm from beef, pork, and fish, and to control a number of other diseases caused by parasites. The irradiation of potatoes and wheat, as well as other grains, is considered to be feasible on a mass scale from the viewpoint of both engineering and economics. Because of the tremendous quantities of these staple foods, the application of radiation would be on a large scale. B. PRELIMINARY STUDIES OF HIGH RADIOPASTEURIZATION Recently some limited studies have been made by graduate students of one course in Nuclear Engineering at The University of Michigan using a "high-radiopasteurization" dose of gamma radiation of about 1 megarep. This dose is not sufficient to sterilize completely, but is sufficient to preserve food. Thus, this process could not be used where the possibility of growth of Clostridium botulinum exists. Destruction of the spores of this organism is the first requisite in successful thermal processing of canned foods. However, if the danger of botulism is avoided by control of pH or oxygen level and temperature, a dose of 1 megarep would be sufficient to preserve food from spoilage by vegetative microorganisms, mold, yeasts, etc. In these limited tests, smoked fish (salmon and chub) packaged in 2-mil heat-sealed polyethylene bags and given a radiation dose of 1 and 0.8 lJegarep, respectively, "kept" at room temperature for several months. The irradiated salmon and chub were considered to have very good flavor immediately after irradiation and the flavor was still good after storage for one month at room temperature. After three months' storage at room temperature, the salmon developed a slightly rancid taste. Two packages of salmon that received 1-megarep dosages and eventually spoiled did so as a result of mold growth. Figure - shows a photograph of the irradiated salmon and control after storage for nine days at room temperature. The samples of salmon were removed from the polyethylene bags for photographing. Note the development of mold on the control sample. Mold of this type first appeared after storage for about three days, whereas no mold growth appeared on the irradiated salmon. Figure 2 shows a plot of the original salmon samples and, although only a few samples were used in this limited study, the curves are indicative of subsequent data obtained with larger numbers of samples. 1.2

Fig. 1. Samples of irradiated and nonirradiated smoked salmon after removal from sealed polyethylene bags. Figure 3 shows some broiled breast of chicken packaged in polyethylene, heat sealed, irradiated at a dose of 1 megarep, and stored for two months at room temperature. The irradiated chicken did not spoil during this period and the meat was considered td have a satisfactory flavor after irradiation. However, a slight off-flavor characteristic of irradiated meat could be detected by persons familiar with these Off-flavors. There was some rancidity in the fat-saturated chicken skin of the irradiated samples after storage for one month. Figure 4 shows similar samples of chicken breasts that were given the same treatment, except that they were not irradiated. Evidence of spoilage was visible within a week to ten days after packaging, although spoilage presumably commenced at an earlier date. Two types of spoilage were observed. On the right of Fig. 4, chicken breasts with a white mold growth show one type of spoilage. This type was easily recognized by the presence of the mold. The package on the left side of Fig. 4 shows a different type of spoilage that was visibly evident by the collapse of the polyethylene container. If refrigerator storage had been used, the development of rancidity could have been delayed in both the chicken skin and the fish and, possibly, the fish could have been kept for several months. The test with smoked chub was repeated with storage at 400F, and the irradiated fish still has excellent flavor after storage for 3 months. The fact that the polyethylene bags pass oxygen readily can be used to maintain aerobic conditions inside the package. However, there is still some slight chance of anaerobic spores such as Clostridium botulinum growing in pieces of meat stored in air at room temperature. Therefore, the storage temperature should be lowered to about 40~F for a more positive guarantee against botulism. Tests also were made with blanched peas, blanched string beans, boiled shrimp, and whole roast chicken. Although there was a very slight ir1.5

1,000,000 REP 100 0 DC. c+P ~ I 8 uo o w 00c+H. ( Ft 0. 050 (1D z (1) o _ ^ 0 Zw "' o () \J1 CO\ CONTROL 100,000 REP 2/4 2/8 2/12 2/16 0 4 8 DAYS 12 14 16 DAYS

::~:::7_-'-iij: IRRADIATED Fige. Irradiated broiled breast of chicken stored for two weeks at room temperature (75~ -85F ).:': CONTROL Fig. I4 Control broiled breast of chicken stored for two weeks at room temperature (75 -8 ~F). radiation flavor in the chicken, shrimpand beans at 1 megarep, each was considered to be acceptable. The peas bleached slightly but had good flavor. The high-radiopasteurization dose of about 1 megarep is proposed as a possible "new" process by which many foods may be stored for several weeks. In this process, cooked meats, blanched vegetables, and other perishable items in which the enzymes have been inactivated would be packaged in heat-sealed 1 5

polyethylene bags and other types of flexible packaging and given a dose of about 1 megarep followed by storage under refrigeration. This dose avoids, in many cases, or minimizes the off-flavors resulting from sterilizing doses of radiation. This process might make possible the sale of such items as roast whole chicken, cooked cleaned shrimp, blanched green peas, and other vegetables packaged in plastic containers and capable of being stored unfrozen for long periods at refrigerator temperatures. This process could produce great changes in commercial channels in the handling of food. If the food is acid, the storage temperature probably could be raised to room temperature without danger of food poisoning. Additional experimental studies with various foods are required to evaluate the process and, although support for such studies is not available at present, it is hoped that additional work in this direction will be possible. C. THE WHOLESOMENESS OF HIGH-RADIOPASTEURIZED FOODS The question of wholesomeness of irradiated foods is being studied at The University of Michigan'4 and at many other laboratories. These studies are primarily concerned with any changes in wholesomeness as a result of irradiation. Such studies must be completed and the wholesomeness established to the satisfaction of the representatives of the Food and Drug Administration before the commercial irradiation of food will be approved. However, when nonsterilizing doses of radiation are used, the question of loss in wholesomeness as a result of microbial action is also introduced. The following is a brief review of the problem of food poisoning from the microorganisms and their toxins. 1. Botulism.-The most deadly type of food poisoning7 which is of particular concern in packaged foods, is known as botulism and is produced by the toxin of the anaerobe Clostridium botulinum. Because of the seriousness of this type of food poisoning, a brief review of botulism is deemed desirable when considering the storage of packaged food which has not been completely sterilized. a. History of Botulism. —The first case of botulism was recorded in Europe in 1735.9 In Southern Germany, cases were reported from spoiled sausages and the name botulism is derived from botulus, the name of a sausage. In 1895, Van Ermengem9 succeeded in isolating a variety of bacteria from ham which had been responsible for botulism. Dickerson9 surveyed the cases up to 1918, and Meyer10 made a survey of cases from 1931 to 1941, as summarized in Table I. 1.6

TABLE I RECENT HISTORY OF OUTBREAKS OF BOTULISM, 1931-1941 (According to Meyerl~) Year No. of Outbreaks 1931 16 1932 19 1933 22 1934 9 1935 21 1936 9 1937 14 1938 13 1939 16 1940 11 1941 12 Between 1899 and 1941, 357 outbreaks have been reported in the United States. b. Origin of Botulism. —In Europe, preserved meats and, in America, home-canned vegetables (peas, beans, corn, and asparagus) have been responsible for the recent outbreaks. Since 1925, no outbreak has been reported from the commercially canned foods.ll This excellent record is largely due to the extensive research supported by the National Canners Association and to good operation by commercial canners. 12 The study of soil samples by Meyer and Dubovsky and others indicates the presence of organisms in the soil. But it is remarkable to note that fresh food, including tubers grown underground, cooked or uncooked, are harmless. On the other hand, smoked, pickled, or home-canned food, when eaten raw or with inadequate cooking, have caused outbreaks of botulism. It is important to note that botulism is the result of the ingestion of a toxin already present in the food and is not an infection. c. Morphology.-Clostridium botulinum is a large, pleomorphic, grampositive, mobile, sporulating rod 4-6't in length and 0.9-1.2 i in width. Its cells occur singly, in pairs, or in chains. Strains producing five types of toxins, A, B, C, D, and E, have been reported. d. Culture Characteristics.-It has been reported that the optimum temperature of growth for Clostridium botulinum is 250C, while there is limited growth at temperatures of 35~C and above. This bacterium grows readily in neutral or moderately alkaline media, but is sensitive to acidic media. 3 1-7

Saleh and Ordal14 have recently reported a study on growth and toxin production of Clostridium botulinum in precooked food. In this study strain62 type-A Clostridium botulinum was used in precooked frozen chicken a la king. Botulinum toxin was found only in samples incubated at 86~F (300C). No toxin was formed in samples incubated at 500F (100C), which is a very significant observation. e. Spores.(1) Heat Resistance. —Dry spores are resistant to heat, and young spores have been reported to be more heat resistant than the old spores.l5 The population of spores also influences the heat-resistant property. When the spores are few in number, they are destroyed by heating for 10 minutes at 100~C; on the other hand, larger populations:.require more intensive heat treatment.17 Meyer, Dubovsky, and EstyL8 studied the heat-resistant property of all three types of spores-A, B, and D-while types C and E were studied by Bengston19 20 and Hazen,2 respectively. Meyer and Dubovsky studied 109 strains (78 strains of type A, 30 strains of type B, and 1 nontoxic strain). Table II summarizes the results of the findings on type A and type B. TABLE II HEAT RESISTANCE OF TYPES A AND B CLOSTRIDIUM BOTULINUM Temperature Time of Destruction ~C Minutes 120 4 115 12 110 36 105 120 100 300 Type C was destroyed in 60-90 minutes at 100~C; type D in 120 minutes. Type E was destroyed in 10 minutes at 80~C. (2) Resistance to Ionizing Radiation —The studies by Dack and Wagenaar2' with gamma radiation from cobalt-60 have indicated that type-A spores are destroyed by a dose of from 8 x 105 to 11 x 105 rep, while type-B spores required only 5 x 105 rep. They also reported that the spores continued to produce toxin after receiving high but sub-lethal dosages. 1.8

Kempe, et al.22 reported tests on the effects of gamma radiation on the spores of strain 62-A Clostridium botulinum. The sterility dosage for canned beef was found to increase from 2.5 to 4 megarep when the concentration of spores of this organism was increased from 0.4 to 40,000 per gram of meat. In tests using 40,000 spores per gram of meat of strain 213-B Clostridium botulinum (or an equal inoculation of putrefactive anaerobe No. 3679), 3.5 and 2.5 megarep, respectively, were required for sterilization. f. Botulinum Toxin. —Botulinum toxin is more poisonous than any other toxin known. A small dose of 0,0084 mg23 is lethal to an adult human. The toxin is unaffected by the digestive enzymes of the gastro-internal tract; hence it is effective when given by mouth. (1) Heat Resistance.-The toxin can be completely destroyed by heating for 30 minutes at 800C. Results of a study on different types of toxins were carried out by Meyerl~ and are summarized in Table III. TABLE III HEAT RESISTANCE OF TOXINS OF CLOSTRIDIUM BOTULINUM (According to Meyer ) Temperature Time of Destruction of Toxin _____C _ Minutes 80 1/2 - 6 72 2 - 18 Type A 65 l0 - 85 80 15 Type B 80 30 Type C (2) Radiation Resistance.-Dack and Wagenaar 2 reported that typeA toxin required a dose of 7.8 megarep for the reduction of toxin level from 1000 mid (minimal lethal dose) to 20 mid, while the toxin of type B required 4.3 to 5.3 megarep. Reduction of toxin level from 20 mid to the endpoint required 2.2 megarep. 2. Staphylococcus Food Poisoning.-The most common type of food poisoning is that produced by toxin from staphylococcal organisms. Unlike the toxin of botulinum, the toxin produced by staphylococci seldom produces fatal attacks of food poisoning. Almost every individual has had some experience with this type of food poisoning, as it is often encountered in foods prepared for banquets, public institutions, large-scale picnics and the armed services. 1.9

The symptoms usually appear about three hours after ingestion of the contaminated food and involve salivation, nausea, cramps in the abdominal region, and diarrhea. Recovery is usually quite rapid, with no aftereffects. Lethal cases are very rare. Staphylococcal organisms are very widespread and exist in the throat and nasal passages of individuals and are particularly abundant in individuals suffering from colds. These organisms are the causative agents of local skin infections such as boils, pimples, and carbuncles. The wide distribution of these organisms in individuals and the fact that the food may be easily contaminated by the hands or from the air by sneezing account in part for the frequency of this type of food poisoning. As in the case of Clostridium botulinum, the organism itself does not produce the illness, although it may underother circumstances produce infections in various parts of the body. This type of food poisoning is caused by the enterotoxin produced after sufficient growth of the organisms in the contaminated food. In addition to following good sanitary procedures in food preparation, refrigeration should be used to prevent growth of new organisms. Segalove and Dack24 have shown that enterotoxin is not formed in foods stored for four weeks at normal refrigerator temperatures (40-70C). Dack25 summarizes three conditions necessary for the development of the staphylococcus enterotoxin: (1) there must be sufficient contamination of the food with an enterotoxin-producing strain of staphylococcus; (2) the food must be a good medium for the growth of the organisms and the production of enterotoxin; (3) the food must remain at about room temperature or above for several hours. Common foods which have often produced this type of food poisoning are potato and macaroni salads for picnics, chocolate eclairs, cream puffs and other cream-type pastries, ham salad, egg-salad sandwiches, and other sandwiches with mayonnaise sold at drugstores. The enterotoxin produced by staphylococcal organisms differs from the toxin produced by Clostridium botulinum with regard to its resistance to heat. Whereas a short cooking destroys the botulinum toxin, boiling for thirty minutes was reported by Dack25 to be insufficient to reduce the toxicity of staphylococcal enterotoxin. On the other hand, Dack reports in a preliminary study that, when using a radiation dosage approximately ten times the dosage reported lethal for staphylococci (about 3.5 megarep), the neterotoxin was inactivated. 3. Salmonella Food Poisoning.- Salmonella is a generic name used to describe a group of bacteria previously known as "paratyphoid bacteria." The organisms were named for D. E. Salmon who was one of the early workers to describe it. The food poisoning caused by Salmonella organisms differs from that caused by organisms previously described in that this illness is 1.10

produced by an invection rather than by a toxin. Two types of infection are common. In one type, found only in man, the symptoms are similar to those of typhoid fever, but less severe. The second type produces a disease in either man or animals with symptoms similar to typhoid fever and accompanied by nausea, vomiting, cramps in the abdominal region, diarrhea, and sometimes fever and leucocytosis. The severity of the disease varies considerably but, like staphylococcus poisoning, it is seldom fatal. Salmonella infections account for only a small portion of food-poisoning outbreaks. Although the symptoms are often similar to those produced by staphylococcal enterotoxin, the incubation period is usually about 24 hours after ingestion of the contaminated food, as compared to about 3 hours for the onset of symptoms of staphylococcal food poisoning. Salmonella infection is often produced from eating raw or undercooked meats. The organism is common in the intestinal tract of animals and fish, and, as a result, it may be found in fresh meat. The organism also can be carried by the feces of rodents to types of food other than meat. Also, the common housefly may be a carrier. The organism has been reported by Dack25 to grow in foods such as asparagus, string beans, peas, corn, salmon, shrimp, and tomato juice. Some large-scale outbreaks of Salmonella infection during World War II were traced to Salmonella organisms in dried eggs. 4. Alpha-Type Streptococci Food Poisoning. — Another type of organism which may cause food poisoning is the alpha-type streptococci. Cases of food poisoning from this organism are less common and usually less severe than those from either staphylococcus or Salmonella organisms and are usually associated with the ingestion of foods contaminated with extremely high populations of the organism Streptococcus faecalis. The symptoms are similar to those of staphylococcus food poisoning but milder and the onset of illness is usually later. Symptoms are nausea, colicky pains, and diarrhea. The illness is the result of an infection by the organism, as in the case of Salmonella, and is not the result of ingestion of toxin. The organism has been found in outbreaks of food poisoning from eating canned Vienna sausages, beef croquettes, turkey dressing, canned evaporated milk, dried eggs, and charlotte russe. Streptococci grow fairly rapidly over a wide range of temperatures from 10~ to 45~C. These organisms are relatively heat resistant, will survive thermal pasteurization, and can grow in salt concentrations of 6.5%. They are natural inhabitants of the intestinal tract of man and animals, and humans can tolerate a considerable number of them without becoming ill. Illnesses result when the population counts reach the range of from 1 x l1C to 1 x 107 organisms per gram of good. The organisms may be spread by the feces of rodents and may be found in fresh meat, fish, and fowl as a result of carelessness. 5. Summary.-A summary of these four principal types of food poisoning caused by microorganisms or their toxins is given in Table IV. 1.11

TAFLP E IV SUMMARY OF CHARACTERISTICS OF FOOD POISONING CAUSED BY BACTERIA OR THEIR PRODUCTS Onset of Symptoms Disease Specific Agent Intoxication Infection Symptoms After Eating Botulism Clostridium botulinum + Difficulty in swallowing, f hours to 8 days; which produces toxin double vision (diplopia), average 1-2 days difficulty in speech (aphonia), difficulty in respiration, followed by death from paralysis of muscles of respiration Staphylococcus Staphylococci which + - Nausea, vomiting, diar- 1-6 hours; food poisoning produce enterotoxin rhea, and acute prostra- average 2-1/2-3 H tion; abdominal cramps hours ro Salmonella S. typhimurium + Abdominal pain, diarrhea, 7-72 hours infection S. eateritidis chills, fever, frequent S. choleraesuis vomiting, prostration Streptococcus A-type + Nausea, sometimes vom- 2-18 hours food poisoning (S. faecalis) iting, colicky pains, and diarrhea

6. Discussion. -At Michigan and elsewhere, radiation dosages of 1 megarep have been shown to destroy vegetative organisms. Thus, the vegetative cells of staphylococcal, Salmonella, and streptococcal organisms can be inactivated by dosages used in the proposed process of high radiopasteurization. This dosage of about 1 megarep also would destroy the vegetative cells but not the spores of Clostridium botulinum. Thus, the primary danger of food poisoning, using dosages in this range, would be that of botulism which, of course, is a serious consideration. Storage conditions should be maintained that would prevent the development of spores of this organism to the vegetative state with the accompanying production of toxin. As these spores do not develop at refrigerator temperatures, storage at 40-50~F should provide ample protection. In the case of mishandling or storage for some time at room temperature, additional safeguards can be used. As the vegetative cells of Clostridium botulinum are destroyed by high radiopasteurization, and as some time is required for spores to develop into vegetative cells, accidental storage for a few days at the high temperatures should be entirely safe. But as a further precaution, it is proposed that such food items to be processed in this manner be packaged aerobically in containers such as polyethylene, which readily transmits oxygen. Aerobic conditions are unfavorable to the development of the spores of Clostridium botulinum into vegetative cells. As a further precaution, it is suggested that the foods to be treated with high-radiopasteurization doses first be given a heat treatment such a cooking, in the case of seafoods and meat, or blanching, in the case of freshvegetables. Although such a limited heat treatment would not destroy all the spores of anaerobes, when used in combination with the subsequent radiation treatment of 1 megarep it will provide an additional factor of safety to this process. II. DESIGN OF A RADIATION FACILITY FOR HIGH RADIOPASTEURIZATION A radiation dose of from 0.8 to 1 megarep would be required for high radiopasteurization. As this is an appreciable radiation dose, radiation costs will be high and a radiation facility which makes efficient use of radiation should be used. For this reason, a multipass conveyor, similar to that considered for the irradiation of prepackaged raw meat or the irradiation of potatoes, 24 is proposed. If cesium-137 sources were purchased for such a facility, four passes, each containing 1/2-value thickness of food, are recommended. However, if cooling-reactor fuel elements were used as a source of radiation, the cost might be reduced from that of purchased cesium-137 sources. In using cooling-reactor fuel elements, two passes are recommended. It has been shown previously that a number of cooling-reactor fuel elements properly arranged can be used to provide a uniform radiation field in one plane at selected distances from the source.26'27 Such a scheme is proposed for the high-radiopasteurization facility. 1.13

A. DESIGN OF A RADIATION CHAMBER The radiation chamber for a high-radiopasteurization gamma facility was considered, using the same basic design as the irradiation facility designed to pasteurize prepackaged meat.2 However, a number of changes were made, such as increasing the tray width from 8 to 12 inches and the tray height from 18 to 30 inches. This will require an increase in the conveyor pitch of from 4-1/2 to 7-1/2 inches. Also, because of the increase in the width of the conveyor trays, the spacing between each pass will be increased from 15 to 24 inches. The increase in width of conveyor trays and the increase in spacing between conveyor passes increase the distance of the absorber from the source. The radiation field is decreased with distance. Therefore, only two passes of the conveyer will be used on either side of the radiation source rather than four passes as used in the previous design. Figure 5 shows a section of the elevation view of the modified radiation chamber designed to high radiopasteurized bulk prepackaged food items or cartons of such prepackaged foods. Kraft cardboard cartons filled with food in sealed plastic bags and having a size of 1 x 2 x 2-1/2 feet, or plastic bags of food in bulk, are brought by conveyor and transferred to the irradiation conveyor at point A. As the irradiation conveyor moves, the cartons or bulk packages of prepackaged food are carried down into the radiation chamber through openings, B and C, past concrete shields, D and E. Two vertical passes, F and G, are made on the left side of the row of source rods, H, and two passes, I and J, are made on the right side of the source. This arrangement permits irradiation of the food items from both sides so as to produce a more uniform dose of radiation. The well, K, is filled with water as in previous designs and is used to hold the source when the radiation must be shut off to permit entry into the radiation chamber for maintenance, routine inspection, or addition of source rods. If the radiation chamber is located above grade as shown in Fig. 5, a concrete wall, L, which is 3 feet 10 inches thick, is used for shielding. If the radiation chamber is placed below grade, the wall thickness may be reduced to that required for structural strength alone, since the earth will act as a radiation shield. A labyrinthine entrance to the radiation chamber is provided at the lower left as shown in Fig. 5. A plan view of the radiation chamber is presented in Fig. 6. This view shows the simple labyrinth used as an access passage for routine inspection and maintenance. The conveyor in the radiation chamber may be driven by sprockets on stub shafts. Some of the sprockets may be "idlers," with one or more sprockets to be used as a "driver." 1.14

Nonirradiated Food In Irradiated Food Out V, ~.. 6~ A ~ ~ ~ b' e * ~. ~' *1 11 " i\~ b ~ ~~~ * *E 6'''. I u,,. ]0 ] 3'- 0" "' ~~~. ~, ]. r ^.~~~ ] 3^^ ~ L; ~~' ] 26' F G " ~ ~ ~ ^ ___ - TG I J~ __[_ Access Passagei~ I " \ - ~ r ~' 9 ^ ~' K I' 0'.,.~ -~ I- * fr 4C L^.. ~ I y A A'. ~ L,.I ~ ~W I - ] y j Fig.., o o.,: ~ ~ 11 AccessI Iosge4 ~ F G_ i I dI1 \ t. I" —''':'P rl',' Fig. 5. EZevation view of high-radiopasteurization chamber. 1.15

00 ___ __ I) ^_____-o____________^ N~~~~~~~~~~~~~~ C) p CM C -' ~ *' * ". " 9-''9 - 9 * ^' * ~ 9. 9...'. - C L9 9. 9 9.~ I' -' / \ -\ \ \ \ \ \\ ^ - \ "'^''.9' c 9. ~ _______________..'~~. — <~ H r ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~~~< ~ r-r.~ f 91~~~~~~ ~~~~~~~~~~~~~~~~~~~ ~. 9.. I * ~ ~~ ____ __ _ ~ r Q~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~) -I~~~~~~~~ ~~~~~~~~~ 9-.. *9 -9'. 9.-' ~ 9 ~ ~~~~~~ ~ ~ \'~''''~9.' " bD 4'H~~~~~.99*A~~~~~~~~~~~C 99 9-.~~~~~~~ 9 9 ~~~~~~~~~~~~~~~.I *'4~3 ~

B. RADIATION SOURCE Packaged mixed fission products or packaged cesium-137 separated from fission products might be used as the sources of radiation for a high-radiopasteurization gamma facility. However, such sources are not presently available and will not be available until suitable plants are put into operation to process fission-products wastes. On the other hand, cooling-reactor fuel elements are being removed constantly:-from. reactors mnow.pperating,:and the supply will increase as new reactors come into operation. The supply of such cooling-reactor fuel elements is limited, but it is believed that a sufficient number could be made available to establish a limited number of radiation facilities capable of processing foods on a commercial scale. It is not proposed that cooling-reactor fuel elements be considered as the answer to the problem of suitable gamma sources for general use in industrial plants, but they might fill the need for radiation sources for the immediate future. Reactor fuel elements may be too expensive to use if the high inventory costs of fissionable materials were charged against the fuel elements when used as a source of radiation. However, for reasons relating to the processing techniques, it is the practice in present fuel-processing plants to store these elements under water for several weeks before they are processed. During this period, the intense radiation is dissipated in the water used to shield the cooling elements. Except when used in some research experiments, this radiation is being wasted at present. It is proposed that some of these elements be used as sources of radiation for a limited number of radiation facilities designed for high radiopasteurization of foods. The reactor fuel elements proposed for use in this facility have a very high gamma activity but a very rapid decay rate. It is suggested that each fuel element be used for a period of about two months and then replaced with a new one. If the replacement schedules for different fuel elements are staggered, greater uniformity of radiation flux will be possible. However, it probably will be necessary to make adjustments in the material flow rate through the facility during the period of operation to compensate for the depcay of the fuel elements. The irradiation of a large volume of foods necessitates continuous operation involving the use of a conveyor system to pass the foods into the chamber, past the radiation source, and out of the radiation chamber. Efficient operation requires that the total thickness of foods being conveyed through the chamber absorb most of the radiation. The decision was made to specify 20 reactor fuel elements as the source of radiation after considering the radiation flux available from one fuel element and the amount of radiation required to affect radiopasteurization. A dose of I megarep was selected as being most suitable for high radiopasteurization. The productive capacity for the radiation chamber is a function of this required dose and also a function of the radiation field provided by the source. 1417

The radiation field will, of course, vary with the geometry of the source. If the fuel elements were arranged side by side with no distance separating them, the radiation field would vary in all directions and would appear as if emanating from a plaque source of uniform concentration. This type of source previously was found too inefficient.2 A more efficient design would be to distribute the activity of the source in such a way as to provide a uniform radiation field in one direction. In the case of fuel elements, the activity may be distributed by spacing the fuel elements. Since the foods will be transported through the chamber on a conveyor in a number of vertical passes, it was decided to establish a uniform radiation fibld in the horizontal direction. This would mean that although the food travels in a varying radiation field in the vertical direction, the uniform horizontal field would' insure that the food on one end of the conveyor would receive the same dose as those foods located on the other end, at a fixed lateral distance. The uniform horizontal field can be accomplished by aligning the long axis of the fuel elements in a direction parallel to the direction of the two passes. In addition, the elements would be arranged with horizontal spacings as shown in Fig. 7. The smaller pitch of the fuel elements near the ends is used to produce a more uniform radiation field at the extremities of the source. 5'1 _ 10" " L_ 1 " 151" II"' 5" 5"1" r5" 7'6" L HORIZONTAL DISTANCE FROM CENTER LINE OF SOURCE - Fig. 7. Plan view showing spacing of one half of fuel elements for irradiation facility. ROD NO.-I 10 I" 11 20 24 —" 1 5 I Y 1 Fig. 8. Source elements, elevation view. 1 18

The optimum spacing of the fuel elements was determined by trial and error by calculating the dose rate in air at certain positions and then plotting the dose rate vs horizontal distances for a definite vertical distance from the source to ascertain the effect of a particular spacing scheme. The procedure for calculation of the dose rate in air was quite extensive because of the irregular spacings of the 20 different components of the source contributing to the flux at any arbitrary point. The total flux at a point is a scalar sum of the contributions from each of the fuel elements. The calculations were simplified by assuming that at a sufficient distance from the fuel elements the source may be considered as being comprised of 20 line segents. The dose-rate contribution of one of the fuel elements is given by I = a(H + H2), (1) where a = concentration coefficient for each fuel element. The calculation of the radiation flux at any point in a given plane parallel to the face of the group of source rods will be demonstrated. The values of Hi and H2 for one fuel element are obtained at any point P from the general equations H1 F dz 1 tan Z (2) x x + y 2+ z + x _2 and 12 2 dz 1i tZ J X2 + y2 + = y2 + x2 tan 2 where P = the point where dose rate is to be calculated, z = length along the vertical axis of element, x = lateral distance between the vertical plane of source elements and the parallel plane containing point P, yn = horizontal distance between point P and the nth source element, and Hi and 12 = lengths along the axes of the fuel elements between the base of perpendicular from point P and the extremities of fuel element (see Fig. 8). The "H" function was evaluated as defined above for different distances between the field point P and one of the fuel elements. The "H" curve, as a function of the distance between a given fuel element and point P, was drawn (Fig. 9). Since the activity of the fuel elements is not accurately de1.19

8.0 7.0 ~ 6.0 cr 550... II %r.. C) 0 o 3.0 2.0 1.01.20 0 5 I0 15 18 DISTANCE FROM [ OF FUEL ELEMENT, FEET Fig. 9< H function vs distance from one fuel element (dose rate normalized to 10s r/hr at 3 feet from one fuel element). 1l20

terminable in terms of curies and a is not known accurately, the H-function curve was normalized to 105 rep/hr at a distance of 3 feet from one of the fuel elements. This radiation field was considered typical of cooling fuel elements from high-neutron-flux reactors cooled from 1 to 5 months and in use for 2 months. In order to determine the total dose rate at a point, the distances from different elements were calculated and the corresponding dose rates were obtained from the curve in Fig. 9: total dose rate I = Il + I2 +... I2c This procedure of calculation was adopted to obtain dose rates at any point in space surrounding the fuel elements. C. ISODOSE CURVES In order to obtain isodose curves in space, three sets of curves were obtained. 1. Dose Rate-vertical distance (z) for different lateral distances (x) (Fig. 10). 2. Dose Rate-lateral distance (x) for different vertical distances (z) (Fig. 11). 3. Dose Rate-horizontal distance (y) for different lateral distances (x) (Fig. 12). The set of curves obtained in Fig. 12 demonstrates the uniformity of dose rate at the central lines of trays at 24- and 48-in. lateral distances (x) from the i of source elements. Thus, the horizontal coordinate (y) may be eliminated in the determination of isodose curves. Isodose curves in the plane (x,z) perpendicular to the face of the source have been obtained (Fig. 13) by cross-plotting data obtained from the curves given in Figs. 10 and 11. Since gamma rays must pass through the food, the isodose curves were corrected for the absorption due to the food in trays. A value of 12 inches for the half-value thickness was selected, based upon previously determined experimental values.6 According to the well-known exponential law, and assuming that the radiation passes through 12 inches of meat with an average absorption efficiency of 85%, and neglecting build-up-factor correction, 1.21

ZZI ~X JO SanrTA q.uaGaJJ: P J J: GSp SoA aoux'.ST!.p TOT'1:-aA *0T ITJ (133-) 33nOSS0 O O 3N ILOS 3NVISI1C 331183A-Z 01 6 8 L 9 g i7 ~ Z I 301 I.... I \ I m 0 ~~ ~ ~ ~ ~ ~~. ^H ~^^-~T T ~~~~~~~00......... 001 ~~ ~ ~~ ~ ~~ ~ \ - ~ ~, -. o z \ ~~ ~ ~ ~ ~ ~ ~ ~, ~ ~ ^ s0 l I' ~' ogre02

125,~~~~ 120 c100 ~~~ ~~ 90 80 20....I......'0 rz2 I w60.... 1 2 3 4 5 6 7 8 9 x-LATERAL DISTANCE FROM OF SOURCE (FEET) Fig. 11. Dose rate vs lateral distance from. of source for different values of z. 1.23

20 i I,,, 18 I 16 I ~X=2' i,-'o 12 x W w 0 8 X= 41 4 2 0 2 3 4 5 6 y- HORIZONTAL DISTANCE FROM ( OF SOURCE (FEET) Fig. 12. Dose rate vs horizontal distance for different values of x. 1.24

z - VERTICAL DISTANCE FROM _ OF SOURCE (FEET) 0 - ______o 01 ( o 4 00 CD \J o r i i P P- CDb (0 0 r - r / 00 P. C) i O" H ~ O1 ~~ o 0)~gs(0^_______________ OCD M 0 m (D~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~iii

eI = I IeX = decay constant or X = 0.693 (4) xl/2 = half-value thickness (taken as 1 foot),.. x = 0.693 feet, and I = 0.425. Io Isodose curves corrected for absorption, and assuming 85$ absorption efficiency, are shown in Fig. 14. These curves are utilized to give data for the variation of dose in the vertical direction at lateral distances (24 and 48 inches). The latter relationship is plotted in Fig. 15 for x = 2 feet and x = 4 feet. Figure 15 facilitated the preparation of the integral dose curve needed for the capacity calculation. D. INTEGRAL DOSE CURVE With the use of the curves of Fig. 15, the integral dose curve (dose vs distance of travel by the tray in the radiation chamber) shown in Fig. 16 was prepared. From Fig. 16 the total dose accumulated along the central line of the tray during the travel of 88 feet was calculated, using Simpson's Numerical Integration Rule: b I = f(x) dx = [Yo + 4(Y + Y3 + Yn + a 2(y2 +.. Yn-2) + Yn ] (5) For a travel of 88 feet, an accumulated dose at the central line of the tray was calculated and found to be 21.17 x 108 rep for a tray speed of 1 foot per hour. E. CAPACITY CALCULATION Distance of travel per cycle = 88 feet Radiation dose = 106 rep (e 8 ee Radiation time per cycle = 20 (r eyc 21.17 x 10 \ hr cycle = 4.15 hour/cycle. 1.26

..:':......:..:..........:::: _.v~~~~~~~~~~~:::.....:.:::."\,:::::.:::::.......:::...:...:.:...'::... X (04~/h~ ~::::::::::::::::::: ~:.:.:.:.:.:.:.:.:,........... llJ t:............... 32.5 - i. ^...... i*^..\.. s,:....:....... 10.7551 rS X r L.......... w. > 5.\.' 37.5' \;3,Xi,,:3,: *.5 N................. **@w@@@@ 7.5 ~~~~r ~ 17.25:~ ~ ~L,:..... ~.. L..................... I 2 4 _5 20172 Fig.... Asorp_ in-'et i:: c u rves..... 0.0 2 Fig. 1 Aot - rt i o cv 1.27 w4~~~~~~~~~~~ 0~~~~~~~~~~~~~~~~~~~~~~~~~~I~~ z~~~~~~~~~~~~~~~~~~~~~~~~r~~~r I- ~ ~ ~ ~ ~~~~~r~~~ -'3~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ____________ 275 ____________~~~~~~~~~~~~~ 2~~~~~~~~~~~~~~~~ 3 4 5 8~~ 7~~~ LATERAL. DISANE RO.OSORC(FET Fig. ~ ~. ih~~~ Abortin orete ioos crvs 1.27~~~~~~ ~~~~~

90 80~ 70 --- "- 2' LATERAL DISTANCE - ~ 4' LATERAL DISTANCE 60 I \ 0 r 40 w 5 30 20 \ 0 mom \2 4 5 6 7 8 9 10 12 -VRTIAL 2 D FEET 20 ~~ ~' ~~~~ x=4 FEET,I0 ____ ____ I 2 3 4 5 6 7 8 9 10 II 12 z- VERTICAL DISTANCE (FEET) Fig. 15. Absorption-corrected dose vs vertical distance. 1.28

90 90,,___________,_~~~... 80 ^ AT 2' HORIZONTAL DISTANCE 70 _________I I INTEGRAL DOSE FOR I CYCLE (SIMPSON'S RULE) =2 f(x)dx 60 ~ ~ 02(10.587)X 106rep - 0 I \ =21.174 X 106rep o50 __ QA AT 4' HORIZONTAL DISTANCE 0'0 0 - 5D 1340 D TNw C) 0 30 0 20 5 I 0 15 20 25 30 35 40 45 50 DISTANCE TRAVELED IN FEET

The total number of trays in the radiation chamber equals 29. Each tray (2-1/2 x 1 x 12 feet) has six compartments, each considered to contain 100 lb of food packed in polyethylene bags. Capacity per cycle = 600 x 29 lb/cycle = 1.74 x 104 lb/cycle 1.74 x 104 lb/cycle (cycle/hr) Capacity per hour = 4.15 = 4.2 x 103 lb/hr = 4 2 x 103 lb/hr 1 / = 2.1 tons/hr 2000 b/t..Capacity per hour = 2.1 tons. F. CAPACITY COMPARISONS The capacity per hour can be increased by decreasing the radiation dose and also by increasing source strength. In Table V the radiation dose was varied from 104 rep to 4 x 106 rep while the normalized-radiation-field strength was varied from 105 r/hr (r = roentgen unit) to 106 r/hr and the corresponding capacities calculated. However, it should be pointed out that continued increase in source strength would increase the absorption of radiation by the source, which would result in the increase in temperature, possibly requiring a cooling system for the source. TABLE V CAPACITY COMPARISONS N = radiation field at a distance of 3 feet from midpoint of one fuel element in r/hr Dose Capacity Capacity Capacity Capacity Capacity No. (rep) (tons/hr) (tons/hr) (tons/hr) (tons/hr) (tons/hr) N=105 N=2.5x105 N=5.0x105 N=7.5x105 N=106 1. 10,000 210 525.0 1,050.0 1,575-0 2,100.' 2. 50,000 42.0 105.0 210.0 315.0 420.0 3. 75,000 28.0 70.0 140.0 210.0 280.0 4. 100,000 21.0 52.5 105.0 157.5 210.0 5- 150,000 14.0 35.0 70.0 105.0 140.0 6. 200,000 11.5 28.8 57.6 86.4 115.0 7. 500,000 4.2 10.5 21.0 31.5 42.0 8. 1,000,000 2.1 5.25 11.5 15.75 21.0 9. 2,000,000 1.05 2.62 5.24 7.86 10.5 10. 4,000,000 0.53 1.31 2.62 3.93 5.25 103o

G. COST ESTIMATES 1. Total InvestmentEstimated cost of radiation chamber, $66,000 2. Operation Costa. Wages and salaries: (1) Two operators with limited HealthPhysics training $10,000 (2) Supervision and clerical labor 2,000 (3) Salaries and wages not associated with operation of radiation chamber 6,000 Total $ 18,000 b. Other operation costs: (1) Shipping cost for 20 reactor fuel elements (every two months) $12,000 (2) Handling cost for fuel elements during transfer and installation 10,000 (3) Rental of 20 fuel elements for 12 months ($5,000 per month) 60,000 (4) Repairs and maintenance on chamber (5% of chamber and conveyor costs) 3,300 (5) Miscellaneous 1,000 Total $ 86,300 3. Overheada. Payroll overhead (15% of wages and salaries) $ 2,700 b. General plant overhead (50% of wages, salaries, and operation) 52,150 c. General administration (10% of costof labor and operation) 10,430 Total $ 65,280 4. Taxes, Insurance, and Interest10% of total investment $ 6,600 5. Depreciation and Obsolescence of Radiation Chamber$66,000ooo x 0.08 $ 5,280 TOTAL $181,460 1.31

H. UNIT COSTS Capacity = 2.1 tons (for 106-rep dose) hr 1. 260 days/yr (16 hr/day) — Capacity per year = 2.1 x 16 x 260 tons = 8.74 x 10 tons dollars.'.Unit'cost = 20.6 ton cents = 1.03 lb 2. 100 days/yr (24 hr/day) — Capacity per year = 2.1 x 24 x 100 tons = 04 x l03 tons dollars:.Unit cost = 35.8 -ton cents 179 lb TABLE VI Dose I (260 Days) II (100 Days) No. Dollars Cents Dollars Cents (rep) Cost Cost Cost Cost lb 1. 105 2.06 0.1 3.06 0.18 2. 2.5 x 105 5.15 0.25 7.65 0.45 3. 5.0 x 105 10.30 0.51 15.30 0.90 4. 7.5 x 105 15.45 0.76 22.95 1.35 5. 106 20.60 1.03 30.6 1.79 I. SHIELDING CALCULAT IONS 28 Using broad-beam attenuation data,28 it has been found that reduction of intensity by a factor of 4.66 x 10"8 from 15 x 104 r/hr at 9 feet from the source to a tolerance dose of 7 mr/hr (permitted for operators) would require 3 feet 10 inches of concrete (see Fig. 17). For the general public, a tolerance dose of I mr/hr would require 4 feet 3 inches of concrete. 1.32

1.0 10 _ i02... 10 ~3~~ z 5 -3 _ -J 10 z -: -5 0 f10 0 -6 < 10 X I0 - 8 0 10_______ 0 10 10 20 30 40 50 INCHES OF CONCRETE BROAD-BEAM ATTENUATION IN CONCRETE FOR 0.75-MEV X- RAYS Fig. 17. Extrapolated curve for shielding calculations. 1.33

J. DISCUSSION AND SUMMARY A "new" process in which high gamma radiation is combined with refrigeration has been proposed to increase the storage life of cooked meats, blanched vegetables, and perhaps other food items packaged in plastic bags. A review has been made of the various types of food poisoning caused by microorganisms and their toxins. Storage at refrigerator temperatures of around 40OF is considered to offer protection against the growth of the microorganisms that might possibly cause food poisoning. The use of plastic films that transmit oxygen readily, such as polyethylene, so as to maintain aerobic conditions within the package offers additional protection against the growth of the anaerobic spores of Clostridium botulinum. When spoilage does occur in packaged foods treated in this manner, the evidence has been visible, usually as a mold growth. Such samples of food are not toxic, but would be considered nonedible, and, in the commercial use of the process, any packages with spoiled foods of course would not be offered for sale. In regard to spoilage, the problem would be similar to that of handling fresh meats and produce, except that the loss due to spoilage could be reduced to almost zero percentage, if retail sales were made within a few weeks. The commercial development of the process of high gamma radiopasteurization probably would increase greatly the use of refrigeration both in the commercial handling of food and in the storage of foods in the home. If foods could be kept for two or three months or longer by such a process, the housewife might use an additional refrigerator solely for storage. In this regard, the process would be competing with the use of a deepfreezer, but it would be used for food stored for shorter periods. Foods can be stored at 405 more cheaply than at deepfreezer temperatures, and the waiting period required for thawing would be eliminated. It is believed that the added convenience to the housewife of such a process and the savings in prevention of food spoilage would justify its use. Cost estimates given in Table VI indicate that a large-sized plant capable of processing about two tons per hour with two eight-hour shifts per day for 260 days per year could irradiate foods with a high-radiopasteurization dose of 1 megarep at an estimated cost of about one cent per pound. This cost is considered to be in the range of commercial feasibility. The design was based on the use of 20 cooling-reactor fuel elements rented at an estimated rental charge of $5,000 per month, plus handling and shipping charges. It is believed that such a rental charge might be helpful in making nuclear-power reactors more profitable and thereby hasten the day when electric power from nuclear reactors will be able to compete with electric power from fossil fuels. Limited academic tests have demonstrated that a number of foods which were considered to have a satisfactory flavor would keep at refrigerator temperatures for an extended period of time. Additional tests along these 1034

lines should be made. Also, the process cannot be used commercially until approval has been obtained from the Food and Drug Administration. In addition to the long-term feeding and breeding studies presently being conducted with irradiated food at the Fission Products Laboratory and elsewhere, additional feeding experiments should be made with high-radiopasteurized foods that have been stored for selected periods of time. 1.35

REFERENCES 1. Brownell, L. E., et al., "Utilization of the Gross Fission Products," Progress Report No. 6 (C00-198) Univ. of Mich., Ann Arbor, Eng. Res. Inst. Proj. M943, April, 1954. 2. Brownell, L. E., et al., "A New Method of Wholesaling Fresh Meat Based Upon Gamma Irradiation," Proceedings of the 1955 Nuclear Engineering Conference, Univ. of Calif., Los Angeles, April, 1955. 3. Brownell, L. E., et al., "Gamma Rays: The Hope of Researchers to Lengthen Refrigerated Life of Fresh Foods," Refrigerating Engineering, March, 1955. 4. Brownell, L. E., et al., "Utilization of the Gross Fission Products," Progress Report No. 7, Univ. of Mich., Ann Arbor, Eng. Res. Inst. Proj. M943, Dec., 1954. 5. Baker, V. H., et al., "Lethal Effect of Electrons on Insects Which Infest Wheat Flour and Beans - Parts I and II," Agricultural Engineering, 4, No. 11, 755-8, (Nov., 1953); and 35, No. 6, 407-10 (June, 1954). 6. Brownell, L. E., et al., "The Design of a Gamma Irradiation Facility for the Control of Insect Infestation in Flour, Meal, or Grain," Univ. of Mich., Ann Arbor, Eng. Res. Inst. Proj. M943, May, 1955. 7. Gomberg, H. J., et al., "Design Fission Irradiator to Break Trichinosis Cycle," Food Engineering, 26, No. 9 (Sept., 1954). 8. Brownell, L. E., et al., "Utilization of the Gross Fission Products," Progress Report No. 5 (C00-196), Univ. of Mich, Ann Arbor, Eng. Res. Inst. Proj. M943, Sept, 1953. 9. Dickson, E. C., Monograph, Rockefeller Inst. Med. Research, No. 8, 1918. 10. Meyer, K. F., Hand. D. Path. Mikroorg., 4:1261-1364 (1928). 11. Geiger, J. C., J. A. M. A., 117:22, 1941. 12. Meyer, K. F., and B. J. Dubovsky, J. Infect. Dis., 31:541-55 (1922). 13. Smith, D. T., and D. S. Markin, Zinserr's Textbook of Bacteriology, 9th Edition. New York: Appleton-Century Crofts, Inc., 1948. 14. Saleh, M. A., and Z. Jo Ordal, "Studies on Growth and Toxin Production of Clostridium Botulinum in Precooked Frozen Food," Univ. of Ill., Urbana, Feb., 1955 (thesis paper). 15. Tanner, F. W., and G. M. Dack, J. Infect. Dis., 31:92-100 (1922). 16. Starin, W. A., J. Infect. Dis., 28:101 (1926). 17. Meyer, K. F., and B. J. Dubovksy, J. Infect. Dis., 31:650-63 (1922); and J. R. Esty, Am. J. Pub. Health, 13:108-13 (1923). 18. Meyer, K. F., and B. J. Dubovsky, J. Infect. Dis., 31:600-9 (1922). 19. Bengtson, I. A., Hy. Lab. Bull., 36, 1924. 20. Hazen, E. L., J. Infect. Dis., 60:259-64 (1937). 21. Dack, G. M. and R. D. Wagenaar, "Effect of Irradiation on the Spores and Toxin of Clostridium Botulinum,j" Paper read at the 15th annual meeting of the Institute of Food Technologists, Paper No. 102. 22. Kempe, L. L., et al., "Gamma Ray Sterilization of Canned Meat Previously Inoculated with Anaerobic Bacterial Spores," Reprinted from Applied Microbiology, Vol. 2, No. 6, Nov., 1954. 1.36

23. Topley, W. W.,and G. S. Wilson, Principles of Bacteriology and Immunity, 2nd Edition..Baltimore: William Wood and Co., 1938. 24. Segalove, M., and G. M. Dack, Food Research, 6:127-33 (1941). 25. Dack, G. M., Food Poisoning. Chicago: Univ. of Chicago Press, 1949. 26. Brownell, L. E., et al., "Quarterly Progress Report No. 2., Operation of the Fission Products Laboratory," Univ. of Mich., Ann Arbor, Eng. Res. Inst. Proj. 1943-7, Aug., 1955. 27. Brownell, L. E., and J. J. Bulmer, "Sterilization of Medical Supplies with Gamma Radiation," Proceedings of the United Nations Conference on Peaceful Uses of Atomic Energy, Geneva, Aug., 1955. 28. National Bureau of Standards Handbook for 1954. 1.37

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