第50篇来源：www.newdu.com
The food irradiation process is a simple one. The new U.S. plant， Vindicator of Florida Incorporated in Mulberry， Fla.， uses a material called cobalt 60 to irradiate food. Cobalt 60 is radioactive isotope （form） of the metallic element cobalt. Cobalt 60， which gives off radiation in the form of gamma rays， is also used for radiation therapy for cancer patients and for sterilizing hospital equipment. The radioactive isotope is created by bombarding cobalt with subatomic particles in a nuclear reactor. However， irradiation plants do not themselves contain nuclear reactors.
In the irradiation plant， food is exposed to thin rods of cobalt 60. The rods give off gamma rays， which disrupt chemical processes in contaminating organisms. The disruption breaks down the cell walls of organisms or destroys their genetic material. The dose， set by the U.S. Food and Drug Administration （FDA）， is enough to kill organisms on food， but not enough to produce significant changes in the food itself.来源：www.newdu.com
Although irradiation slightly decreases the nutritive value of foods， the loss is less than that produced by some other methods of food preservation. Canning， for example， results in a much greater loss of nutrients.
Those who object to irradiation say that the process may create substances not found in nonirradiated food. Since the 1960‘s researchers have studied irradiated food at microscopic levels to try to find such substances， called unique radiolytic products. After reviewing these studies， the FDA determined that compounds formed during irradiation are similar to substance found in nonirradiated foods and are not dangerous to consume.
Destruction of microorganisms that cause illness is an important goal of irradiation. About 250 million cases of food poisoning or 1 per person—occur every year in the U.S.， according to FDA estimates. Food poisoning can cause vomiting， diarrhea， fever， headache—and， occasionally， death.
Because of the apparent safety of food irradiation， and the problems presented by contaminated food， scientific groups—including the American Medical Association， the World Health Organization， and the United Nations food and Agriculture Association—have voiced nearly universal support for the process. Worldwide， 38 nations have approved irradiation for 355 products.
Like microwave ovens， food irradiation has aroused apprehension and misunderstanding. Yet it has been scrutinized more thoroughly than other methods of food treatment that we have come to regard as safe， and it appears to be a method whose time has come.
1.Cobalt 60， besides irradiating food， is also employed to ___.
A.detect metallic flaws
B.run a nuclear reactor
C.cure cancer patients
D.strengthen concrete walls
2.Gamma rays used to irradiate food ___.来源：www.newdu.com
A.are generally not strong enough to destroy contaminating organisms
B.do not bring about significant changes in the food itself
C.may destroy some of the nutrients in the food
D.should be submitted to FDA for approval
3.Irradiated food ___.
A.certainly loses its nutritive value
B.maintains its nutritive value no different from the nonirradiated
C.keeps its nutritive value better than canned food
D.is recommended as the best of all preserved foods
4.With cases of food poisoning increasing， ___.
A.food irradiation should be carried out with care
B.it is more urgent to irradiate foods
C.medical researches into treatment of the diseased should be strengthened
D.Americans are beginning to accept food irradiation
5.The passage may be taken from ___.来源：www.newdu.com
A.a news report
B.a textbook of food processing
C.a book of popular science
D.a manual of food irradiation
答案：CBCCD
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