June 2009 Chemistry Regents #68-70

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Base your answers to questions 68 through 70 on the information below.

Cobalt-60 is commonly used as a source of radiation for the prevention of food spoilage. Bombarding cobalt-59 nuclei with neutrons produces the nuclide cobalt-60. A food irradiation facility replaces the cobalt-60, a source of gamma rays, when the radioactivity level falls to 1/8 of its initial level. The nuclide cesium-137 is also a source of radiation for the prevention of food spoilage.

68 Identify one emission spontaneously released by a cobalt-60 nucleus. [1]

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beta particle or gamma

69 Determine the total number of years that elapse before an original cobalt-60 source in an irradiation facility must be replaced. [1]

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15.78y

1-->1/2-->1/4-->1/8, so 3 half lives

3 x 5.26y

70 Complete the nuclear equation in your answer booklet for the decay of cesium-137. Your response must include the symbol, atomic number, and mass number of the missing particle. [1]

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137 Cs==> 0 e + 137 Ba
55 -1 56

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