Question

An isotope of cesium (Cesium-137) has a half-life of 30 years. If 1.0 mg of cesium-137 disintegrates over a period of 90 years, how many mg of cesium-137 would remain? 14. Thallium-208 has a half-life of 3.053 min. How long will it take for 120.0g to decay to 7.500 15. Element-106 has a half-life of 0.90 seconds. If one million atoms of it were prepared, how many atoms would remain after 4.5 seconds? 16. A 2.5 gram sample of an isotope of strontium-90 was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test Site. The half-life of strontium-90 is 28 years. In what year will only 0.625 grams of this strontium-90 remain? 17. Thallium-201 has a half-life of 73 hours. If 4.0 mg of thallium-201 disintegrates over a period of 5.0 days, how many mg of thallium-201 will remain? 18. The half-life of "C is 20.3 min. What percentage of a sample will have decayed after 1.69 hours? 19. Radioactive copper, 5Cu, is found in quantities exceeding pollution standards in the sediments of a reservoir in a routine check on Monday. The standard allows up to 14 ppm/cubic meter of sediment On Monday at 8 am, 59ppm/cubic meter were measured. The half life of Cu is 12.7 hours. When will the pollution level return to 14ppm?

Answer 1

13). This question is solved as follows

13. Gluen that Cesium-137 has half life of 30 years. Initial concentration is loma they have asked to send the concentration remains after go years. we will use the equation for helf K = 0.699 or 1/2 = 0.693 we knew that k = 2.303 + oH K = 0.693 - 2.303 109[%a-] le 0.693 - 2:303109 (10) 30 90 = 0.0231 = 0·02559 logart = 0.902696 = logama I - Antilog [o-902696] a-u I = 7.991 Ax = 0.125 14 mg. 0. 12514ng will remain after goyears.