аЯрЁБс>ўџ 02ўџџџ/џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџьЅСs ПГjbjbР Р ф-ЊkЊkШ ъџџџџџџ]BBBBBBB4ФФФФh, 84ФH^xxxxxЙЙЙ,Ієš њ3BЙšЙЙЙ3 BBxxЇx   Й"BxBxvŽ6BBBBЙ ќ BBl /Р ЖФФл.Lab: DETERMINING RADIOACTIVE HALF-LIFE  Introduction Radioactive atoms decay at a rate that has been found to be independent of the factors that normally influence ordinary chemical reactions--temperature, pressure, concentration, and the presence of a catalyst. It has been discovered that each radioisotope decays at a particular rate that is distinctive for that isotope and serves as a partial means of identification. Rather than attempt to measure the time required for practically all of a given sample of isotope to decay, an inordinately long time in many instances, the chemist and physicist use another criterion: the time required for half of a given sample of radioactive atoms to decay. This period of time is known as the half-life of the radioisotope. The purpose of this experiment is to measure the half-life of an isotope of indium. This will be done by watching a video on determining the radioactive half-life, taking data on the radioactive decay and using the data obtained to determine the half-life of the indium isotope. Procedure 1. Since the work involved requires handling a radioactive source, we will watch the experiment performed for us on a videotape. 2. The amount of the radioactive isotope can be determined by the number of counts per minute (cpm) detected by a Geiger counter. We will make a reading every half hour for a period of three hours. (Because the radioisotope is decaying, the cpm will decrease as time proceeds.) 3. Before we proceed with the isotope, however, we must determine the background count, the level of radioactivity always present in the environment. To obtain an accurate count on the isotope, the background count should be subtracted from cpm of the isotope. 4. When you have completed your data collection (background count and then the isotope count), construct a graph of actual counts per minute (cpm) of the isotope (y-axis) vs. time (x-axis). 5. Since the half-life is the time required for the cpm to fall to half of the original cpm, you can now determine the half-life of radioactive indium from your graph. Data BACKGROUND COUNT DATA TRIALCOUNTS PER MINUTE (CPM)#1#2#3#4AVERAGE RADIOACTIVE COUNTS FOR INDIUM ISOTOPE TIME (HOURS)MEASURED CPMBACKGROUND COUNT CPMACTUAL CPM Analysis 1. From your graph, determine and record the half-life. Write a conclusion. AFTER YOU HAVE COMPLETED THE CONCLUSION, ANSWER THE FOLLOWING QUESTIONS: 1. How does a Geiger counter work? 2. From where does the background radiation come? 3. What is radioactivity? 4. Why are nuclear reactions called transmutation reactions? 5. What is meant by the terms “parent” and “daughter” isotopes? RADIOACTIVITY Name: _______________________ Partner #1: _______________________ Partner #2: _______________________ Acton-Boxborough Regional High School Due Date: ______________________ Acton-Boxborough Regional High School &'()*8$%0: = > D \ a b z Ш с т і ї  2 3 = ЧШж?d‰ЎГіьсмсмсмсмжмжмжмжмжмсмЮЦЦ5CJOJQJ5CJOJQJ 5OJQJOJQJjOJQJUmH5:CJ(OJQJ5:CJ(OJQJ"')789  "#$/01ДЫ б  7 8 9 : ; < = C D §§ћћ§§§§§§§ћћѕяяяяяяяящћћћћ„„ђў„„ђў„h„˜ў  Ц Ч Ш е т ї                          ! 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