Question

<Chapter 20 practice for Quiz 12 on 23 April Smoke Detectors and Radioactive Isotopes ® 18 of 28 > 1 Review | Constants Periodic Table Part A A particular smoke detector contains 1.35 uCi of 241 Am, with a half-life of 458 years. The isotope is encased in a thin aluminum container. Calculate the mass of 241 Am in grams in the detector. Americium is used in household smoke detectors as a source of a particles. The device actually responds to the presence of ions from a fire, rather than responding to smoke. A schematic is shown in the image. (Figure 1) The entire setup is enclosed in the familiar plastic housing. The 241 Am, which is an a-emitter, is encased in an aluminum container with an opening that aims the a particles through an air gap between electrically charged plates. The a particles ionize some of the air molecules, which are attracted to the electrical plates. This produces a current that is detected by the ammeter in the circuit. When smoke is present, a different number of ions form, altering the current and setting off the alarm. Express your answer numerically in grams. View Available Hint(s) V ADV A O O ? Submit Figure < 1 of 1 > Part B Fears of radiation exposure from normal use of such detectors are largely unfounded. Identify reasons why 4 Am smoke detectors are perfectly safe. battery Choose all that apply. ► View Available Hint(s) a particles 241 Am The detector is housed in an aluminum case. O The detector has a plastic cover. ions from air ammeter O lons get trapped by electrodes. O The penetrating power of a radiation is limited. positive ions negative ions alarm The number of a particles leaving the case is low. The amount of americium is very little.

Answer 1

Part -A According to the condition given in question, Activity = DN Activity is given as 1035 Mei Ici - 317X10 10 -6 30 Activity = 1,35 x 3, 7X10 X 10 dps 49950 half life = 458 years - 458 x 365 x 86400 - 1.44 x 10'0 sec Therefore n= ACARRAY 0.693 2 = 0.693 1.44x10 sec a = 4.813x10 Now N = Activity N = 49950 4.813x10 15 N- 1.038 X10 atoms

6.093 x 1093 a toms can weigh 941 grams. Therefore 1.038 xid" atoms weigh 15 241 X 1.038 X10 6.023 x 1023 - 4.15 x 10 grams These fore mass of 241Am is) 4.15 x 10 grams in the detector

PART -B:-

i) the detector has a plastic cover

ii) the detector is housed in aluminum case

iii) the amount of aluminum is very little

iv) the penetrating power of alpha radiation is limited

v) Ions get trapped by electrodes

vi) the number of alpha particles leaving the case is low

HENCE ALL THE ABOVE OPTIONS ARE CORRECT

SO CHECK THEM ALL