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Science Test 1

Page history last edited by Anna Gay 11 years, 8 months ago

Day Four: Science Test

Medical researchers and technicians can track the characteristic radiation patterns emitted by certain inherently unstable isotopes as they spontaneously decay into other elements. The half-life of a radioactive isotope is the amount of time necessary for one-half of the initial amount of its nuclei to decay. The decay curves of isotopes 3990Yand 3991Yare graphed below as functions of the ratio of N, the number of nuclei remaining after a given period, to N0, the initial number of nuclei.














  1. The half-life of 3990Y is approximately:

    1. 2.3 days.

    2. 5.4 days.

    3. 27 days.

    4. 58 days.


  1. What will the approximate ratio of 3990Y to 3991Y be after 2.3 days if the initial samples of the two isotopes contain equal numbers of nuclei?

    1. 1:1

    2. 1:2

    3. 2:1

    4. 10:1


  1. When inhaled by humans, 3990Y accumulates in the gastrointestinal tract, whereas 3991Y accumulates in the bones. If the total amount of each isotope inhaled goes to the specified area, which of the following situations will exist three days after a patient inhales these substances, assuming none of the isotopes leave the specified areas due to pathological factors?

    1. The amount of 3991Y in the gastrointestinal tract will be approximately equal to the total amount inhaled.

    2. The amount of 3991Y in the bones will be approximately one-half of the total amount inhaled.

    3. The amount of 3991Y in the gastrointestinal tract will be approximately one-half of the total amount inhaled.

    4. None of the 3991Y inhaled will be left in the bones.

  2. Approximately how many 3991Y nuclei will exist after three half-lives have passed, if there are 1,000 nuclei to begin with?

    1. 50

    2. 125

    3. 250

    4. 500


  1. Which of the following conclusions is/are supported by the information given in the passage?

  1. 3990Y is less stable than 3991Y

  1. Only one-quarter of the original amount of 3990Y will remain after 116 days.

  2. 3990Y and 3991Y are both radioactive.

  1. I only

  2. III only

  3. I and II only

  4. I and III only

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