LAB EXERCISE #3: DETERMINATION OF THE HALF-LIFE OF SHORT-LIVED RADIOACTIVE ISOTOPE

       A major medical diagnostic tool involves the use of radioactive tracers that emit gamma radiation. Given in small amounts they may be selected to travel or accumulate in certain parts or organs of the human body. It is of course imperative that these radioactive tracers have extremely short half-lives such that they will decay and be eliminated from the body in relatively short time periods preventing undo radiation exposure. Technetium-99m is a typical short-lived isotope used in nuclear medicine in the diagnosis of disorders associated with a number of body organs. The m associated with the mass number indicates that it is metastable, and will yield gamma radiation to produce a more stable isotope of technetium.

      

The half-life of this radioisotope has been determined to be 6 hours. In order to obtain the Technetium-99m the radiologist must use a Molybdenum 99 / Technetium 99m generator.

You may wish to review the section on  Applications of Radioactive Isotopes.

 

       In Experiment #3 you will use a similar generator to produce a short-lived radioisotope and then determine its half life. The Cesium 137/Barium 137m Minigenerator is a miniature eluting system or radionuclide "cow" containing a long-lived radionuclide which decays to a short-lived radionuclide. It is designed so that the short-lived daughter can be separated easily, rapidly, and repeatedly from the long-lived parent. This miniature radioisotope generator contains a minute quantity of Cs-137 which has a half-life of about 30 years and decays by beta-ray emission to Ba-137m. The Barium 137m, in turn, decays to stable Barium 137 by gamma emission. By elution with 0.04 molar hydrochloric acid solution, the short-lived daughter Ba-137m can be milked from this miniaturized "cow" in less than one minute. After each milking, you will isolate the Ba-137m and using your Scaler/Timer with G-M tube collect the appropriate data to allow you to then determine the half-life of Ba-137m.

PROCEDURE:

  1. Turn on the Scaler/Timer with G-M tube.
  2. Record the background activities (the data obtained in experiment 1 may be used).
  3. ELUTION OF GENERATOR
    1. Fill to the line of the plastic bottle supplied with the generator [Safety: Rubber gloves, Lab aprons, Goggles] with approximately 3 ml of 0.04 M hydrochloric acid-saline solution.

      2. Filling the Eluent Bottle Movie

    2. For elution of the generator remove the plastic cap from spout of the plastic bottle and place tip of bottle firmly into the Larger opening of the generator. The tip should snap into place securing bottle to the generator.
    3. Gently squeeze plastic bottle to force eluting solution through the generator at a rate of 2 to 3 drops per second, and collect eluate in a 5 ml plastic vial. Cap the vial and place on the third level of the detector.
    4. Extreme care must be taken not to spill the liquid. In case of a spill wipe up immediately and notify your instructor.

    Eluting the Generator Movie

  4. Count the sample for one minute and record the activity. Wait one minute(a clock on the screen maybe activated to time one minute periods between readings). It is critical that you wait exactly one minute before you start the next reading. Continue recording one-minute activity readings every other minute until your readings approach background levels. (Approximately a total of six- ten recordings.)

Counting the Sample Movie

Go to Experiment

       In order to be allowed to complete the remainder of this laboratory exercises you will first be required to select appropriate safety precautions which you would be expected to meet when working with radiaoactive materials. Select from the list below all safety precautions required on completion of any of the laboratory experiments. Incorrect selection and/or insufficient numbers of the appropriate safety requirements will prevent you from continuing on with this program. Select only those procedures that are required for safe handling of radioactive materials.

Select Safety Precautions:

Place liquid radioactive waste in the drain and add water.
Before leaving the area survey for contamination.
Place gloves in appropriate disposal containers.
Place all waste paper in in normal trash recepticles.
Wash your hands.
Notify personnel that you intend to leave radiation area.


Go to Result and Calculation