AL Lab Edited Assigned to Hurryson

Activated Aluminum Half-Life Measurement

Objective: In this laboratory you’ll be given a thin aluminum foil that has been activated in the OSU TRIGA Reactor. Your objective is to familiarize yourself with the laboratory equipment (with Dr. Farsoni’s assistance) and to determine the half-life of the radioactive isotope of aluminum using the activated foil.

Procedure: 1. Set up the GM counter and its supporting electronics so that it is ready for use as a scalar

(counter). 2. Confirm that the GM is operating properly and collect any preliminary data that you might

need. 3. Set the dual counter/timer to the aluminum-lab counting time (hint: perform this sequence on

the counter/time to find the preset program: Mode “Config Module” => scroll to “recall” => scroll to “AL-LAB” => Mode “Oper”. At this setting, the counter/time will automatically count for 12 seconds, rest for 48 seconds, and count again in this pattern until stopped.)

4. Aluminum foils (1 cm diameter x 56 micron thickness) will be exposed to a thermal neutron flux of 1x109 n s-1 cm-2

5. When the aluminum source is in place, start the timer and record each 12-second count for a total of at least 15 trials.

for 60 seconds. After a 5-minute cool-down period, the foils will be brought to the lab.

Note the time

6. Determine the decay constant and calculate the half-life.

(relative to the end of the irradiation time) that your first count begins.

Questions: 1. Considering dead-time correction, determine the decay constant (λ) from your graph and

calculate the half-life of the appropriate aluminum isotope. 2. Why is it important to include the effects of dead time? 3. What is the known radio-aluminum half-life and how different (%) is the known from your

calculated half-life? 4. Estimate the activity of the foil (assume pure aluminum) when it emerged from the reactor

and at the beginning of your first count. Estimate both the intrinsic and the absolute efficiency of your GM detector.