Procedure for Aluminum activation experiment; Mar 2, 2017.
This supersedes the procedure in the course website.
Set up the detector as in the first two experiments. Calibrate the spectrum using
1) 662 keV gamma from 137Cs and 1173 and 1332 keV gammas from 60Co
2) Room background 1461 from 40K and 2614 keV from 232Th
You may have to lower the HV on the PMT so that the two 60Co gammas are in about channel 400.
a) Make plot of Energy versus channel for the 5 gamma rays noted above. From this plot located the approximate
channels of the 843 and 1014 keV gammas from 27Mg and the1779 keV gamma from 28Al. Define ROI’s at each
of these 3 gammas (about the same as the widths of the gammas in the calibration spectra.
b) You will be taking TWO sets of measurements; the first to optimize the yield of the 28Al (1779 keV) and the
second to optimize the yield of the 27Mg (843 and 1014 keV).
c) Set live time of 60 sec. Set the activated Al cylinder RIGHT up against the face of the detector.
d) Start a count, Note the time of day when the count started (upper right hand corner of the screen)
e) At end of count record 1779 keV Net +/- Error. Save spectrum under name “Al_m2_01”, etc.. Take 10 60 sec
counts. This should take maybe 15 minutes. Then repeat for Al trapezoids looking at 843 and 1014 keV. Save
spectra Mg27_m2_01. Take 40 measurements, this should take about an hour
Your results will be a five column spread sheet (name Al28_m2_01 for first measurement, Al28_m2_02 second set etc.
Time of day
Start(sec)
Net 1779
Error 1779
Name
10:00:00
0
5000
100
Al28_m2_01
For the second set looking at the 843 and 1014 keV gammas, your data will be a seven column spread sheet
Time of day
Start(sec)
Net 843
Error 843
Net 1014
Error 1014
Name
10:30:00
0
4000
85
2500
65
Mg27_m2_01
f) At end counts, make one semi-log plot (with error bars) of Count rates for all three gamma rays (Net/live time) +/(Error/livetime) as a function of real time at start of count (in sec after start of first count). Email this with both
lab partner names to [email protected] BEFORE you leave the lab.
g) To be included in report
1) Abstract giving results of measured half-lives with uncertainties
2) Calibration spectra (Cs-Co 662, 1173, 1332 keV); Room background (1461 2614 keV)
3) Calibration plot (Energy versus channel)
4) Typical spectrum of activated Aluminum with 843, 1014 and 1779 keV peaks indicated (first trapezoid
spectrum)
5) One semi-log plot of count rates (with errors) of 1779, 843 and 1014 keV showing exponential fit.
6) Table of half-lives with uncertainties. See attached MATHEMATICA notebook for calculation of
uncertainties in half-lives. Show all steps in calculation of uncertainty for first 1779 keV as Appendix A.
Portion of Table of Isotopes indicating todays activation products
27Al(n,γ) 28Al
27Al(n,α)24Na
27Al(n,p) 27Mg
Analysis guide for calculating half lives and errors in half lives