1 Introduction

In this experiment we used a radioactive particle generator to obtain samples of Barium for counting the gamma-decays it releases, this should confirm very nicely the proper halflife of Barium.

2 Procedure

2.1 Instruments and materials

The measuring instruments used in this experiment were suggested as the standardized γ ray measurement equipment. They are the following instruments:
1. Geiger tube. Welch Scientific #1216
2. Scalar-timer. Sargent-Welch model S-72095-10.
3. Radioactive source. Particles from an isotope generator.

2.2 Obtaining the experimental data

After obtaining the sample of Barium from the generator, we instantly placed it under the gaze of the geiger counter and began counting particle decays with a 10 second on, 20 second off time base. After about 10 minutes it was obvious that all of the numbers were fluctuating as if it were background radiation rather than a close and powerful source. So we attempted to obtain another sample to test. The same result happened.
While taking a break from data-taking, we decided to utilize our time semi-efficiently, and measure the background radiation. We recorded a result of 3cts∕10sec. After we had established the background, we attempted again to record the decay of barium.
Success! we were finally able to get an initial count value high enough to enable a reasonable number of counts. Very rapidly however it decayed down to a count level that fluctuated as though it were background radiation, one problem though, the numbers were consistenly higher than our 3cts∕10sec!!

3 Analysis and conclusions

Our data evaluation exploration begins thusly. We began by plotting our data obtained against the time counts.

We estimated that at about 600s the data started to be obscured by the background radiation. From that point until the end of the data we averaged the values, and elected to use that value as the background noise level. This did not solve the mystery but it gave us a basis to start from. The average of the data from point 600 through the end of the data is 13.4348. We subtracted this from all of the data points then ran a linear regression on the log of the data through 600 sec.

Above is a log-graph of our data through 600s along with the regression line for the data. Although our data gives us a nice determination of the Half-life of Barium, it still doesn’t explain the dichotomy of the background radiation levels. That suggested contamination. In discussion with our mentor we came upon an interesting suggestion. That perhaps the generator was aged to a point that when the acid was dripped down to strip off Barium particles, we were getting contamination from the Cesium.The old Cesium sample inside may have corroded to the point where particles of it were flushed into the sample as well. This would account for the higher background radiation after the initial Barium sample completely decayed. The Cesium, with it’s much longer Half-life would continue to Beta-decay into Barium which then excited counts in our counter as it decayed by gamma emission.

To determine the measured half-life of Barium we implemented the following.

Given that our regression slope was -0.00443691 we reached an answer of 156 sec. or 2.6037 min. which is in good accordance with the accepted value.