From the data collected, it was clearly found that the distance between the Geiger Counter and the radioactive source is inversely proportional to the amount of radiation detected by the Geiger Counter. This can be seen as when the distance was 1mm, the average reading was 4533 counts. When the distance was 10mm, the average reading was 48 counts. When the distance was was 20mm the average reading was 11 counts.
We can also conclude that the rate of the decrease in radioactivity detected decreased as the distance increased. This can be seen as from 1mm to 2mm, the decrease is by 428.166667 counts. While the from 11mm-12mm, the decrease is 7 counts. And from 21mm to 22mm, the decrease is 0.5 counts. Hence, we conclude that not only does the amount of radiation detected decreases as the distance between the Geiger counter and the Americium increases, but that the decrease in radioactivity declines as the distance between the two object increases.
Explanation of key findings
To begin, since our radioactive source consists mostly of Americium-241, it undergoes mostly Alpha decay according to Thomas Jefferson National Accelerator Facility (n.d.). This is further supported by our own experimentation which showed that the radioactivity of the radioactive source was only in small range of less than 5 cm before only background radiation was detected. This small range suggests that the radioactive source mostly undergoes Alpha decay. Alpha particles are helium particles with a charge of +2 and hence they are highly ionising. These particles have much lower penetrating power compared to Beta or Gamma particles (Nuffield Foundation, n.d.).This means that even a layer of air can block the Alpha particles. Henceforth, the amount of radiation detected decreases as the distance between the radioactive source and the Geiger counter increases.
Evaluation of hypothesis
Hypothesis: “We hypothesize that the greater the distance between the Geiger counter and the radioactive source, the lesser the amount of radiation detected by the Geiger counter.”
The hypothesis was proven to be correct and this is supported by our data analysis.
This can be seen as when the distance was 1mm, the average reading was 4533 counts.
When the distance was 10mm, the average reading was 48 counts.
When the distance was was 20mm the average reading was 11 counts.
Distance between Geiger Counter and Radioactive source/counts recorded
From this, we can conclude that the greater the distance between the Geiger counter and the radioactive source, the lesser the amount of radiation detected by the Geiger counter. This is plotted below:
Areas for improvement
There are a several things on which can be improved on.
First, the process of measuring the distance between the Geiger Counter and the radioactive source was done. These inaccuracies may be minor but after a greater amount of data point, they accumulate and will cause the results to vary. We suggest using devices to do these measurements in order to prevent such inaccuracies.
Second, our radioactive source is from a commercial smoke detector, meaning that the radioactive source could consist other radioactive materials such as it’s daughter elements, Neptunium-237, Protactinium-233 and Uranium-233 (Gray, 2007). These daughter elements would affect the amount of radiation detected during the experiment since they have different decay rates and half-lives compared to our main source, Americium-241.
Thirdly, the Geiger counter is unable to tell Alpha, Beta and Gamma radiation apart. To add on, the radiation source does not emit purely Alpha particles (Andrew C., 2013)leading to Beta and Gamma radiation being released. Henceforth, the results are not based solely on the Alpha particles, leading to an inaccurate result due to the additional radiation.
Fourthly, since Alpha particles are helium nuclei and have a very high ionising power, even water vapour in the air can block them. Due to Singapore’s humid climate, there is a high amount of water vapour in the air. This leads to the Alpha particles having to travel through air that is high in water vapour during our experiments, meaning that the water vapour had blocked many Alpha particles during the experiments, These lost Alpha particles lead to a number of discrepancies in the results.