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# Radioactivity Experiments: To determine the penetrating power and the range in air of the three radioactive emissions alpha, beta and gamma.

Extracts from this document...

Introduction

Majid Khan

Aim:

To determine the penetrating power and the range in air of the three radioactive emissions alpha, beta and gamma.

Apparatus:

• gm tube,
• clamp stand,
• the counter thing,
• ruler,
• set-square

Method of penetrating power of Alpha particles, Beta particles & Gamma Rays:

The equipment was set up as shown below to measure the penetrating power of each radioactive source.

Again the measurements were taken without the absorber to measure background radiation.  The source was placed quite close to the counter (1cm) and the thickness of the absorber was increased each measurement.

Experimental precautions:

The distance between the tube and the source was kept constant

The material used in each experiment was kept constant.

Safety precautions were the same as the previous method but the absorber was changed using a stand and tweezers.

Method for range in air of Alpha particles, Beta particles & Gamma rays:

The apparatus were set up as in the diagram below to measure the range in air up to 50 cm for each source.

Before the experiment took place we measured the background radiation in one minute.

Middle

0.1

1231

1250

0.21

916

935

0.385

721

740

1

456

475

1.28

261

280

2.06

49

68

3.27

7

26

As the thickness of the aluminium increases the counts per minute of alpha particles decreases. This true because alpha particle cannot pass through 1mm aluminium. From the above it can be seen that some beta particles were still absorbed when the thickness of the aluminium was more than 1mm whereas in the text book it says that beta is stopped by 1mm of aluminium which my experiment doest actually prove to be correct as beta particles are stopped after 2.5mm of aluminium. By 3mm thickness the power is reduced from about 1231 to 7 counts per minute

 Gamma - lead (distance between source and GM tube = 14 cm) Thickness (cm) Corrected counts per min Counts per minute (original data) 0 122.3 143.3 0.2 73.3 94.3 0.35 64 85 0.7 47.67 68.67 1.3 34.67 55.67

As the thickness of the paper increases the counts per minute of gamma rays decreases. This is true because gamma rays cannot pass through lead.

The penetrating power of the gamma radiation decreased as the thickness

Conclusion

 Gamma Distance (cm) Corrected counts per min Counts per minute (original data) 10 2565 2586 20 395 416 30 157 178 40 93 114 50 65 86 60 43 64

The count decreases as the distance increases with a steep curve line. The experiment supports the theory that gamma is not stopped by air but is reduced because at 50 cm there is still a count of about 65 counts per minute.

The range in air experiments agree with the properties of alpha with the least range in air and gamma with the greatest range in air.

Evaluation:

The results were quite accurate as they corresponded with evidence in the AS/A2 Physics (Mee, Cundell, Arnold and Brown) and the Nelson Modular Science (Mark Elise and Chris Honey) books. The results were precise as they followed a nearly uniform pattern of an exponential graph.

However in some of the graphs the results were a bit anomalous. For example on the Beta particles graph the beta particles were was absorbed by 1mm aluminium which isn’t really correct as beta particles should be stopped after about 2.5mm of aluminium

This student written piece of work is one of many that can be found in our GCSE Radioactivity section.

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