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Aim: I will investigate how the field strength varies the deflection of Beta Particles. Preliminary Work I started my preliminary work because, when I started my measurements using 2 coils used in experiments to deflect electrons from and electron gun. While testing for the deflection of beta particles, I found that beta radiation was scattered in a very large cone, I can not get any readings with amount of beta radiation scattering. So I would have to construct some type of shielding for this investigation, this is so I can measure the deflection more easily. The angle at which the beta particles are being scattered is 48 o. Deciding on the Type of Shielding I will test for the best shielding.
The best properties of the shield will be; it can be malleable to form different shapes and can be punctured, can stop radiation at a small thickness. Equipment Strontium 90 beta source GM tube + counter Different thickness of different metals Clamps, bosses and clamp stand to hold the source and the material being tested. Method 1. Set-up equipment as in the diagram 2. Record the thickness and the material being used. 3. Record 5 readings of the radiation count, and record them in a table 4.
Replace material being tested with different material or a different sized material. 5. Repeat steps 2 to 4 as required. Results The background radiation reading i The average count is 3. 8 (1 dp). Conclusion This shows that aluminium stops radiation at 3. 5 mm, this would be difficult to use because, this thickness of Aluminium is not malleable and the aluminium is not soft enough to puncture. Lead can stop radiation at very thin thickness', also lead is very malleable and is soft enough to puncture.
I will use Lead shield at 0. 6 mm thick, since it is the most abundant thickness' available and it is the easiest to form to any shape I want. Deciding how the shielding can be used. I want to have a tight beam of beta particles in this investigation, so I will use my knowledge on what would be the best way to shield the source. An unshielded source The source is unshielded and has beta particles spreading out. Angle Theta is the angle which the beta particles are scattered through. The path of the beta particles is not a straight line, but a curve because the beta particle are deflected by the moles in the air.
The points A B are the furthest points where beta ration is detected. Using a plate shielding The beta particles have a smaller angle, that they are being scattered through. Also if the shield isn't wide enough the beta particles that travelled either side of the shielding could cause problems. For example, when measuring the deflection of the beta particles in the electric field, the beta particles that passes outside of the shield will interfere with detecting the deflection of the Beta. Using a cylindrical shielding The cylindrical shielding produces a smaller angle which the beta particles are being scattered through than the source. But this is too wide to for I want to use.
So I will need a compromise of the plate shielding and the cylindrical shielding. Using Compressive Shielding This shielding produces the smallest angle for scattering because the cylinder stops the beta particles that spread out to the side, the plate stops all the beta particles that don't pass through the hole. The smaller the hole in the plate shield will affect the counts, because the smaller the hole then greater the number of beta particles are absorbed by the shielding. The size of the cylinder does not matter as long it has a diameter greater than sources width, because the beta particles will do the same thing as in fig 3. Making the shielding To make the shielding, I must be accurate in making the hole in the plate, I will do this by using a tool designed to make regular indentations. This tool can make holes from 5 mm wide to 9 mm with intervals of 1 mm.
In making the cylindrical shielding, it doesn't have to be a cylinder to produce the same desired affect. I will use a round metal bar with which to roll the lead shielding. The both parts of the shield will be stuck together with tape, because if I piece become damaged or deformed, it can replaced easily. Measuring the Angle at Which Beta Particles Are Scattered Through With different Diameters of punctures Equipment Strontium 90 beta source GM Tube Lead Shielding (43. 6 mm long) Counter Method Note: To make sure that the GM tube, the puncture and the source is in alignment, draw a straight-line with a rule on the table. Then use a set square to get the perpendicular vertical line.
Mark a set distance, this mark will be placed in the centre of the source, GM and the punter along the table. (Careful with the source, approximate the centre, see safety notes). 1. Set-up the equipment as the diagram, measure the distance (20 cm) with an accurate rule, stating with plate shield have in a puncture of 5 mm to start with. 2. Take 10 readings per 100 s, record these results in a table 3. Change the time base for the counter to 10 s and move the GM tube along parallel with the shielding. Using the method of trial and improvement, find the places where the is a sufficient drop in counts, mark this with a sharp piece of chalk or any other marker. 4. Measure the distance between each point and record the results in the table 5.
Repeat step 1 to 4 replacing the plate shielding. Results The background count had an average of 28. 9 per 100 seconds. I worked out the angle by using this equation Tan- 1 (AB/D) = Angle beta particles scatter though. Conclusion The graphs show a linear relationship between the puncture size and distance form AB. I would of expected an squared relation ships because as the diameter increases with a factor, the area would increase with 4 times that factor, so less beta particles would be stopped by the shielding.
If I had more time to investigate this I would take more readings and examine the relationship. The best puncture size is 5 mm, it has the smallest angle which the beta particles scatter through and the count is sufficient to use in my final experiment. Measuring the Deflection of Beta Particles. Equipment Strontium 90 beta source Shielding 2 electric plates EHT cables GM tube and counter Method 1.
Set up equipment as in the diagram 2. Make sure that all the equipment is i...
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