Retort stand and clamp

In reference to the safety aspect, the radiation source is kept inside a lead block, inside a wooden box, inside another wooden block, tongues are present for the movement of the source so it never directly handled. The sources themselves are in holders, which channel the radioactive output in one direction alone. However as I am working with Gamma radiation this is slightly irrelevant. Also the rad-count dector will be placed in a clamp, to ensure it’s constant position. The radiation source itself is placed in a L-frame; this will keep it at a constant height.

It also reduces the amount of handling needed of the sample. I also made sure that I was over 16 years of age before beginning, and made a concerted effort not to ingest the radiation source. Method  Take the background count of radiation by turning on the digital radcount, and setting to detection for 1 minute three times. Remove the cobalt-60 from its lead container, and using tweezers put in the l-frame source rig.

Securely attach a metre rule to the desk, brace the l-frame against it, with the vertical section corresponding to a whole number on the metre rule

Secure the digital rad-count dector in a clamp attached to a retort stand, align this with the cobalt-60 and place it to be touching. 5. ) Set the digital rad-count to detection, for one minute, do this three times  Move the l-frame what you estimate to be 2. 5 mm from the digital rad-count, and set the digital vernier callipers to 2.

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5 mm, cheek the distance of the l-frame and refine as necessary. 7. ) Repeat steps five and six until a distance of 3cm is achieved. Repeat step 1 at distance 1. 5 cm and 3cm. Analysis of Results

I feel that my results prove that gamma radiation does obey the inverse square law; to begin with we will look at the graph in which the radiation count is plotted against distance A curve is described thus suggesting that intensity is inversely proportional to the distance. However this graph goes no way to prove that it is inversely proportional to the square of the distance, for that we need to construct a graph with one over the square root of the radiation count plotted against distance. My graph clearly shows a straight line.

Thus it is shown that Gamma radiation obeys the inverse square law. However the Equation I achieve is actually Y= -0. 77X + 3. 02, but rather than proving that gamma radiation doesn’t obey the inverse square law, I feel it merely points out certain experimental errors, namely the inaccuracies in distance. Although they may only have been +- 0. 5 mm, when working on a scale of 2. 5 mm at times the percentage error is very high. So I feel that these graphs more than adequately prove the inverse square law holds for gamma radiation.

My trial experiment in light also proves that the inverse square law holds for light. In a similar method to the gamma experiment if we plot a graph of light intensity against distance, we obtain a curve. The fact it is a curve is good, however it is more than that it is a curve, with an almost perfect half life, the value not changing significantly for each half-life. Being around 2. 5cm. The fact it has such a good half-life makes the need for further graphs redundant, it conclusively proves the inverse square law.

The half-life shows that if the distance is doubled the intensity is decreased by a factor of four. The fact that light and gamma radiation obey the inverse square law is solid proof that all members of the electromagnetic spectrum will obey the inverse square law. Evaluation Systematic Errors There was a high uncertainty in my measurement of distance. The cobalt 60 is kept within a metal tube. During my experimental procedure, I measured from the front of this tube, however the source could have been up to 5mm into the tube.

Over short distances this leads to very high percentage errors. A similar thing is present in the Geiger-muller counter and tube. Like previously the actual dector is set inside the plastic casing, and could have been up to 5mm inside the tube. This leads to very high percentage errors again, which I will calculate later. There is a possibility that the counter and radiation source were actually slightly out of line, so as the two moved apart, there would be a horizontal angular discrepancy, this would lead to a count lower than it should be.

However, attaching a meter rule to the desktop and bracing both the source clamp and the retort stand against it, and ensuring the two align as closely as possible, this problem is solved, this should also solve the problem on the vertical angular discrepancy. More extreme measures include bracing the equipment against the secure ruler to eliminate horizontal angular discrepancies, and attaching mini spirit levels to the source and detector to ensure the vertical angular discrepancies are kept to a minimum.

It could also be possible to attach a laser pen to one of the pieces of equipment and ensuring the position of the laser light on the opposing piece of equipment doesn’t change. This will eliminate both horizontal and vertical angular discrepancies. However these tow suggestions are impractical, the only laser light I have access to is actually very powerful, and could easily blind if directed at the ye, so I feel the danger levels here are to high. I only have access to large sprit levels, which would not be practical to attach to the equipment.

Plus as I am only working over small distances any angular discrepancy will not produce high percentage errors. Another possible error would be if the count exceeds the level at which the dector could perceive. This would lead to what is known as ‘dead time. ‘ As there is radioactive activity not being detected hence a deceptively low count would be present. But for this to occur it would require radiation counts far in excess of what the weak Gamma source I used was capable of, so this can be ignored.

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Retort stand and clamp
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