Chapter 7 Test: Radioactivity

When a radioactive substance is placed in a cloud chamber, we can actually see the evidence that radioactive decay releases tiny particles--individual atoms. This is because the cloud chamber allows us to visualize the paths of these particles as they ionize the vapor in the chamber, creating visible trails. This observation provides direct evidence that radioactive substances undergo decay, where unstable atomic nuclei break down and emit particles in the process.

Based on the data from location Z, the conclusion that can be reached is that there was no radioactive material floating in the air. This is indicated by the fact that the filter has a net count of basically zero, meaning that it did not remove any radiation from the air.

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The difference between the two results can be explained by the fact that radioactivity is not perfectly predictable. Therefore, the number of counts measured in a short time span may or may not match up with the long-term average. In this case, something may have blocked the radiation from reaching the counter in the second measurement, resulting in fewer counts being recorded in just one minute compared to the average counts recorded in one hour.

Lowering the temperature of the sample would not affect the counting rate because temperature does not have a direct impact on the radioactive decay process. Radioactive decay is a random process that is not influenced by external factors such as temperature. Therefore, changing the temperature of the sample would not alter the rate at which the radioactive material emits particles that can be detected by the Geiger counter.

All of the materials mentioned in the options are able to block some form of radiation. Lead foil is commonly used as a radiation shield due to its high density and ability to absorb radiation. Skin acts as a natural barrier and provides some protection against radiation. Clothing, especially thick and tightly woven fabrics, can also block certain forms of radiation from reaching the body. Therefore, all of the above options are correct as they can block some form of radiation.

Gamma radiation is the correct answer because it consists of high-energy photons that can easily penetrate through most materials. Unlike alpha and beta radiation, which are made up of particles that can be stopped by a sheet of paper or a few centimeters of air, gamma radiation has no mass or charge, allowing it to pass through objects more easily. Delta radiation is not a recognized type of radiation, making it an incorrect answer.

The correct answer is Location Y because it is the only location mentioned that has radioactive material floating in the air. The other locations, X and Z, do not specify the presence of radioactive material in the air.

Based on the given information, the element that would probably be gone if we came back and tested again in 500 million years is W only. This is because the other elements X and Y are not mentioned to be gone, and the element Z is not mentioned at all. Therefore, the most likely answer is that only element W would be gone in 500 million years.

If a chunk of compound XY with the same mass as the samples used above is held at the same distance from the counter and the counter is run for one minute, it would be expected to see a range of counts per minute between 5 and 13.

The Geiger counter counted 1440 counts in 60 minutes. To find the background radiation, we divide the total counts by the time in minutes: 1440 counts / 60 minutes = 24 counts per minute. Therefore, the background radiation is 24 counts per minute.

Based on the results of the experiment, we can determine that compound 3, which contains barium and bromine, is non-radioactive. Therefore, we can conclude that barium and bromine are definitely not radioactive.