1. John Frontczak<br />IB HL Physics, Young<br />22/11/10<br />Half-Life of 137Ba Lab<br />Background:<br />1. Half-life is the amount of time it takes for a substance to decrease by half while undergoing decay.<br />2. Equation for beta decay of 137-Ba: 55137Cs->-10e+56137Ba<br />3.<br />Geiger-Muller Tube:<br /> It's a cylinder surrounding a wire that's kept at a high voltage. The cylinder is filled with low pressure gas, and when ionizing radiation passes through it, it can knock some of the electrons off of the gas particles. Those electrons are then accelerated towards the center wire. As they accelerate towards the central wire they pick up speed, and they are eventually able to knock other electrons off other gas particles. And those accelerate and hit other electrons and so on, and so forth, until you get large amount of electrons moving towards the central wire. That creates a current that is then detected and measured with the scalar.<br />Photomultiplier Tube:<br />Coupled with a scintillator, the scintillator gives off a little flash of light as radiation passes through it. The light it gives off hits the front of the photomultiplier tube, knocking an electron off of the surface of the coating in the front. The electron is then accelerated through a series of little panels in the tube (Dynodes), and when an electron hits a dynode, more than one electron get knocked off. This also causes a large amount of electrons that can be counted and collected.<br />4. The photomultiplier tube is able to take more samples at a faster rate than the Geiger-Muller tube, making it more likely to get more accurate data.<br />Analysis:<br />Table 1: Data-<br />timecountevents(raw)events0:000000:15220072200721143.40:30430982109120227.40:45628881979018926.41:00812991841117547.41:15985641726516401.41:301147621619815334.41:451296881492614062.42:001437501406213198.42:151565211277111907.42:301693881286712003.42:451809881160010736.43:00191734107469882.43:15202475107419877.43:3021217196968832.43:4522113489638099.44:0022979886647800.44:1523794481467282.44:3024549875546690.44:4525258970916227.45:0025929967105846.4<br />Graph 1: The number of events that occurred between 15 second intervals<br />Calculating the Equation:<br />At=A0e-λt<br />AtA0=e-λt<br />λt=-ln⁡(AtA0)<br />λ=-ln⁡(AtA0)t<br />Calculating λ:<br />λ=-ln⁡(780016400)165sec<br />λ=0.7432165<br />λ=0.0045<br />Calculating the decay constant:<br />T12=ln2λ T12=ln20.0045<br />T12=153.8964072≈153.9 sec.<br />Final Notes:<br />The official (researched and agreed upon) half of 55137Ba is about 152 seconds. The value calculated in this lab, based upon the data provided was about 154 seconds. Without further context, this value seems to be close to the official value, implying that the experiment and the data is (at least) partial valid and accurate. The two second difference however would add up to a huge difference in the calculated mass of the remain Ba after a even a day.<br />