CEB558Gearns
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11 September 2007
Abaid Rehman, Daniel Hafner and I collected efficiency data for scintillator 703979. The voltage was changed in increments of 1/10 volts (starting at 5.0v through and including 6.0v) and then applied to the phototube in 60 second increments.
Data and preliminary anaylsis:
Efficiency Data 703979(.xls)
Efficiency Data 703979(.pdf)
18 September
The class lecture focused on error and error analysis. This is an area that very little time seems to be spent on in most class settings, and this has helped to clear out some misconceptions in my mind about reporting error. In particular, we had a small group discussion on error bars and their use.
Error as a concept taught in high school has been difficult. This is mainly because students typically see error as "mistakes' rather than a fundamental element to every measuremnt that is taken in a laboratory.
2 October 2007
SLAC Data
I've been playing around with the SLAC data from their virtual data center. The minimum time interval is 60 seconds for cosmic ray rate, so I dowloaded all of the one minute (1440) intervals for the 24 hour period of September 1, 2007.
Plotting all of the one minute intervals does not yield a particularly interesting graph in Excel mostly because their are too many time intervals, so I decided to sum each of the minute rates into hourly totals. I am interested to see if there are fluctuations from day to night.
Cloud Chamber
On the cloud chamber project, I have all of the materials need to begin putting together and operating the chamber. Last week, I received the plastic hinges and picked up the glass panels. There are two glass panels measuring 13in x 13in (sorry, glaziers use inches) and three panels measuring 7in x 13in. The glass is 1/8" thick. This plastic hinge and glass panel configuration will allow for easy changes of geometry. My goal is to optimize the geometry for largest viewing area while still meeting the 10 degree/centimeter temperature gradient necessary for a thick active layer.
9 October
SLAC Data
Last week, I downloaded one days worth of data from the virtual vistor's center. I leaned how to histogram the data using an Excel spreadsheet. One thing that I found rather interesting is that the histogram has a pronounced bulge just ahead of the peak. In other words, bins 14, 15,and 16 occur more often than 18, 19, and 20 (with 17 being the peak). Not sure of the statistical significance of this, I decided to download all of the week's data (September 1 to September 7, 2007) to see if this trend continues for the full week. It still appears in the week-long histogram. I also decided to histogram a random 24 hour period to see if this bulge appears again. The histogram of the random period is inconclusive.
So what does this mean? Does this have something to do with the efficiency curve of the SLAC detector? Perhaps it has something to do with the geometry of the detector system? This is something I am thinking about. Perhaps, I am thinking for nothing.
16 October
This week Jay gave a talk on the radar. I was interesting to see how the radar can be used to see objects in the sky by see the relection of radio waves from the objects. He spoke about the characteristics of the signal and how a signal from a large distance away can be used to identify meteors.
On the cloud chamber front, I was able to layout and mark the aluminum base plate. The plate will have the 4 peltier elements sandwiched between it and the copper heat exchangers. The layout includes space for the magnet which will be placed in between the heat exchangers in the center of the plate. Some space has been left to insulate the ceramic magnet which has a large thermal mass.
 Layout for peltier elements, heat exchangers, and magnet |
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23 October
This session was spent in the machine shop. All of the mounting holes were drilled into the plate. Each heat exchanger has 6 holes for mounting to the aluminum plate. I chose fine threads for the mounting bolts so that I can make controlled contact with the peltier elements. This is essential as the elements are fragile. The bolts are all countersunk so that the plate should have a flat surface for observing cosmic rays. Unfortunately, while functional, the holes in the plate will not get the Augie seal of quality.
 Mounting holes |
 Plate with heat exchangers mounted |
31 October
Gaussmeter Construction
The ultimate goal of the cloud chamber is to take measurements of the ionization trails of the cosmic rays. This means that the magnetic field of the permanent magnet needs to be measured and mapped. So I had to make a gaussmeter. The gaussmeter is a simple design using a hall effect sensor and a VOM. Once the map of the field has been created, the next step is to create curvature templates. The curvature templates must be linked to the strength of the field and will tell you the amount of bending the cosmic ray particle experiences as it enters the magnetic field. Only charged particles will bend in the magnetic field. The direction of curvature coupled with the radius of curvature and some imaginative thinking can help determine what kind of particle you are observing. One weakness of the curvature template is that it assumes that the ionization trails in a 2-dimensional plane. More often than not this is not the case, and so the templates are at best a close approximation. The bubble chamber picture below, is a good example of the problem. The "corkscrew" in the picture could be also be seen as an inward spiral if the the image vantage point were changed. As a corkscrew, the curvature templates are useless, but as an inward spiral as seen in the correct two dimensional plane, the templates could yield useful information.
20 November
The big chill. Ok, maybe not the big chill. In a preliminary test, the plate temperature got down to -5C. Not quite cold enough to she cosmic rays. The minimum temperature for cosmic rays is -25C. Hopefully, with the four peltier units pumping heat out, this chamber will reach -30C.
23 November
In an after Thanksgiving mood, I spent some time in the woodshop at Sachem creating a wood box to house the cooling system. The next step is to start insulating the box.
26 November
Time for the insulation. I used "GREATSTUFF" to fill a bag that conformed to the shape of the cooling system under the plate. The curing time is usually 24 hours, but because of the large layer of foam and the lack of exposure of the foam to the air, this process will take 4 days.
27 November
This week's session included mapping the magnetic field of the magnet under the aluminum plate. As discussed earlier, the mapping is necessary to estimate the momentum of charged particles by seeing how they curve in the magnetic field. The field map consists of only the 21 cm2 directly over the magnet. Only the center of this area has field lines perpendicular to the surface. The lines point out of the plate (the north side points up). If you look at the 3-D surface representation taken at plate level, the data reveal that the surface directly over the magnet consistently has a field strength of 466 +/- 5 gauss. I do not think this adequately describes the field at thses points, but rather the magnetometer becomes saturated here. Further investigation to follow. I think the field should look more like a bread loaf. Looking at the the upper level (.5" above), the field map looks like a loaf here. There are some interesting edge effects here. The edges on the map are located where the heat exchangers are attached to the bottom of the plate. I am not sure why the field drops out and them strengthens again.
 This carefully placed grid paper corresponds to fiducial marks that will be placed on the plate. |
 These measurements were taken directly on the plate. |
 Grid paper on 1/2" plywood that is the same size (l x w) as the plate. |
15 November
In another attempt at chilling down the plate, I wa able to achieve a low temperature of -12C. Still not cool enough but getting closer. I checked to see that all of the peltier elements were working in the right direction. They are. I checked both the physical position and wiring of the units. So the next step was to check the heat flow. I did this by checking the input and output temperatures. Input from the ice bath 0C with an output of 3 to 4C. Flow rate of 212L/hr. This turns out to be 900 to 1000 J/s which compares favorably with the ratings of the peltier units (280 x 4) x 70% efficiency. So it looks as though more work will need to be done with insulation.
18 November
The next step is to work on the insulation. There are some heat leaks. I will be spending the next several weeks working to achieve the elusive -30C goal.
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