The summer is drawing to a close and soon the two of us will be back at school for the year. Here are a few more updates on our experiments.
This past week has been full of crushing rocks and putting together a video of the "Best of Rock Crushing". This video has been uploaded to the youtube and can be seen by clicking the link above! Some notes to keep in mind while watching:
1. In the first few clips there is a streak of white light that looks like a piece of broken glass. This is light reflecting off the plexiglass shield as it fell off the platform. Later, in the tall red granite test some specks of light appear to be coming through the granite, this is simply the reflection off the surface.
2. During the first granite triangle test the detector on the right became detached and fell onto the plate causing it to break in two. We took extra measures to protect the surviving detector by wrapping it it foam, visible in the following tests.
3. Some of the noise is the rock cracking (most obvious in the close-up video) while other noises are background from the shop. In some cases there are things falling after the rock cracks, usually this was the plexiglass shield before it was secured properly, or the lever for the press when I dropped it out of surprise.
4. For a detailed, day-by-day analysis please refer to my experiment document (below) or to the experiment spreadsheet summarizing the results.
To summarize the results seen so far:
Out of the 13 pieces of granite crushed, only two tests resulted in bubbles. These were also the only two tests to reach above 60,000 pounds of force. It appears that the first of these two tests produced shock bubbles when the detector hit the plate, and the second produced various bubbles, most likely also due to shock that broke one of the detectors.
Unfortunately next Wednesday will be my last day. With that in mind, what’s planned for these last days? Instead of a formal presentation to my group, who have all been involved in my experiment, I will be creating a video explaining the experiment. Keep on the lookout for its appearance.
Howdy y’all, well the story of the CR-39 experiment has thus far been a troubled one. The first hiccup in the procedure I discussed in our last post: in our first run, the etching solution reached 100oC, where it stayed for approximately 4 hours, boiling off about half of the solution, leaving the top corners of each chip removed from the solution. This resulted in an uneven etch in the exposed area and a very intense etch in the area that remained submerged (the protocol is 6 hours at 70oC, and the etch rate increases exponentially with temperature, as shown in Figure 3 of this Korean Study). When a particle tracks are etched for too long a period of time (or with too hot a solution), they become very large circular tracks that lose all indication of direction. Tracks become visible after etching because the etchant attacks the ionized trails left behind by charged particles more quickly than it attacks the bulk of the chip, so these tracks will show up as pits on an otherwise flat surface. Also, if a particle hits the detector with anything other than a normal incidence, the track openings will appear as ellipses rather than circles, allowing one to determine any particle’s direction of origin. However, once the etchant reaches the bottom of the ionized track (which is roughly shaped like a cone), it will continue etching the track in all directions at the same rate as the bulk material, so if a chip is left to etch too long (or etch rate is too high, as in our case), the otherwise well-defined tracks become large, circular, and direction-less. These direction-less tracks can be seen in the picture below, which was exposed overnight to an Americium alpha source (from a smoke detector).
Macroscopic picture of the same chip
So in order to remedy our temperature control problems, for the second etch, I set up camp at the vent hood (which is located at the local high school’s chemistry lab) and watched the temperature during the whole process. Though tedious, this approach worked, and we got the chips etched at the perfect conditions (6.5M NaOH at 70oC for 6 hours). Upon removing these chips from the solution, it was obvious that they were far less etched than the previous chips. Below, 005 is from the second etching, and 003 is from the previous, flawed etching.
After solving the etching problem, we encountered another problem: physical damage on the chips. In our discussions with others who have used CR-39 in their experimentation, we have gathered that TasTrak, the CR-39 that we are using, is much more prone to damage than the more widely used Landauer/Fukuvi CR-39. Also, the Landauer/Fukuvi CR-39 comes covered in a blue polyethylene film that is removed immediately before experimentation, providing protection from physical damage and from airborne particle contaminants. Unfortunately, the TasTrak CR-39 chips (from Track Analysis Systems, Ltd.) come in a large sheet (pictured below) that is relatively exposed to the environment, and any handling (even as little as letting the bag rub against the chips when they’re removed) can cause tiny scratches and pits that are exacerbated by the etching process. These physical damage artifacts make it extremely difficult to determine what marks on the chip were caused by particles and what were caused by damage.
I would post pictures to illustrate my point, but… PROBLEM #3: We don’t have a microscopic camera capable of taking pictures at high enough resolution or magnification (see picture below, the tiny black marks are what we are looking to count). So to solve this problem, we’re ordering a 10MP microscope/camera capable of taking high-res pictures between 40 and 2000x, so pictures will be coming soon. In the meantime, in an attempt to make the tracks easier to count, we tried dying the chips. Our though process is that if we can get a dye to sink into the pits, we can wipe off the rest and we’ll be left with pits of much higher contrast, allowing us to take more macroscopic pictures for counting. So far we’ve tried three methods: a Sharpie, food coloring, and an all-purpose black dye (again, if we had the means, I would post pictures of the results of these methods). None of the three were wildly successful, the Sharpie seems to color the surface of the material and not penetrate the tracks, leaving white spots at every track, which could be used to our advantage, but it also leaves many other white spots that seem to not be tracks and frankly, I’m not too keen on drawing all over our detectors with Sharpies. The food coloring and the dye had about the same effect: some of the tracks appeared slightly dyed under the microscope, but not nearly enough to really make the counting job any easier (the dyed chip and microscope are also below)… Hopefully, when the new microscope/camera arrives, these problems will become non-issues.
Another problem that we are encountering is the conundrum of how exactly we’re going to count these tracks. Most of the big labs who have done CR-39 work in the past have used automated microscope cameras and expensive software packages that automatically count tracks and discount physical damages. We can’t afford those nice toys so the best we can do at this point is draw a fine grid (pictured below) underneath the chip and count manually under a microscope, box by box… That sounds like a job for… Interns! The problem with this is that track counts are going to be very inexact as we have to manually decide which tracks we think are from physical damage and which are from particles… so if anyone has a better idea for this process, I would LOVE to hear it!
Well, to keep this bummer train rolling, I recently had a conversation with Rick Cantwell of Coolescence, who has done several CR-39 experiments in the past. We discussed the many issues with CR-39 particle detection, not the least of which is radon contamination. Chip 001 (below) was left out overnight in the shop, and after just 10 hours of exposure to the shop air, it was covered in etch marks from airborne radon. It is Mr. Cantwell’s belief that a lot the results in CR-39 experiments that have been considered positive can actually be contributed to radon contamination from the air, a hypothesis that is starting to look more and more valid. Mr. Cantwell also turned me on to an Oriani replication attempt of which I was previously unaware. A research facility called EarthTech did a replication of exactly the same experiment that I am doing now, finding many of the same results as Oriani, but they were able to attribute all of the “positive” results to airborne radon contamination. Their report can be found here.
If I ever happen to get around to it, the rest of the experimental cell, complete with Pt anode and flame sealed glass tubing around the Ni cathode is pictured below. the cell on the left is to be the experimental cell, and the right will be control.
Plus, in case anybody missed it, Angie and Jordan made the local news as some Minnesota big-wigs came through our facility.