July 26th- Day 20

Comparisons.

We set up the PET(002) with a Bragg angle of 11.81 degrees and an IFD of 121mm with a Cobalt source. The optic on the rotational stage was plugged into axis 6. We hooked up the camera with the gain and gamma settings all the way to the right. We took an image and aligned the optic. Afterward, we placed the detector back in position and hooked back up the z axis of the detector in axis 6. We placed the orange film in front of the detector and took another image. The spot was not in the center of the detector, so we moved the detector and tried again. This time the spot was closer to the center. We took the film off the detector and ran scans to find the Co peak. Scans were taken at 25kV, 30kV and 50kV and the number of counts was recorded. The solid angle of each optic was calculated using the equation below:

solid angle = area*sin(Bragg angle)

                                                                   IFD^2
Since the PET optic is comprised of several pieces, the solid angle was only an approximation. The solid angle for the Ge optic was also an approximation, but would be closer to the actual number due to the single piece. The solid angle for Ge(111) was calculated to be 0.0031 and for PET(002) is was 0.024. For each optic, the number of counts at 25kV was divided by the solid angle. This allows the optics to be compared 'apples to apples' by taking into account the differing solid angles. Dividing takes out the solid angle factor. By dividing, the flux is calculated for each of the optics. For Ge(111) it was 3.4E6 and for PET(002) is was 3.8E6. The higher the flux, the higher the efficiency making the PET optic more efficient. The flux for PET might even be higher because the solid angle could be an over approximation making it even more efficient. The optics were scanned using a different source to compare efficiencies.The new source is a Moly source. We calibrated the detector to pick up a certain peak. With this source, the peak moves as a result of varying Bragg angles. For finding the correct peak, specific ROI of 218 and 251 were set. The peak needed to be centered in this range. We tried taking an image using the film, but the detector needed to be realigned. Even after moving the detector the spot was still fairly large. A spectrum was taken but the results were not what we were looking for. Alex messed around with a few things and then took spectra once again at 25kV, 30kV and 50kV. Using the counts at 25kV the flux was calculated to be 2.2E6. Since this number is less than previously calculated, the efficiency of the Moly source was calculated to be less than the Cobalt source.
Once these calculations were complete, spot size measurements were to be taken. Unfortunately, scans were going haywire and were not producing the desired results. The detector had somehow become extremely out of place. After fixing the setup, the background ratios were lower than normal. The spot size was expected to be much larger than that of the Si(111) optic. We tried taking an image of the optic using the film, but could not find the spot. Tomorrow we will attempt to fix the problem.

July 25th- Day 19

Not so successful.

Once the new power and x-ray sources became available, Alex and Zewu were pressed for time to get data. Using the Co source, they first found an image using the camera. The image of the Ge(111) was more of a square compared to the image we obtained using the Si(111) optic. We were back to using the SDD high intensity detector that we were having problems with previously. Zewu and Alex were looking for a high flux which would mean a high efficiency. To compare sources, they would look at the intensity, from which they could calculate flux. A 127 micron Ni filter was used when taking the spectra. After they got the data they needed, we tried to minimize the spot size. We found the spot fairly quickly in the vertical, but had very different luck trying to find the spot in the horizontal direction. The spot size kept decreasing and the astigmatism would have been extremely large (~12mm minimum). Since the astigmatism should not be that large, we abandoned the scans. Alex said the tools were not right to make the optic so it would not be precise like the Si(111) optic. This spot size would have been significantly larger than the Si spot size due to the differing lattice structures. Due to being pressed for time, we would have to move on to test the PET(002) optic and come back to the Ge(111) spot size measurements.

July 22nd- Day 18

Imaging optic measurements.

Alex had finished aligning the new Si(220) optic and was ready to take the final measurements. This optic was being manufactured for Bruker for some imaging purpose. Vertical and horizontal spot size measurements were taken at 30mm, 70mm and 3mm. The OFD of 30mm produced the smallest spot (x- 152.4um, y- 217.4um) as expected. Measurements were taken at these distances to see how well aligned the source was and to see how good the optic is. A Mo source was used. This beam is used for divergence. The company has a sharp tolerance for the location of the beam. It needs to be in the center of the detector, so it can be blocked easily. If the beam was allowed to hit the detector, the detector would become over-saturated. When the beam is stopped, one can see the rings of the pattern diffraction on the beam stop.
The flux was calculated to be 4.85E7. To find the tilt, we focused and zeroed the detector at the normal OFD. Then the detector was moved back 500mm and the beam was scanned using the detector to locate the center. The difference between the two points of focus and the length of 500mm was used to construct a triangle of the vertical tilt. The angle was found to be 0.04 degrees. Calculating the tilt in x makes no sense because the error is so large.
__________calculations_________________
To calculate divergence, the optic was rotated to find the peak. While the beam was slightly focusing, the divergence was still calculable. The divergence shows the crystal diffract different energies. Doing a horizontal scans shows a shoulder off to the left of the main peak we were looking at. This was Mo K alpha2. Each angle represents a different energy. An intensity measurement was taken to observe the number of photons hitting the detector. The divergence can be taken for the 90th, 95th, or 99th percentile.
.......
The vertical divergence was calculated to be 0.66 and the horizontal divergence was 0.63.

July 21st- Day 17

Flux. Questions. Germanium. Fire drill. Heatwave. BBQ.

After fitting the intensity data we plotted in matlab, we used the equation of the line to estimate the number of counts at full power (50 keV and 0.6 mA) <2712700 counts>. Because we took 100 second spectra, we then divided this number by 100 to get the estimated counts per 1 second at full power <27127 counts>. We then took this number and divided it by the transmission of air (0.62670) found using the www.cxro.lbl.gov website <43285.46>. Then to account for varying spot sizes, we had to divide by 16 because the area of the spot size we obtained was 16 times smaller than the area of the 200 micron spot size pin hole we had taken the spectra with <2705.341>. This flux calculation is significantly smaller than the flux we had previously calculated using the optic and copper filter. This was the expected result. Because the detector has such a high efficiency, taking the detector's transmission efficiency into account has no significant contribution to the flux. This is because all of the x-rays pass through the Be window.
We got a chance to ask Alex a bunch of questions. What we had been doing for the past month or so was characterizing the optic, Si(111) to be specific. This optic would stay at XOS to be used as a reference when making other optics. However, similar optics would be sent to customers, companies like Jordan Valley. JV could be using the optic as a part of their semiconductor for some imaging purpose. Their semiconductor might use multiple beams to collect different data. Alex wasn't too sure sure exactly what they were using the optic for. We used a monochromatic convergent beam to take measurements. Applications could include anything from edxrf or wdxrf to imaging. Based on the customers' desired spot size, energy, and total working distance, XOS picks out a crystal that will fit the parameters. Crystals will accept different energies based on their lattice structure. The lower the spot size, the lower the acceptance. Graphite, if used as a crystal, accepts a much wider range of energies when compared to silicon. As a result the resolution of graphite suffers. When a crystal is bent it can accept an even greater range of energies. With our Si(111) optic, the divergence was large because of the convergent beam. A parallel beam would have a divergence of around 0.01 degrees.
We also started setting up a new set up for Ge(111). The Bragg angle is 15.89 degrees and the IFD/ OFD is 123mm. However, we would need a new source/ power supply that would not be available until next week, so we could not get very far. 

*Numbers in brackets represent the calculated number after doing the described operations.

July 19th- Day 16

Roughly perfect.


We went to XOS to work on the new optic, but upon walking into the building, Alex told us he had taken apart our new set up. He needed to test another optic and figure out why all the optics are turning out bad. So far the one we had was defected and another was broken. They aren't having very good luck making optics as of recently apparently. We went through and wrote down all the information we could get about the equipment and took pictures of the things we hadn't before. We got knife-edge scan data that we will plot in matlab in both the x and y directions. We took spectra during the knife edge scans, but they didn't turn out how we wanted. Then we took 100 second spectra with and without the lead tape so you can see the effect the tape has on the x-rays and what the detector picks up. The one without the tape shows Cu K beta, which is minimized on the spectrum with the tape barrier in place. With the data, he showed us a new program, Origin. It is like excel and using it, he plotted the data from the spectrum scan. He also showed us how to plot it in excel and tricks for importing data in various programs. He explained all the different peaks and what was causing them. This would be the energy scan. Alex also had us calculate what the energies should be using the channels the peaks were located at. Using these energies we made another graph (energy vs. channel) which produced a linear line. The equation from this line allowed us to change the x axis from channel to energy on our spectrum graph. We have all the data in excel from XOS and will enter it all into matlab between the two of us. We then took spectra for intensity to calculate flux without the crystal with a distance of 400mm. 

July 12th- Day 15

Just our luck.

Using the new software Alex showed us how to use on Friday, our goal was to minimize the spot size. We were shooting for a vertical spot size (FWHM) of either 8 or 9. He had everything aligned Friday and just had to move the z axis of the optic to try and further minimize the spot size. When we got there, we turned all the equipment on and started up the software. Our FWHM in y was 11.0. We went to move the actuator controlling axis z of the optic, but it did not want to go any further than 0.275mm in the positive direction. It had worked just fine Friday, but we did not want to force anything, so we went 1.0mm in the negative direction. We scanned axis 1 (rotation) and axis 4 (horizontal), but neither of the scans produced the desired results. We even 'went to home' with everything in between scans, so we shouls have at least gotten something. We moved the z axis actuator as far positive as it would go (0.25mm) and ran a scan. This should have produced somewhat better results because we proved the z axis needed to move further in the positive direction before we left on Friday. The FWHM was around 50. Then we notied axis 4, 5, and 6 all said they were at +8.0mm, but when we went to move them, they jumped back to 0.0mm after displaying '+Inf' and we have no idea what happened. After that the computer started running slower than normal and none of the actuators would move at all. Renee and I tried restarting the computer, but it was unsuccessful. We did not want to break anything so we called it a day and went back to the lab. We didn't do anything we hadn't done before, and hopefully Alex will know what to do.

July 8th- Day 14

New Setup!

Alex showed us the new setup and told us all about it. This new crystal was Si (220) and had a Bragg angle of 1.06 degrees. The IFD is 75mm and the OFD is 328mm. This setup has a fixed source instead of a fixed optic, so the crystal can be moved in the x, y, and z axis as well ab rotated and tilted. The detector is the same as our previous setup having mobility in the x, y, and z axis. We used a shadobox (1024) camera to view the image of the optic. The camera was placed close to the optic and we would be using it to not only make sure the optic was aligned but to find the focal point as well. Most of the day was trying to find the focal point. Once we found a good spot size, we then had to move the z axis to try to further decrease the spot size. However, the FWHM the camera gave us is not the actual spot size.