How to Extract a Polarization from an NMR Measurement

• NMR Analysis can be done at any time, so please make sure the target is in the proper position and configuration before beginning any analysis.
• To begin the analysis, press the button next to 'Extract Polarization' on the Target Operator Screen
• On the 'Extract Polarization' screen press 'Go'
• You'll be asked whether you want to fit the latest NMR. Press 'Yes' if you want to do this and it will automatically load the latest 'X' channel file. You will still have to analyze the 'Y' channel seperately.
• If you hit 'No', it will bring up a browser. The NMR files are located in the 'E:\A1n Data\Nmr\' Directory. You can get there by typing the directory name in, or pressing the Up Folder Key several times, until you the see the 'A1n Data' directory. Click on the 'A1n Data' and the 'Nmr' directory. Select the file you would like to analyze. The files are time stamped in the following format '(x or y)-(month)-(day)-(hour)-(minute)(am or pm).dat'. Simply pick the file from the time you did the NMR. There is a file for the X and Y channel. At this time, you have to analyze both. Start with the 'X'.
• Once you pick your file, the program will try to fit the function. The top graph is the data in blue and the fit in red. The bottom graph is the difference between the two. The program fits the Up and Down sweeps simultaneously.
• If the red line is pretty much on top of the blue one, then the fit is successful. If not then you need to do it again with a better set of starting parameters. We use five parameters to fit the curve :
  • FWHM - The full width half max of the signal corresponds to the magnitude of the RF Field. Since this doesn't change it should always be around 0.080 G.
  • Background Slope - A linear slope in the background. It should always be around 0.0.
  • Resonance Field - The field strength where the resonance occurs. This parameter will change, since the field drifts around a bit. Generally if you get this parameter correct the fit should succeed. Simply look at the data and read the x-value of the peak.
  • Signal Height - This is the actual parameter that is proportional to the $^{3}$He polarization. It is approximately equal to the peak height.
  • Background Offset - A constant offset. Again should be near 0.0.
  To adjust these parameters, change the 'UP Initial Coeffecients' and 'DOWN Initial Coefficients' at the bottom of the screen. Then simply press 'Go' again and choose the same file. Repeat this process until you get a nice fit. If you never get a nice fit, that's okay. Just make an entry in the log book that you took the NMR and an expert will analyze it later.
• Write down the signal height in the log book of both the UP and DOWN sweeps. Then repeat this for the Y channel file.
• Once you have the UP and DOWN signal heights for both X and Y files. Youare to compute the polarization. Apply this formula:
  

  $$P = \frac{C}{2} * \left (\sqrt{X_{Up}*X_{Up}+Y_{Up}*Y_{Up}}+\sqrt{X_{Down}*X_{Down}+Y_{Down}*Y_{Down}} \right )$$ (1)

  
  
  where $P$ is the target polarization, $C$ is the calibration constant that you can get from a yellow post-it note attached to the monitor (make sure you use the correct one), $X_{Up}$ is the signal height of the Up sweep in the x-channel, $Y_{Up}$ is the signal height of the UP sweep in the y-channel, and $X_{Down}$ and $Y_{Down}$ are the signal heights of the DOWN sweep.
• Write down the polarization in the log book, make a halog entry and write the polarization on the white board.