Notes from Robert Rider who polished CsI for me in Dec, 2022

Here is what I did previously. This procedure was designed with input from a previous Lee Sobotka Student who had also polished some scintillator materials. 

1. I used a really flat table to prevent any bumps from digging into the CsI (they have a metal one in the machine shop that I cleaned off and chose the smoothest spot for polishing).

2. I placed a clean soft white t-shirt piece the machine shop had on the flat table and stretched it out with heavy objects so that it was taught and would not move around. 

3. The Yennello group has a 3 step polishing kit and I used the 2nd step solution for the actual polishing. It should be in one of our chemical cabinets in the hallway by the astatine lab (Kris will know). Step 1 is too abrasive (contains grains), and step 3 is just a polishing spray.

4. I would place a small dab of the step 2 solution on the t-shirt and slide the CsI in one direction as flat as possible. I would then lift up and go over the same spot on the t-shirt multiple times. To remove the residue and check the polishing, I would do the same one direction motion a couple of times on a different spot on the t-shirt with no polishing solution. If scratches remained, I would repeat the process. Going in the opposite direction may also help with removing scratches. 

5. I would complete one side at a time and once finished, I gently wiped off the remaining solution and placed it back into the desiccator. 

Important Notes: 

• Always wear gloves to prevent oil from your hands getting onto the CsI
• Place CsI once the cleaning solution is removed, quickly back into the desiccator or low humidity area due to its slight hygroscopicity.
• Apply minimal pressure when polishing the crystal to prevent removal of too much material
• Apply as even as pressure on the flat surface as possible to prevent rounding of the edges
• I have only done the rectangular CsI, a circular CsI may be fine polishing in a circular motion
• May be good to check resolution before and after polishing the first one to see the improvement or to determine if polishing gets you to the resolution needed

Reply from Lee Sobotka regarding CsI polishing

1. Polish with plastic polish on silk. (We use Novus Plastic polish # 2).

Put a drop or two on the silk, spread with finger, polish with smooth strokes trying not to break edges. There may be some residue of the polishing on the crystal edges. Wipe off with cue tip. Otherwise do not touch. The polishing will leave the crystal dry. We tape the silk to a large glass plate and stretch is taut.  (In our lab we have several polishing stations with different taut cloths and polishes. Silk is used for CsI(Tl))

2. Do not use grease on front

3. Precut cut a piece of Al-mylar and some thin strips of scotch tape.

4. Put mylar, Al side up on a piece of clean glass. You can use some of the tape to temporarily hold mylar.

5. Wrap CsI(Tl) in teflon tape aside from the front.

6. Put CsI(Tl) on mylar, you can use some grease on the Teflon sides to initially hold mylar when pulled up the side.

7. Wrap the mylar around CsI like gift wrapping the CsI. The grease on the side can help making taut, but make sure grease not on outside of mylar

8. Use scotch tape to pull mylar tight and fix.  If the “gift wrapping” is done well. The scotch tape is mylar to mylar.

The grease on the sides is only needed for difficult geometries. Try wrapping without it.