Photos from refurbishing another HPGe detector

[Carl Willis]

I bought another HPGe detector from the "Black Hole" surplus store in Los Alamos. Sale price: $100. It had been on the shelf for many years, with vacuum released (per LANL requirements for ensuring public safety). I thought repair was a long shot, but a risk I was willing to take after restoring the smaller Ortec I have been using.

Tonight I successfully operated the "new" HPGe for the first time, and have some photos from the lead-up to this happy occasion. I should mention that the crystal cannot hold its rated 3 kV at the moment; leakage current rises seriously after about 2 kV and the best resolution (about 0.38% FWHM for Cs-137) is obtained near 1400V right now. This is probably caused by contaminants or condensation on the crystal surface, and a repumping and perhaps baking of the crystal in my toaster oven for an hour are likely to cure that.

Refurbishment entailed (1) replacing the thoroughly-roasted PGT RG-11 preamplifier and its FET with a Canberra 2001 from my boneyard, and mounting the Canberra's FET on the cold finger where the PGT transistor used to be; (2) making my own evacuation fixture out of a male 3/8" flare fitting and 1-1/3" Conflat components to replace the custom PGT valve operator interface on the Dewar; (3) re-evacuation of the Dewar with a turbopump; (4) cooling with liquid nitrogen; and (5) electrical tune-up and operation.

[Doug Coulter]

You're almost convincing me I should look for one of these and put up with the cryo requirement. Good stuff!

Seriously - anyone skilled who does something like this that (re) creates value should always take some pix along the way for their own documentation to help out the rest of us. You just get so much more from pictures (not all necessarily realized at the time) than a dry notebook full of text.

This sort of thing gives us the power of the skills of the many, while retaining the freedom of the one to follow his nose in research. In some ways I think we might be doing this better than big science.

At least this site doesn't cost $35 a page...

[Richard Hull]

Another Carl Willis coup! These are really simple systems, observed at a distance and taken section by section, but require meticulous cleanliness and control. The big money is always in the crystal and often a selected FET. Carl is now the defacto expert on these systems.

Way back in the late 80's, I took apart two Princeton Gamma Tech detector heads just for the Germanium!!! Now, I wish I had left one intact. These Ge slugs can weigh as much as a pound or two! That's over $1,000.00 worth of pure Ge on the scrap market! I still have both giant Linde dewars from the 80's in an out building. They still have good vacuums.

Really a nice piece of work, Carl

Richard Hull

[Jon Rosenstiel]

As usual, excellent work Carl. When you had it apart did you happen to get the dimensions off of the xtal?

Jon