PIPS Detectors

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PIPS Detectors

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I was lucky enough to score a set of Canberra 300 mm^2 PIPS detectors on Ebay just before Christmas. The PIPS (Passivated Implanted Planar Silicon) detectors are ruggedized passivated silicon detectors used for detecting charged particles. These are the guys that the U. of Wisconsin researchers use to detect the proton flux from D-D and D-3He reactions in their fusor. They use a 0.001" thick lead foil to filter out some of the soft X-rays that add annoyingly to the noise floor of the device. It's possible a thicker Ti or Ta foil might do the same job, and be more rugged. Since the PIPS is a charged particle detector, it must be located inside the fusor vacuum envelope to detect anything. However, once the necessary mounting arrangements are made, counting protons with this detector might be more straightforward than counting neutrons from the outside. Time will tell. In the meantime, I'll try to fit up one as an alpha detector to test it and the electronics. I plan to use a discrete FET input charge sensitive amplifier similar to the circuit I posted a few weeks back, possibly with a small swtichng boost regulator/shunt regulator to generate the detector bias voltage. I have a 226Ra check source that has never registered well on my other detectors because a lot of the energy is coming out as alpha particles. Now I can give it a chance to strut its stuff...
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Re: P.I.P.S. Detectors

Post by Captain_Proton »

The Wisconsin team's lead foil is exactly 25 micrometers thick and allows passage of the D3He and D-D protons, but probably lets through too much background noise. Go a step further...consider this...A proton's diameter is 10e-15 m. An X-ray is 10e-11 m. In your quest for a better material, consider Barium or another large-radius diameter molecule that fits in this window to lower the noise floor substantially.
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Richard Hull
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Re: P.I.P.S. Detectors

Post by Richard Hull »

I now have 9 of those PIPS detectors myself. They do not require a vacuum to detect per se.

A vacuum is used to assure that the energies of the alpha's arrive unsullied for spectroscopic puposes. The normal vacuum needed is only 100 microns or so. Most alpha sources are still placed only millimeters from the detector's face, even in vacuuo.

The detecors just won't detect gammas or most betas due to the thin depletion regions being made specifically for alpha spectroscopy and rejection of most other sources. I have tested mine and their Data sheets are correct ...left to background these puppies only issue about one count every DAY!!

I tuned one of my NIM bins up using 3 modules to detect only the alpha from Am241 (5.44-5.48mev). it sat for one hour on my bench with no source and registered zero counts.

I took three sources and checked with a geiger counter. The Am241 swamped the counter at 20K+CPM. A thorium foil registered about 16k CPM. and a heavy radium source I have also pegged out at 20K++CPM. That means the weakest source produced about 270 counts each second or MORE (this was by a swamped geiger counter).

Placing the AM241 before the PIPS spectrometer, I counted 13,000 counts in 10 seconds.

The thorium counted about 12 counts in 10 seconds and the radium about 205 in 10 seconds.

The radium was undoubtedly counting the radon alpha which is almost smack in the middle of the Am241 alpha range. The weak thorium counts were most likely thorium X (radium 224) whose alpha lay in that range.

The upshot is that, as I made the test, only alpha particles and those alone of 4.4-4.9mev would even report a count. These are great toys guys, albiet expensive, unless you hit E-bay.

*****note*****
I used no vacuum, therefore my range was about 2mm from the detector face! at 1" virtually no counts were seen with Am241, but the radium started registering due to straggling real high energy alphas which started out at over 6-8 mev from the ultra short lived daughters. You gotta' know your particles, attenuation factors and setups plus, have a chart of the nuclides and familiarity with it and its use. These are musts to delve into any form of nuclear spectroscopy. Lots of gotcha's waiting to bite you in th' butt.

Again, the data sheets remind the user to never place the detectors in a beam of charged particles or it is curtains instantly. A mere hail of them will shorten detector life tremendously. Be careful in a fusor or you'll need a belt feed mechanism like a machine gun to plugin live detectors and remove dead ones.

OH! One more thing......... PIPS detectors are extremely light sensitive! Ideally, the room should be dark or the detector needs to be placed in a light tight box. The normal usage for these is in a well shielded, evacuuated, light proof, metallic chamber with easy access, (hinged, gasketed door with vacuum bleed control, etc.).

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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