Search For Isolated Fractionally Charged Particles


Optimal Test Material for a Fractional Charge Search

Take in account the altered electronegativity of atoms with an attached fractional charge


Possible test materials

In order to test the ground solid material in a Millikan apparatus it must be put into the form of a liquid. A fluid suspension containing finely ground solids is superior to that of a dissolved solution because it reduces the possibility that the atom with an attached fractional charge will react or bind to the droplet ejector.

Ideally the ground material should be made into a stable colloid. Since this was not found to be possible for some of the materials we are interested in we have developed ways to artificially stabilize and eject non-colloidal suspensions.

Silicone Oil

We used silicone oil for our initial experiments because it was an easy to eject, nontoxic, low vapor pressure, low viscosity fluid. Silicone oil, being a highly refined synthetic fluid, is not considered a good candidate material for containing atoms with attached fractional charges. The first experiments were performed primarily to verify the accuracy of the charge measurement technique. Silicone oil, being an easy to eject well characterized fluid, was used to establish the intrinsic measurement accuracy of our updated Millikan techniques without the complications involved in using multicomponent fluid drops. We are currently making the transition to testing fluid-particle suspensions.


Meteorite Suspension in Oil


The meteoric material must be fragmented to sizes small enough to remain in suspension and pass through the 10 - 20 micron diameter drop generator ejection aperture holes.  This requires that we reduce the mean particle size to about 1 micron.

This fragmenting was done in two steps:

First the meteorite, in this case a carbonaceous chondrite, was ground by hand with a conventional mortar and pestle.

Next these fragments which were in the tens of microns in diameter range were passed through a jet pulverizer (photo at right) which accelerates these particles using pressurized air to supersonic speeds and collides them with each other to break them up into submicron fragments.

Jet_pul_3.jpg (122568 bytes)
These particles must next be dispersed in the carrier fluid.  Very high shear is required to deagglomerate and thoroughly wet the particles.  This mixing action was achieved using a rotary blade homogenizing mixer (photo at right).

The carrier fluid for stable suspensions usually contains surfactants to coat the particles to prevent agglomeration.

The carrier fluid used was a commercial low viscosity mineral oil with 5 percent Castrol Motor oil added for its surfactant additives.

The meteorite dust and the carrier fluid was mixed for 20 hours and left to settle for 5 days after which the top half of the fluid was extracted.  This settling time before use allows the larger unfragmented particles to settle out to the bottom of the fluid.

Polytron1.jpg (142641 bytes)
Meteorite suspension loaded into a microdrop generator ejecting 20 micron diameter fluid drops. wpe8.jpg (28481 bytes)


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January 8, 2001
Stanford Linear Accelerator Center
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