White Paper: What Is A Particle?

By Bruce B. Weiner Ph.D., Brookhaven Instruments Corporation

The question embodied in the title might seem strange until you consider the many different ways particles play a part in science and engineering. For example, if you do a web search using just the word particle, you will get more hits for atomic, nuclear, and elementary or subatomic particles than you will for pharmaceutical particles, nanoparticles, clay particles, etc. You will get a lot of hits for particle accelerators, particle colliders, particle physics as well as a few hits that really interest you.

It was once proposed by the Fine Particle Society that the term "fine particle" be used as a keyword grouping to avoid confusion with atomic and nuclear particles. The New York State Department of Health defines a fine particle as any particle causing pollution with a diameter of less than 2.5 micron. Such a partial definition undoubtedly arises because of concerns over respiration, but does not cover the lower end, and, of course, it assumes all fine particles cause pollution. They don't. If you do use the search term "fine particle", you usually don't get hits for particle sizers, possibly because the Fine Particle Society in the U.S.A. is not as strong as it used to be, or perhaps because, ultimately, there is no universally agreed upon keywords in this field.

So the first thing to know about "What Is a Particle?" is to use keywords like these: "particle characterization", which also includes zeta potential and shape; "particle size"; and "particle size analyzer". When you see the term "particle analyzer", do not think it means a chemical analyzer. While a misnomer, a particle analyzer is most often an instrument for measuring particle size not a particle's chemical makeup.