## Determining the Boltzmann Constant

Checking a plug in a hemisphere

Cleaning a hemisphere

I am finding it very hard to keep posting articles on this blog, because work is so intense at the moment. In my work I am operating way outside my comfort zone. Allow me please to just take a moment to say a word or two about this.

The main focus of my work at the moment is measuring the Boltzmann constant. This is a number which relates the magnitude of a degree of temperature to the energy of molecules at that temperature. The experiment I am carrying out to determine this involves determination of the speed of sound in Argon gas. We determine this inside a rather perfectly manufactured nearly spherical acoustic resonator.

The resonator was manufactured out of copper at Cranfield University. The nearly-spherical resonator is made from two hemispheres, each of which is turned on a lathe, but the tool used to cut the nearly-hemispherical surface is made of diamond rather than the conventional tungsten carbide. This results in a surface finish which has a surface roughness of only a few tens of atoms. The surface is mirror perfect. At the moment we are trying to determine the exact size of these hemispheres using conventional dimensional metrology. The details don’t matter, but the main thing I want to communicate is that what I am doing is just so hard. Our measurement requirements seem to naturally exceed eveything that anyone else has ever been interested in! So each day I am learning, learning, learning and each evening I am analysing, analysing; analysing.

And in amongst that pressure is the sheer physical beauty and perfection of the objects I am dealing with. Look for example at the perfection of the silicon sphere. I stare at this each day and I am in awe of the object and my friend and colleague Rob Ferguson who manufactured it. It looks perfect, yet I know from my measurements that it is not quite spherical by literally hundreds of atoms.

Silicon Sphere NPL2

And I am overwhelmed by the beauty of the instruments I am using, and the care and ingenuity of the designers and engineers who created them, and the scientists who operate them.