It's most likely Reticulitermes, R. hesperus maybe. Measurements would still be useful.
You need to pair them (termites need a king and queen) and house them in a setup with cellulose, preferably softwood or card board as well as substrate. Setup also needs to be damp/moist.
To pair them just put them in a large container and they will separate themselves by tandem running. Keep an eye on them as they dry up easily.
So far I've come across a few methods including wet cardboard in a small container, a cylindrical wooden piece with grooves filled with substrate in a container (termites stay in the grooves) and a normal test tube setup with wood and substrate or just wood that and the many large containers just full of substrate and cellulose of varying degrees people use. I can't personally attest for any of these methods regarding subterranean termite imagoes but I believe number 1 and 2 are used in laboratories. The container should be something like a pill bottle, cylindrical and small.
The problem with test tube setups I find is that often when the colony reaches sufficient size there's a risk they start burrowing and eating the cotton to the point it breaks and they drown. If you have them in an airtight setup like a container or a test tube with a mostly air tight plug then hydration is less of a concern and you can probably keep it mostly hydrated externally or with just a very wet piece of cotton just a little bit of water.
Edited by LC3, April 14 2018 - 10:14 PM.