Cooling the Cloud Chamber Shane Spivey UTA Cloud Chamber Cooling Team

Outline Brief explanation of cloud chamber Motivation Design requirements Design considerations and tests Conclusions

The Cloud Chamber Uses a supersaturated layer of vapor to detect ionizing radiation Can see tracks of subatomic particles, and study how they bend in a magnetic field Using a cloud chamber, Carl Anderson discovered the positron by observing the track it made

Motivation To build a working, continuously running cloud chamber for public display in the new Chemistry and Physics building To inspire and inform people about the importance of physics To gain experience in working with a group to design and construct a large-scale physics experiment To bring notoriety to the UTA physics department

Design requirements for the cooling system Create a temperature gradient of 100° C Produce a bottom plate temperature of about 70° C Run in perpetuity Require only infrequent maintenance Cost a reasonable amount Be safe for public interaction Be aesthetically pleasing

Design considerations: Thermoelectric modules Chosen for original 10-layered cloud chamber design Powered by only electricity Wafer-thin design Cooling power too small

Design considerations: Liquid cooling Most common method of refrigeration, compression/expansion Need liquid with very low evaporation point, like nitrogen Dangerous and difficult to build

Design considerations: Liquid cooling We tested the surface of an aluminum cold plate with liquid nitrogen running through it

Design tests: Liquid cooling, kerosene pump test Pump worked but froze up after seconds We increased the voltage from 3V first using tape and wire, then a DC power supply At 12V or higher it didn’t freeze At any voltage, the heat from the pump caused the nitrogen to evaporate rapidly

Design tests: Liquid cooling, gravity Using a simple gravity setup, the cold plate achieved -70° C after ten minutes

Design considerations: Commercial refrigeration Commercially manufactured By nature, large Costly, but still cheaper than building it from scratch

Conclusions The cooling requirements for a cloud chamber are monumental Construction requires expertise as well as equipment and facilities suited to the purpose Non-professional job has a high risk of yielding an unsafe end product Commercial grade chillers will be more effective, more economical, and safer