This month’s selection is wine bottled shaped single crystals of CaWO4. Grown by a team working on the CRESST dark matter detection project, these high-purity scintillating CaWO4 single crystals are used as detectors for Weakly Interacting Massive Particles (WIMPs), which are one of the best candidates for dark matter.
To detect the elusive WIMPs, these crystals have to be of a very high purity and have fairly similar weights (approx. 300g). The high melting temperature (around 1600oC) of the crystal, as well as the fact that it has to be grown in an atmosphere containing oxygen, provided additional challenges to the growth process.
Starting with very high purity CaCO3 and WO3, the team used the Czochralski technique in an industrial furnace to produce these crystals. As the experiment requires the crystals to be transparent to scintillating light, the crystals were oxygenated at high temperatures after growth, which produced very clear crystals. (You can spot which one is the final product in the photo!)
The CRESST team has now adopted this technique to set up an in-house CaWO4 growing facility. This means the number of detectors that they can build has increased significantly. Watch out for interesting experimental results…
Find out more about the use of CaWO4 crystals in the dark matter experiment, and learn how to grow your own CaWO4 wine bottles from the article, which is free to access for 4 weeks.
Growth of high-purity scintillating CaWO4 single crystals for the low-temperature direct dark matter search experiments CRESST-II and EURECA
Andreas Erb and Jean-Côme Lanfranchi
CrystEngComm, 2013, 15, 2301-2304