# In the Homestake experiment, why did they alternate runs with $^{36}\rm Ar$ and $^{38}\rm Ar$?

In the Homestake experiment, why did they alternate runs with $^{36}\rm Ar$ and $^{38}\rm Ar$? I understand why they use a carrier isotope like $^{36}\rm Ar$ or $^{38}\rm Ar$ to mesure the efficiency of the extraction process. But I can't understand how it is useful to alternate the isotope to mesure also the purification efficiency separately.

For the details of this, see B.T. Cleveland et al., Measurement of the Solar Electron Neutrino Flux with the Homestake Chlorine Detector, Astrophys. J. 496, 505 (1998), with the description of alternate runs in §4.3.3. A summary of the extraction process is in p48, §4, of Neutrino 94: Proceedings of the 16th International Conference on Neutrino (Nucl. Phys. B (Proc. Suppl) 38, 47-53 (1995); Google Books link).

• Good question. Is there some particular reason you linked to those resources? I wonder if you meant to refer to something specific within each source, or if you're just giving them as background reading for people who aren't familiar with the experiment (which is generally a good idea). – David Z Nov 10 '17 at 5:46
• No partical reason for thoses resources. Just for having a support on what I am asking. – Lery_Phys Nov 10 '17 at 15:01