  The beta-decay of a tritium nucleus produces an entangled quantum system, a
beta electron, a helium nucleus, and an antineutrino. For finite collapse
times, the post-collapse beta electron energy can originate from a range of
pre-collapse energies due to the uncertainty principle. Long collapse times
give negligible uncertainty, so the pre-collapse spectrum must approach that of
isolated nuclei. We calculate the post-collapse electron spectrum which shows a
collapse-dependent pileup near the endpoint. Comparison with observation shows
that a collapse time of 1 x 10^-17 s explains the observed pileup. The collapse
of the entangled quantum system must be triggered by the environment: most
likely an atomic (molecular) electron initially bound to the atomic (molecular)
tritium source or perhaps ambient gas molecules. Coincidentally, the 40 eV
tritium atom-helium ion energy level shift is unobservably small for times
shorter than the system collapse time. We conclude that an atomic (molecular)
electron triggers the collapse once the 40 eV shift becomes detectible and the
electron detects the helium nucleus. Thus collapse may explain the tritium
endpoint pileup.
