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Prof. Eduard Y. Chekmenev received his PhD in Physical Chemistry (supervisor Prof. Richard J. Wittebort) in 2003 at the University of Louisville, KY (USA). He conducted postdoctoral research at the National High Magnetic Field Laboratory in Tallahassee, FL (with Prof. Timothy Cross), Caltech (Prof. Daniel P. Weitekamp) and HMRI in Pasadena, CA (USA) (with Dr.B rian D. Ross). In 2009, Dr.C hekmenev started his hyperpolarization program at Vanderbilt University (Nashville, TN) and he was tenured in 2015. In 2018, he moved to Wayne State University (Detroit, MI) to continue his research on MR hyperpolarization.Figure 1. Thermal equilibrium polarizationp roduces asmall excess of spins in one state. When the sample undergoes hyperpolarization, alarge excess of spins exists in one state producingaconsiderably stronger signal since more spins contribute.

In dynamic nuclear polarization (DNP), radicals such as trityl provide a source for high nuclear spin polarization. Conversely, during the low-field transfer of hyperpolarized solids, the radicals' dipolar or Non-Zeeman reservoir may act as a powerful nuclear polarization sink. Here, we report the low-temperature proton spin relaxation in pyruvic acid doped with trityl, for fields from 5 mT to 2 T. We estimate the heat capacity of the radical Non-Zeeman reservoir experimentally and show that a recent formalism by Wenckebach yields a parameterfree, yet quantitative model for the entire field range.