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Noise measurements in light water reactor systems aid in generating validation data for integral point kinetic parameter predictions and generating monitoring parameters for reactor safety and safeguards. The CROCUS zero-power reactor has been used to support both efforts via measurements with thermal neutron detectors to observe neutron noise and inorganic scintillators to observe gamma noise. The cross-correlation of gamma and neutron noise has been investigated at CROCUS with separate gamma-only and neutron-only detectors. Organic scintillators, sensitive to both neutrons and gamma rays, can be used to cross-correlate gamma-ray and neutron noise with a single detector type. Herein, we present noise measurements using organic scintillators in a light-water, zero-power research reactor for the first time. We discuss data obtained with two 5.08-cm-length by 5.08-cm-diameter cylindrical trans-stilbene detectors and two 6-mm cubic scintillators&#x2014;one trans-stilbene and one organic glass (OGS)&#x2014;set in the water reflector of CROCUS and outside the reactor vessel. The prompt neutron decay constant was estimated to be    $\alpha _{\text {CPSD}}=(154 \pm 1) \hspace {2pt} \text {s}^{-1}$    at 3 mW critical from the (   $\gamma $   ,   $\gamma $   ) signal, which agrees within one standard deviation overlap with previous measurements with CeBr3 and simulation in Serpent 2. The (   $n,n$   ) estimate of    $\alpha _{\text {CPSD}}=(145 \pm 23) \hspace {2pt} \text {s}^{-1}$    at 3 mW critical lacked precision but agreed within one standard deviation overlap with previous 235U fission chamber estimates and simulation in Serpent 2. The 6-mm cubic scintillators were too inefficient to estimate    $\alpha $   , but informed possible small-cell, high-volume detection systems to improve the (   $n,n$   ) estimate capabilities. Based on the high-precision estimate of    $\alpha $    from the (   $\gamma $   ,   $\gamma $   ) cross power spectral density (CPSD) signal, we suggest further development of theory to calculate    $\beta _{\text {eff}}$    and    $\Lambda $    from gamma-ray noise measurements and recommend gamma noise measurements for future simulation validation and as a method of reactor monitoring.

Neutron-Gamma Noise Measurements in a Zero-Power Reactor Using Organic Scintillators