Commonly occurring infrasonic waves recorded during the winter months are believed to originate by means of aerodynamic source mechanisms. Acoustic power spectra of these commonly observed signals are compared to the power spectra one would observe from theoretical source mechanisms. From this comparison, the theoretical source mechanism believed responsible for production of the observed signals is thought to be isotropic turbulence in the lee of mountain peaks. Experimentally recorded signals and their power spectra are shown. Source regions of three signals are identified.

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We investigated a method for monitoring a typical large storage vault for unauthorized removal of plutonium. The method is based on the assumption that .the neutron field in a vault produced by a particular geometric configuration of bulk plutonium remains constant in time and space as long as the configuration is undisturbed. To observe such a neutron field, we installed an array of 25 neutron detectors in the ceiling of a plutonium storage vault at Argonne National Laboratory West. Each neutron detector provided an independent spatial measurement of the vauit neutron field. Data collected by• each detector were processed to determine whether statistically significant changes had occurred in the neutron field. Continuous observation experiments •measured the long-term stability of the system. Removal experiments were performed in which known quantities of plutonium were removed from the vault. Both types of experiments demonstrated that the neutron monitoring system can detect removal or addition of bulk plutonium (11% 240 Pu) whose mass is as small as 0.04% of the total inventory.