Active special nuclear material (SNM) photoneutron interrogation research with acoustically tensioned metastable fluid detector (ATMFD) sensor technology is discussed, which provides evidence for enabling real-time detection of SNM even when deployed under extreme 15,000 R h−1 (9 MeV endpoint) X-ray beams. Experiments to detect 3.2 kg depleted uranium (DU) are described with the use of two designs of the economical acoustically tensioned metastable fluid detector (E-ATMFD), viz., E-ATMFD.Ver.0 and E-ATMFD.Ver.1, respectively, at standoffs ranging from 0.1 m to 10 m—including with the E-ATMFD directly within the interrogating beam. Under similar conditions and with 100% photon rejection (i.e., 0 cpm with beam on, and without SNM), the E-ATMFD.Ver.1 design operating at ∼0.9 W of drive power was shown capable of ∼6× (600%) higher gain over E-ATMFD.Ver.0 operating at ∼7 W (with beam on and with SNM). The sensitivity gain rises to ∼27× (i.e., 2700%) with the E-ATMFD.Ver.1 operating at 0.99 W and a background count rate of ∼1 cpm. The E-ATMFD.Ver.1 demonstrated 100% photon blindness (0 cpm) while operating at ∼0.56 W drive power and placed directly within the beam under 15,000 R/h; including the SNM target led to a count rate of up to 50 cpm—revealing the E-ATMFD.Ver.1 is potential field capable of detecting U-based SNMs within seconds from photofission neutron signals, even when deployed directly within the intense (15,000 R/h) high energy (9 MeV endpoint X-Ray) interrogating photon beam.