The feasibility of a practical switchable radioactive neutron source (SRNS) that can be switched on and off like an accelerator and is field portable has been demonstrated. A stable, thin film of 238 Pu oxide deposited on a stainless steel planchet was the alpha source and beryllium was the light element target that produced neutrons. This device requires minimal, if any, shielding when not in use. Design specifications and performance of this proof-in-principle instrument are discussed.

The development and investigation of a small associated-particle sealed-tube neutron generator (APSTNG) show potential for the associated-particle method to move out of the laboratory into field applications. This paper is a review of ANL investigations of this technology. Alpha particles associated with 14-MeV neutrons generated from the D-T reaction travel in the opposite direction and are detected inside the sealed tube. Gamma-ray spectra of resulting neutron reactions in the inspected volume encompassed by the alpha-detector solid angle identify many nuclides. Flight-times determined from detection times of the gamma rays and alpha particles separate the prompt and delayed gamma-rays and can yield a separate coarse tomographic image of each identified nuclide, from a single orientation without collimation. A continuous ion beam allows data acquisition by relatively low-bandwidth electronics. When a compact sealed-tube neutron generator is used, a relatively small and easily maintainable inspection system can be developed, that is rugged enough to be transportable. Proof-of-concept laboratory experiments have been performed for simulated explosives, drugs, special nuclear materials, and chemical warfare agents. Efficient collection of maximum information from each detected neutron with low background rates can allow a much lower source intensity than pulsed accelerator methods and yield a preference for an APSTNG system, when it can provide adequate usable source intensity. Based on lessons learned with the present system, an advanced APSTNG system is being designed and built that will be transportable and yield substantial increases in neutron output and target lifetime.

The development and investigation of a small associated-particle sealed-tube neutron generator (APSTNG) show potential to allow the associated-particle diagnostic method to be moved out of the laboratory into field applications. The APSTNG interrogates the inspected object with 14-MeV neutrons generated from the deuterium-tritium reaction and detects the alpha-particle associated with each neutron inside a cone encompassing the region of interest. Gamma-ray spectra of resulting neutron reactions identify many nuclides. Flight-times determined from detection times of the gamma-rays and alpha-particles separate the prompt and delayed gamma-ray spectra and can yield a separate coarse tomographic image of each identified nuclide, from a single orientation. Chemical substances are identified by comparing relative spectral line intensities with ratios of elements in reference compounds. The high-energy neutrons and gamma-rays penetrate large objects and dense materials. The gamma-ray dector and neutron generator can be located on the same side of the interrogated object, so spaces behind walls and other confirmed areas can be inspected. No collimators or radiation shielding are needed, the neutron generator is relatively simple and small, and commercial-grade electronics are employed. A complete system could be transported in an automotive van. Proof-of-concept laboratory experiments have been successfully performed for simulated nuclear, chemical warfare, and conventional munitions. Inspection applications have been investigated for presence of cocaine in propane tanks, uranium and plutonium smuggling, and radioactive and toxic waste characterization. An advanced APSTNG tube is being designed and constructed that will be transportable and rugged, yield a substantial neutron output increase, and provide sufficiently improved lifetime to allow operation at more than an order of magnitude increase in neutron flux.

An advanced concept proof-of-principle demonstration was successfully performed to show the feasibility of a practical switchable radioactive neutron source (SRNS) that can be switched on and off like an accelerator, but without requiring accelerator equipment such as high voltage supply, control unit, etc. This source concept would provide a highly portable neutron source for field radiation measurement applications. Such a source would require minimal, if any, shielding when not in use. The SRNS, previously patented by Argonne staff, provides a means of constructing the alpha-emitting and light-element components of a radioactive neutron source, in such a fashion that these two components can brought together to turn the source ``on`` and then be separated to turn the source ``off``. An SRNS could be used for such field applications as active neutron interrogation of objects to detect fissile materials or to measure their concentration; and to excite gamma-ray emission for detection of specific elements that indicate toxic chemicals, drugs, explosives, etc. The demonstration was performed using Pu-238 as the alpha emitter and Be as the light element, in an air-atmosphere glovebox having no atmosphere purification capability. A stable, thin film of Pu-238 oxide was deposited on a stainless steel planchet. The ``on`` output of the demonstration Pu-238 film was measured to be 2.5 {times} 10{sup 6} neutrons/sec-gram of Pu-238. The measured ``off`` neutron rate was satisfactory, only about 5% of the ``on`` output, after two weeks of exposure to the glovebox atmosphere. After several weeks additional exposure, the ``off`` rate had increased to about 15%. This work demonstrates the feasibility of constructing practical, highly portable SRNS units with very low gamma-ray dose in the ``off`` position.

The development and investigation of a small associated-particle sealed-tube neutron generator (APSTNG) shows potential to allow the associated-particle diagnostic method to be moved out of the laboratory into field applications. The APSTNG interrogates the inspected object with 14-MeV neutrons generated from the deuterium-tritium reaction and detects the alpha-particle associated with each neutron inside a cone encompassing the region of interest. Gamma-ray spectra of resulting neutron reactions identify many nuclides. Flight-times determined from detection times of the gamma-rays and alpha-particles can yield a separate coarse tomographic image of each identified nuclide, from a single orientation. Chemical substances are identified by comparing relative spectral line intensities with ratios of elements in reference compounds. The high-energy neutrons and gamma-rays penetrate large objects and dense materials. Generally no collimators or radiation shielding are needed. Proof-of-concept laboratory experiments have been successfully performed for simulated nuclear, chemical warfare, and conventional munitions. Most recently, inspection applications have been investigated for radioactive waste characterization, presence of cocaine in propane tanks, and uranium and plutonium smuggling. Based on lessons learned with the present APSTNG system, an advanced APSTNG tube (along with improved high voltage supply and control units) is being designed and fabricated that will be transportable and rugged,more » yield a substantial neutron output increase, and provide sufficiently improved lifetime to allow operation at more than an order of magnitude increase in neutron flux.« less

A relatively small and inexpensive neutron diagnostic probe system has been developed that can identify and image most elements having a larger atomic number than boron. It has the potential to satisfy van-mobile and fixed-portal requirements for nondestructive detection of contraband drugs, explosives, and nuclear and chemical warfare weapon materials, and for treaty verification of sealed munitions and remediation of radioactive waste.

TREAT test M8 will be performed to determine, for IFR fuel, the transient fuel-failure threshold and pre- and postfailure fuel movement that could lead to shutdown. The fast-neutron hodoscope, an ex-reactor instrument, measures test fuel motion in a 10-wide by 36-high array of channels. Hodoscope data—both transient and steady state—obtained in M8 power calibration tests are analyzed. Since the transient data are for an unfueled test vehicle, corrections to them are formulated to attain a constant, power-normalized reactor-background response for all channels in a transient. Corrections for axial flux tilt, detector deadtime, detector nonlinearities, and detector efficiencies are described. Scan data are reported for both fueled and unfueled scans. The hodoscope signal-to-noise ratio is determined from scan data. Finally, both transient and scan data are used to derive a hodoscope performance estimation for test M8. One conclusion is that the smallest mass change that can be detected by the hodoscope on a 4-ms time scale is of the order of 0.55 g of fissile material per pixel, which is some 8% of the portion of the fissile mass of a fuel pin that is subtended by a hodoscope row. Systematic errors that may raise this minimum sensitivity are also evaluated. The M8CAL data show that there is appreciable axial flux tilting as a function of control-rod position, with the variation from top to bottom of the hodoscope array approaching 20%. Rod-position changes perturb ion-chamber readings as well. Refinements of the hodoscope data-handling algorithms to compensate for those effects are described; some anomalies remain unexplained.

A recently developed neutron diagnostic probe system has the potential to satisfy a significant number of van-mobile and fixed- portal requirements for nondestructive verification of sealed munitions and detection of contraband explosives and drugs. The probe is based on a unique associated-particle sealed-tube neutron generator (APSTNG) that interrogates the object of interest with a low-intensity beam of 14-MeV neutrons generated from the deuterium-tritium reaction and that detects the alpha-particle associated with each neutron. Gamma-ray spectra of resulting neutron inelastic scattering and fission reactions identify nuclides associated with all major chemicals in chemical warfare agents, explosives, and drugs, as well as many pollutants and fissile and fertile special nuclear material. Flight times determined from determined from detection times of the gamma-rays and alpha-particles yield a separate tomographic image of each identified nuclide. The APSTNG also forms the basis for a compact fast-neutron transmission imaging system that can be used along with or instead of the emission imaging system; a collimator is not required since scattered neutrons are removed by ``electronic collimation`` (detected neutrons not having the proper flight time to be uncollided are discarded). The small and relatively inexpensive APSTNG exhibits high reliability and can be quickly replaced. Proof-of-concept experiments havemore » been performed under laboratory conditions for simulated nuclear and chemical warfare munitions and for explosives and drugs.« less

Results from hodoscope data analyses are presented for transient overpower (TOP) tests M5, M6, and M7 at the Transient Reactor Test Facility, with emphasis on transient feedback mechanisms, including prefailure expansion at the tops of the fuel pins, subsequent dispersive axial fuel motion, and losses in relative worth of the fuel pins during the tests. Tests M5 and M6 were the first TOP tests of margin to cladding breach and prefailure elongation of D9-clad ternary (U-Pu-Zr) integral fast reactor-type fuel. Test M7 extended these results to high-burnup fuel and also initiated transient testing of HT-9-clad binary (U-Zr) Fast Flux Test Facility driver fuel. Results show significant prefailure negative reactivity feedback and strongly negative feedback from fuel driven to failure.

A neutron diagnostic probe system which has the potential to satisfy a significant number of van-mobile and fixed-portal requirements for nondestructive verification of sealed munitions is described. The probe is based on a unique associated-particle sealed-tube neutron generator (APSTNG) that interrogates a treaty-limited item (TLI) with a low-intensity beam of 14 MeV neutrons generated from the deuterium-tritium reaction and that detects the alpha-particle associated with each neutron. Gamma-ray spectra of resulting neutron inelastic scattering and fission reaction identify nuclides associated with all major chemicals in chemical warfare agents, explosives, and drugs, as well as many pollutants and fissile and fertile special nuclear material. Flight times determined from detection times of the gamma-rays and alpha-particles yield a separate tomographic image of each nuclide. The APSTNG also forms the basis for a compact fast-neutron transmission imaging system that can be used along with or instead of the emission imaging system. The small and relatively inexpensive APSTNG exhibits high reliability and can be quickly replaced.< >

It is pointed out that new developments in hodoscope radiation detection technology offer a wide range of capabilities for arms control treaty verification (ACTV) applications. This concept uses an array of radiation detectors to image or detect objects inside opaque containments. Hodoscope systems can detect neutrons and/or gamma-rays. The systems can be based on transmission of radiation through the objects, can detect radiation stimulated in the objects, or can detect intrinsic object radiation. Laboratory measurements to demonstrate a range of potential applications have been performed. Gamma-ray transmission hodoscopes can be used to inspect canisters, rail cars, etc. to monitor objects such as rocket motors. The use of relatively weak isotopic radiation sources makes it unnecessary to employ expensive and high-intensity accelerators. The heavy metal of nuclear warheads is characterized by strong gamma-ray absorption, and these materials could be counted by low-resolution tomography. Absorbers located in line with objects will themselves be detected, and sources located in the object region will be subtracted out as background. Intrinsic gamma-ray radiation from warheads can also be detected in a passive-instrument mode.< >

At the Transient Reactor Test (TREAT) Facility, reactor transients induce destructive fuel motion in test capsules to study the effects of simulated LMFBR hypothetical core disruptive accidents. In TREAT Upgrade (TU), capsule size will increase to 37 or more fuel pins with steel casings up to 7.2 cm thick. Neutron radiography is used in determining final material disposition and sectioning planes for post-mortems. For TU, objectives are to provide mass and 3D spatial resolution of displaced fuel and to identify steel and sodium. A number of penetrating radiographic techniques were investigated for large fuel bundles, including the use of cold, epithermal, 24-keV, and 14-MeV neutrons. It is found that through a combination of techniques, TU radiography needs can likely be met, if sources of sufficient intensity and detection methods of adequate sensitivity are made available.