Developments in Capture- γ Libraries for Nonproliferation Applications

The neutron-capture reaction is fundamental for identifying and analyzing the γ-ray spectrum from an unknown assembly because it provides unambiguous information on the neutron-absorbing isotopes. Nondestructive-assay applications may exploit this phenomenon passively, for example, in the presence of spontaneous-fission neutrons, or actively where an external neutron source is used as a probe. There are known gaps in the Evaluated Nuclear Data File libraries corresponding to neutron-capture γ-ray data that otherwise limit transport-modeling applications. In this work, we describe how new thermal neutron-capture data are being used to improve information in the neutron-data libraries for isotopes relevant to nonproliferation applications. We address this problem by providing new experimentally-deduced partial and total neutron-capture reaction cross sections and then evaluate these data by comparison with statistical-model calculations

FaNGaS: a New Instrument for Fast Neutron Gamma Spectroscopy at FRM II Research Reactor at Garching

For the identication and quantication of actinides in radioactive packages,the non-destructive method of Prompt-Gamma Activation Analysis (PGAA)is applied. To investigate the inelastic (n; n0) scattering, a new instrumen-tation was installed at the FRM II research reactor. It is designed to exploitthe 108 cm2s1 neutrons at an average neutron energy of 1:9 MeV deliveredby the SR10 beam line. The outgoing prompt -rays are measured utilizinga 50% eciency HPGe detector. Since the cross sections are expected to below for such a process, two related factors had to be taken into account for thedesign of the instrumentation: the high beam intensity at the sample positionand the high signal-to-background ratio seen by the detector. Eventual lowenergy neutrons due to the multiple scatterings through the beam line can beminimized using collimators in the beam tube. This has also an eect to a priorneutrons and photons background reduction of the experimental environment.A higher eciency of the counting can be achieved by the lowering of back-ground at the detector. In this case, a heavy shielding for both neutrons andphotons, is designed around the detector while optimizing the sample-detectordistance. Monte-Carlo simulation studies were conducted to eectively designthe fast neutron beam collimators and the detector shield. A detailed descrip-tion of the setup characterization and results from simulations and experimentalmeasurements will be discussed through this contribution

Determination of (n,γ) Cross Sections of 241^{241}Am by Cold Neutron Activation

Accurate cross section data of actinides are crucial for criticality calculations of GEN IV reactors and transmutation but also for analytical purposes such as nuclear waste characterization, decommissioning of nuclear installations and safeguard applications. Tabulated data are inconsistent and sometimes associated with large uncertainties. Neutron activation with external cold neutron beams from high flux reactors offers a chance for determination of accurate capture cross sections scalable to the whole View the MathML source1/E-region even for isotopes with low-lying resonances like 241Am. Preparation of 241Am samples for irradiation at the PGAA station of the FRM II in Garching has been optimized together with PTB in Braunschweig. Two samples were irradiated together with gold flux monitors to extract the thermal neutron capture cross section after appropriate corrections for attenuation of neutrons and photons in the sample. For one sample, the thermal ground state neutron capture cross section was measured as 663.0 ± 28.8 b. The thermal neutron capture cross section was calculated to 725.4 ± 34.4 b. For the other sample, a ground state neutron capture cross section of 649.9 ± 28.2 b was measured and a thermal neutron capture cross section of 711.1 ± 33.9 b was derived

High-flux PGAA for milligram-weight samples

With the high-intensity cold neutron flux available at the Prompt Gamma Activation Analysis (PGAA) instrument of the research reactor FRM II at the Heinz Maier-Leibnitz Zentrum (MLZ), samples with a weight of 1 mg or even less can be investigated for their elemental compositions using the (n,γ) capture reaction. In such cases, the typical sample packing material for PGAA experiments made of 25 μm thick PTFE foil (ca. 80 mg) can be orders of magnitude more massive than the sample weight itself. Proper choice of the packing material and measuring conditions are then of the highest importance [1]

High-flux PGAA for milligram-weight samples

With the high-intensity cold neutron flux available at the Prompt Gamma Activation Analysis (PGAA) instrument of the research reactor FRM II at the Heinz Maier-Leibnitz Zentrum (MLZ), samples with a weight of 1 mg or even less can be investigated for their elemental compositions using the (n,γ) capture reaction. In such cases, the typical sample packing material for PGAA experiments made of 25 μm thick PTFE foil (ca. 80 mg) can be orders of magnitude more massive than the sample weight itself. Proper choice of the packing material and measuring conditions are then of the highest importance [1]