Richard E. Russo

Nuclear forensics in law enforcement applications

Over the past several years, the Livermore Forensic Science Center has conducted analyses of nuclear-related samples in conjunction with domestic and international criminal investigations. Law enforcement officials have sought conventional and nuclear-forensic analyses of questioned specimens that have typically consisted of miscellaneous metal species or actinide salts. The investigated activities have included nuclear smuggling and the proliferation of alleged fissionable materials, nonradioactive hoaxes such as “Red Mercury,” and the interdiction of illegal laboratories engaged in methamphetamine synthesis.

Core-Based Intrinsic Fiber-Optic Absorption Sensor for the Detection of Volatile Organic Compounds

A core-based intrinsic fiber-optic absorption sensor has been developed and tested for the detection of volatile organic compounds. The distal ends of transmitting and receiving fibers are connected by a small cylindrical section of an optically clear silicone rubber. The silicone rubber acts both as a light pipe and as a selective membrane into which the analyte molecules can diffuse. The sensor has been used to detect volatile organics (trichloroethylene, 1,1-dichloroethylene, and benzene) in both aqueous solutions and in the vapor phase or headspace. Absorption spectra obtained in the near-infrared (near-IR) provide qualitative and quantitative information about the analyte. Water, which has strong broad-band absorption in the near-IR, is excluded from the spectra because of the hydrophobic properties of the silicone rubber. The rate-limiting step is shown to be the diffusion through the Nernstian boundary layer surrounding the sensor and not the diffusion through the silicone polymer. The rate of analyte diffusion into the sensor, as measured by the t90 values (the time required for the sensor to reach 90% of the equilibrium value), is 30 min for measurements in aqueous solutions and approximately 3 min for measurements made in the headspace. The limit of detection obtained with this sensor is approximately 1.1 ppm for trichloroethylene in an aqueous solution.

Photothermal deflection measurements for monitoring heat transfer during modulated laser heating of solids

Photothermal deflection (PTD) techniques have been used to monitor various laser‐heating processes, including melt, vaporization, and ablation of solids. To interpret the complex signal response resulting from transient phase changes at a surface, the temporal profile of the PTD signal response must be considered. In doing so, the case of the linear heating of a target without phase change is first studied here. Numerical and experimental work is presented to show the effect on the shape, magnitude, and phase of a PTD signal due to changes in (1) the thermophysical properties of the target material and deflecting medium, (2) the dimensions and boundary conditions of the target, (3) the distance of the probe beam from the surface of the target, and (4) the modulation frequency of the heating source. Copper and lead target materials heated in air are used in the experimental work. The PTD signals show qualitative agreement with the temperature gradient normal to the surface calculated using a numerical finite‐difference two‐dimensional thermal‐diffusion model. The results also show that an unusual phenomenon occurs when heating with a laser or other finite‐sized heating source. When the thermal diffusivity of the target and deflecting medium are different and the probe beam is close to the surface, a local maximum is observed in the time‐response profile of the PTD signal during the heating cycle. The maximum occurs as a result of asymmetric changes in the temperature field over time. The shape of the PTD signal, therefore, can provide information about the laser‐heating process at a surface in real time.

Detecting laser‐induced phase change at the surface of solids via latent heat of melting with a photothermal deflection technique

The detection of laser‐induced melt at the surface of a solid in real time is demonstrated using a photothermal deflection (PTD) technique. Experimental results for indium and tin show that a local maximum and minimum pair can occur in the temporal profile of the PTD signal when melt occurs. A local minimum does not occur without phase change. Analytical work is presented which explicitly shows the effect of the latent heat of melting, thermal properties, and probe‐beam size and offset on the shape of a PTD signal. Results are presented which demonstrate that the observed change in shape will not occur with planar heating, with or without phase transition. However, results derived for point‐source heating show that it is possible for the maximum/minimum pair to occur when melting with a focused laser beam. The ratio of the sensible heat to the latent heat, and the ratio of the thermal diffusivities of the target and deflecting medium are the key factors which govern the deflection response. Computations f...

Differential Photothermal Deflection Spectroscopy Using a Single Position Sensor

A differential dual-beam photothermal deflection spectrometer using a single position sensor is described. An excitation and a probe laser beam are directed simultaneously into a sample solution and a reference solution to provide real-time background correction. The probe beam that passes through the reference cell is folded back into the path of the sample-cell probe beam in such a way that only one position sensor is needed to monitor the deflection in both cells. Nd3+ solutions are used to demonstrate the effect of background correction and the sensitivity of this dual-beam photothermal deflection arrangement.

Forensic Analyses of Suspect Illicit Nuclear Material

A small metal sample, alleged to be a substance that could substitute for highly enriched uranium in a nuclear weapon, was subjected to qualitative and quantitative forensic analyses using methods of materials science, radioisotopic chemistry, inorganic chemistry, and organic chemistry. The specimen was determined to be moderately pure Sc, likely derived from a uranium refining operation. Although no fissionable species or weaponization signatures were detected, the sample did exhibit some unusual properties. These anomalies included lanthanide fractionation, with concentrations of Dy, Ho, and Er elevated by factors greater than 100 over normal levels, and the presence of long, odd-chain fatty acids.

Nuclear fission product analysis using capillary separation techniques

Capillary electrophoresis has been used to separate metal ions characteristically associated with nuclear fission. Electrokinetic injections and transient isotachophoretic techniques were employed to increase sample loading and provide on-column concentration of the analyte. On-line concentration factors of approximately 700-fold have been achieved. Indirect-UV absorbance, on-line radioactivity, and indirect laser-induced fluorescence detection were used to monitor analytes of interest. The radioactivity detector consists of a plastic scintillator and photomultiplier tube with a 4π detection geometry. The efficiency was determined to be approximately 80%, enabling samples resident in the detector window for 0.1 minutes to be reliably assayed. Detection of152Eu and137Cs was achieved at the low nCi level. Indirect fluorescence was performed with quinine sulfate as the background fluorophor with α-hydroxysobutyric acid added as a complexing agent. An argon ion laser was used as the excitation source with a diode array detector. Limits of detection for La3+, Ce3+, Pr3+, Nd3+, Sm3+, and Eu3+ were determined to be in the sub — 10 ppb range (6–11 nM) with indirect laser-induced fluorescence detection.

Monitoring laser-energy coupling to solid materials: plasma-shielding and phase change

Abstract For many laser-material processes, new methods are needed to monitor laser-energy coupling to solid materials. Different methods will be presented which can detect changes in laser-energy coupling due to plasma shielding, phase change, and surface alterations. The techniques used are inductively coupled plasma-atomic emission spectroscopy (ICP-AES), mechanical stress power (MSP), and photothermal deflection (PTD). This work demonstrates that the onset of plasma shielding can be detected for ns and ps laser interactions with solids, using ICP-AES and MSP, and that the onset of melt at a surface can be detected using PTD.

Search for evidence of nuclear involvement in the fatal explosion of a “cold fusion” experiment

Forensic analyses of debris from the fatal explosion of an electrochemical “cold fusion” cell at SRI International were conducted at LLNL at the request of Cal-OSHA. One investigation focused on the possibility of conventional nuclear reaction mechanisms contributing to the total energy inventory of the incident. Selected metal components of the electrolysis apparatus were subjected to nondestructive γ-ray spectrometry with high-sensitivity, low-background Ge detector systems. The anticipated analytes in these studies were radioactivation products potentially induced in the explosion residue by either fast or thermal neutrons. The results of this investigation were negative within the temporal constraints of the incident and the analytical sensitivities of the instrumentation.

Characterization of High Temperature Superconductors with Raman Spectroscopy

Among vibrational spectroscopies, Raman spectroscopy is a powerful analytical investigation technique for studying phonons in solids with relatively simple instrumentation. Raman scattering can provide various types of information, for instance, concerning the behavior of the oxygen atoms or information about the electronic band structure. As soon as high temperature superconductivity in La1-xBaxCuO4 was discovered by Bednorz and Muller,1 Raman spectra have been studied to determine the structure, composition, and phases of these perovskite-like superconducting copper oxides.