F. E. Dunnam

Elemental analysis of bone: proton-induced X-ray emission testing in forensic cases

Proton-induced X-ray emission (PIXE) is a spectroscopic technique that provides the researcher with the elemental composition of a given target material. In this paper, we illustrate the utility of PIXE analysis in two forensic contexts: (1) case of cremation in which the nature of the remains is questioned and (2) cases of death by gunshot wound. In the first case, elemental analysis by PIXE reveals that the purported cremated remains are not bone. The last two cases show that radiopaque metallic residue embedded in bone is composed of lead from a projectile.

Levels in 36Ar and 38Ar from alpha capture in 32S and 34S

Abstract The 32 , 34 S(α,γ) 36 , 38 Ar reactions have been studied over an energy range E x = 3.2–4.3 MeV. Of the thirteen resonances observed in this energy region, three are attributed to 32 S and ten to 34 S. The excitation energies and resonance strengths are reported. The main decay of all levels is directly to the ground state, permitting definite spin and parity assignments to all resonances from angular distribution data. The resonance strengths support the isobaric spin selection rule for electric dipole transitions in self-conjugate nuclei.

Observation of T = 0 and T = 1 alpha-particle states in 16O between Ex = 26 and 29 MeV

Abstract A measurement of the 13 C ( 3 He ,αγ 15.1 ) 12 C reaction at bombarding energies below 8.0 MeV indicates three T = 1 states in 16 O between E x = 26 and 29 MeV. These are compared to the T = 0 states in the same region.

The Use of a Pulsed Van de Graaff Accelerator and Time‐of‐Flight Techniques to Reduce Backgrounds in (α,γ) Spectroscopy Experiments

A pulsed beam of alpha particles from a 5.5 MV Van de Graaff accelerator has been used to study radiative capture reactions. Time‐of‐flight techniques are used to discriminate against neutrons produced when the beam interacts with collimator‐target contaminants, as well as against beam independent background due to cosmic rays. With a beam pulse of less than 4 nsec (FWHM) duration and a repetition rate of 2 MHz, a portion of the 34S(α,γ)38Ar excitation function was examined near Eα=3.6 MeV and the background found to be an approximate factor of 15 below that of the effective dc excitation function. In addition it is demonstrated that an angular distribution taken on resonance by this method requires substantially less background subtraction. The method has also been successfully applied to radiative capture studies in which the incident beam energy is above the neutron threshold for the target nuclei.

Levels in 30Si excited by the 26Mg(α, n)29Si, 26Mg(α, γ)30Si and 26Mg(α, α)26Mg reactions

Abstract The reactions 26 Mg(α, n) 29 Si, 26 Mg(α, γ) 30 Si and 26 Mg(α, α) 26 Mg have been investigated for E α = 2.5−4.3 MeV. Twenty-nine resonances were observed in the 26 Mg(α, n) 29 Si reaction and the total widths of the corresponding 30 Si levels were estimated. Three of the resonances were also seen in the 26 Mg(α, γ) 30 Si reaction and their spin and parity could be determined from angular distribution data for the ground state transition. The measured resonance strengths were found to support the isobaric spin selection rule for El transitions in self-conjugate nuclei. A multi-channel multi-level R -matrix calculation was used to analyse the elastic scattering data, yielding spin, parity and partial widths of the observed levels.

Interaction of multi‐MeV gamma rays with matter

The code BSIMUL is used to simulate the interaction of a 10.76‐MeV gamma ray with a 5 cm×6 cm germanium detector crystal. The Monte Carlo calculation includes the following interactions: the photoelectric effect, Compton scattering, pair‐production, pair annihilation, and bremsstrahlung. In this work we investigate the effect of the simplifying assumption that the electrons and positrons do not travel significant distances in the material. The simulation is compared to experiment by following the decay of the 12.54‐MeV resonance produced by 992‐keV protons on 27Al in the reaction 27Al(p,γ)28Si. In 75% of the reactions this resonance decays by a 10.76‐MeV gamma ray whose interactions with the detector dominate the spectrum in the energy region between 8 and 11 MeV.

A forensic application of PIXE analysis

PIXE measurements were performed on various calcareous materials including identified bone residues, human cremains, and samples of disputed origin. In a forensic application, the elemental analysis suggests that the origin of a sample suspectly classified as human cremains can tentatively be identified as a mixture of sandy soil and dolomitic limestone.

Elemental Levels Analyzed by PIXE in Florida Alligators

Unusual and alarming mortality of alligators (Alligator mississippiensis) has been reported from Lake Griffin, Florida, where almost 400 dead alligators have been observed since 1997. In addition, the hatch rate for alligator eggs around Lake Griffin fell below 10% and remains low (30–45%) while the normal hatch rate is typically 80%. Standard diagnostic methods have been ineffective in determining the cause of the phenomenon. Many possibilities have been considered including pollutants, nutrition, and toxic algae. Particle Induced X‐ray Emission (PIXE) analysis is highly suitable for investigating concentrations of a wide range of elements in animal tissue. Liver, kidney and spinal cord tissues from healthy and sick alligators have been analyzed by PIXE for elemental content. Initial results showed positive correlation between certain elements and neural impairment and morbidity of alligators in Lake Griffin, but have failed to prove significant.

Proton induced X-ray emission analysis of aberrant cowrie shells

It is hypothesized that the irregular growth and coloring of aberrant rostrate and melanistic cowrie shells are the result of intensification of the melanain biochemical pathway caused by an overabundance of spin-stabilizing heavy metals. PIXE measurements have shown no pattern in elemental composition to stand out as a distinct difference between the normal and aberrant shells. Therefore, no evidence was found in the shell to corroborate the role of heavy metals in causing these teratologies. The absence of heavy element abundance in rostrate and melanistic shells does not exclude the possible role that these elements play within the soft tissue, as these metals may be too large to pass through membrane channels into the extracellular space where shell deposition occurs.

Leaching from CCA‐Treated Wood into Soils: Preliminary PIXE Studies

Widespread use of chromated copper arsenate (CCA) as a wood preservative has led to increasing public concern regarding possible toxic contamination of areas surrounding CCA‐treated structures, e.g., decks, playground equipment, etc. Appreciable leaching of arsenic, chromium, and copper into soils adjacent to such structures has been demonstrated via standard techniques of analytical chemistry. The advantages of PIXE [rapid analysis, quick sample turnover, possible lower cost] suggest its application to this area of interest. PIXE studies in our laboratory of CCA‐contaminated soil samples show good agreement with previous analyses of As, Cu, Cr, and other heavy‐elemental content, with some variability in diffusion rates.