LEY DE HOOKE

Identification of unknown and suspect materials is a major task for the forensic scientist. In view of legal requirements and often limited amounts of samples, analyses have to be carried out using sensitive, but non-destructive methods. The applications of NAA and XRF have been very valuable. The XRF technique provides clues on the nature of materials that are confirmed by the use of NAA.

In connection with a criminal case, a shining piece of metal was recovered from an incoherent suspect. It was not clear whether the metal was radioactive or precious. Chemical analysis was not possible in view of the need for preser- vation as evidence and the absence of information on possible composition. The use of an HPGe detector confirmed the absence of radioactivity while X ray analysis indicated that the material was steel and, with more detailed analysis, it was possible to infer the nature of the alloy.

TABLE II. FORENSIC MATERIALS ANALYSED BY NAA

Type of exhibit Element Remarks

Transmission copper Ag, Au, Sb and Se Discriminating parameters

wire pieces (at trace level) established and reported

for SC/100

Transmission aluminium Mn, Cr, Hf, Sc and Fe — ditto —

wire pieces (at trace level)

Glass pieces Eu, U, Co, Fe, Th, Sb Reported trace element

and Sc pattern observed

Cannabis Mn, Cu, K, Cl, Br, Fe, Sc, Observed and reported

Hf and Zn trace element profile

Animal hair Mn, Cl, Na, K, Cu, Br, Au General picture with res-

and Zn pect to different varieties

of animal hair samples. This can be helpful to ascertain differentiation between human and animal hairs.

Ornamental gold Cd, Zn, Cu, As and Ag Nature of composition can

provide proper characteri- zation particularly relevant to burglary cases.

In a similar manner, we were able to identify an unknown white powder. An XRF analysis indicated the presence of gold, which was confirmed by NAA. Further study suggested that the compound might be a gold cyanide complex, which was later confirmed by chemical analysis. By this procedure, it was possible to determine that gold was being smuggled as a nondescript white powder.

Neutron activation analysis is a powerful tool for analysis of metals, even in very minute amounts. In an interesting case, the analysis of the jacket belt of a person suspected to be smuggling gold indicated the presence of traces of gold. This helped the investigating officer to decide whether the suspect was involved and whether the belt was the means of carrying the gold. But for the availability of a very sensitive technique like NAA, it would have been difficult to establish the role of the belt.

Nuclear analytical techniques are valuable for studies connected with source correspondence. One of our studies was in connection with the theft of copper transmission wires. The trace element profile provided a valuable clue as to the nature of material. In this respect, NAA is a valuable technique in view of its high sensitivity and specificity, and the absence of need for a blank, normally associated with solution techniques. Thus, NAA is useful for analysis of hair, nail, body tissues, vegetable products, medicines, etc., for source corre- spondence. Some of the matrices analysed for forensic purposes are summa- rized in Table III.

Another area in which analytical techniques, especially NAA, are becoming important is the characterization of medicinal preparations.

TABLE III. BIOLOGICAL, PHARMACEUTICAL AND RELATED PRODUCTS ANALYSED BY NAA AND ALLIED TECHNIQUES

Nature Elements

Hair, nail, bones, body tissues, blood As and Hg in general for detection of heavy-metal poisons

Ayurvedic drugs, synthetic medicines, As, Hg, Se, Sb, Pb, Al tea, materials of plant origin for

estimation of trace quantities of toxic elements

Acetic anhydride (used as a reagent Trace element abundance for informa- in the preparation of heroin) tion on the source of raw materials and

Investigation of illicit trafficking in narcotics requires information on sources of raw materials and chemicals used for preparation, and identification of products from various cities or countries. For example, in the case of prepara- tion of heroin, acetic anhydride is used as a reagent. Materials may be grown illegally or smuggled from other countries. A trace element profile may provide more insight on the nature of a material than major component analysis by indicating the nature of the raw materials, the catalyst employed during synthesis, the method of synthesis, and the trace metal ions that have leached from the container during storage and transport. In this connection, an analysis of acetic anhydride manufactured by different companies was carried out by nuclear and atomic absorption analysis method. A direct analysis by AAS was not possible in view of the high viscosity of the sample, and dilution of the sample limited the scope of analysis for the presence of metal ions at trace or ultra-trace levels. This necessitated various pre-concentration procedures such as evaporation of acid, removal of matrix material by suitable oxidation or other separation procedures. Nuclear techniques have a definite advantage in this analysis in view of the direct irradiation of the sample. The matrix induced activity is not generally significant since the common constituents of organic materials like carbon, hydrogen, oxygen and nitrogen do not contribute to matrix activity while the presence of even traces of metallic ions is indicated by their characteristic g rays after irradiation of the sample. This procedure consid- erably enhances the scope of analytical techniques for characterization of organic compounds or pharmaceutical products for toxic metal ions. A radio- chemical procedure enhances specificity by removal of unwanted radioactivity. An important aspect of accurate analysis is the removal of effects due to the matrix materials. This activity calls for considerable insight into the chemistry of the process so as to use the best route for analysis. It also requires considerable expertise in sample preparation and group separation of the constituents in order to avoid interference from the commonly occurring materials like sodium, manganese, bromine, chlorine, etc. Some of the proce- dures developed and employed are listed in Table IV.

4. CONCLUSION

Characterization of forensic samples is a challenging task in view of the unknown nature of the materials, their limited availability and the need to preserve samples for possible subsequent investigation. These requirements make the analyses very specialized, requiring judicious use of sensitive analyt- ical techniques, clean operating conditions, use of non-destructive and multi- element analytical techniques, and proper cross-validation of results. These

requirements make nuclear analytical techniques vital for the characterization of forensic samples. Modern separation and complementary analytical tech- niques are a very powerful aid in forensic analysis for conviction of criminals and, more importantly, for acquittal of the innocent.

ACKNOWLEDGEMENTS

The authors wish to thank various scientists who contributed to the analytical data presented in this work. Thanks are also due to M.S. Rao, Chief Forensic Scientist, BPR&D, and J.P. Mittal, Director, C&I Group, BARC, for their encouragement during the course of this work.

TABLE IV. SEPARATION PROCEDURES DEVELOPED FOR

FORENSIC APPLICATIONS

Method Elements/Usefulness

1. A sequential RNAA procedure in Ba, Cu, Sb, Pb, Ni, Zn combination with complementary

analytical techniques like AAS or DPASV

2. A sequential RNAA procedure for Sn, Cu, As, Sb for characterization trace analysis of various bullet leads

of Indian origin

3. Simultaneous determination of an Sn along with Ba, Cu and Sb additional indicator for GSR —

a sequential RNAA procedure

4. A method for trace analysis of lead Quantitative separation of Pb from the in copper matrix employing DPASV matrix followed by determination technique — by use of ion exchanger

DOWEX 1 ¥ 4

5. Zinc as one of the characteristic trace Zinc included in the RNAA steps along elements in GSR/bullet residues apart with Ba, Cu, Sb

from Ba, Cu and Sb by a sequential RNAA

6. An anion-exchange separation method Concentration of As(iii) in the effluent for As(iii) for As(v) from aqueous and that of As(v) in the eluted solutions mixture for speciation of inorganic will allow to assess toxicity level due to

ATTRIBUTION OF NUCLEAR MATERIAL