Single Bullet Theory - Neutron Activation Analysis of Bullet Fragments

Neutron Activation Analysis of Bullet Fragments

Warren Commission documents released after the publication of its report revealed that the FBI had arranged for bullet CE 399 and the various fragments found in the car and in Governor Connally’s wounds to be examined using a method known as neutron activation analysis (NAA). NAA is a very accurate, non-destructive method of determining the relative concentrations of trace elements in a sample of matter. The data from the tests performed for the FBI were inconclusive as to the origins of the fragments.

In 1978 the HSCA asked physicist Dr. Vincent P. Guinn to review the NAA data and conduct new tests. Dr. Guinn did so and presented his results and analysis to the Committee. Dr. Guinn stated that initially he agreed with the earlier conclusion. However, after examining the old and new NAA data further, he concluded that all the fragments probably came from two bullets, one of which was the whole bullet, CE 399.

WC Exhibit	Silver (ppm)	Antimony (ppm)
399 Whole bullet (labeled Q1)	7.9 ± 1.4	833 ± 9
567 Limousine fragment (labeled Q2)	8.1 ± 0.6	602 ± 4
843 Fragments from head wound (labeled Q4 and Q5)	7.9 ± 0.3	621 ± 4
842 Wrist fragment (labeled Q9)	9.8 ± 0.5	797 ± 7
840 Limousine fragment (labeled Q14)	8.6 ± 0.3	638 ± 4
- second (labeled Q14)	7.9 ± 0.5	647 ± 4
573 fragment from bullet fired at Gen. Walker 's residence	20.6 ± 0.6	17 ± 2
141 unfired bullet recovered from Oswald's rifle	-	15 ± 1
- second	22.4 ±1.0	-

The NAA data obtained from the various bullet samples (1 HSCA 538 and 1 HSCA 550)

Dr. Guinn compared antimony concentrations of Exhibits CE 840, 843 and 567 with that of Exhibits CE 399 and 842. He reasoned:

Accordingly, neutron activation analysis of the evidence specimens tested indicates the presence of only two bullets in Group I. It is highly probable that the specimen tested from Ql (the stretcher bullet) and the specimen tested from Q9 (the fragments from Governor Connally's wrist) are from the same bullet. It is highly probable that Q2 (large fragment found in the limousine), Q4 and 5 (fragments from President Kennedy's brain) and Q14 (smaller fragments found in limousine) are all from a second bullet. There is no evidence of a third bullet from any of the evidence specimens tested.

Dr. Guinn had some difficulty in stating the precision that he could give to this probability:

Dr. GUINN. I wish that I could put a number on it, as we often can do, that is, calculate a probability, but we really don’t have the background information to make a numerical calculation in this case. One can only show what information we do have, and that is that you simply do not find a wide variation in composition within individual WCC Mannlicher-Carcano bullets, but you do find wide composition differences from bullet to bullet for this kind of bullet lead. Thus, when you find two specimens that agree this closely, you can say it looks indeed like they are pieces from the same bullet. Mr. WOLF. Would you state that your conclusion is more probable than not, highly probable, or what is the degree of certainty of your conclusion? Dr. GUINN. I would say highly probable, yes. I would not want to say how high, whether it was 99 percent or 90 percent or 99.9 percent. I can’t make a calculation like that.

The underlying assumption in Dr. Guinn’s analysis was that silver and antimony concentrations in the bullet lead varied significantly between bullets but not within individual bullets. Significant differences in concentrations between samples, therefore, would mean that the samples originated with different bullets. Dr. Guinn’s assumption was based on sample data that he had obtained by analysing concentrations of antimony, silver and other trace elements in Mannlicher-Carcano ammunition from Western Cartridge Co., which was the ammunition found with Oswald’s rifle. He observed that while there was some variation of concentrations within individual bullets, he found that the variation between bullets is wider.

There seems to be relatively greater heterogeneity between bullets from Dr. Guinn’s data, although it may be noted that the concentrations of antimony, for example, varied substantially within a sample bullet. This lack of perfect homogeneity within individual bullets was acknowledged by Dr. Guinn:

The results are shown in Table II-C. As can be seen, of the three bullets sampled, one (6001 C) is fairly homogeneous in all three elements; one (6002 A) is fairly homogeneous in Ag and Cu, but not so homogeneous in Sb; and one (6003 A) is fairly homogeneous in Cu, but not homogeneous in Sb or Ag. However, comparison of Table II-C with Table II-A indicates that, in general, the heterogeneity within an individual Mannlicher-Carcano bullet is much less than the heterogeneity from one bullet to another. One of the primary conclusions, therefore, of the results of the UCI background study of MC bullet lead indicates a wide range of Sb values, from bullet to bullet, but reasonable homogeneity within an individual bullet.

Guinn, however, acknowledged that the assumption of heterogeneity between bullets was not necessarily true for all bullets:

However, the earlier data and these more recent data do show some Mannlicher-Carcano bullets that cannot be distinguished from one another via only their antimony and silver concentrations. From these data, it appears that if 2 cartridges are removed at random from a box of Mannlicher-Carcano cartridges, although it is highly probable that they would differ significantly in their antimony and silver concentrations, it is at least possible that they might not. (1 HSCA 534 - footnote)

Dr. Guinn's observation appears to be borne out by the profiles of CE 141 and CE 573 which have very similar silver and antimony concentrations but are from two different bullets.

Dr. Guinn’s data and analysis was thought to provide important support for the Single Bullet Theory. If there had been greater differences in concentrations of trace elements between fragments, the theory could not stand.