Thermal neutron analysis

The investigation into the sabotage of Pan Am Flight 103, which left 269 dead, indicated that the explosive used was Semtex H, a plasticized mixture of hexahydro-l,3,5-trinitro-s-triazine and pentaerythritol tetranitrate, and that the amount used was half the quantity that the fledgling technique of Thermal Neutron Analysis (TNA) was designed to detect. Although the placement of the explosive device was fortuitous (from the terrorists point of view) and the suitcase had not been screened by TNA, this event killed the TNA prototype program. 

M. J. Hurwitz, W. P. Noronba, T. A. Atwell, Airport Testing of a New Thermal Neutron Analysis Explosives Detection System, Proceedings of the First International Symposium on Explosive Detection Technology, pp. 388—395, 13—15 November 1991. US Department of Transportation, February 1992. 

The 1985 tragedy of Air India Flight 182, which exploded off Ireland en route from Montreal to London, stimulated an intensified effort to thwart terrorists. The International Security and Development Act of 1985 provided for air marshals and expanded FAA s R D for airport security. Thermal neutron analysis (TNA) and a number of sniffer technologies for trace explosives detection, which had been developed under FAA sponsorship, were accelerated toward commercial production. 

API, associated particle interogation FNA, fast neutron analysis PFNA, pulsed fast neutron analysis TNA, thermal neutron analysis. 

W.C. Lee, D.B. Mahood, P. Ryge, P. Shea and T. Gozani, Thermal neutron analysis (TNA) explosive detection based on electronic neutron generators, Nucl. Instrum. Methods Phys. Res. Sec. B, 99(1 1) (1995) 739-742. 

P.C. Womble, G. Vourvopoulos, J. Paschal and P.A. Dokhale, Multi-element analysis utilizing pulsed fast/thermal neutron analysis for contraband detection, Proc. SPIE, 3769 (1999) 189-195. 

Nuclear or thermal neutron analysis One application uses californium (a radioactive element) to excite explosive material to release gamma rays that can be detected. Another application excites hydrogen in an explosive that releases neutrons that can be detected. Early in development. Has a small footprint. Hydrogen sensors are not effective in moist soil. 

Advanced sensor technologies with application to detection and clearance can be grouped as follows infrared sensors, ground-penetrating radars, microwave, photon backscatter, nuclear or thermal neutron analysis, and lasers. Their characteristics were summarized in Table 12.1. 

Thermal neutron activation analysis has been used for archeological samples, such as amber, coins, ceramics, and glass biological samples and forensic samples (see Forensic chemistry) as weU as human tissues, including bile, blood, bone, teeth, and urine laboratory animals geological samples, such as meteorites and ores and a variety of industrial products (166). 

MetaUic impurities in beryUium metal were formerly determined by d-c arc emission spectrography, foUowing dissolution of the sample in sulfuric acid and calcination to the oxide (16) and this technique is stUl used to determine less common trace elements in nuclear-grade beryUium. However, the common metallic impurities are more conveniently and accurately determined by d-c plasma emission spectrometry, foUowing dissolution of the sample in a hydrochloric—nitric—hydrofluoric acid mixture. Thermal neutron activation analysis has been used to complement d-c plasma and d-c arc emission spectrometry in the analysis of nuclear-grade beryUium. 

Picatinny Arsenal Thermal Neutron Activation Analysis Facility. N... 

H. Kramer, S. Semel J.E. Abel, Trace Elemental Survey Analysis of Trinitrotoluene , PATR 4767 (1975) (An evaluation of the applicability of spark source mass spectrometry and thermal neutron activation for the detn of origin-related trace elemental impurities in TNT) 10) C. Ribando J. Haber-man, Origin-Identification of Explosives Via Their Composite Impurity Profiles I. The... 

This can result in a radioactive product from the A(n, t)A reaction where A is the stable element, n is a thermal neutron, A is the radioactive product of one atomic mass unit greater than A, and y is the prompt gamma ray resulting from the reaction. A is usually a beta and/or gamma emitter of reasonably long half-life. Where access to a nuclear reactor has been convenient, thermal neutron activation analysis has proven to be an extremely valuable nondestructive analytical tool and in many cases, the only method for performing specific analyses at high sensitivities... 

Individual sources of 252Cf are currently available in quantities up to 10—50mgs of the element. Such sources, when contained in a suitable hydrogenous moderator, can provide thermal neutron outputs adequate for the activation analysis of many elements in the fraction of a percent wt range... 

The apphed pretreatment techniques were digestion with a combination of acids in the pressurized or atmospheric mode, programmed dry ashing, microwave digestion and irradiation with thermal neutrons. The analytical methods of final determination, at least four different for each element, covered all modern plasma techniques, various AAS modes, voltammetry, instrumental and radiochemical neutron activation analysis and isotope dilution MS. Each participating laboratory was requested to make a minimum of five independent rephcate determinations of each element on at least two different bottles on different days. Moreover, a series of different steps was undertaken in order to ensure that no substantial systematic errors were left undetected. 

Applications NAA is a powerful technique for ultratrace analysis of metallic impurities in plastics. PE is one of the most important canning materials for NAA, mainly on account of its high purity and low price. The cross-section of PE for thermal neutrons amounts to... 

Nuclear bombardment reactions in which the product is radioactive constitute the basis of radioactivation analysis (p. 456). Although in principle any bombardment-decay sequence may be used the analyst is largely concerned with thermal neutron activation. Equation (10.13) relates the induced activity to the amount of the parent nucleide (analyte). However, practical difficulties arise because of flux inhomogeneities. It is common therefore to irradiate a standard with very similar characteristics alongside the sample, e.g. for a silicate rock sample a standard solution would be evaporated on to a similar amount of pure silica. On the assumption that identical specific activities for the analyte are then induced in the sample and standard, the amount w2 of analyte is readily calculated from... 

Randle and Hartman [12] used thermal neutron activation in analysis to investigate total bromine in humic compounds in soil. Bromine was extracted from the soil water with sodium hydroxide or sodium pyrophosphate, then the extract dried prior to analysis. 

In general, scattering of thermal neutrons yields information on the sample by measurement and analysis of the double differential cross section ... 

A technique for the determination of Tc amounts as little as 4 x 10 g by neutron activation analysis has been described by Foti et al. . Tc in triply distilled water is irradiated in a thermal neutron flux of 5 x 10 neutrons per cm and per second to produce °°Tc. Other radionuclides are removed by co-precipi-tation with Fe(OH)j. Then, °°Tc is co-precipitated twice with tetraphenylarsonium perrhenate which can be removed by sublimation. The chemical purification of °°Tc requires 40-45 s and the technetium yield is about 53%. 

Trace amounts of Tc are also determined in filter paper and vegetable samples by neutron activation analysis The procedure consists of the following major steps separation of technetium from the sample, thermal neutron irradiation of the Tc fraction to produce °°Tc, post-irradiation separation and purification of °°Tc from other activated nuclides, and counting of the 16 s Tc in a low-background P counter. The estimated detection limits for Tc in this procedure are 5 x 10 g in filter paper and 9 x 10 g in vegetable samples. 

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