J Radioanal Nucl Chem (2013) 298:993–1003 DOI 10.1007/s10967-013-2497-8 A multi-method approach for determination of radionuclide distribution in trinitite Christine Wallace • Jeremy J. Bellucci • Antonio Simonetti • Tim Hainley • Elizabeth C. Koeman • Peter C. Burns Received: 21 January 2013 / Published online: 13 April 2013 Ó Akade´miai Kiado´, Budapest, Hungary 2013 Abstract The spatial distribution of radiation within trin- The results from this study indicate that the device-related ititethinsectionshavebeenmappedusingalphatrack radionuclides were preferentially incorporated into the radiography and beta autoradiography in combination with glassy matrix in trinitite. optical microscopy and scanning electron microscopy. Alpha and beta maps have identified areas of higher activity, Keywords Trinitite Á Nuclear forensics Á Radionuclides Á and these are concentrated predominantly within the surfi- Fission and activation products Á Laser ablation inductively cial glassy component of trinitite. Laser ablation-inductively coupled plasma mass spectrometry coupled plasma mass spectrometry (LA-ICP-MS) analyses conducted at high spatial resolution yield weighted average 235U/238Uand240Pu/239Pu ratios of 0.00718 ± 0.00018 (2r) Introduction and 0.0208 ± 0.0012 (2r), respectively, and also reveal the presence of some fission (137Cs) and activation products Nuclear proliferation and terrorism are arguably the gravest (152,154Eu). The LA-ICP-MS results indicate positive cor- of threats to the security of any nation. The ability to relations between Pu ion signal intensities and abundances decipher forensic signatures in post-detonation nuclear of Fe, Ca, U and 137Cs. These trends suggest that Pu in debris is essential, both to provide a deterrence and to trinitite is associated with remnants of certain chemical permit a response to an incident. Impacted material components from the device and surrounding Trinity test- obtained from historical nuclear tests offers a unique related structures at ground zero. In contrast, negative cor- opportunity for nuclear forensics method development, as relations between Pu ion signals and SiO2 and K2O contents the radioactive components of the weapons have been were observed within the glassy matrix of trinitite. This LA- documented. Therefore, results obtained in a forensic ICP-MS result was corroborated by combined back-scat- investigation from the latter are verifiable. tered electron imaging and alpha radiography, and indicates Post-detonation material from the Trinity test, the that Pu was not incorporated into unmelted crystalline grains world’s first nuclear explosion, provides an opportunity for of precursor minerals (i.e., quartz-SiO2 and K-feldspar- forensic studies, as most of the government literature on KAlSi3O8) present within the desert sand at the Trinity site. the test has been declassified and samples are available from public and private collections. The Trinity test was conducted on July 16, 1945 at the White Sands Missile Electronic supplementary material The online version of this Range near Alamogordo, NM, and represented the first of article (doi:10.1007/s10967-013-2497-8) contains supplementary over 1000 nuclear tests conducted by the United States material, which is available to authorized users. between 1945 and 1992 [1]. The Trinity ‘‘Gadget’’ was an C. Wallace (&) Á J. J. Bellucci Á A. Simonetti Á T. Hainley Á implosion-type fission device containing *6 kg of ‘‘super- E. C. Koeman Á P. C. Burns grade’’ 239Pu [2, 3]. The device was detonated from atop a Department of Civil and Environmental Engineering and Earth 30.5 m steel tower at 5:29:45 a.m. local time, generating an Sciences, University of Notre Dame, Notre Dame, IN 46556, USA explosion equivalent to that from *21 kt of TNT [4]. The e-mail: [email protected]; [email protected] Trinity test created a fireball with a height of 15.2–21.3 km 123 994 J Radioanal Nucl Chem (2013) 298:993–1003 and a temperature of *8430 K [4]. The explosion engulfed explosion [14]. It is assumed that the remaining *4.8 kg the device and components, as well as the tower and the of Pu did not fission and was consequently dispersed in the surrounding desert sand. Radionuclides, including un-fis- explosion. sioned Pu, fission products, and neutron activation products Past studies of trinitite have documented the presence of were also entrained in the cloud. When the debris 239Pu [2, 6, 8, 11], as well as 238Pu, 240Pu, 241Pu, and re-solidified, it formed a layer of glassy material known as 241Am [2, 6]. 238Pu, 240Pu, and 241Pu could have been ‘‘trinitite’’ with a radial extent of 370 m [5]. created during reactor irradiation via (n,2n), (n, c), and A two-step formation mechanism has been proposed for (2n, c) reactions, respectively. However, it is more likely trinitite [6, 7]: (1) formation of molten glass both on the that these isotopes were actually produced during the ground and in the mushroom cloud, and (2) subsequent explosion, due to the high purity of the original fuel [2]. incorporation of solid material (non-molten mineral phases, 241Am is present as a b-decay product of 241Pu, which has a metal, and droplets) raining down from the cloud on the half-life of 14.3 years. Consequently, 241Am has accumu- upper surface of this solidifying glass. Of importance in lated in trinitite since 1945 from the decay of 241Pu relation to the forensic analysis of trinitite’s glass matrix is [2, 6, 8]. the fact that the arid conditions of New Mexico’s desert have likely prevented mobilization and leaching of long- Uranium lived radionuclides [2]; these include remnants of Pu fuel, fission products, and neutron activation products. Natural uranium in trinitite may originate from two Several previous studies of trinitite have focused on sources. Firstly, uranium is indigenous in mineral phases radiochemical analysis [2, 8, 9]. Recently, several studies found within the desert sand at the Trinity site, including have highlighted the importance of examining trinitite at zircon, monazite, and apatite [10]. Additionally, the Gadget the micron scale for forensic purposes [6, 10, 11]. To date, contained a 120-kg tamper composed of natural uranium, an investigation describing the spatially resolved distribu- which functioned to avert a premature disassembly of the tion of radionuclides within trinitite is lacking; however, Pu core and to restrict initial movement of neutrons [15]. given its heterogeneous nature at the micron scale, spatial The tamper was dispersed in the explosion and incorpo- resolution is deemed of utmost importance for under- rated into the melt material. Semkow (2006) [15] reported standing dispersion of radionuclides during a nuclear that *30 % of the Gadget’s explosive yield resulted from explosion. Hence, the purpose of this study is to investigate fission of 235U within the tamper, and fission product ratios the distribution of radionuclides via methodologies that determined via gamma spectroscopy are consistent with provide reasonably rapid and quasi non-destructive analy- fission of both 239Pu and 235U[8]. As a result, it is possible ses of trinitite. that 235U/238U ratios in trinitite will be slightly lower than natural. Remnants of Pu fuel Fission products The Pu used in the Trinity device was produced at the The Trinity test was conducted over six decades ago, and Hanford site, with the natural U fuel being subjected to consequently only fission products with sufficiently long extremely short irradiation time as a result of the urgency half-lives should still be detectable. For example, 137Cs during the Manhattan Project era [3]. During irradiation, (t1/2 = 30.17 years) is formed from the beta decay of short- 239Pu is created via neutron capture on 238U (creating lived fission products 137Xe and 137I, whereas 90Sr 239 90 U), followed by two successive b-decays. During this (t1/2 = 28.8 years) is derived from the short-lived Rb. process, 240Pu and 241Pu are also produced in situ by 90Sr and 137Cs have cumulative fission yields of 2.17 and neutron capture on 239Pu, with longer irradiation times 6.76 % from the fission of 239Pu, respectively [16]. resulting in a higher 240Pu and 241Pu content. The extre- mely low burn-ups used to produce the Pu fuel for the Neutron activation products Trinity device resulted in 239Pu that was nearly isotopically pure, as higher Pu isotopes did not have time to accumu- Upon detonation, the Pu core of the Gadget initiated a late. Sublette estimated the original (pre-detonation) 240Pu neutron flux that caused neutron activation of both device content of the Gadget to be *0.9–1.0 %, with only trace components and the surrounding sand. Previous studies amounts of other isotopes [12]. The Trinity device con- have documented the presence of 60Co, 133Ba, 152Eu, and tained a total of 6 kg of Pu; based on Glasstone and 154Eu in trinitite [2, 8]. 60Co is derived from the (n, c) Dolan’s estimate of 1.45 9 1023 fissions occur per kiloton reaction of 59Co, which was present in the steel tower. of yield [13], only 1.2 kg of 239Pu were fissioned in the Similarly, 133Ba is produced via (n, c)on132Ba, which 123 J Radioanal Nucl Chem (2013) 298:993–1003 995 originated from the explosive lens system in the Gadget Dame Integrated Imaging Facility using a EVO 50 LEO and in mineral phases, such as barite, within the desert sand Environmental SEM (Carl Zeiss). This instrument is [10]. 152Eu and 154Eu are neutron activation products of equipped with both secondary electron and backscatter 151Eu and 153Eu, respectively. These isotopes are also electron (BSE) detectors. An accelerating voltage of 30 kV present naturally in the desert sand at ground zero. and magnifications of 100–2009 were used for these measurements. Prior to analysis, thin sections were mounted onto SEM stubs with conductive carbon tape and Major and trace elements sputtered with Ir to a thickness of *5 nm.