DETONATION NUCLEAR FORENSICS IN REAL TIME

Currently, gamma-ray spectroscopy and neutron detection are recommended for in-situ analysis of radioactive material in nuclear forensics, while these techniques cannot identify emitting alpha and beta isotopes, as well as non-radioactive impurities. To remedy the weakness of such techniques, LIBS can be applied to nuclear forensics in situ, thanks to its speed and adaptability to different circumstances. LIBS is very applicable in nuclear forensics in situ, enabling the analysis of radioactive isotopes and non-radioactive impurities, especially when combined with Raman spectroscopy and conventional gamma-ray spectroscopy.

Introduction

What is Nuclear Forensics?

Both analysis time and pre-processing time before analysis are the most important criteria that determine the speed of characterization for post-detonation nuclear forensics. LIBS, Raman spectroscopy, FT-IR (Fourier transform infrared), and gamma ray spectroscopy are techniques that enable in situ NDA. Therefore, through a literature review in Section 3, we identify how LIBS can be used for nuclear forensics in various circumstances and demonstrate its applicability by conducting a LIBS experiment under the assumption of potential sources of terrorism in Sections 4 and 5.

Table 1. Recommended categories for nuclear materials [32].

Literature Review: LIBS

LIBS Principles

Basic concept of laser is established by Einstein in and the history of laser development started from it. Runge et al., in 1964, mentioned that spark induced by Q-switched pulse laser can be used to analyze metals [42]. More specifically, we selected five topics; reduction of instrument size (section 3.2), remote detection and analysis (section 3.3), analysis in liquid matrix (section 3.4), isotope analysis technique (section 3.5), new isotope analysis technique (LAMIS, laser ablation molecular isotopic spectroscopy) in pt. 3.6.

Figure 4. Schematic diagram of LIBS system (Source: Applied Photonics Ltd.).

Reduction of Instrument Size

The portable LIBS system, currently only available to the IAEA, analyzed 74 yellow cake samples from different origins and 7 non-radioactive signatures in the world. As shown in Figure 10 [49], the system was able to identify all non-radioactive signatures and origins of yellow cake type such as UO2, UO4, U3O8 and Na2U2O7. LIBS test sample of yellow cake normalized probability of class membership against three reference characterizations for each location with 9 origins [ 49 ].

Figure 6. The portable LIBS surface analyzer [5].

Remote Detection and Analysis

LIBS spectra of surrogates on Al substrate confirm that there is at least one useful spectral line from each surrogate (Figure 16). For example, SrO radical emission spectra were shown in the wavelength range of 590-690 nm, rather than AlO radical emission spectra. For example, LODs of glass were lower than those of mortar and clay because they ablated in smaller amounts.

Figure 12. Examples of LIBS detection system designs developed by Applied Photonics Ltd

Analysis in Liquid Matrix

They identified that the normalized intensity can be appropriately applied to the calibration process, improving accurate correlations.

Figure 18 shows calibration curve of varying amount of Fe 2 O 3 and Na 2 CO 3 after selecting characteristic wavelengths

Isotopes Analysis

They identified that Stark broadening of the Hα spectral line would likely limit the application of the Lorentzian deconvolution method to molal concentration ratios of 1H:2H in the range 0.5 – 1. Because Stark broadening and Doppler broadening effects become larger in air, they used the PLS (partial least squares) regression method rather than baseline resolution. In the case of H, a 240 mJ pulse energy beam was used because the mixtures of D2O and H2O are liquid phase.

They calculated isotopic compositions of 1H / 2H, 6Li / 7Li and 235U / 238U in air using laser of 14 mJ pulse energy coupled to high-resolution spectrometer. a) Person-portable LIBS backpack instrument.

Figure 20 LIBS spectrum of plutonium metal sample with isotope ratio 93/6 [24].

New Isotopes Analysis Technique: LAMIS

SrCO3 and Sr halides (SrF2, SrCl2 and SrBr2) were selected as samples to check whether different diatomic radical spectra could be useful for LAMIS or not. After measuring the SrO spectra of SrCO3 radicals with different delays from 0.26 µs to 30 µs, it was found that the radical spectrum. Emission spectra from ablation of a SrCO3 sample at different delay times on a semi-logarithmic scale [30].

Such SrO radical is likely to come from the intact molecule directly, or the combination with O after the evaporation of the Sr element [30]. The isotopic composition of each sample can be found by quantitative calibration of the measured radical spectrum of the samples. Experimental emission spectra of the (2,0) band of the A→X system of SrO measured from enriched samples 88SrCO3, 87SrCO3 and 86SrCO3 [30].

After calibration of spectra of reference samples, unknown samples were analyzed by the PLS regression method. Isotopic composition of natural SrCO3, predicted empirically, was in good agreement with the real composition. Spectra of diatomic molecules obtained from ablation of SrCO3, SrF2, SrCl2, SrBr2 and SrI2 samples [30].

The literature review in Section 3 suggests that LIBS can be handheld, identify more than 1000 samples in real time in less than 1 minute, analyze samples from very long distances up to 200 m, analyze samples in water up to 30 m deep, identify isotopic composition of all elements under normal air conditions using conventional LIBS or LAMIS techniques.

Table 8. Molecular isotope shifts calculated using molecular constants [29].

Material Selection: Theft Scenarios of Radioactive Materials

Pathway Analysis until Disposal
Historical Cases: Theft Attempts and Incidents
Evaluation of Theft Possibility from Nuclear Facilities and Devices

Reprocessing and Interim Storage Facility
Dismantling and Production Facility
Industrial Devices

Material Selection

The isotope 90Sr is generated and recovered from nuclear reactors in the form of spent nuclear fuel [60]. To reduce the temperature of the waste tanks in Hanford site, in the early 1970s, extracted Sr was solidified in the form of SrF2 and double-encapsulated in WESF (waste encapsulation and storage facility), as shown in Figure 28 [61]. This means that Sr can be in the form of high concentration Sr borosilicate.

In 2003, an intact RTG core was found at a depth of about 1 meter, near the coast in the Gulf of Finland. Therefore, in section 4.3 we evaluate whether sufficient physical protection has been achieved and what the risk of theft would be during the investigated route of radioactive materials in section 4.2, from production, storage and disposal of the materials. In particular, we divided the scenarios into three parts: a reprocessing and intermediate storage facility in section 4.3.1, a dismantling and production facility in section 4.3.2, and industrial equipment in section 4.3.3.

Because some countries (eg South Korea) have considered pyroprocessing as future reprocessing technology, it would be valuable to check whether the theft of radioactive material is easy or not in the facility depending on various categorization methods. Physical barriers Not considered Indirectly not consideredc Considered considered considered not considered Chemical barriers not considered not considered. is not considered. In the general case, the theft probability for this scenario will be similar to Section 4.3.2, because RTGs are classified as Security Group A.

After reprocessing the spent fuel, Sr is extracted and encapsulated or produced in RTG in the form of SrTiO3 and SrF2 usually.

Experiment: Post-Detonation of RDDs

Experimental Methods

Samples Preparation
Analytical Tools

ICP-OES was selected to quantify the elemental composition of Sr, where the technique uses the same atomic emission spectra as LIBS. SEM/EDX was selected to identify morphology and elemental compositions of samples before and after laser shot. Raman spectroscopy was chosen to identify molecular spectra which can provide evidence to identify anions.

Specifically, a 532 nm Nd:YAG laser was used, and its continuous energy and accumulation time were set to 9 mW and 5 s, respectively. LIBS, ICP-OES, SEM/EDX and Raman spectroscopy were all used for analysis and the results for each technique were compared. In addition to the substrates, characteristic wavelengths of Y and Zr were also considered as effects of impurities arising from the decay of 90Sr, because they can influence the characteristic wavelengths of other elements.

The relative abundances of 90Y and 90Zr were calculated using the ORIGEN-ARP code [85] and the spectra were analyzed using the NIST atomic spectra database [86]. Materials on different substrates were distinguished using the same method proposed in the previous experiment. We checked whether the method really works in the case of simulated samples that do not interfere with the signal of the material.

RSD (relative standard deviation) was calculated for each blank (background) substrate, and SNRs (signal-to-noise ratios) of simulated samples and background substrates were calculated to evaluate LODs.

Results and Discussion

Experiment 1: Reference Samples Analysis
Experiment 2: Simulated Samples Analysis
Suggestion of On-Site Analysis Algorithm for Nuclear Forensics

In Figure 43, the spectrum of the blank Al substrate, a high intensity was observed due to the low ionization energy (5.99 eV). In the case of the blank mortar base, we observed that the spectrum (Figure 45) has a similar shape to the mortar spectrum of Gaon et al. The LIBS signal was very low for the bare soil substrate in Figure 47 because Si is the main element of soil.

We have calculated the Ti:Sr ratio of the highest intensity near the target wavelengths, using the Gaussian deconvolution method as in Figure 50. SrF2 can be differentiated from the SrF radical band (577-588 nm), as shown in Figure 51. The area of was chosen as the target wavelength range to be determined. Because Na impurity spectral lines exist, the region at 577–585 nm was again selected for integration as in Figure 52 .

In the case of Al and Mortar (Figures 56 and 57), no peaks are observed due to fluorescence. We can find that simulated samples are well distinguished from each other by signature, as in Figure 59, including Ti peak and SrF band. Calculated SNRs and LODs (±95% confidence interval) for simulated samples at target wavelengths of 460.7 nm and 707.0 nm.

It could be a more realistic assumption for the fabrication of RDDs, considering the 1994 Munich Pu mixture case as in Figure 68 [90]. It is noteworthy that LIBS and Raman information can be obtained simultaneously with one pulse of laser shot, as shown in Figure 69, by using different delay times of CCDs [51]. Based on the problems, we proposed an analysis algorithm for real-time nuclear exploration, as in Figure 70.

Figure 38. SEM/EDX result of blank mortar substrate.

Conclusion

Cremers, "A brief history of laser-induced breakdown spectroscopy: from the concept of atoms to LIBS Spectrochimica Acta Part B: Atomic Spectroscopy, vol. Foster, "Detection of metals in the environment using a portable laser-induced breakdown spectroscopy instrument," Applied Spectroscopy, vol. Ferris, "Characterization of laser-induced breakdown spectroscopy (LIBS) for space exploration applications,” Applied Spectroscopy , vol.

Wright, “Remote material analysis of nuclear power station steam generator tubes by laser-induced breakdown spectroscopy,” Spectrochimica Acta Part B: Atomic Spectroscopy, vol. Kasparian, et al., "Far-range laser-induced decay spectroscopy using filamentation in air," Applied Physics Letters, vol. 34;Filament-induced remote surface ablation for laser-induced long-range decay spectroscopy operation,” Spectrochimica Acta Part B: Atomic Spectroscopy, vol.

Laserna, "Evaluating the Potential of Laser Degradation Spectroscopic Analysis for Addressing Remote Radiological Threats". Rose, et al., "Test of a stand-off laser-induced breakdown spectroscopy sensor for detection of explosive residues on solid surfaces," Journal of Analytical Atomic Spectrometry, vol. Singh, "Laser-Induced Breakdown Spectroscopy: Application to Nuclear Waste Management", presented at WM2009 Conference, Phoenix, AZ 2009.

34; Determination of the deuterium/hydrogen ratio in gas reaction products by laser-induced breakdown spectroscopy", Spectrochimica Acta Part B: Atomic Spectroscopy, vol.