# Improving a PGNAA Technique to Detect Heavy Metals in Solid Samples
## 1 Introduction  
Several analytical methods have been developed to determine the presence of hazardous metals and their concentration levels in environmental samples, including prompt gamma-ray neutron activation analysis (PGNAA). The PGNAA technique's key advantage was its capacity to accommodate relatively large bulk samples without incurring fees for chemical preparation, losing volatile components, or changing the materials' original phase. It has been used to determine the chemical composition of materials based on their neutron interaction probability. Only elements with large neutron cross-sections release visible gamma rays, which can happen through thermal neutron capture (TNC) or neutron inelastic scattering (NIS). PGNAA approaches are now being developed to increase heavy metal detection performance in a variety of sectors [1], including anthropology [2], health sciences [3], mining industries [4], homeland security [5], and even landmine detection [6]. The rapid rise of modern lives and technology necessitates a high level of heavy metal consumption. Exposure to these metals in the soil, whether direct or indirect, can result in unintended discharging or deposition of pollutants [7], which can happen by volatilization, leaching, erosion, or suspension of soil particles [8]. As a result, pollutant exchange between soil, water, and air will spread pollution from agricultural soil to the food chain. The effects on mankind of eating food cultivated in contaminated soil are a topic of concern [9; 10; 11; 12; 13; 14]. Although PGNAA is commonly used to identify and quantify chemical elements in aqueous samples or solid matrices such as soil and rocks [15; 16; 17; 18], it suffers from a signal-to-background ratio problem, which affects its ability to recognize the components present in minute concentrations in a sample. This is usually the case when the neutron flux ismodest or diffuse. Recent research revealed that identifying the silicon and phosphorus gamma-ray lines following the NIS reaction was difficult because their peaks were formed on wide continuum slopes [19]. Another issue arises from the activation of the detector's components, which add the dominant detector's peaks to the spectrum, sweeping the peaks from the sample under activation. Two recent studies [20,21] employing the portable neutron generator Genie 16 reported strong detector peaks following 2.5 MeV neutron irradiation of soil samples. Both investigations used two separate reaction processes to measure sulfur contents in the soil. For energies below 1.3 MeV, the first study used the NIS technique, and the acquired spectra using the CeBr\({}_{3}\) detector display multiple strong gamma-ray peaks from cerium (Ce) and bromine (Br) components [20]. Figure 1 depicts several of these peaks as well. Using a bismuth germanate (BGO) detector, the TNC reaction was used in the other investigation to observe the sulfur peak at 5.42 MeV. Similarly, the recorded spectrum revealed two strong BGO peaks in the 6-8 MeV energy range [21]. The current research proposed a new optimization for the PGNAA setup located at King Fahd University of Petroleum and Minerals (KFUPM). The optimization aimed to improve the signal-to-noise ratio by adjusting the setup to directly impact both the signal and background simultaneously. This achievement would allow us to observe the prompt gamma rays from specific elements upon neutron activation, assuming that the gamma-ray peaks overlap with the detector's peaks. As a result, we sought to improve the setup's measurement performance. Three groups of contaminated soil samples were created to demonstrate the quality of the new setup's adjustment. Each group represents a different element that has been blended with the soil in various amounts.