Assessing Radiological Risks of Natural Radionuclides on Sustainable Campus Environment

Abstract

Soil samples were collected from a college campus in Taiwan to measure the levels of radionuclides, contributing to the sustainable management of campus environments. A high-resolution HPGe gamma spectrometry system was utilized to measure the activity concentrations of natural radionuclides (²²⁶Ra, ²³²Th, and ⁴⁰K) and artificial radionuclide (¹³⁷Cs). The activity concentrations of ¹³⁷Cs were not detected in the campus soils, suggesting that artificial radionuclides did not contaminate the soil, supporting sustainable soil quality. However, the average concentrations of ²³²Th and ⁴⁰K with mean values of 53.4 ± 5.1 and 504.5 ± 75.4 Bq/kg dw were higher than the global soil average of 45 and 420 Bq/kg dw, respectively. Meanwhile, the average concentration of ²²⁶Ra with a mean value of 30.1 ± 3.0 Bq/kg dw was similar to the global soil average of 32 Bq/kg. The average outdoor absorbed gamma dose rate (D_ex) and annual effective doses (AED_ex), with a mean of 67.2 nGy/h and 82.4 μSv/y, were found to be higher than the average world levels of 57 nGy/h and 70 μSv/y, respectively. Despite these findings, the radium equivalent activity Ra_eq and external hazard index H_ex, with average values of 145.2 Bq/kg and 0.39, respectively, were below the recommended limit values of 370 Bq/kg and 1.0, respectively. This study provides useful information on the background radioactivity of the study campus, which is crucial for developing sustainable strategies to ensure a safe and healthy environment, indicating that there are no radiological hazards in the soil.

1. Introduction

Researchers worldwide are interested in measuring the levels of natural radioactivity in soil [1,2,3,4]. Soil, as a crucial natural resource, consists of the top layer of the Earth’s crust, containing mineral particles, organic matter, water, air, and living organisms [2,5,6,7]. Primordial radionuclides are embedded in the soil through the processes of erosion and deposition. These radionuclides, including ²³⁸U, ²³²Th, and their decay series, as well as the radioactive ⁴⁰K, are present in various geological materials such as rocks, granites, and sand [2,5,8,9]. Additionally, artificial radionuclides may be present due to nuclear accidents and weapons testing [10,11,12,13]. The concentration of these radioactive elements in the soil depends on the type of rock in the region [14]. Igneous rocks such as granite tend to have higher radiation levels, while sedimentary rocks exhibit lower levels [1,2,9,15,16]. Additionally, the physical and chemical characteristics of soils significantly impact the concentration, distribution, and behavior of these radionuclides [2,3,5,6,17,18]. These naturally occurring radioactive elements continue to emit radiation as their half-lives are comparable to the age of the Earth [3,19,20]. Living organisms are constantly exposed to ionizing radiation from Naturally Occurring Radioactive Materials (NORMs) in the Earth’s crust, contributing to terrestrial background radiation [4,11,21]. This type of radiation is an inevitable part of life on Earth [5,20]. Natural radiation sources account for a significant portion of the population’s exposure to ionizing radiation, with terrestrial sources being the major contributor [15,22].

Understanding the levels and distribution of radionuclides is essential for assessing radiation exposure from terrestrial sources [16,23]. Natural radioactivity levels and associated gamma radiation exposure depend on a region’s geological and geographical conditions [23,24]. This results in different levels of radionuclides in the soil of each region in the world [6,17,25].

Certain radionuclides pose health risks through gamma ray exposure and lung tissue irradiation upon inhalation [3,26,27]. Therefore, it is crucial to evaluate the amount of gamma radiation dose from natural sources. This is because natural radiation is the primary contributor to the external dose of the world population [28]. It is important to continuously measure natural radioactivity due to gamma rays to monitor any changes in radioactivity levels resulting from geological processes and artificial influences [17,18]. Doing so helps identify precautionary measures that must be taken when the dose exceeds the recommended limits.

Numerous research studies have been conducted on soil radiation, including studies on urban soils [7,14,20,24,29,30,31], agricultural lands [10,17,32,33], and residential areas [30,34]. However, there have only been a few studies on campus soils, which were limited to a few samples [13,35,36]. Assessing natural radioactivity in school environments is crucial to implement safety measures and protect students, staff, and faculty when radiation levels exceed the recommended limits.

This study utilizes gamma ray spectrometry to measure the primordial radionuclide levels in soil samples from the National Pingtung University of Science and Technology campus in Taiwan. Understanding these levels is essential for the sustainable development of the campus environment as it informs strategies to maintain soil health and safety. This research also assesses the radiological risks associated with the soil samples, specifically the radium equivalent activity (Ra_eq), the external hazard index (H_ex), the outdoor gamma dose rate (D_ex), and the outdoor annual effective dose equivalent (AED_ex) [11,13,37,38]. These assessments are vital for ensuring that the campus remains a safe and healthy environment for all its inhabitants, aligning with the Sustainable Development Goals. Additionally, this study evaluates the frequency distribution and activity ratios of ²³²Th/²²⁶Ra in the soil samples, which further supports the development of informed and sustainable environmental management practices.

2. Materials and Methods

2.1. Geological and Geographical Conditions of the Sampling Area

Figure 1 displays the campus’ geological location, as well as the soil sampling locations. The sampling area is the campus of the National Pingtung University of Science and Technology located on Neipu Township, Pingtung County, southern Taiwan, specifically on Laopi Terrace. Its altitude is approximately 100 m. The campus area is the largest single area of a college in Taiwan, and the area is about 298 hectares. The area has a tropical climate with an average temperature of 25.5 °C and an annual rainfall of around 2600 mm. It belongs to the fourth-generation Pleistocene foothill platform accumulation layer above the modern alluvial layer. This Terrace is situated in the depression of the structure below the Chaozhou fault and has developed into an alluvial fan. The soil composition is predominantly made up of gravel layers with sandy, sandy shale, and siliceous shale mixed in small quantities. The soil profile texture is mainly sandy clay loam and loam, with a reddish-brown color and a strong acid reaction [6,39].

2.2. Sampling and Samples’ Pretreatment

The soil samples were taken from different locations at the campus, as shown in Figure 1. Each soil sample weighing approximately 1.5 kg was first cleared of impurities such as grass, twigs, and small stones before being placed into labeled plastic bags. The soil samples were collected from February to April 2019. A total of 120 soil samples were collected. The collected soil samples were taken back to the laboratory and spread evenly on plastic trays to air dry for at least seven days at room temperature (about 25–30 °C). Following this, the samples were further purified to remove any dried grass and small stones and then sieved through a 0.2 mm sieve to ensure consistency. The dried and sieved samples were placed in air-tight containers with a capacity of about 150 g. They were stored for a month to achieve secular equilibrium between ²³⁸U, ²³²Th, and their progenies. Additionally, the dried soil samples were tested for their pH level, electric conductivity (EC) following the standard method [40], and total organic carbon by following the standard method [40]. The results showed that the average values and standard deviations of the soil properties were 4.99 ± 1.01 for pH, 98.4 ± 61.9 μS/cm for EC, and 21.4 ± 12.6 g/kg for total organic carbon. These soil properties indicated that the soil environment was acidic, had low EC, and low organic carbon levels [6,39].

2.3. Analyses of ²²⁶Ra, ²²⁸Ra, ²³²Th, and ⁴⁰K in the Soil Samples

The experiment involved counting each sample and the background using a high-purity germanium detector (ORTEC, GEM40P4-79-SMP, Oak Ridge, TN, USA). The HPGe detector is known for its high stability, attributed to the exceptional purity of its germanium crystal (99.999% or higher). This purity significantly reduces dark current and noise levels, enhancing the precision of the measurements. This detector was surrounded by a cylindrical lead shield with a 10 cm thickness, 28 cm inner diameter, and 40 cm height. To ensure the accuracy of the measurement results in our study, efficiency calibration was performed using certified standard sources. This calibration process minimizes potential measurement errors and guarantees reliable data. The counting system was connected to a multi-channel analyzer and had a 1.85 keV FWHM energy resolution at the 1.33 MeV ⁶⁰Co photopeak and a 40% relative efficiency.

In order to ensure accurate and reliable measurements, the detector underwent a rigorous calibration process. Specifically, a series of standard gamma sources (Eckert & Ziegler, Berlin, Germany) were utilized, including ¹⁰⁹Cd, ⁵⁷Co, ²⁰³Hg, ⁵¹Cr, ¹¹³Sn, ⁸⁵Sr, ¹³⁷Cs, ⁶⁰Co, and ⁸⁸Y, for energy calibration. Efficiency calibration was conducted over the energy range of 88–2000 keV using these sources. The calibration sources are traceable to the National Institute of Standards and Technology (NIST) through Eckert & Ziegler’s participation in the NIST measurement assurance program. This program establishes and maintains traceability for various nuclides based on blind assays and subsequent NIST certification. This rigorous calibration ensures the detector’s capability to accurately measure radiation across a broad energy spectrum.

The samples were counted for 30,000 s, and a background count was conducted using an empty container under the same conditions. The Gamma Vision software (Gamma Vision-32 V6) was used to analyze the spectrum, focusing on the photopeaks at 609.3, 1120.3, and 1764.5 keV for ²²⁶Ra, 911.07, 968.90, and 338.40 keV for ²²⁸Ra, 583.0 keV for ²³²Th, and 1460.8 keV for ⁴⁰K. The 661.66 keV emission line was also used to determine the ¹³⁷Cs concentration. The MDA were 10.2 ± 1.8, 2.7 ± 0.7, 3.8 ± 0.8, 3.7 ± 0.8, and 1.3 ± 0.2 Bq/kg for ⁴⁰K, ²²⁶Ra, ²³²Th, ²²⁸Ra, and ¹³⁷Cs, respectively.

2.4. Radiological Risk Calculation

This study examined the potential radiological risks in the soil samples by analyzing the activity concentrations of three radioactive isotopes: ⁴⁰K, ²²⁶Ra, and ²³²Th. The researchers measured four radiological hazard indices, including radium equivalent activity (Ra_eq), external hazard index (H_ex), external absorbed dose rate in the air (D_ex), and external annual effective dose equivalents (AED_ex) [11,13,37,38]. Equations (1)–(4) were used to calculate the four indices, respectively.

$${\mathrm{R}\mathrm{a}}_{\mathrm{e}\mathrm{q}}\left({\displaystyle \frac{\mathrm{B}\mathrm{q}}{\mathrm{k}\mathrm{g}}}\right)=0.077{\mathrm{A}}_{\mathrm{k}}+{\mathrm{A}}_{\mathrm{R}\mathrm{a}}+1.43{\mathrm{A}}_{\mathrm{T}\mathrm{h}}$$

(1)

$${\mathrm{H}}_{\mathrm{e}\mathrm{x}}={\displaystyle \frac{{\mathrm{A}}_{\mathrm{k}}}{4810}}+{\displaystyle \frac{{\mathrm{A}}_{\mathrm{R}\mathrm{a}}}{370}}+{\displaystyle \frac{{\mathrm{A}}_{\mathrm{T}\mathrm{h}}}{259}}$$

(2)

$${\mathrm{D}}_{\mathrm{e}\mathrm{x}}\left({\displaystyle \frac{\mathrm{n}\mathrm{G}\mathrm{y}}{\mathrm{y}}}\right)=0.0417{\mathrm{A}}_{\mathrm{k}}+0.462{\mathrm{A}}_{\mathrm{R}\mathrm{a}}+0.604{\mathrm{A}}_{\mathrm{T}\mathrm{h}}$$

(3)

$${\mathrm{A}\mathrm{E}\mathrm{D}}_{\mathrm{e}\mathrm{x}}\left({\displaystyle \frac{\mathrm{n}\mathrm{S}\mathrm{v}}{\mathrm{y}}}\right)={\mathrm{D}}_{\mathrm{e}\mathrm{x}}\left({\displaystyle \frac{\mathrm{n}\mathrm{G}\mathrm{y}}{\mathrm{y}}}\right)\times 8760\left({\displaystyle \frac{\mathrm{h}}{\mathrm{y}}}\right)\times 0.2\times 0.7\left({\displaystyle \frac{\mathrm{S}\mathrm{v}}{\mathrm{G}\mathrm{y}}}\right)\times {10}^{-3}$$

(4)

where A_K, A_Ra, and A_Th are the activity concentrations (Bq/kg) of ⁴⁰K, ²²⁶Ra, and ²³²Th, respectively, measured in the samples.

2.5. Statistics

Data analysis was conducted using two software programs: statistical software S-plus (V6.2) and Microsoft Excel. The significance level was set at 0.05. The descriptive statistics were generated in Excel, while the activity ratio of ²³²Th/²²⁶Ra was calculated using the same software. For the graphical representation of the data, the plot, linear regression, and normality were measured by the Kolmogorov–Smirnov (K-S) [41,42] test in S-plus.

3. Results

3.1. Activity Concentration and Correlation of Nuclides

The activity concentrations of ²²⁶Ra, ²²⁸Ra, ²³²Th, and ⁴⁰K in the soil samples were measured and are listed in

Table 1. The soil samples’ GPS coordinates and activity concentrations of ⁴⁰K, ²³²Th, ²²⁶Ra, and ²²⁸Ra (Bq/kg dw) along with their associated uncertainties (1 σ).

Sample No	40K	232Th	226Ra	228Ra
	Bq/kg
1	557.2 ± 2.6	55.3 ± 3.6	32.2 ± 5.5	63.4 ± 3.7
2	454.6 ± 2.8	58.6 ± 4.0	30.6 ± 6.4	60.1 ± 3.9
3	488.5 ± 2.6	48.9 ± 3.8	26.1 ± 5.4	51.2 ± 3.3
4	492.7 ± 2.8	55.6 ± 4.2	30.9 ± 5.7	57.2 ± 3.4
5	518.3 ± 2.6	56.5 ± 3.9	29.6 ± 5.3	58.4 ± 2.9
6	509.6 ± 2.9	55.3 ± 4.1	30.2 ± 5.9	59.2 ± 3.5
7	494.7 ± 2.6	55.7 ± 3.5	30.9 ± 5.3	61.6 ± 3.0
8	579.9 ± 2.7	56.8 ± 4.6	32.0 ± 5.5	60.0 ± 4.1
9	520.4 ± 3.0	58.0 ± 3.9	33.8 ± 6.3	61.3 ± 4.5
10	531.3 ± 2.5	39.1 ± 3.8	24.6 ± 5.0	44.1 ± 3.4
11	453.0 ± 2.8	53.6 ± 3.7	32.6 ± 5.5	54.8 ± 3.9
12	534.8 ± 2.7	49.7 ± 3.8	28.3 ± 5.7	54.5 ± 3.7
13	594.8 ± 2.7	60.3 ± 3.9	33.7 ± 5.9	63.6 ± 4.0
14	532.1 ± 2.5	40.5 ± 4.2	21.8 ± 6.5	44.7 ± 3.7
15	532.6 ± 2.5	53.9 ± 3.5	30.0 ± 5.2	60.7 ± 3.0
16	471.4 ± 2.9	51.2 ± 4.1	29.8 ± 5.6	51.0 ± 3.7
17	604.7 ± 2.5	43.0 ± 4.4	23.0 ± 6.7	42.5 ± 4.2
18	393.6 ± 3.5	52.3 ± 4.6	34.6 ± 6.0	57.8 ± 4.5
19	570.5 ± 2.8	57.0 ± 3.6	31.1 ± 6.5	65.9 ± 4.1
20	493.3 ± 2.9	54.5 ± 4.3	30.5 ± 6.5	56.0 ± 4.7
21	595.9 ± 2.4	55.5 ± 3.3	30.9 ± 5.2	57.5 ± 3.8
22	614.8 ± 2.4	58.6 ± 3.5	33.4 ± 5.4	60.6 ± 3.8
23	507.4 ± 2.9	48.8 ± 4.4	28.7 ± 5.7	55.9 ± 3.8
24	447.0 ± 3.0	53.7 ± 4.1	35.0 ± 5.5	60.4 ± 4.2
25	585.9 ± 2.4	56.3 ± 3.5	32.4 ± 5.2	63.1 ± 3.5
26	663.1 ± 2.5	60.5 ± 4.1	35.1 ± 6.2	62.0 ± 4.9
27	467.3 ± 2.6	42.8 ± 4.0	24.6 ± 5.8	44.5 ± 3.4
28	578.7 ± 2.7	58.6 ± 4.5	30.8 ± 5.9	58.2 ± 3.5
29	531.2 ± 2.7	49.7 ± 4.0	31.9 ± 6.5	55.4 ± 4.4
30	488.8 ± 2.6	53.9 ± 3.5	28.8 ± 5.3	56.9 ± 3.2
31	396.1 ± 2.9	46.0 ± 4.0	26.6 ± 5.5	51.4 ± 3.3
32	534.9 ± 2.8	57.0 ± 3.9	29.7 ± 5.7	54.8 ± 3.6
33	570.3 ± 2.5	41.2 ± 3.9	21.1 ± 6.8	41.8 ± 3.9
34	553.8 ± 2.8	60.4 ± 4.0	32.4 ± 5.6	61.9 ± 3.1
35	489.0 ± 2.6	41.9 ± 4.3	24.0 ± 5.6	45.7 ± 3.6
36	474.7 ± 3.0	55.7 ± 3.8	29.3 ± 5.7	56.6 ± 3.5
37	528.7 ± 3.0	54.0 ± 4.4	31.0 ± 5.7	58.3 ± 4.9
38	508.2 ± 2.6	41.5 ± 4.2	26.2 ± 5.5	42.0 ± 3.8
39	457.7 ± 2.7	41.2 ± 4.3	24.2 ± 5.5	41.2 ± 4.2
40	457.1 ± 3.3	52.5 ± 4.4	28.1 ± 6.5	54.7 ± 4.7
41	474.5 ± 2.8	53.4 ± 3.5	27.2 ± 5.3	52.0 ± 3.9
42	499.4 ± 2.7	55.9 ± 3.6	30.5 ± 5.7	58.3 ± 3.3
43	498.2 ± 2.7	55.4 ± 3.7	30.8 ± 5.5	55.7 ± 3.9
44	497.4 ± 2.9	58.8 ± 4.5	32.8 ± 5.7	57.0 ± 4.3
45	447.5 ± 3.2	58.1 ± 3.9	36.4 ± 6.0	58.8 ± 3.7
46	457.1 ± 2.6	52.4 ± 3.7	29.6 ± 5.5	55.4 ± 2.9
47	610.9 ± 2.6	58.9 ± 3.6	29.2 ± 5.7	59.7 ± 3.3
48	418.7 ± 3.3	48.6 ± 4.8	30.0 ± 6.3	49.7 ± 5.6
49	420.3 ± 3.2	51.2 ± 4.0	31.0 ± 5.9	53.3 ± 3.9
50	514.1 ± 2.6	46.7 ± 4.1	24.7 ± 5.6	49.9 ± 3.6
51	474.6 ± 2.9	54.3 ± 4.3	32.5 ± 6.1	59.7 ± 4.5
52	474.6 ± 3.2	54.8 ± 4.4	30.7 ± 5.6	57.4 ± 3.7
53	443.6 ± 2.9	52.4 ± 3.8	31.3 ± 5.4	55.0 ± 3.3
54	539.4 ± 2.6	53.5 ± 3.9	33.8 ± 5.1	58.4 ± 3.4
55	537.3 ± 3.0	52.9 ± 4.3	31.0 ± 5.8	51.3 ± 4.0
56	434.8 ± 2.9	57.1 ± 3.8	33.7 ± 5.3	58.9 ± 3.2
57	538.2 ± 2.8	50.9 ± 4.3	32.5 ± 6.0	55.8 ± 3.6
58	378.4 ± 3.2	45.5 ± 4.4	30.0 ± 5.9	48.7 ± 3.7
59	950.9 ± 2.2	66.1 ± 3.9	31.5 ± 6.1	61.3 ± 3.4
60	593.7 ± 2.6	55.9 ± 3.2	33.5 ± 5.6	63.4 ± 3.7
61	446.1 ± 3.0	54.8 ± 4.5	28.7 ± 6.7	51.4 ± 4.1
62	495.1 ± 2.8	51.7 ± 3.9	31.1 ± 5.4	56.3 ± 4.2
63	511.3 ± 2.5	55.3 ± 3.7	28.2 ± 5.5	57.0 ± 3.1
64	491.3 ± 2.7	54.9 ± 4.0	32.0 ± 5.5	59.4 ± 3.2
65	589.3 ± 2.7	58.3 ± 3.8	30.4 ± 5.7	58.3 ± 3.6
66	465.7 ± 2.9	52.8 ± 4.2	29.3 ± 5.7	56.6 ± 3.3
67	567.5 ± 2.9	52.0 ± 4.5	35.6 ± 5.4	51.0 ± 4.1
68	569.5 ± 2.5	58.8 ± 3.5	31.4 ± 5.6	58.0 ± 3.8
69	375.9 ± 3.4	57.5 ± 4.1	32.5 ± 5.6	57.7 ± 4.9
70	432.2 ± 3.2	51.5 ± 4.3	29.5 ± 6.2	50.2 ± 3.7
71	576.3 ± 2.7	59.9 ± 4.0	34.6 ± 5.5	61.9 ± 4.3
72	487.4 ± 3.2	61.7 ± 4.3	32.5 ± 6.0	59.9 ± 3.7
73	527.8 ± 3.0	50.1 ± 4.3	28.4 ± 6.4	50.7 ± 3.7
74	551.0 ± 2.6	57.2 ± 3.8	30.9 ± 5.7	62.7 ± 3.3
75	506.4 ± 2.9	52.1 ± 4.4	30.3 ± 5.5	58.3 ± 4.5
76	425.3 ± 3.0	55.0 ± 4.1	34.7 ± 5.3	57.9 ± 3.3
77	460.7 ± 3.0	47.4 ± 4.2	26.7 ± 6.4	48.3 ± 4.0
78	381.6 ± 3.2	55.1 ± 4.3	38.2 ± 5.6	57.2 ± 3.5
79	496.8 ± 2.7	51.5 ± 4.1	26.3 ± 5.7	50.7 ± 3.6
80	514.4 ± 2.6	54.3 ± 4.0	31.0 ± 5.4	56.8 ± 3.2
81	418.2 ± 3.0	48.4 ± 3.9	28.2 ± 5.6	52.7 ± 3.2
82	463.5 ± 3.0	51.4 ± 4.0	26.6 ± 5.8	51.6 ± 3.5
83	359.2 ± 3.4	46.8 ± 4.6	29.6 ± 6.3	49.2 ± 3.9
84	449.6 ± 3.0	52.7 ± 4.4	27.5 ± 6.1	52.3 ± 3.6
85	478.1 ± 2.7	50.5 ± 3.7	29.6 ± 5.2	55.1 ± 3.7
86	505.6 ± 3.1	57.0 ± 5.0	31.1 ± 6.1	56.3 ± 4.9
87	479.4 ± 2.8	49.9 ± 3.7	30.6 ± 5.4	56.1 ± 3.4
88	428.0 ± 3.2	53.5 ± 4.0	27.9 ± 6.1	55.5 ± 4.1
89	621.3 ± 2.4	54.4 ± 3.8	31.6 ± 5.0	62.2 ± 3.0
90	481.5 ± 3.0	61.3 ± 3.9	36.9 ± 5.4	63.0 ± 3.2
91	496.6 ± 2.9	56.3 ± 3.7	29.9 ± 6.6	60.5 ± 4.6
92	531.9 ± 3.0	57.0 ± 5.3	30.5 ± 6.1	60.5 ± 4.5
93	490.6 ± 2.8	56.4 ± 3.8	30.7 ± 5.5	57.5 ± 3.4
94	419.8 ± 3.3	55.9 ± 3.7	30.3 ± 5.9	58.3 ± 3.5
95	513.5 ± 2.7	56.7 ± 3.8	31.6 ± 6.0	60.4 ± 3.3
96	540.6 ± 2.7	59.0 ± 3.6	31.0 ± 5.4	61.1 ± 3.4
97	312.6 ± 3.3	44.9 ± 4.2	28.7 ± 5.4	47.6 ± 3.6
98	520.4 ± 3.0	62.7 ± 4.1	30.3 ± 5.8	65.4 ± 3.5
99	517.7 ± 2.7	54.2 ± 4.0	29.5 ± 5.6	60.7 ± 3.1
100	527.9 ± 2.7	54.0 ± 4.0	28.9 ± 5.9	58.1 ± 3.3
101	479.6 ± 3.2	56.5 ± 4.3	29.9 ± 5.8	59.1 ± 3.7
102	557.3 ± 2.9	57.4 ± 4.0	29.4 ± 5.8	61.8 ± 4.3
103	522.3 ± 3.1	54.3 ± 5.2	28.1 ± 7.0	56.7 ± 5.3
104	569.5 ± 2.9	54.7 ± 4.3	29.6 ± 6.5	55.1 ± 4.1
105	544.5 ± 2.6	44.8 ± 4.0	26.1 ± 5.9	49.3 ± 3.7
106	723.8 ± 2.1	44.4 ± 3.7	26.6 ± 5.3	49.7 ± 3.9
107	417.6 ± 3.5	57.6 ± 4.7	33.1 ± 6.6	59.3 ± 3.7
108	485.9 ± 2.9	55.4 ± 4.3	29.8 ± 5.8	54.7 ± 3.5
109	482.4 ± 3.0	54.9 ± 4.1	32.9 ± 6.5	57.0 ± 5.3
110	463.6 ± 2.8	49.3 ± 3.8	26.4 ± 5.8	51.0 ± 3.5
111	422.0 ± 3.4	56.7 ± 4.4	31.9 ± 6.1	60.1 ± 3.8
112	565.0 ± 2.6	56.3 ± 3.6	27.8 ± 5.8	55.7 ± 3.4
113	514.2 ± 2.5	53.3 ± 3.6	27.6 ± 5.3	53.9 ± 3.2
114	457.8 ± 2.9	53.4 ± 4.4	26.8 ± 6.3	56.3 ± 4.1
115	432.4 ± 3.0	55.4 ± 3.7	31.2 ± 5.9	62.0 ± 3.9
116	485.4 ± 2.9	48.2 ± 4.4	27.6 ± 6.6	53.8 ± 4.5
117	475.3 ± 2.6	51.7 ± 3.6	27.8 ± 5.5	53.3 ± 3.2
118	497.2 ± 2.8	47.5 ± 4.9	28.0 ± 5.9	48.5 ± 4.6
119	504.4 ± 3.0	56.6 ± 4.2	30.4 ± 6.7	56.2 ± 4.8
120	432.1 ± 3.1	53.6 ± 3.8	31.8 ± 5.4	60.0 ± 3.3

with their associated uncertainties (1 σ). The activity concentrations of ²²⁶Ra, ²²⁸Ra, ²³²Th, and ⁴⁰K in the soil samples varied between 21.1 and 38.2, 41.2 and 65.9, 39.1 and 66.1, and 312.6 and 950.9 Bq/kg dw (dry weight), respectively. The average and standard deviation of the activity concentrations were 30.1 ± 3.0, 55.9 ± 5.3, 53.4 ± 5.1, and 504.5 ± 75.4 Bq/kg dw, respectively. The relative uncertainties of the measurements showed good analytical precision, with average relative standard deviations of 2.83% for ⁴⁰K, 4.04% for ²³²Th, 5.79% for ²²⁶Ra, and 3.78% for ²²⁸Ra. The observed variation in uncertainties primarily reflects counting statistics and sample matrix effects. The relatively lower uncertainties for ⁴⁰K measurements 2.83% indicate the particularly robust analytical quality for this radionuclide.

It is worth noting that ²²⁸Ra is the decay progeny of the thorium series. The activity concentrations of ²²⁸Ra and ²³²Th had a significantly positive correlation (r = 0.88, p < 0.001, as shown in Figure 2a), and the activity ratios of ²²⁸Ra/²³²Th ranged from 0.93 to 1.16 with a mean of 1.05 ± 0.05. When the activity ratios of ²³²Th and ²²⁸Ra are close to 1.0, it is identified that the decay series involving the radioactive element thorium are in a state of secure equilibrium [2,21]. Similarly, other studies have also reported secure equilibrium in the uranium decay series due to the activity ratios of ²³⁸U and ²²⁶Ra being close to 1.0. This finding has been reported in various studies [4,6,18,20,43]. In the present study, radionuclide ²³²Th was represented for the radionuclide thorium.

Linear correlation studies were performed to find the strength and relationships between pairs of nuclide activities in soil samples [1,3,44,45]. The studies were conducted between radionuclides concentrations of ²³²Th/²²⁶Ra, ⁴⁰K/²³²Th, and ⁴⁰K/²²⁶Ra. The results indicate that there is a significantly positive correlation between ²³²Th and ²²⁶Ra (r = 0.70, p < 0.001, as shown in Figure 2a). However, the relationship between the ⁴⁰K activity concentrations with the ²³²Th and ²²⁶Ra concentrations shows a weak linear correlation (r = 0.28, p = 0.002 for ²³²Th; r = 0.003, p = 0.98 for ²²⁶Ra), as shown in Figure 2b.

The relationship of the nuclide concentrations obtained in the present study was similar to that observed by Alazemi et al. [46]. They found a significantly positive correlation between ²³⁸U (²²⁶Ra) and ²³²Th, and between ⁴⁰K and ²³²Th. However, there is a weak correlation between ⁴⁰K and ²³⁸U. It was concluded that these nuclides have similar responses to soil chemical behavior and other environmental processes [1,3,9]. Several studies also reported that ²²⁶Ra and ²³²Th had strong positive correlation coefficients because the uranium and thorium decay series commonly occur together in nature [1,3,6,9,11,25,47]. However, a weak correlation was observed for ⁴⁰K with ²²⁶Ra and ²³²Th because ⁴⁰K origins are in a different decay series [1,17,22,31,48].

3.2. Descript Statistic and Frequency Distribution of Activity Concentration

The descriptive statistic was used to determine the frequency distributions of the radionuclide activity concentrations [11,19,24,44,45,49].

Table 2. Descriptive statistics of activity concentrations of ⁴⁰K, ²²⁶Ra, and ²³²Th in soils.

Parameters	40K	232Th	226Ra	232Th/226Ra
Mean, Bq/kg	504.5	53.4	30.1	1.78
SD a, Bq/kg	75.4	5.1	3.0	0.13
Minimum, Bq/kg	312.6	39.1	21.1	1.44
Maximum, Bq/kg	950.7	66.1	38.2	2.10
Median, Bq/kg	497.3	54.3	30.4	1.78
Kurtosis	9.80	0.57	0.77	−0.13
Skewness	1.78	−0.73	−0.29	−0.21
CV, %	15.0	9.5	10.0	7.3
p-value b	0.27	0.09	0.44	0.68
Global average, Bq/kg	420	45	32	1.41

^a standard deviation; ^b normality test by K-S method.

presents the statistical data and analyses using various measures such as skewness, kurtosis, coefficients of variation (CV), and p-values obtained from a normality test. Additionally, Figure 3a–c illustrate the frequency distribution and frequency cumulated percentage plots of the concentration of radionuclides ⁴⁰K, ²²⁶Ra, and ²³²Th, respectively.

Skewness is a statistical parameter that measures the asymmetry in the probability distribution of activity concentrations [19,44,49]. If skewness is less than 0, the frequency distribution graph is left-biased. If skewness is 0, data are evenly distributed on both sides of the average value. If skewness exceeds 0, the frequency distribution graph is biased to the right [44,49]. In this particular study, the skewness value for ⁴⁰K was found to be 1.78. This value indicates an asymmetrical and right-biased distribution, as shown in Figure 3a. However, the parameters of the ²²⁶Ra and ²³²Th activity concentrations were negative values of −0.29 and −0.73, respectively, and were close to zero. These values suggest a left-biased near-symmetric distribution, as shown in Figure 3b,c.

Kurtosis is a statistical measure that indicates the peak in the probability distribution of activity concentrations [44,49], with higher values indicating a more peaked (leptokurtic) distribution. The measurement of kurtosis for ⁴⁰K was found to be 9.80, which suggests a more peaked distribution than a normal distribution, as shown in Figure 3a. However, the kurtosis values for ²²⁶Ra and ²³²Th were close to zero, indicating a normal (mesokurtic) distribution [19,24,44], as shown in Figure 3b,c.

The coefficient of variation (CV) is a measure used to determine the level of spread of activity concentrations. In the current study, the CV value was about 15.0% for ⁴⁰K concentrations, while for ²²⁶Ra and ²³²Th concentrations, it was less than 10%. This indicates that there was low variation in the concentrations, as most activity concentrations were within a small range. Specifically, the activity concentration of ²²⁶Ra ranged between 26.0 and 34.0 Bq/kg at 86%, while the activity concentration of ²³²Th was between 49.0 and 61.0 Bq/kg at 78%. The activity concentration of ⁴⁰K was between 400 and 600 Bq/kg at 88%.

To check the normality of the activity concentrations, the Kolmogorov–Smirnov (K-S) test was conducted, and the significant values are listed in Table 2. The test results showed that each nuclide concentration was normally distributed on the studied campus (p > 0.05). The results clearly demonstrate that the geological conditions on the campus were consistently homogeneous [45].

3.3. Comparison with Reported Activity Concentrations

Table 3 presents the average activity concentrations of radionuclides and the activity ratios of ²³²Th/²²⁶Ra from this study compared with other studies, including soil type classifications. The surface soil (SS) samples analyzed in our study showed activity concentrations of 505, 53.4, and 30.1 Bq/kg for ⁴⁰K, ²³²Th, and ²²⁶Ra, respectively. These values are comparable to previous studies conducted across Taiwan, where surface soils showed ranges of 407–609 Bq/kg for ⁴⁰K, 31–45 Bq/kg for ²³²Th, and 21.1–31.1 Bq/g for ²²⁶Ra [47,50,51].

The variation in radionuclide concentrations can be attributed to differences in soil types and local geological conditions. For instance, paddy field soils (PFSs) in Taiwan [50,52] showed generally higher ⁴⁰K concentrations (609–670 Bq/kg) compared to our surface soil measurements. This difference might be related to agricultural practices and soil management in paddy fields.

Globally, soil type appears to significantly influence radionuclide distributions. Higher activity concentrations of ²³²Th and ²²⁶Ra were observed in granite soils (GSs) of Guangdong, China [18], and Bangladesh [53] and in alluvial soils (ALSs) of Bangladesh [1]. In contrast, agricultural soils (ASs) from Egypt [33] and urban soils (USs) from Jordan [29] showed lower concentrations. The ²³²Th/²²⁶Ra activity ratios in our study (1.78) were comparable to those found in surface soils across Taiwan [47,51] but higher than those typically found in agricultural and urban soils worldwide.

The presence of ¹³⁷Cs, with an activity concentration of 5.6 Bq/kg in Taiwan’s paddy field soils [50] and 7.1 Bq/kg near NPP IV [36], reflects the historical fallout from nuclear weapons testing and the Chernobyl accident, providing an important temporal marker for soil studies.

Table 3. The means activity concentrations of ⁴⁰K, ²³²Th, ²²⁶Ra, and ¹³⁷Cs and activity ratios of ²³²Th/²²⁶Ra for soil in this study compared to reported activity concentrations and activity ratios from soils in Taiwan and other countries.

Area/Country (Soil Type) **	40K	232Th	226Ra	137Cs	232Th/226Ra	References
Neipu/TW (SS)	505	53.4	30.1	-	1.78	PS *
Whole Island/TW (PFSs)	609	45.0	31.1	5.6	1.45	[50]
Whole Island/TW (SS)	407	33	23	-	1.50	[47]
Whole Island/TW (SS)	539	41	23	-	1.78	[51]
Near NPP IV/TW (SS)	436	26	24	7.1	1.08	[36]
Whole Island/TW (PFSs)	670	-	21.1	6.7		[52]
Pingtung/TW (TFS)	702	55.1	36.3	-	1.52	[54]
Global average	420	45	32		1.41	[28]
Guangdong/China (SS)	536	101.0	75.1	-	1.34	[4]
Shangrao/China (SS)	742	59	63	-	1.30	[7]
Bangladesh (ALSs)	762	64	47	-	1.36	[1]
India (SS)	792	77.4	33.8	-	2.31	[3]
Tamil Nadu/India (HS)	840	48	52	-	0.92	[17]
Guangdong/China (GSs)	680	187	134	-	1.40	[18]
Dhanbad/India (SLSs)	570	44.3	61.7	-	1.40	[55]
Bangladesh (GSs)	947	83.2	65.9	-	1.30	[53]
Pernambuco/Brazil (TSSs)	548	38	20	-	2.1	[2]
Alagoas/Brazil (SS)	630	54 *	28	-	1.93	[21]
Pakistan (Sand)	509	43.2	24.5	-	1.76	[27]
Bulgaria/Turkey (SS)	617	42.4	24.0	-	1.77	[9]
Spain (FSs)	335–562	24–48	19–33	-	1.29–1.48	[6]
HCMC/Vietnam (SS)	279	36.6	21.1	-	1.73	[20]
Tamil Nadu/India (IEDSs)	253	39.9	22.8	-	1.75	[31]
Jeju Island/Korea (VS)	314	35.6	32.4	20.8	1.10	[5]
Chittagong/Bangladesh (RDSs)	321	46	18	-	2.56	[30]
Yerevan/Armenia	424	37.3	45.7	8.0	2.26	[11]
Saudi Arabia (Sand)	380	29.7	23.4	-	0.77	[56]
Qassim/Saudi Arabia (RS)	67–94	6–19	10–19	-	0.86–1.18	[25]
Abu Qurqas/Egypt (ASs)	158	12.2	22.3	-	0.85	[33]
India (SS)	567	51.6	36.9	-	1.40	[22]
Bartin/Turkey (SS)	136	7	8	2	1.14	[57]
Nigeria (TESs)	70.4	17.7	11.9	-	1.53	[8]
Ptolemais/Greece (SS)	496	36	27	-	1.33	[14]
Saudi Arabia (SS)	790	24.3	23.8	-	1.02	[37]
Canary Island/Spain (VS)	384	28.9	25.2	-	1.15	[16]
Amman City/Jordan (USs)	266	35.5	29.0	-	1.22	[29]

* PS: present study. ** Abbreviations for different soil types: (PFSs) paddy field soils, (SS) surface soil, (US) urban soil, (RS) red soil, (VS) volcanic soil, (ASs) agricultural soils, (HS) hill soils, (TESs) tailing-enriched soils, (RDSs) residential soils, (IEDSs) industrial effluent-disposed soils, (TSSs) tropical and semiarid soils, (FSs) Flysch soils, (SLSs) sandy-loam soils, (ALSs) alluvial soils, and (TFSs) tobacco field soils. - undetected or unmentioned.

Table 3. The means activity concentrations of ⁴⁰K, ²³²Th, ²²⁶Ra, and ¹³⁷Cs and activity ratios of ²³²Th/²²⁶Ra for soil in this study compared to reported activity concentrations and activity ratios from soils in Taiwan and other countries.

Area/Country (Soil Type) **	40K	232Th	226Ra	137Cs	232Th/226Ra	References
Neipu/TW (SS)	505	53.4	30.1	-	1.78	PS *
Whole Island/TW (PFSs)	609	45.0	31.1	5.6	1.45	[50]
Whole Island/TW (SS)	407	33	23	-	1.50	[47]
Whole Island/TW (SS)	539	41	23	-	1.78	[51]
Near NPP IV/TW (SS)	436	26	24	7.1	1.08	[36]
Whole Island/TW (PFSs)	670	-	21.1	6.7		[52]
Pingtung/TW (TFS)	702	55.1	36.3	-	1.52	[54]
Global average	420	45	32		1.41	[28]
Guangdong/China (SS)	536	101.0	75.1	-	1.34	[4]
Shangrao/China (SS)	742	59	63	-	1.30	[7]
Bangladesh (ALSs)	762	64	47	-	1.36	[1]
India (SS)	792	77.4	33.8	-	2.31	[3]
Tamil Nadu/India (HS)	840	48	52	-	0.92	[17]
Guangdong/China (GSs)	680	187	134	-	1.40	[18]
Dhanbad/India (SLSs)	570	44.3	61.7	-	1.40	[55]
Bangladesh (GSs)	947	83.2	65.9	-	1.30	[53]
Pernambuco/Brazil (TSSs)	548	38	20	-	2.1	[2]
Alagoas/Brazil (SS)	630	54 *	28	-	1.93	[21]
Pakistan (Sand)	509	43.2	24.5	-	1.76	[27]
Bulgaria/Turkey (SS)	617	42.4	24.0	-	1.77	[9]
Spain (FSs)	335–562	24–48	19–33	-	1.29–1.48	[6]
HCMC/Vietnam (SS)	279	36.6	21.1	-	1.73	[20]
Tamil Nadu/India (IEDSs)	253	39.9	22.8	-	1.75	[31]
Jeju Island/Korea (VS)	314	35.6	32.4	20.8	1.10	[5]
Chittagong/Bangladesh (RDSs)	321	46	18	-	2.56	[30]
Yerevan/Armenia	424	37.3	45.7	8.0	2.26	[11]
Saudi Arabia (Sand)	380	29.7	23.4	-	0.77	[56]
Qassim/Saudi Arabia (RS)	67–94	6–19	10–19	-	0.86–1.18	[25]
Abu Qurqas/Egypt (ASs)	158	12.2	22.3	-	0.85	[33]
India (SS)	567	51.6	36.9	-	1.40	[22]
Bartin/Turkey (SS)	136	7	8	2	1.14	[57]
Nigeria (TESs)	70.4	17.7	11.9	-	1.53	[8]
Ptolemais/Greece (SS)	496	36	27	-	1.33	[14]
Saudi Arabia (SS)	790	24.3	23.8	-	1.02	[37]
Canary Island/Spain (VS)	384	28.9	25.2	-	1.15	[16]
Amman City/Jordan (USs)	266	35.5	29.0	-	1.22	[29]

* PS: present study. ** Abbreviations for different soil types: (PFSs) paddy field soils, (SS) surface soil, (US) urban soil, (RS) red soil, (VS) volcanic soil, (ASs) agricultural soils, (HS) hill soils, (TESs) tailing-enriched soils, (RDSs) residential soils, (IEDSs) industrial effluent-disposed soils, (TSSs) tropical and semiarid soils, (FSs) Flysch soils, (SLSs) sandy-loam soils, (ALSs) alluvial soils, and (TFSs) tobacco field soils. - undetected or unmentioned.

3.4. Activity Ratio of ²³²Th/²²⁶Ra

In nature, two series of radioactive isotopes, uranium and thorium, are commonly found [58]. The activity ratios (ARs) of ²³²Th/²²⁶Ra can indicate the relative presence of these isotopes and their origin in natural systems [43,58,59]. Moreover, the AR value can detect changes in its content and measure various environmental geochemical processes [2,3,6,58,60].

Figure 4a shows a line and scatter plot of ²³²Th/²²⁶Ra ARs, while Figure 4b displays a histogram of frequency distribution and a frequency cumulated percentage plot of ²³²Th/²²⁶Ra ARs. Table 2 shows the descriptive statistical data of ²³²Th/²²⁶Ra ARs. The ARs ranged from 1.44 to 2.10, with a mean and standard deviation of 1.78 ± 0.13. The skewness, kurtosis, and CV values were −0.21, −0.13, and 7.2%, respectively. The normality test resulted in a significant p-value of 0.81. The kurtosis and skewness values were close to 0, indicating that the ²³²Th/²²⁶Ra ARs were normally distributed. The low CV value and the significance of the normality test further confirmed this. The median value was 1.779, which is similar to the mean value of 1.780, thus providing further evidence of the normality of the ²³²Th/²²⁶Ra ARs.

The global data collected indicate that the average activity concentration of ²²⁶Ra and ²³²Th in the soils was 32 Bq/kg and 45 Bq/kg, respectively [28]. The average ²³²Th/²²⁶Ra activity ratio was found to be 1.78 in this study, which is higher than the global soil average of 1.41. The ²³²Th/²²⁶Ra ratios in Table 3 varied from 0.77 to 2.56, with most values exceeding 1.0, indicating higher thorium levels in the soil compared to uranium. This study revealed that the soil contained 1.78 times more thorium than uranium minerals. The recorded ²³²Th/²²⁶Ra activity ratios in this study were similar to those observed in the soil of Pernambuco State, Brazil. Additionally, the median activity ratios of ²²⁸Ra (²³²Th)/²²⁶Ra ranged from 1.6 to 2.2, with red-yellow Acrisols and red-yellow Ferrosols having ratios of 1.8 and 1.9, respectively [2]. This study also found that the acidic soil condition increased radium solubility, resulting in a higher ²³²Th/²²⁶Ra activity ratio [2,28].

3.5. Radiological Hazard Indices

Four radiological hazard indices were utilized to assess the radiological risk in the soils. Figure 5a–d show the line and scatter plots, alongside the mean value plots, for these indices.

Table 4. Descriptive statistics of investigated radiological hazard indices in the studied soils.

Parameter	Raeq (Bq/kg)	Dex (nGy/h)	Hex	AEDex (μSv/y)
Mean	145.2	67.2	0.39	82.4
SD a	12.2	5.7	0.03	7.0
Minimum	117.0	53.4	0.32	65.5
Maximum	199.3	94.2	0.54	115.5
Median	146.4	67.5	0.40	82.8
Kurtosis	2.51	3.43	2.51	3.43
Skewness	0.36	0.61	0.36	0.61
CV	8.4	8.5	8.4	8.5
p-value b	0.54	0.58	0.13	0.54

^a standard deviation; ^b normality test by K-S method.

lists the descriptive statistics of the radiological hazard indices obtained from soil samples.

The radium equivalent activity (Ra_eq, Bq/kg) is a single index that calculates the gamma radiation emitted by three types of radionuclides (⁴⁰K, ²²⁶Ra, and ²³²Th) from the soil sample. In this study, the Ra_eq values of the soil samples ranged from 117.0 to 199.3 Bq/kg, with an average of 145.2 Bq/kg. These values are well below the maximum permissible limit of 370 Bq/kg [3,18,61]. According to the statistical analysis of Ra_eq, the values for kurtosis, skewness, and coefficient of variation (CV) were 2.51, 0.36, and 8.4%, respectively. The normality test significance was 0.54, as shown in Table 4, indicating that the Ra_eq values were distributed normally. Additionally, the median value of 146.2 Bq/kg is close to the mean value of 145.2 Bq/kg, further supporting the normal distribution of the Ra_eq values.

The external hazard index (H_ex) is a measure used to assess the level of external gamma radiation from soils to determine if they are safe for use as construction materials. The maximum permissible limit for H_ex is 1.0, which corresponds to the highest acceptable limit of Ra_eq of 370 Bq/kg [17,28,61,62]. This ensures that these materials are safe to use in building construction. In this study, the H_ex values ranged from 0.32 to 0.54, with an average value of 0.39 and a standard deviation of 0.03. All H_ex values in the study area were less than 1.0, indicating that the soil is safe for use in construction. The H_ex values had a kurtosis of 2.51, a skewness of 0.36, and a CV value of 8.2%. The normality test significance was 0.13, confirming the normal distribution. The median value of H_ex was 0.395, which is similar to the mean value of 0.392 (Table 4).

To estimate the outdoor absorbed gamma dose rate (D_ex) 1 m above the ground surface, the concentration of radionuclides (⁴⁰K, ²²⁶Ra, and ²³²Th) in the samples is taken into consideration. It is assumed that the radionuclides are evenly distributed, and the contribution of other naturally occurring radionuclides is insignificant [11,37]. The D_ex values in this study ranged from 53.4 to 94.2 nGy/h, with an average of 67.2 nGy/h. This is 13.9% higher than the population-weighted world average of 59 nGy/h [11,28,45].

The external annual effective dose equivalent (AED_ex) is a measure of the annual dose people receive when outdoors [11,37]. It is estimated using a conversion factor of 0.7 Sv/Gy, and the outdoor occupancy factor is 0.2 (Equation (4)). The calculated AED_ex values ranged from 65.5 to 115.5 μSv/y, with a mean value of 82.4 μSv/y. This value is 17.7% higher than the world average of 70 μSv/y [11,28,45]. However, it is important to note that the average AED_ex recorded in this study is still below the maximum recommended worldwide level of 1 mSv/y of doses received from natural radiation sources [13,28,37].

The gamma ray activity released by natural radionuclides in campus soils was converted into an annual effective dose and compared with the annual exposure dose of the Taiwanese population (external terrestrial radiation: 0.58 mSv/y; total dose: 1.56 mSv/y) [63]. The calculated annual effective dose from gamma rays in this study is 0.082 mSv/y, accounting for 5.3% of the total dose, which is within the reasonable background radiation range.

The kurtosis, skewness, and CV values for D_ex and AED_ex were identical and were 3.43, 0.61, and 8.5%, respectively. The significance of the normality test was 0.58 and 0.54 for D_ex and AED_ex, respectively. The low skewness and CV values confirmed the normal distribution and median value of 67.5 nGy/h and 82.7 μSv/y, which were similar to the corresponding mean values. The CV for the annual external effective dose is 8.5%, indicating low variability in the external dose generated by campus soils. Therefore, it can be inferred that the effective dose from gamma ray activity in campus soils is within the reasonable range of background radiation.

The soil samples in the area under investigation do not pose any significant health risks from radiation, and exposure to natural radionuclides is harmless to the public.

4. Conclusions

This study conducted a measurement of gamma-emitted radionuclide levels in soil samples from the NPUST in Taiwan. The results indicated that there was no contamination from man-made radionuclides, as the activity concentrations of ¹³⁷Cs were below the detected limit. However, the average activity concentrations of ²³²Th and ⁴⁰K were higher, while the average ²²⁶Ra activity concentration was similar to the world soil average concentration. The average ²³²Th/²²⁶Ra activity ratio of 1.78 was higher than the global average of 1.41 due to the solubility of ²²⁶Ra in the acidic soil. The average radiological hazard indices Ra_eq and H_ex were 145.2 Bq/kg and 0.39, which were lower than the recommended limit values of 370 Bq/kg and 1.0, respectively. Similarly, the average D_ex and AED_ex were 67.2 nGy/h and 82.4 μSv/y, and the AED_ex was less than the maximum recommended value of 1000 μSv/y. These index values indicate that there is no significant radiological risk to the public in the campus soils. Although this study primarily focused on soil, we recognize the importance of evaluating the distribution and persistence of radionuclides in other environmental media, such as water and air. Future research efforts should aim to investigate these media to provide a more comprehensive understanding of the campus radiation environment. The results of this study can serve as a baseline for such future investigations and for developing strategies to ensure a safe and sustainable campus environment. This not only helps protect the local ecosystem but also provides a scientific basis for future environmental planning and management.