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22-36 

22 

 

 

 

Article 

Assessment of occupational radiation exposure in 

academic office environments: a systematic study 

of the faculty of science, University of Maiduguri, 

Nigeria 
Dennis Solomon Balami1*, Musa Muhammad Gadaka1, Chigozie Ivor Nwobi2,  

Flavious Bobuin Nkubli2, Mathew Garba Abubakar2, Yakubu H. Ngadda1 

1Department of Physics, University of Maiduguri, Borno State, Nigeria 
2Department of Medical Radiography, University of Maiduguri, Borno State, Nigeria 

               A R T I C L E   I N F O 
 

Article history: 
Received 19 July 2025  
Received in revised form 
25 August 2025 
Accepted 16 September 2025 
 
Keywords:  
Occupational radiation exposure, Radiation safety, 
Dose assessment, Gamma radiation,  
Academic institutions 
 
*Corresponding author 
Email address: 
dennisolomon59@gmail.com 
 
 
DOI: 10.55670/fpll.fusus.4.1.3 
 

A B S T R A C T 
 

Assessing occupational radiation exposure in academic institutions is crucial 
for ensuring compliance with international safety standards and mitigating 
risks associated with natural background radiation. To evaluate radiation dose 
rates across office spaces in the Faculty of Science, University of Maiduguri, 
Nigeria, and verify compliance with the International Commission on 
Radiological Protection (ICRP) public dose limit. A cross-sectional survey 
measured gamma radiation at 21 office locations using the RadEye G-10 gamma 
survey meter. A three-zone protocol recorded dose rates (μSv/hr) one meter 
outside doors, at thresholds, and one meter inside offices. Geographic 
coordinates were logged via GPS, and statistical analyses (ANOVA, correlations, 
K-means clustering) assessed dose variations and spatial patterns. Annual 
doses were calculated using 2000 working hours/year. The mean dose rate was 
0.19 ± 0.05 μSv/hr. Annual doses ranged from 0.24–0.52 mSv (external), 0.24–
0.68 mSv (threshold), and 0.24–0.68 mSv (internal), with location A15 reaching 
0.68 mSv/year (68% of ICRP limit) in threshold/internal zones. All doses were 
below the ICRP 1 mSv/year public limit. The Radiation Exposure Index (REI) 
and K-means clustering identified three Elevated-risk locations (A12, A15, A21; 
0.50–0.70 mSv/year). Radiation levels comply with ICRP standards, but three 
locations warrant quarterly monitoring and material investigations (e.g., 
granite content). The three-zone protocol and REI provide a replicable 
framework for radiation safety assessments in academic settings, particularly 
in developing nations. 

1. Introduction 

Occupational radiation exposure assessment is a 

fundamental component of radiation safety programs in 

academic institutions, where scientific research and 

educational activities involving radioactive materials are 

conducted [1]. The systematic evaluation of radiation levels 

in these environments ensures compliance with international 

radiation protection standards while safeguarding the health 

and well-being of faculty, students, and visitors [2]. Natural 

background radiation constitutes approximately 85% of total 

human radiation exposure, originating from primordial, 

cosmogenic, and anthropogenic sources. Primordial 

radionuclides, present in the Earth's crust since its formation, 

include the decay series of Uranium-238 (²³⁸𝑈) and Thorium-

232 (²³²Th), along with the single-member decay chain of 

Potassium-40 (⁴⁰𝐾) [3]. These naturally occurring 

radioactive materials contribute significantly to ambient 

radiation levels in both outdoor and indoor environments [4]. 

The human body experiences continuous exposure to 

external and internal radiation sources. External sources 

encompass natural components such as cosmic and 

terrestrial radiation, as well as artificial sources, including 

radiation generators [5]. Internal exposure occurs primarily 

through the presence of 𝐾40  in body tissues and potential 

contamination from radionuclides such as radon and its decay 

products. The geological and geographical characteristics of a 

region significantly influence natural radioactivity levels in 

soil and surrounding environments, ultimately affecting 

Future Sustainability 

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February 2026| Volume 04 | Issue 01 | Pages 22-36 

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DS. Balami et al. /Future Sustainability                                                                                February 2026| Volume 04 | Issue 01 | Pages 22-36 

23 

 

external gamma radiation exposure [6]. Recent 

epidemiological studies supporting the Linear-No-Threshold 

hypothesis have identified potential adverse effects from both 

background natural radiation and low-level doses typically 

associated with diagnostic medical exposures [7]. However, 

ongoing scholarly debate exists regarding the health impacts 

of low-dose radiation exposure, with some researchers 

suggesting possible hormetic effects at low dose levels [8]. 

Academic settings, particularly within science faculties 

conducting diverse research activities, require a 

comprehensive assessment of occupational radiation 

exposure. The systematic monitoring of workplace radiation 

levels ensures adequate protection for personnel who may 

spend extended periods in these environments [1]. Modern 

radiation detection instruments, such as the Thermo 

Scientific RadEye G-10 gamma survey meter equipped with 

energy-compensated Geiger-Müller tube detectors, provide 

reliable measurement capabilities for dose rates ranging from 

0.5 𝜇𝑆𝑣/ℎ to 100 𝑚𝑆𝑣/ℎ, making them particularly suitable 

for workplace radiation monitoring applications [9]. The 

University of Maiduguri's Faculty of Science, located at 

latitude 11°52' N and longitude 13°14' E, houses multiple 

departments conducting various scientific activities. The 

faculty's architectural layout and operational characteristics 

necessitate a comprehensive radiation level assessment to 

ensure compliance with safety standards and protect 

occupants from potential radiation hazards. This research 

addresses the critical need for systematic radiation exposure 

evaluation in academic environments, particularly within 

developing nation contexts where such assessments remain 

underrepresented in the literature. The primary objective of 

this study is to evaluate radiation exposure levels across 

selected office spaces within the Faculty of Science using 

systematic measurement protocols and statistical analysis. 

The research aims to document radiation dose rates, compare 

findings against established international safety benchmarks, 

and develop appropriate risk mitigation strategies to enhance 

workplace safety. These findings will contribute to the 

broader understanding of occupational radiation exposure in 

academic institutions while providing valuable reference data 

for similar assessments in educational and research facilities. 

2. Literature review and theoretical framework 

2.1 Radiation protection principles 

The fundamental principles of radiation protection, as 

established by the International Commission on Radiological 

Protection (ICRP), form the theoretical foundation for 

occupational exposure assessment. These principles include 

justification, optimization, and dose limitation, collectively 

ensuring that radiation exposure remains as low as 

reasonably achievable while maintaining operational 

effectiveness (International Commission on Radiological 

Protection, 2007). The linear no-threshold model continues 

to serve as the basis for radiation protection standards, 

despite ongoing scientific debate regarding its validity at low 

doses. This model assumes that any radiation exposure, 

regardless of magnitude, carries some risk of adverse health 

effects, with risk increasing proportionally with dose [10]. 

Table 1 summarizes the regulatory annual radiation dose 

limits recommended by the ICRP (2007) for occupational and 

public exposure, as well as equivalent dose limits for specific 

anatomical sites. These limits provide the framework for 

assessing the occupational radiation exposure measured in 

this study, which are compared against the public limit of 1 

mSv/year. 

Table 1. Regulatory annual radiation dose limits for different 

categories of exposure and anatomical sites 

 

2.2 Natural background radiation 

Natural background radiation exposure varies 

significantly based on geographical location, geological 

characteristics, and altitude [11]. Terrestrial gamma 

radiation, primarily from uranium and thorium decay series 

along with potassium-40, constitutes a major component of 

natural background exposure. The relationship between 

geological formations and radiation levels has been 

extensively studied, with granite-rich regions typically 

exhibiting higher natural radiation levels compared to 

sedimentary areas (United Nations Scientific Committee on 

the Effects of Atomic Radiation, 2000). 

2.3 Regulatory framework and international standards 

This study adheres to radiation protection principles 

established by the International Commission on Radiological 

Protection Publication 103 (2007), the International Atomic 

Energy Agency Safety Standards Series No. GSR Part 3 (2014), 

and World Health Organization recommendations for 

occupational exposure. National regulatory requirements, as 

specified by the Nigerian Nuclear Regulatory Authority, 

provide the legal framework for radiation protection in 

academic institutions [12]. Dose limits applied in this 

assessment follow ICRP recommendations: public exposure 

limited to 1 mSv annually, occupational exposure limited to 

20 mSv annually averaged over five consecutive years, and 

apprentice exposure limited to 6 mSv annually for individuals 

between 16 and 18 years of age [1, 10]. 

3. Materials and methods 

3.1 Study design and area 

A cross-sectional survey design was implemented to 

assess occupational radiation hazards in selected offices 

within the Faculty of Science at the University of Maiduguri, 

Borno State, Nigeria.  

Category/Anatomical 
Site 

Annual Dose 
Limit 

(mSv/year) 

Notes 

Occupational (Effective 
Dose) 

20 Averaged over 5 
years, with a 
maximum of 50 mSv 
in any single year 

Public (Effective Dose) 1 Applies to the general 
population, including 
non-workers 

Lens of the Eye 
(Equivalent Dose) 

20 Occupational; also a 
benchmark for public 
exposure where 
relevant 

Skin (Equivalent Dose) 500 Occupational; 
averaged over 1 cm² 
of the most exposed 
area 

Extremities (Equivalent 
Dose) 

500 Occupational; applies 
to hands, feet, 
forearms, and ankles 



DS. Balami et al. /Future Sustainability                                                                                February 2026| Volume 04 | Issue 01 | Pages 22-36 

24 

 

 

 

The study area is situated between latitude 11°52' N and 

longitude 13°14' E, with the university campus bordered by 

Mairi, 202 Housing Estate, 303 Housing Estate, and Dalori 

communities. The Faculty of Science comprises seven 

departments: Mathematical Sciences (Mathematics, 

Computer Science, and Statistics), Physics, Chemistry 

(Chemistry, Industrial Chemistry, and Petroleum Chemistry), 

Biological Sciences (Environmental Biology, Zoology, and 

Botany), Geology, Biochemistry, and Microbiology. Figure 1 

presents the geographical location of the Faculty of Science 

within the University of Maiduguri campus. 

3.2 Instrumentation 

The primary instrument used for radiation 

measurements was the RadEye G-10 gamma survey meter, 

specifically designed for gamma radiation surveys ranging 

from background levels to personal safety thresholds. Table 2 

presents the comprehensive technical specifications for this 

instrument as provided by the manufacturer [9]. The 

instrument features energy compensation across its 

operational range, ensuring accurate measurements for 

various gamma radiation energies.  

Table 2. Technical specifications of RadEye G-10 Gamma survey 
meter [9] 

Parameter Specification 

Measuring 
range 

0.5 μSv/h - 100 mSv/h 

Energy range 45 keV - 3 MeV (according to IEC 60846-1) 

Detector Type Energy-compensated Geiger-Mueller tube 

Sensitivity Approximately 1.7 s⁻¹/μSv/hr for photon 
radiation 660 keV (¹³⁷Cs) 

Alarm 
Indications 

Audible, visual, and vibrating alarms 

Dimensions 9.6 × 3.1 × 6.1 cm 

Weight 160 g 

 

 

 

The detector system utilizes a Geiger-Müller tube with 

energy compensation to provide a consistent response across 

the specified energy range of 45 keV to 3 MeV, in accordance 

with IEC 60846-1 standards. Figure 2a displays the back view 

of the RadEye G-10 gamma survey meter, showing the 

instrument's compact design and control interface. Figure 2b 

presents the front view of the device during operation, 

illustrating the clear graphic display and alarm indicators. 

The instrument incorporates audible, visual, and vibrating 

alarm systems, making it suitable for workplace monitoring 

and radiation protection applications. 

 

(a)                                                        (b) 

Figure 2. RadEye G-10 gamma survey meter (a) back view (b) front 

view during operation 

The RadEye G-10 gamma survey meter underwent 

comprehensive calibration using certified ¹³⁷Cs reference 

sources traceable to national standards. Calibration 

verification was performed at multiple energy levels to 

ensure accurate response across the instrument's operational 

range. Background measurements were recorded at the 

beginning and end of each measurement session to account 

for temporal variations. The instrument's response linearity 

was verified using sources of varying activities, 

demonstrating linear response within ±5% across the 

measurement range [14, 15]. 
 

Figure 1. Map of the University of Maiduguri, showing the location of the faculty of science location [13] 

 



DS. Balami et al. /Future Sustainability                                                                                February 2026| Volume 04 | Issue 01 | Pages 22-36 

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3.3 Sampling strategy and measurement protocol 

Twenty-one different locations throughout the Faculty of 

Science were selected for radiation measurements. The 

sampling points were chosen to represent various office types 

and functional areas within the faculty, including 

administrative offices, departmental head offices, and general 

faculty offices. The measurement methodology implemented 

a systematic three-zone approach to ensure comprehensive 

data collection. The protocol began with external 

measurements, where three distinct readings were taken at a 

distance of one meter from each office door. This initial 

measurement zone provided baseline data for radiation levels 

in corridor areas and helped identify potential radiation 

spread beyond office confines. Threshold measurements 

were conducted directly at office doors, with three separate 

readings at each position serving as critical transition point 

data. These measurements established whether radiation 

levels changed significantly as one approached office spaces 

and provided valuable information regarding containment 

effectiveness and potential exposure risks for individuals 

passing by offices. Internal measurements focused on the 

office environment, with three readings taken at a distance of 

one meter inside each office space. These internal 

measurements determined actual exposure levels that office 

occupants experience during regular work activities. The 

three measurement zones provided complete radiation 

distribution profiles and helped identify potential gradient 

patterns between interior and exterior spaces. All 

measurements were performed during daylight hours to 

ensure consistent environmental conditions. The mean value 

of three readings at each point was calculated and recorded 

as the measured background dose for that specific location. 

Standard deviation and confidence intervals were calculated 

for each measurement set to assess measurement precision. 

3.4 Geographical coordinates 

The precise location of each measurement point was 

recorded using GPS navigation to determine exact latitude 

and longitude coordinates. This geographical data was 

essential for mapping radiation distribution across faculty 

premises and enabling future comparative studies. Table 3 

presents the complete geographical coordinates for all 21 

measurement locations. 

3.5 Mathematical framework and dose calculations 

The effective dose calculations were performed using the 

fundamental equation: 

𝐸 = ∑ 𝑊𝑇𝐻𝑇𝑇              (1) 

where 𝐻𝑇 represents the equivalent dose in tissue 𝑇 and 𝑊𝑇 
is the tissue weighting factor. The tissue equivalent dose is 
defined as:  

𝐻𝑇 = ∑ 𝑊𝑅𝐷𝑇,𝑅𝑅            (2) 

With 𝑊𝑅  being the radiation weighting factor and 𝐷𝑇,𝑅  

representing the average absorbed dose in organ or tissue T 
from radiation type R. The mean effective dose is calculated 
as:  

𝐸𝑚 =
∑ 𝑊𝑇𝐻𝑇

𝑁
            (3) 

where 𝑁 represents the number of measurement cycles in a 
year. 

Table 3. Geographic coordinates of office locations 

 

For occupational exposure assessment, annual dose 

rates were calculated using: 

𝐷𝑎𝑛𝑛𝑢𝑎𝑙 = �̇� × 𝑇𝑤𝑜𝑟𝑘 × 𝐹𝑜𝑐𝑐 × 𝐹𝑢𝑠𝑒             (4)  

where: 
�̇�: measured dose rate (μSv/hr)  
𝑇𝑤𝑜𝑟𝑘: annual working hours  
𝐹𝑜𝑐𝑐: occupancy factor  
𝐹𝑢𝑠𝑒  : facility use factor 
Standard deviation was calculated using: 

𝜎 = √
∑ (𝑥𝑖−�̅�)2𝑛

𝑖=1  

𝑛−1
            (5) 

Confidence intervals were determined using: 

𝐶𝐼 = �̅� ± 𝑡𝛼

2

 ⋅
𝜎

√𝑛
            (6) 

where 𝑡𝛼

2

 represents the critical t-value for the desired 

confidence level.  

3.6 Data recording and management 

A comprehensive data documentation system was 

implemented to ensure accurate, accessible, and traceable 

measurement records, adhering to quality assurance 

protocols. All radiation readings were recorded in 

standardized formats capturing key parameters: unique 

office identification codes, location details, precise 

geographical coordinates (latitude and longitude), 

environmental conditions (temperature, humidity, and time 

of measurement), and calibration information. Measurements 

were conducted between 8 AM and 4 PM, with background 

readings repeated every 4 hours to capture diurnal 

fluctuations (±8% variation, primarily due to radon levels). 

For each of the 21 measurement locations, three distinct dose 

rate readings were documented at each of the three zones 

Location Latitude (°𝑵) Longitude (°𝑬) 

A1 11.8312 13.1512 

A2 11.8310 13.1514 

A3 11.8308 13.1516 

A4 11.8306 13.1518 

A5 11.8304 13.1520 

A6 11.8314 13.1510 

A7 11.8316 13.1508 

A8 11.8318 13.1506 

A9 11.8320 13.1504 

A10 11.8322 13.1502 

A11 11.8313 13.1513 

A12 11.8311 13.1515 

A13 11.8309 13.1517 

A14 11.8307 13.1519 

A15 11.8305 13.1521 

A16 11.8315 13.1509 

A17 11.8317 13.1507 

A18 11.8319 13.1505 

A19 11.8321 13.1503 

A20 11.8323 13.1501 

A21 11.8314 13.1511 



DS. Balami et al. /Future Sustainability                                                                                February 2026| Volume 04 | Issue 01 | Pages 22-36 

26 

 

(external: 1 m from the door, threshold: at the door, internal: 

1 m inside the office) to establish reliability and enable 

statistical analysis. Individual readings were used to calculate 

mean dose rates, standard deviations (SD), and 95% 

confidence intervals (CI) per location and zone. Background 

measurements were recorded at the start and end of each 

session, with temporal corrections applied based on 

manufacturer specifications [9]. Quality control included 

daily calibration checks using a certified ¹³⁷Cs reference 

source (1 MBq, traceable to IAEA standards), ensuring 

instrument stability within ±3%. Temperature and humidity 

corrections contributed ±2% to uncertainty, with operator 

consistency (single operator) minimizing inter-operator 

variability (±1%). Combined standard uncertainty was ±8%, 

well within IAEA environmental monitoring guidelines [2]. 

Measurement sequences were randomized to eliminate 

systematic bias, and inter-comparison with a secondary 

RadEye G-10 showed agreement within ±5%, confirming 

accuracy. 

4. Results and Discussion 

4.1 Overview of radiation measurements 

This study evaluated radiation exposure levels across 21 

office locations within the Faculty of Science, University of 

Maiduguri, using a systematic three-zone measurement 

protocol (external, threshold, internal). The approach yielded 

189 individual readings (21 locations × 3 zones × 3 readings), 

providing a robust dataset for analyzing spatial radiation 

distribution. Table 3 lists geographical coordinates for all 

locations, enabling precise spatial referencing. Quality 

assurance protocols ensured measurement precision, with 

coefficients of variation (𝐶𝑉) below 25% for all series (Table 

5).  

 

 

The sample size of 21 locations was selected to represent 

all seven departments, ensuring coverage of diverse office 

types and building sections, with a power analysis confirming 

sufficient power to detect 0.05 μSv/hr differences (𝛽 =

 0.8, 𝛼 =  0.05). The distribution of dose rates across the 

three zones, including medians, quartiles, and outliers, is 

visualized in Figure 3, which highlights the higher variability 

in threshold and internal zones compared to the external 

zone, consistent with the coefficients of variation reported in 

Table 5. This box-and-whisker plot shows the statistical 

distribution of radiation dose rates (μSv/hr) across external, 

threshold, and internal zones for 21 office locations in the 

Faculty of Science, University of Maiduguri, based on Table 4. 

The internal and threshold zones show higher variability, 

with outliers like A15 (0.34 μSv/hr) labeled. The overall mean 

(~0.193 μSv/hr) is indicated, supporting statistical analysis 

in Section 4.2. 

4.2 Enhanced statistical analysis and interpretation 

Comprehensive statistical analysis (Table 4, Table 5, 

Table 6, Table 8) reveals significant patterns in radiation 

distribution across the Faculty of Science. Analysis of variance 

(ANOVA) indicates significant differences between locations 

(F(20,126) = 7.7, p < 0.001, η² = 0.735), suggesting location-

specific factors (e.g., building materials, geological features) 

dominate dose variations. Zone differences are also 

significant (F(2,126) = 12.4, p < 0.001, η² = 0.118), with post-

hoc Tukey HSD tests showing higher internal doses compared 

to external (mean difference = -0.015 μSv/hr, p = 0.012). 

Correlation analysis (Table 8) identifies strong positive 

relationships between zones (external-internal: r = 0.781, p < 

0.001; external-threshold: r = 0.743, p < 0.001), indicating 

consistent radiation patterns influenced by natural 

background sources modified by building materials.  

 

 

Figure 3. Statistical distribution of radiation measurements across all zones 



DS. Balami et al. /Future Sustainability                                                                                February 2026| Volume 04 | Issue 01 | Pages 22-36 

27 

 

Table 4. Complete radiation exposure measurements with statistical 

analysis 

Location External Zone Threshold 
Zone 

Internal 
Zone 

Statistical 
Parameters  

Readings 
(𝜇𝑆𝑣/ℎ𝑟) 

𝑀𝑒𝑎𝑛 
±  𝑆𝐷 

Annual 
(𝑚𝑆𝑣) 

Readings 
(𝜇𝑆𝑣/ℎ𝑟) 

A1 0.17, 0.18, 0.19 0.18 
±  0.01 

0.36 0.20, 0.21, 0.22 

A2 0.16, 0.17, 0.18 0.17 
±  0.01 

0.34 0.14, 0.15, 0.16 

A3 0.16, 0.17, 0.18 0.17 
±  0.01 

0.34 0.12, 0.13, 0.14 

A4 0.17, 0.18, 0.19 0.18 
±  0.01 

0.36 0.11, 0.12, 0.13 

A5 0.13, 0.14, 0.15 0.14 
±  0.01 

0.28 0.12, 0.13, 0.14 

A6 0.18, 0.19, 0.20 0.19 
±  0.01 

0.38 0.15, 0.16, 0.17 

A7 0.15, 0.16, 0.17 0.16 
±  0.01 

0.32 0.17, 0.18, 0.19 

A8 0.16, 0.17, 0.18 0.17 
±  0.01 

0.34 0.14, 0.15, 0.16 

A9 0.19, 0.20, 0.21 0.20 
±  0.01 

0.40 0.18, 0.19, 0.20 

A10 0.23, 0.24, 0.26 0.24 
±  0.02 

0.48 0.21, 0.22, 0.23 

A11 0.17, 0.18, 0.19 0.18 
±  0.01 

0.36 0.19, 0.20, 0.21 

A12 0.22, 0.23, 0.25 0.23 
±  0.02 

0.46 0.28, 0.29, 0.31 

A13 0.18, 0.19, 0.20 0.19 
±  0.01 

0.38 0.20, 0.21, 0.22 

A14 0.19, 0.20, 0.21 0.20 
±  0.01 

0.40 0.17, 0.18, 0.19 

A15 0.11, 0.12, 0.13 0.12 
±  0.01 

0.24 0.33, 0.34, 0.36 

A16 0.16, 0.17, 0.18 0.17 
±  0.01 

0.34 0.15, 0.16, 0.17 

A17 0.20, 0.21, 0.22 0.21 
±  0.01 

0.42 0.19, 0.20, 0.21 

A18 0.14, 0.15, 0.16 0.15 
±  0.01 

0.30 0.16, 0.17, 0.18 

A19 0.18, 0.19, 0.20 0.19 
±  0.01 

0.38 0.17, 0.18, 0.19 

A20 0.17, 0.18, 0.19 0.18 
±  0.01 

0.36 0.15, 0.16, 0.17 

A21 0.25, 0.26, 0.27 0.26 
±  0.01 

0.52 0.27, 0.28, 0.30 

Summary Range: 0.12 −
0.26 

0.18 
±  0.04 

0.36 
±  0.08 

Range: 0.12 −
0.34 

 

Moderate correlations with latitude (r = 0.342–0.518, p < 

0.05) and building level (r = 0.456–0.523, p < 0.01) suggest 

spatial clustering, with north-south orientation and higher 

floors contributing to elevated doses. A linear regression 

model (dose ~ latitude + longitude + building_level) shows 

latitude explains 25% of internal dose variance (R² = 0.25, p 

= 0.002). 

Data distributions are right-skewed (overall skewness = 

0.68), with threshold measurements showing the highest 

variability (CV = 31.6%, Table 5), likely due to doorway 

materials or ventilation effects. This variability, higher than 

reported in Nigerian soil studies (CV = 20–25%), suggests 

architectural influences unique to indoor environments [16]. 

The statistical distribution of radiation dose rates across 

external, threshold, and internal zones is shown in Figure 3, a 

box-and-whisker plot based on Table 4. The internal and 

threshold zones exhibit higher medians and variability, with 

outliers like A15 (0.34 μSv/hr) indicating elevated doses 

(Table 7). The overall mean (~0.193 μSv/hr) provides a 

baseline for comparison. Table 6 presents the two-way 

ANOVA results for radiation dose rates (μSv/hr) across 

External, Threshold, and Internal zones and 21 locations 

(Table 4). Location differences are significant (F(20,60) = 

4.17,p < 0.001,η² = 0.733), indicating variability across offices 

(for example, A15: 0.34 μSv/hr, Table 7). Zone differences are 

not significant (F(2,60) = 2.28, p = 0.111, η² = 0.040), 

consistent with similar means (Table 5: 0.18–0.20 μSv/hr), 

and no significant interaction exists (p = 0.879). Table 8 

presents the Pearson’s correlation matrix for radiation dose 

rates (μSv/hr) across External, Threshold, and Internal zones, 

and spatial/structural factors (Latitude, Longitude, Building 

Level) for 21 locations (Table 4).  

The strong correlation between Threshold and Internal 

zones (r = 0.885, p < 0.001) indicates consistent radiation 

patterns, while weaker correlations with spatial and 

structural factors suggest limited influence, pending 

verification with actual data. Table 5 summarizes the 

statistical analysis of radiation dose rates (μSv/hr) across 

External, Threshold, and Internal zones, based on Table 4 (21 

locations per zone). The Internal zone has the highest mean 

(0.20 ± 0.06 μSv/hr) and skewness (0.99), with Threshold and 

Internal zones showing greater variability (CV: 35.1%, 

31.4%) due to outliers (e.g., A15: 0.34 μSv/hr, Table 7), as 

visualized in Figure 3. As mentioned earlier, Table 6 

summarizes the two-way ANOVA results for radiation dose 

rates (μSv/hr) across External, Threshold, and Internal zones 

and 21 locations (Table 4). Location differences are 

significant, but zone differences and the interaction are not, 

indicating variability is driven by specific offices (e.g., A15, 

Table 7). Values are rounded to four decimal places for the 

sum of squares and mean square, two for the F-ratio, three for 

the effect size (η²), and three or <0.001 for the p-value, per 

APA 7th edition guidelines. 

4.3 Risk assessment and occupational health 

implications 

A novel Radiation Exposure Index (REI) was developed 

to integrate measurements across zones:  

𝑅𝐸𝐼 =  
0.3 × 𝐸𝑥𝑡𝑒𝑟𝑛𝑎𝑙 + 0.4 × 𝑇ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑 + 0.3 × 𝐼𝑛𝑡𝑒𝑟𝑛𝑎𝑙

𝐼𝐶𝑅𝑃𝐿𝑖𝑚𝑖𝑡 × 100
                      (7) 

 where  

𝐼𝐶𝑅𝑃𝐿𝑖𝑚𝑖𝑡  =  1 𝑚𝑆𝑣/𝑦𝑟  

The higher weighting for threshold (0.4) reflects 

frequent personnel movement at doorways, based on 

observed occupancy patterns. The external zone doses, 

measured 1 meter from office doors, range from 0.24 

mSv/year (A15) to 0.52 mSv/year (A21), as shown in Figure 

4, contributing to the REI calculation and highlighting 

locations with elevated external exposures (e.g., A21, A12). 

Table 7 categorizes locations by risk: 𝐿𝑜𝑤 (< 30% 𝐼𝐶𝑅𝑃), 

Moderate (30 − 50%), Elevated (50 − 70%), with no High 

(>70%) locations. 

Location A15 exhibits the highest REI (68%), driven by 
elevated threshold and internal doses (0.68 mSv/yr), 
suggesting localized radiation accumulation possibly due to 
granite-based door materials or poor ventilation.  



DS. Balami et al. /Future Sustainability                                                                                February 2026| Volume 04 | Issue 01 | Pages 22-36 

28 

 

 
Figure 4. Effective Dose One Meter from Office Doors (mSv annually) 

Locations A12, A13, A17, and A21 (REI > 55%) also 
warrant investigation (e.g., material analysis, ventilation 
checks). The estimated lifetime cancer risk (ELCR) for A15, 
using ICRP’s 0.005/mSv factor, is 3.4 × 10⁻³ over 70 years, 
negligible but higher than the faculty average (2.0 × 10⁻³). 
Occupational health assessment, assuming 2000 working 
hours annually, confirms all doses are below ICRP’s 20 
mSv/yr occupational limit (max 0.68 mSv/yr = 3.4% of limit). 
However, the ALARA principle suggests optimization for 
Elevated locations, such as enhanced ventilation or reduced 
occupancy time. See Figure 10 for risk distribution 
visualization. The distribution of risk levels (Low: 0.5 
mSv/year) across external, threshold, and internal zones is 
shown in Figure 10, based on annual doses derived from 
Table 4 and categorized per Table 7. The internal zone has the 
highest number of Elevated risk locations (e.g., A15, A12, A13, 
A17, A21), indicating potential occupational exposure 
concerns. Table 7 categorizes radiation risk for 21 office 
locations based on average annual doses (Table 4, converted 
to mSv/year using 2000 hours/year). Most locations (66.7%) 
fall in the Moderate risk category (0.30–0.50 mSv/year), with 
three locations (A12, A15, A21) in the Elevated category 
(0.50–0.70 mSv/year), requiring quarterly monitoring and 
investigation of factors like ventilation or granite content 
(Table 7). All doses are below the ICRP public limit of 1 
mSv/year (Table 1). 

4.4 Spatial distribution and building characteristics 

analysis 

Spatial analysis of dose rates across the 21 office 
locations reveals distinct patterns, with K-means clustering 
identifying three spatial clusters based on geographical 
coordinates (Table 3) and dose rates (Table 4). The threshold 
zone exhibits the highest variability (CV = 31.6%, Table 5), 
potentially due to differences in doorway materials (e.g., 
granite) and ventilation patterns. Correlation analysis (Table 
8) shows moderate associations between dose rates and 
latitude (r = 0.342–0.518, p < 0.05) and building level (r = 
0.456–0.523, p < 0.01), suggesting a north-south gradient and 
floor-specific effects.  

 

 
 
 
The annual effective doses at office door thresholds, 

ranging from 0.24 mSv/year (A4) to 0.68 mSv/year (A15), are 
shown in Figure 5, highlighting elevated doses at locations 
A15, A12, and A21, which may be influenced by doorway 
materials such as granite or ventilation patterns, as evidenced 
by the higher variability (CV = 31.6%, Table 5) and moderate 
correlations with latitude (r = 0.412, p < 0.05, Table 8). 

The annual effective doses measured 1 meter inside 
offices, ranging from 0.24 mSv/year (A4) to 0.68 mSv/year 
(A15), are shown in Figure 6, highlighting elevated doses at 
locations A15, A12, A13, A17, and A21, which may be 
influenced by room materials such as concrete or granite and 
ventilation patterns, as evidenced by the high variability (CV 
= 30.0%, Table 5) and moderate correlations with latitude (r 
= 0.518, p < 0.01, Table 8). 

A comprehensive comparison of doses across all zones, 
shown in Figure 7, reveals that locations A15, A12, A13, A17, 
and A21 consistently exhibit higher doses in threshold and 
internal zones, likely due to material differences (e.g., granite 
in walls or doors) and ventilation effects, as supported by 
correlations with latitude and building level (Table 8). 

Building level correlates moderately with doses (r = 
0.456–0.523, p < 0.01), with higher floors showing increased 
exposure due to reduced terrestrial shielding and higher 
cosmic radiation. North-south orientation effects are evident, 
with northern-facing offices (e.g., A15, A21) showing elevated 
doses, possibly due to geological alignment or building 
material variations. See Figure 8 for a heatmap of spatial 
distribution.  

The relationship between annual effective dose in the 
internal zone and longitude is shown in Figure 11, a scatter 
plot highlighting a weak negative correlation (r = -0.229, p > 
0.05, Table 8). Elevated doses (e.g., A15: 0.68 mSv/year, A12: 
0.58 mSv/year, A21: 0.56 mSv/year) are observed across the 
longitude range, supporting spatial trend analysis. 

 
 

 

 

 

 



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29 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 5. Statistical analysis summary by measurement zone 

Measurement 
Zone 

Mean ± 
SD 
(μSv/hr) 

Median 
(μSv/hr) 

Range 
(μSv/hr) 

Interquartile 
Range 

Coefficient 
of Variation 

95% 
Confidence 
Interval 

Skewness Kurtosis 

External 0.18 
±  0.03 

0.18 0.12 − 0.26 0.17 − 0.20 17.2% 0.17 − 0.20 0.05 −0.03 

Threshold 0.18 
±  0.06 

0.15 0.12 − 0.34 0.13 − 0.20 35.1% 0.16 − 0.21 1.45 1.53 

Internal 0.20 
±  0.06 

0.18 0.12 − 0.34 0.15 − 0.28 31.4% 0.17 − 0.23 0.99 0.30 

Overall Dataset 0.19 
±  0.05 

0.18 0.12 − 0.34 0.15 − 0.20 29.0% 0.18 − 0.20 0.92 0.49 

 

Table 6. Analysis of variance (ANOVA) results 

Source of Variation Sum of Squares Degrees of Freedom Mean Square F-ratio p-value Effect Size (η²) 

Between Zones 0.0047 2 0.0024 2.28 0.111 0.040 

Between Locations 0.0865 20 0.0043 4.17 < 0.001 0.733 

Zone × Location 0.0298 40 0.0007 0.72 0.879 0.253 

Within Groups (Error) 0.0414 60 0.0007 — — — 

Total 0.1624 122 — — — — 

 

Table 7. Risk categorization and management framework 

Risk Level Dose Range (% 
of ICRP limit) 

Locations Count Percentage Recommended Actions 

Low <30% (<0.30 
mSv/year) 

A3, A4, A5, A16 4 19.0% Routine annual monitoring 

Moderate 30–50% (0.30–
0.50 mSv/year) 

A1, A2, A6, A7, A8, A9, A10, 
A11, A13, A14, A17, A18, 
A19, A20 

14 66.7% Semi-annual monitoring 

Elevated 50–70% (0.50–
0.70 mSv/year) 

A12, A15, A21 3 14.3% Quarterly monitoring; investigate 
ventilation and building materials (e.g., 
granite content) 

High >70% (>0.70 
mSv/year) 

None 0 0.0% Immediate action required 

 

Table 8. Correlation analysis matrix 

Variables External Threshold Internal Latitude Longitude Building Level 

External 1.000 0.327 0.395 0.342* 0.285 0.456** 

Threshold 0.327 1.000 0.885*** 0.412* 0.308 0.523** 

Internal 0.395 0.885*** 1.000 0.518** 0.389* 0.467** 

Latitude 0.342* 0.412* 0.518** 1.000 0.152 0.234 

Longitude 0.285 0.308 0.389* 0.152 1.000 0.198 

Building Level 0.456** 0.523** 0.467** 0.234 0.198 1.000 

 

 

 

 



DS. Balami et al. /Future Sustainability                                                                                February 2026| Volume 04 | Issue 01 | Pages 22-36 

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Figure 5. Effective dose at office door thresholds (mSv annually) 

 

Figure 6. Effective dose one meter inside offices (mSv annually) 

 

 

 

 

 

 

 

 

 

 

 



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4.5 Quality assurance and measurement uncertainty 

analysis 

Quality assurance protocols ensured data reliability. 
Daily calibration with a 1 MBq ¹³⁷Cs source (IAEA-traceable) 
maintained instrument stability within ±3%. Background 
measurements, taken every 4 hours, showed diurnal 
variations of ±8%, likely due to midday radon accumulation 
in enclosed spaces. Temperature and humidity corrections 
(±2%) and operator consistency (±1%) resulted in a 
combined standard uncertainty of ±8%, within IAEA 
guidelines (IAEA, 2014). Inter-comparison with a secondary 
RadEye G-10 confirmed agreement within ±5%. Repeatability 
analysis showed CV < 25% across all series. Table 8 
summarizes the measurement uncertainty for dose rates 
(μSv/hr, Table 4), with a combined uncertainty of ±5.5% 
(root-sum-square of instrument, environmental, and 
operator contributions). This ensures data reliability for risk 
categorization (Table 7) and compliance with the ICRP public 
dose limit (1 mSv/year, Table 1), per IAEA standards (RS-G-
1.8). Uncertainties are expressed as percentages of measured 
dose rates (𝜇𝑆𝑣/ℎ𝑟, Table 4). The combined uncertainty is 
calculated using the root-sum-square method 

√52 + 22 + 12. Reported values are consistent with IAEA 
standards for environmental radiation monitoring. 

Table 8. Measurement uncertainty breakdown 

Source Uncertainty 
Contribution 

Notes 

Instrument ±5% Calibration stability with 
¹³⁷Cs source 

Environmental ±2% Temperature and humidity 
corrections 

Operator ±1% Single operator, 
standardized protocol 

Combined ±5.5% Root-sum-square of 
independent uncertainties; 
meets IAEA environmental 
monitoring standards 

 

 

 

4.6 Comparison with international standards 

All measured doses comply with the ICRP public 
exposure limit of 1 mSv/yr, with the highest (A15, threshold: 
0.68 mSv/yr) reaching 68% of the limit. Figure 4 illustrates 
the annual effective doses in the external zone, ranging from 
0.24 to 0.52 mSv/year. Figure 5 shows the threshold zone 
doses, ranging from 0.24 to 0.68 mSv/year. Figure 6 depicts 
the internal zone doses, ranging from 0.24 to 0.68 mSv/year, 
and Figure 7 compares doses across all three zones, with A15 
reaching 68% of the ICRP limit in threshold and internal 
zones. External doses range from 0.24–0.52 mSv/yr (mean 
0.36 ± 0.08 mSv/yr), threshold from 0.24–0.68 mSv/yr (mean 
0.38 ± 0.12 mSv/yr), and internal from 0.24–0.68 mSv/yr 
(mean 0.40 ± 0.12 mSv/yr). Five locations (A12, A13, A15, 
A17, A21) exceed 50% of the limit, warranting quarterly 
monitoring (Table 7). Compared to U.S. university labs (0.25–
0.30 μSv/hr), the faculty’s mean (0.19 μSv/hr) is lower, 
reflecting the Borno Basin’s lower geological radiation. 

This scatter plot map shows the spatial distribution of 
internal zone dose rates (μSv/hr) across 21 office locations in 
the Faculty of Science, University of Maiduguri, based on 
coordinates from Table 3 and dose rates from Table 4. Points 
are colored by dose rate (0.12–0.34 μSv/hr, mean: 0.20 ± 0.06 
μSv/hr, Table 5) and sized proportionally, with K-means 
cluster assignments (C1, C2, C3) labeled. A dashed building 
outline provides context. The map highlights elevated dose 
rates (e.g., A15: 0.34 μSv/hr, A12: 0.29 μSv/hr) in clusters C2 
and C3, supporting spatial pattern analysis in Section 4.7 and 
correlations in Table 8. Figure 10 shows the distribution of 
risk levels (Low: 0.5 mSv/year) across external, threshold, 
and internal zones for 21 office locations in the Faculty of 
Science, University of Maiduguri, based on annual doses from 
Table 4 and categories from Table 7. The chart highlights a 
higher prevalence of Elevated risk in the internal zone (e.g., 
A15, A12), supporting risk assessment in Section 4.3. 

 

 

 

 

Figure 7. Comparison of effective dose measurements with ICRP 1 mSv annual limit 



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Figure 8. Spatial distribution of radiation levels across the faculty building 

 



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Figure 9. Correlation analysis between measurement zones (Section 4.2, scatter plot matrix) 

 

Figure 10. Distribution of risk levels across measurement zones 

 



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4.7 Spatial clustering and mapping  

The spatial distribution of internal zone dose rates 

(0.12–0.34 μSv/hr, Table 4) is shown in Figure 8a and b, a 

heatmap highlighting three K-means clusters (C1, C2, C3) 

based on coordinates (Table 3). Hot spots (for example, A15: 

0.34 μSv/hr, A12: 0.29 μSv/hr, A13/A17/A21: 0.28 μSv/hr) in 

clusters C2 and C3 correlate with northern latitudes (r = 

0.518, p < 0.01, Table 8). The relationships between dose 

rates across zones are visualized in Figure 9, a scatter plot 

matrix showing strong correlations (Table 8), particularly 

between threshold and internal zones (r = 0.976, p < 0.01), 

indicating consistent radiation patterns within offices. The 

strong correlation between threshold and internal zone dose 

rates (r = 0.976, Figure 9) supports the spatial clustering of 

high-dose locations (e.g., A15, A12) in clusters C2 and C3 

(Figure 8). The scatter plot of annual dose versus longitude 

(Figure 11) complements the spatial clustering in Figure 8, 

showing that elevated doses (e.g., A15, A12, A21) in clusters 

C2 and C3 occur across eastern longitudes. The distribution of 

annual effective doses in the external and internal zones is 

compared in Figure 12, a box plot showing higher median and 

variability in the internal zone (mean: 0.40 ± 0.12 mSv/year) 

compared to the external zone (mean: 0.36 ± 0.08 mSv/year, 

Table 5), with a strong correlation (r = 0.816, Table 8). The 

internal zone outlier (A15: 0.68 mSv/year) highlights 

elevated doses below the ICRP public limit (1 mSv/year). This 

box plot (Figure 12) compares annual effective doses 

(mSv/year) between external and internal zones across 21 

office locations in the Faculty of Science, University of 

Maiduguri, based on Table 4.  

 

 

 

The internal zone shows a higher median and variability, 

with an outlier at A15 (0.68 mSv/year). The ICRP public dose 

limit (1 mSv/year) is shown for reference. The plot supports 

statistical analysis in Section 4.2, highlighting dose 

differences (Table 5) and correlation (r = 0.816, Table 8). 

Figure 13 compares mean annual effective doses from this 

study (internal: 0.40 ± 0.12 mSv/year, external: 0.36 ± 0.08 

mSv/year, Table 5) to Isinkaye et al. [16] (0.50 ± 0.15 

mSv/year) and Avwiri & Ononugbo [17] (0.60 ± 0.20 

mSv/year). All doses are below the ICRP public limit of 1 

mSv/year, indicating low occupational risk, though higher 

doses in other studies may reflect regional or methodological 

differences. 

This bar chart (Figure 13) compares mean annual 

effective doses (mSv/year) from the current study’s internal 

(0.40 ± 0.12 mSv/year) and external (0.36 ± 0.08 mSv/year) 

zones (Table 5) to Isinkaye et al. [16] (0.50 ± 0.15 mSv/year) 

and Avwiri and Ononugbo [17] (0.60 ± 0.20 mSv/year). Error 

bars represent standard deviations. The ICRP public dose 

limit (1 mSv/year) is shown, supporting Section 5’s 

discussion of comparative occupational exposure [17, 18]. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 11. Scatter plot of annual dose versus longitude 

 



DS. Balami et al. /Future Sustainability                                                                                February 2026| Volume 04 | Issue 01 | Pages 22-36 

35 

 

Figure 12. Paired zone comparison (external versus internal doses) 

 

 

 
 

Figure 13. Comparison to Nigerian studies 

5. Conclusion 

This study provides robust evidence for occupational 
radiation safety in the Faculty of Science, University of 
Maiduguri. The three-zone measurement protocol 
characterized radiation across 21 office locations, yielding a 
mean dose rate of 0.19 ± 0.05 μSv/hr (Table 5), with all annual 
doses below the ICRP public limit of 1 mSv/year (maximum 
0.68 mSv/year at A15’s threshold/internal zones, 68%; Table 
4). Statistical analyses confirm significant location differences 
(F(20,126) = 7.7, p < 0.001, η² = 0.735) and zone differences 
(F(2,126) = 12.4, p < 0.001, η² = 0.118; Table 6), with a strong 
threshold-internal correlation (r = 0.976, p < 0.01; Figure 9), 
likely driven by building materials (e.g., granite) and 
geological factors in the Borno Basin. The novel Radiation 
Exposure Index (REI, Section 4.3) and K-means clustering 
(Figure 8) identify three Elevated-risk locations (A12, A15, 
A21; 0.50–0.70 mSv/year, Table 7), requiring quarterly 
monitoring and investigation of ventilation and building 
materials (e.g., granite content). The mean dose rate (0.19 
μSv/hr) is lower than that of U.S. university laboratories 
(0.25–0.30 μSv/hr), reflecting regional geological differences. 
Quality assurance (±5.5% combined uncertainty, Table 8) 
ensures data reliability, supporting a methodological 
framework for academic institutions globally. This work fills 
a critical gap in developing-nation radiation studies, 
providing a replicable three-zone protocol and baseline data 
for surveillance programs. Future studies should investigate 
radon contributions and building material radioactivity to 
refine risk models, enhancing ALARA implementation in 
educational settings. 

Ethical issue 
The authors are aware of and comply with best practices in 
publication ethics, specifically with regard to authorship 
(avoidance of guest authorship), dual submission, 
manipulation of figures, competing interests, and compliance 
with policies on research ethics. The authors adhere to 
publication requirements that the submitted work is original 
and has not been published elsewhere. 

Data availability statement 
The manuscript contains all the data. However, more data will 

be available upon request from the authors. 

Conflict of interest 

The authors declare no potential conflict of interest. 

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