The team used gamma-ray spectroscopy with a sodium iodide detector coupled to a multichannel analyser, calibrating the system with traceable reference sources to identify the characteristic energy peaks of potassium-40, uranium-238 and thorium-232. Samples were collected in acid-rinsed containers, treated with concentrated hydrochloric acid to fix the radioactive elements, and stored for four weeks to allow secular equilibrium between the parent radionuclides and their decay products before counting. Background radiation was characterised by counting an empty container for 36,000 seconds, and minimum detectable activities were calculated for each radionuclide to ensure the measurements were statistically meaningful rather than noise.

The results show a consistent pattern of elevated radioactivity. In Benin City, mean activity concentrations were 56.1 plus or minus 1.5 becquerels per litre for potassium-40, 4.3 plus or minus 0.8 becquerels per litre for uranium-238 and 9.3 plus or minus 1.5 becquerels per litre for thorium-232. In Ogwa, potassium-40 averaged even higher at 67.3 plus or minus 1.8 becquerels per litre, while uranium-238 and thorium-232 averaged 2.5 and 6.9 becquerels per litre respectively. Against guideline values of roughly 10, 10 and 1.0 becquerels per litre for these three radionuclides, potassium-40 and thorium-232 were clearly out of bounds, with about ninety-three percent of samples exceeding the safe limits for those isotopes. The highest potassium-40 reading in Benin City reached 132.6 becquerels per litre, while uranium-238 remained within acceptable limits everywhere except two locations.

Dose calculations converted these activity concentrations into annual effective doses using standard ingestion coefficients and age-specific water intake rates for six age categories: infants, one-year-olds, five-year-olds, ten-year-olds, fifteen-year-olds and adults. In Benin City, mean annual effective doses ranged from 3.7 millisieverts per year for infants down to 1.3 millisieverts per year for ten-year-olds, while Ogwa produced values between 3.0 and 1.1 millisieverts per year. Every mean value in every age group exceeded the World Health Organization’s tolerable limit of 0.1 millisieverts per year by more than an order of magnitude, and infants emerged as the most vulnerable group because of their comparatively high water intake per unit body mass.

Thorium-232 proved to be the dominant contributor to the total dose, accounting for roughly eighty-one percent of the annual effective dose for infants in Benin City and nearly eighty percent for adults, followed by potassium-40 and finally uranium-238. This ordering matters because the dose conversion factor for ingested thorium is several times higher than for uranium or potassium, meaning even moderate thorium levels translate into disproportionately large effective doses. The researchers attribute the thorium enrichment to the local geology: the region sits atop the Benin Formation, a sedimentary sequence rich in heavy minerals such as monazite and zircon that host thorium in their crystal lattices. Unlike uranium, which migrates readily as soluble U(VI), thorium exists as highly insoluble Th(IV) and reaches groundwater mainly through colloid-mediated transport of fine particles and alpha recoil during prolonged water-rock interaction.

The study also computed a suite of radiological hazard indices. Radium equivalent activity averaged 21.9 becquerels per litre in Benin City and 17.5 in Ogwa, well below the recommended ceiling of 370 becquerels per litre, and the external and internal hazard indices and the representative gamma index all remained far below unity. The annual gonadal equivalent dose averaged 69.7 and 57.6 for the two locations respectively, beneath the standard reference value. In other words, the acute external hazard posed by the water is modest. The concern centres instead on chronic ingestion: the excess lifetime cancer risk exceeded the global mean of 0.2 times ten to the minus three at every sampling point. Mean ELCR values in Benin City reached 10.0 times ten to the minus three per year for infants and 5.3 for adults, while Ogwa’s values, though lower, remained above the safe benchmark.

One of the most striking findings lies in the statistical structure of the data. In Benin City, all radionuclides and hazard indices showed strong positive correlations, statistically significant at the one percent level, with coefficients approaching one for pairs such as radium equivalent and absorbed dose rate. The researchers interpret this as the signature of a homogeneous hydrogeochemical regime in the sedimentary coastal plain aquifer, where high infiltration rates and uniform leaching move the radionuclides together. Ogwa told a different story. Sitting on the fractured Precambrian Basement Complex of the Esan Plateau, the town’s aquifer produced a negative correlation of minus 0.79 between potassium-40 and thorium-232, and potassium-40 correlated negatively with nearly every hazard index. This suggests that thorium and uranium, locked in accessory minerals like zircon and monazite, follow entirely different mobilisation pathways from potassium released by weathering feldspars, and that agricultural fertiliser use may further elevate potassium levels in the rural setting.

Comparisons with international studies place the Edo State values in an intermediate to high range. Uranium concentrations here fall below those reported for crystalline basement regions of Kwara State and Abuja but exceed levels found in Ghana, Burkina Faso, Brazil, Malaysia, Serbia and Spain. Thorium levels are far above the 1.0 becquerel per litre benchmark and comparable to values in Iraq, Pakistan, Bangladesh and Kenya. Perhaps most tellingly, the estimated ingestion doses for adults, between 1.6 and 2.0 millisieverts per year, exceed exposure pathways usually considered dominant in Nigeria, including seafood consumption in petroleum-impacted Niger Delta communities, indoor exposure near petroleum facilities, vegetable intake in Ilorin and even doses received by artisanal gold miners. Untreated groundwater from thorium-enriched formations, the authors conclude, represents a greater cancer burden than industrial pollution or mining occupations in the populations studied.

The researchers acknowledge that the imbalance between thirty samples from Benin City and only four from Ogwa limits statistical power for the rural site, and they frame the Ogwa findings as preliminary. Nevertheless, they argue the case for action is urgent. They recommend continuous radiological monitoring of borehole water, household-level mitigation using reverse osmosis, activated alumina or ion-exchange systems capable of removing more than ninety-five percent of radionuclides, and the integration of radiological screening into borehole registration and drinking water certification by regulatory bodies such as NAFDAC and the Edo State Ministry of Environment. Future work, they suggest, should examine seasonal variation linked to rainfall and recharge, food chain transfer of the isotopes into crops, and epidemiological studies of cancer incidence among dependent populations. For now, the message for the roughly 1.8 million residents of Benin City and the communities of Esan Land is clear: the aquifer beneath their feet is quietly radioactive, and the water drawn from it deserves systematic scrutiny before long-term exposure turns a geological fingerprint into a public health crisis.

Subject of Research: Natural radionuclide contamination and radiological health risks in borehole drinking water in Benin City and Ogwa, Edo State, Nigeria

Article Title: Assessment of natural radionuclides and radiation hazard indices of borehole water samples collected from selected locations in Benin City and Ogwa, Edo State, Nigeria

Article References: Popoola, F. A., & Osahon, O. D. (2026). Assessment of natural radionuclides and radiation hazard indices of borehole water samples collected from selected locations in Benin City and Ogwa, Edo State, Nigeria. BMC Environmental Science, 3(1), Article 14. https://doi.org/10.1186/s44329-026-00057-7

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00057-7

Keywords: radionuclides, borehole water, groundwater, radiation hazard, thorium-232, potassium-40, uranium-238, annual effective dose, excess lifetime cancer risk, gamma-ray spectroscopy, Benin City, Nigeria

Gamma rays act like fingerprints of how nuclei shed energy after being excited. The probability of emitting gamma rays at different energies is summarized by the gamma-ray strength function, a key ingredient used in calculations ranging from laboratory experiments to astrophysical rate predictions. For years, researchers have seen a “low-energy enhancement” (LEE): unexpectedly more gamma rays at the low end of the spectrum than conventional expectations anticipate.

Crucially, the team demonstrates that the excess is tied to magnetic transitions, clarifying what type of nuclear rearrangement is responsible. Electric and magnetic transitions reflect different ways protons and neutrons reorganize as the nucleus moves between energy states, and LEE had been difficult to attribute to either mechanism.

The work used an experimental strategy that begins with beta decay of copper-70, preparing zinc-70 through two distinct initial pathways. By separating copper-70’s ground-state and isomeric-state contributions, the researchers effectively create two complementary “entry routes” into the same nucleus, which improves sensitivity to the structure of zinc-70’s low-energy gamma emissions.

To produce exceptionally pure isomer-separated beams, the collaboration leveraged FRIB’s Low Energy Beam and Ion Trap (LEBIT). The resulting gamma rays from zinc-70 were then captured with the Summing NaI (SuN) detector, enabling precise reconstruction of how the strength function varies with energy.

Instead of relying on a single analysis, the team applied two established extraction approaches—the beta-Oslo method and the Shape method—to independently determine the gamma-ray strength function for each initial state. When the results were compared, magnetic transitions consistently emerged as the driver of the enhancement.

“This is a key step forward,” the researchers note, because it connects the experimental anomaly directly to a theoretical explanation. That means LEE can be treated as a physical mechanism rather than an unresolved systematic effect.

Beyond the nucleus, the implications are practical: LEE increases the likelihood of neutron-capture reactions, influencing the formation of heavy elements during events like supernovae and neutron star mergers. Over many nuclei, even subtle changes can significantly shift reaction-rate estimates used in both astrophysics modeling and nuclear technology planning.

Finally, the study showcases the role of next-generation tools and cross-institution collaboration. By combining FRIB’s rare-isotope capabilities with multi-lab analysis expertise, the researchers also point to a roadmap for extending isomer-separated measurements to other nuclei to map where LEE appears—and why.

Subject of Research: Low-energy enhancement of gamma rays in zinc-70; origin of LEE as magnetic transitions in the nucleus
Article Title: “Magnetic character of the low-energy enhancement in 70Zn”
News Publication Date: July 23, 2026
Web References: https://www.nature.com/articles/s41586-026-10758-3
References: Nature (15-Jul-2026)
Image Credits:

Keywords

Gamma rays; nuclear structure; zinc-70; low-energy enhancement; magnetic transitions; gamma-ray strength function; beta decay; isomer separation; neutron capture; astrophysics

The results come from a collaborative campaign at the GANIL accelerator facility in Caen, northern France. A beryllium-9 target was bombarded with uranium-238 ions, generating short-lived curium-247 nuclei that rapidly split into two lighter fragments. This setup allowed researchers to probe neutron-rich, excited systems whose gamma emission had been difficult to measure systematically.

A key advance was doing it all in one experiment. The team combined two complementary instruments: VAMOS++ to precisely identify the fission products’ masses and charges, and PARIS, a fast scintillation detector array designed to register high-energy gamma rays within extremely tight time windows. Together, the measurements let the researchers assign specific gamma spectra to specific isotopes as they emerged from fission.

Over a two-week campaign, the experiment mapped a “family” of heavy neutron-rich nuclei—well away from the valley of stability—under consistent experimental conditions. By avoiding isotope-by-isotope setups, the dataset provides a rare basis for comparing gamma emission strengths across many isotopes while keeping systematic uncertainties aligned.

Analysis and follow-up theoretical work in France suggest that part of the high-energy gamma signal is connected to pygmy resonances. In these modes, excess neutrons form a neutron-skin layer and, when the nucleus is excited, oscillate collectively against the proton core in a weaker but distinct vibrational response.

The study focuses on isotopes clustered near the doubly magic tin-132 region. For these nuclei, the gamma emission is interpreted as evidence of how neutron-skin dynamics translate into identifiable photon “bumps” during the de-excitation of fission fragments.

The findings arrive in Physics Letters B and include a new experimental isotopic mapping that links the fission gamma enhancement to pygmy dipole behavior. For nuclear modelers, the dataset offers input for recalibrating descriptions of fission dynamics, potentially improving predictions relevant to reactor physics and nuclear safety.

Beyond terrestrial applications, the better characterization of fission properties and excited heavy nuclei may also refine astrophysical scenarios—such as element formation in extreme environments, modeling neutron-star mergers, and estimating black-hole growth timescales.

Subject of Research: Pygmy neutron-skin resonances and high-energy gamma emission in fission fragments
Article Title: First experimental isotopic mapping of the fission “γ-bump” and its connection to the Pygmy dipole resonance
News Publication Date: 8-May-2026
Web References: https://doi.org/10.1016/j.physletb.2026.140506
References: Kumar et al., Physics Letters B 2026, 878, 140506. DOI: 10.1016/j.physletb.2026.140506
Image Credits: Source: IFJ PAN

Keywords

Pygmy resonances, neutron skin, fission gamma rays, curium-247, VAMOS++, PARIS, GANIL, neutron-rich isotopes, nuclear structure, gamma “γ-bump”