Radiation and Nuclear Safety Authority

The Balloon-borne Instrument for Spectral Scanning of high-altitude Environments (BISSE) is a lightweight gamma-ray measurement system designed as a payload of standard weather balloons which can be retrieved after the flight. Its design enables multiple flights at a relatively low cost. The BISSE system automatically records radiation spectra at different altitudes throughout the flight. The sensor is cadmium zinc telluride (CZT) with a crystal volume of 1 cm 3 , providing good spectral resolution while maintaining low weight. The system also includes various auxiliary sensors that enable additional measurements during the flight, such as temperature and pressure monitoring. The Light-weight Aranda-borne Gamma-ray and Environmental Radiation detector (LAGER) is a modification of the BISSE system for underwater measurements. In contrast to the BISSE, the primary limitation for the design is overall size rather than weight; consequently the system is more compact. In this contribution, we discuss the designs of BISSE and LAGER as well as the latest improvements to both systems. The BISSE system is also investigated as a payload for a rotary-wing unmanned aerial vehicle. These flights motivated several crucial modifications to the system for future deployments. Planned balloon flight is also studied using Geant4 simulations.

Background: Health risks from radon exposure depend on long-term radon concentrations. This study quantified interannual variability in residential radon concentrations in Finland and evaluated its implications for exposure assessment and measurement recommendations. Methods: A random sample of 277 dwellings from the national radon registry, representative of Finnish regions, building types, and construction years, was monitored using year-long Makrofol-based track-etch detectors over four consecutive years (2021-2025). Year-to-year variability was characterized using the coefficient of variation (CV). Simulations incorporating the observed CVs, previously established seasonal correction factors, and measurement uncertainty were conducted to determine thresholds for follow-up measurements in relation to reference levels. Results: The coefficient of variation (CV) for normalized annual mean concentrations was 0.16, with 90% of dwellings exhibiting CV <= 0.30. Although substantial variation occurred at the individual dwelling level, no statistically significant differences in overall radon levels were observed between years. Simulations showed that applying a 100 Bq/m3 threshold for recommending follow-up measurements results in an approximately 3% false-negative rate relative to the 200 Bq/m3 reference level. Lowering the threshold to 70 Bq/m3 reduces this probability to approximately 1%. Conclusions: These findings are consistent with international studies and provide an empirical basis for recommendations on follow-up radon measurements and for quantifying uncertainties in radon exposure assessment in Finnish dwellings.

Lifetimes of low-lying states in the yrast ν i 13 / 2 band in W 165 have been measured using the recoil distance Doppler-shift (RDDS) method. The excited states of interest were populated in the Mo 92 ( Kr 78 , 4 p 1 n ) W 165 fusion-evaporation reaction and their decays were investigated via γ rays detected in the Jurogam II detector array in coincidence with nuclei separated and detected using the RITU gas-filled separator. From the experimental lifetimes, corresponding reduced transition strengths, B ( E 2 ) values, were deduced and an unusually low experimental value of the ratio B ( E 2 ; 21 / 2 + → 17 / 2 + ) B ( E 2 ; 17 / 2 + → 13 / 2 + ) = 0.59 ( 7 ) was extracted, similar to what has been observed in neighboring nuclei in this mass region. The experimental results have been compared with Woods-Saxon-type mean field and interacting boson-approximation (IBM-1) calculations.

Understanding the neutron activation of modern urban materials following a nuclear detonation is important for effective emergency rescue and response planning, yet neutron-activation data for contemporary infrastructure remain limited. This study presents a dimensioning assessment of neutron-induced activation in electric vehicle (EV) battery systems, an increasingly common high-mass, high-metal component of modern cities. Using detailed Monte Carlo simulations, supported by controlled activation experiments with a thermalized neutron field, the activation products and resulting dose rates for three major battery chemistries (NMC-811, NCA, and LFP) arranged in a representative battery pack, were evaluated. Results show that EV batteries can generate substantial short-lived gamma activity immediately after neutron exposure, dominated by 28Al, 64Cu and 56Mn for nickel- and cobalt-bearing chemistries, while long-term activity is driven primarily by 60Co (NMC/NCA) and 32P (LFP). Dose rate estimations indicate that elevated fields may be present during the first hours post-detonation but decrease by several orders of magnitude within 24 h. Comparisons with activation of urban road materials reveal that 24Na generated in asphalt and sand substrates can equal or exceed battery-derived dose contributions. Overall, EV batteries constitute a relevant but transient localized radiological hazard in the immediate aftermath of a nuclear detonation, with significance highly dependent on battery chemistry and the timing of response operations. These findings support improved modelling of post-detonation environments and help contextualize EV batteries within broader urban activation scenarios.

X-ray multimeters (XMMs) are widely used for quality control measurements in mammography, providing air kerma, half-value layer (HVL), and tube voltage from a single exposure. The energy dependence of their response was comprehensively investigated for various anode/filter combinations and software selections. However, the influence of a change in the X-ray spectrum due to additional material in the beam has not yet been systematically investigated. The aim of this study is to quantify the sensitivity of XMM calibration coefficients to changes in X-ray spectra introduced by additional polymethyl methacrylate (PMMA) of different thicknesses. Four commercially available XMMs were calibrated at the IAEA dosimetry laboratory for air kerma, HVL, and tube voltage using two anode/filter combinations (Mo/Mo and W/Al) at tube voltages ranging from 25kV to 35kV. Calibration coefficients were determined without additional filtration and with PMMA thicknesses of 2.0mm, 2.8mm, and 4.8mm placed close to the X-ray tube to modify the primary spectrum while minimizing scattered radiation reaching the detectors. In relation to the calibration coefficient determined without PMMA deviations of up to 11% were observed for air kerma rate. HVL and tube voltage calibration coefficients exhibited substantially larger deviations, reaching up to 37% and 42%, respectively. We conclude that changes in the X-ray spectra as from additional PMMA filtration, can substantially alter XMM calibration coefficients, particularly for HVL and tube voltage measurements. XMM responses are highly sensitive to spectral modifications beyond standard anode/filter combinations and tube voltage settings.