The influence of method precision on assessing radiological hazards for patients using radium water in balneotherapy

This research aims to demonstrate the impact of technical precision on assessing radiological risks for patients receiving balneotherapy with radium water.

Sanatorium treatments and SPA services are popular in Poland for patients who have finished hospital treatments and for outpatients. According to the Ministry of Health, there are currently 49 sanatorium complexes in Poland, comprising 286 individual sanatoria. These facilities have the capacity to accommodate thousands of individuals.

Southern Polish health spas, particularly those located in the Sudety Mountains, utilize radioactive mineral waters containing radium and radon. Resorts such as Kamienica, Świeradów Zdrój, and Cieplowody offer radon-enriched water with a minimum activity level of 74 Bq/L [1, 2].

Previous studies predominantly concentrated on monitoring the preservation of therapeutic properties in medicinal water through the measurement of ²²²Rn activity concentration [3]. Limited information is available regarding the effects of bathing in waters containing ²²⁶Ra on external exposure [4].

This study compared several methods for determining the concentration of ²²⁶Ra in water, including γ-spectrometry using both medium-efficiency and high-efficiency high purity germanium (HPGe) detectors, as well as the emanation and the liquid scintillation counting (LSC) methods.

To calculate the radiation hazard, two ICRP models were adopted: (1) the model of Reference Men [5] and (2) the model of external exposure [6]. The adopted model uses coefficients for transforming activity concentration in water into an effective dose in humans.

The report explores the accuracy of evaluating radiation hazards, with a particular focus on the significance of technique uncertainty. When it comes to measuring radiation, accuracy is extremely important because of the potential dangers it poses to both human health and the environment. However, a certain degree of tolerance is also accepted.

The concentration of ²²⁶Ra, as estimated through several methods, is presented in Table 1, together with the associated radiation hazard for patients undergoing balneotherapy.

The most precise methods are the γ-spectrometry techniques, albeit with some reservations outlined below. Their precision ranges from 2.2% to 5.0%. Uncertainty in γ-spectrometry is mostly due to measurement errors and errors related to energy and efficiency calibration execution. The ultimate error is contingent on the approach used for efficiency calibration. For mathematical calibration, the accuracy is approximately 1% or less. The value of calibration using a source relies on the precision of preparing the calibration standard and is around 3%.

The results obtained from direct and indirect calculations using both HPGe detectors show a few differences. The outcome from the 40% relative efficiency detector overestimated values when compared with the other detector, as well as the LSC and emanation methods. The absence of hermetic sealing in Marinelli beakers was considered a potential primary factor contributing to the observed difference. However, a procedure was implemented to confirm or refute this hypothesis, involving the hermetic sealing of Marinelli beakers using silicone glue.

Nevertheless, certain disparities between the Genie2000 calculation method and the techniques based on evaluating FEAPs are noticeable, particularly in the results from the medium efficiency HPGe detector. This suggests that the Genie2000 method might not be the most precise choice in this specific scenario. The direct measurement approach for ²²⁶Ra has the benefit of fast sample preparation and measurement, eliminating the requirement for progeny ingrowth. The drawbacks of this approach principally stem from the low emission probability (3.57%) of the gamma photopeak and the presence of the interfering primary gamma emission of ²³⁵U at 185.7 keV and intensity of 57.24% [9].

The measurement uncertainty of the emanation method is 16% and was calculated using Eq. (3): (3) u(A)A=u2(Np)+u2(Nt)(Np−Nt)2+(u(K)K)2+(u(F)F)2+(u(Y)Y)2+(u(V)V)2 \[\frac{u\left( A \right)}{A}=\sqrt{\begin{array}{*{35}{l}} \frac{{{u}^{2}}\left( {{N}_{p}} \right)+{{u}^{2}}\left( {{N}_{t}} \right)}{{{\left( {{N}_{p}}-{{N}_{t}} \right)}^{2}}}+{{\left( \frac{u\left( K \right)}{K} \right)}^{2}}+{{\left( \frac{u\left( F \right)}{F} \right)}^{2}} \\ +{{\left( \frac{u\left( Y \right)}{Y} \right)}^{2}}+{{\left( \frac{u\left( V \right)}{V} \right)}^{2}} \\ \end{array}}\]

The main factor contributing to the total uncertainty is the first component, which determines the standard uncertainty of the counting, where N_p represents the sample counting with background (imp/min), N_t denotes the background counting (imp/min), t_p and t_t are sample and background measurement times (min): (4) u(Np)=Nptp \[u\left( {{N}_{p}} \right)=\sqrt{\frac{{{N}_{p}}}{{{t}_{p}}}}\] (5) u(Nt)=Nttt \[u\left( {{N}_{t}} \right)=\sqrt{\frac{{{N}_{t}}}{{{t}_{t}}}}\]

The overall uncertainty is influenced by various factors, including the uncertainty of the total correction factor, which considers the buildup and decay of ²²²Rn{[u(F)]/F}², as well as the uncertainty of the sample volume {[u(V)]/V}², chamber calibration factor {[u(K)]/K}, and efficiency {[u(Y)]/Y}². These components have a lesser impact than the measurement error of the counting frequency.

According to observations in the literature, such a range of uncertainty (10–20%) is typical for this type of measurement [14].

Radon emission counting is a favorable choice when there is a need for achieving low detection limits. This method is characterized by its simplicity and insensitivity to sample mineralization, chemical composition, or the presence of contaminants. However, ensuring the tightness of the measurement system poses a challenge, and the necessity of ²²²Rn equilibrium may restrict the application of this method when rapid determinations are required [13].

For the LSC method, the estimated relative uncertainty of the standard radioactive concentration, as per Eq. (6), is 10%, primarily attributed to counting u(N₀) and efficiency u(ε) errors, which constitute the main sources of uncertainty: (6) u(A)=(AN0)2×u(N0)2+(Aε)2×u(ε)2+(AVp)2+u(Vp)2 \[u\left( A \right)=\sqrt{\begin{array}{*{35}{l}} {{\left( \frac{A}{{{N}_{0}}} \right)}^{2}}\times u{{\left( {{N}_{0}} \right)}^{2}}+{{\left( \frac{A}{\text{ }\!\!\varepsilon\!\!\text{ }} \right)}^{2}}\times u{{\left( \text{ }\!\!\varepsilon\!\!\text{ } \right)}^{2}} \\ +{{\left( \frac{A}{{{V}_{p}}} \right)}^{2}}+u{{\left( {{V}_{p}} \right)}^{2}} \\ \end{array}}\] (7) u(ε)=(εN0)2×u(N0)2+(εAW)2×u(AW)2+(εVW)2+u(VW)2 \[u\left( \text{ }\!\!\varepsilon\!\!\text{ } \right)=\sqrt{\begin{array}{*{35}{l}} {{\left( \frac{\text{ }\!\!\varepsilon\!\!\text{ }}{{{N}_{0}}} \right)}^{2}}\times u{{\left( {{N}_{0}} \right)}^{2}}+{{\left( \frac{\text{ }\!\!\varepsilon\!\!\text{ }}{{{A}_{W}}} \right)}^{2}}\times u{{\left( {{A}_{W}} \right)}^{2}} \\ +{{\left( \frac{\text{ }\!\!\varepsilon\!\!\text{ }}{{{V}_{W}}} \right)}^{2}}+u{{\left( {{V}_{W}} \right)}^{2}} \\ \end{array}}\] (8) u(N0)=(Npt)2+(Ntt)2 \[u({{N}_{0}})=\sqrt{{{(\frac{{{N}_{p}}}{t})}^{2}}+{{(\frac{{{N}_{t}}}{t})}^{2}}}\] where N_p represents the sample counting with background (imp/s), N_t is the background counting (imp/s), N₀ is the net counting (imp/s), V_p is volume of sample (L), V_W is volume of standard solution (mL), t is measurement time (s), u(A_W) is working solution activity error (Bq/mL).

Additionally, potential interferences, such as chemiluminescence and photoluminescence, can lead to elevated background levels, thereby reducing measurement precision. The simplicity of execution and the ability to quickly analyze samples enable effective utilization of the LSC method. Although sample preparation involves multiple steps and necessitates special reagents like scintillation cocktails – whose composition significantly impacts counting efficiency – the continual refinement of calibration procedures works to alleviate uncertainties and interferences, thus enhancing the efficacy and dependability of results [12, 13].

The study established a direct proportionality between the effective dose and the concentration of ²²⁶Ra in water. Furthermore, the applied method’s uncertainty intricately ties into the precision of the effective dose measurement.

It is worth noting that γ-spectrometry techniques have demonstrated the highest precision, ranging from 2.2% to 5.0%. However, the discrepancies observed between computational methods and measurement techniques underscore the need for careful consideration when selecting the most suitable approach for specific scenarios.

In circumstances where the radiation hazard nears the dose limit, all methods outlined in the study were deemed applicable. It is noteworthy that the determined values correspond to exceedingly small doses.

Our investigation demonstrates the complex interplay between radium determination methods, accurate dose estimations, and their influence on the assessment of radiation exposure. Comprehending these techniques is crucial for efficient risk mitigation, particularly when approaching dosage limits. Our efforts in providing information for decision-making in exposure monitoring and control directly contribute to safeguarding public health and the environment.