# LyoScope: a portable lyoluminescence reader prototype

Magdalena Biernacka, Krzysztof Maternicki, Michal Sądel, Sebastian Kreutzer

## ► To cite this version:

Magdalena Biernacka, Krzysztof Maternicki, Michal Sądel, Sebastian Kreutzer. LyoScope: a portable lyoluminescence reader prototype. Radiation Measurements, 2025, 189, 10.1016/j.radmeas.2025.107545. hal-05334132

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# LyoScope: a portable lyoluminescence reader prototype

Magdalena Biernacka<sup>a,b,*</sup>, Krzysztof Maternicki<sup>c</sup>, Michał Sądel<sup>d</sup>, Sebastian Kreutzer<sup>a</sup>

## ARTICLE INFO

**Keywords:**

Lyoluminescence
Radiation dosimetry
Portable reader
Geochronology
Halite

## ABSTRACT

We present the design of *LyoScope*, a portable, compact device for measuring lyoluminescence (LL). Lyoluminescence is a phenomenon occurring during the dissolution of previously irradiated material. Measurements facilitate the estimation of the total dose absorbed by the material since its last exposure to light, heat, or moisture. Due to its versatility, *LyoScope* is suitable for both environmental and laboratory measurements. Its elementary design enables self-assembly, such as through 3D printing. We provide a detailed technical description and present first performance tests: the minimum detectable dose for NaCl was determined at ~5 mGy, repeatability tests on natural halite achieved a variation of only ~2.4 %, and fading experiments revealed that ~35–40 % of the LL signal is lost within weeks, followed by stabilization of ~35–60 % of the signal. In addition, we demonstrate the option of attaching an EM-CCD camera to our setup enabling spatially-resolved LL measurements and a visualization of the dissolution process. Our results underscore that *LyoScope* enables reproducible LL measurements and support the potential of LL as a complementary tool for dosimetry and geochronology.

## 1. Introduction

Reliable methods for measuring radiation doses absorbed by passive detectors are in high demand. They are critical for assessing radiation exposure caused by unwanted incidents or as part of geochronology studies in Earth Sciences, such as tracking climate changes in arid environments or in more exotic applications, such as detecting neutrinos and dark matter with rocks (Drukier et al., 2019). Our study focuses on the less commonly used and often overlooked luminescence phenomenon – lyoluminescence (LL) (Wiedemann and Schmidt, 1895). LL is the emission of light when a previously irradiated ionic crystal dissolves in a suitable solvent. It was systematically investigated in the 1970s, among others, by Atari and Ettinger (e.g. Atari and Ettinger, 1975) and Arnikar et al. (e.g. Arnikar et al., 1970). In alkali halides, irradiation creates lattice defects in the form of colour centres (F- and V-centres). During dissolution, hydrated electrons released from F-centres recombine with hole-type centres (V₂) at the solid-liquid interface, producing photons; additional chemiluminescent reactions in solution may also contribute (Atari, 1980). Because LL intensity is approximately proportional to the absorbed dose, the effect has long been considered for ionising radiation dosimetry. In geochronology, LL provides a complementary “clock”: it

reflects the last crystallisation or dissolution of a mineral rather than its last exposure to light or heat, making evaporitic minerals such as halite and sylvite particularly attractive.

Among the materials tested, alkali halides, especially NaCl and its mineral counterpart (blue) halite, have proven the most promising (Atari et al., 1973). They combine high emission efficiency with the simplicity of readout, as the signal can be obtained by dissolution even in pure water. Other geological minerals, including carbonates such as calcite and aragonite, have also shown LL emission when dissolved in dilute hydrochloric acid (Copty-Wergles et al., 1990). Although dissolution in acid is more demanding, it broadens the range of minerals that could serve as LL detectors. These findings highlight the potential of LL as a complementary tool to conventional luminescence dating methods that employ mainly quartz or feldspar across diverse geological contexts.

Unfortunately, despite this promise, LL has remained underutilised compared to established techniques such as optically stimulated luminescence (OSL, Huntley et al., 1985). Unlike OSL, which probes only a subset of electron traps, LL can act as an ‘all-trapped-electron readout’. However, its response is strongly affected by grain size, solvent chemistry and dissolution dynamics, and the LL signal often fades markedly on timescales of hours to weeks (Atari and Ettinger, 1975) where OSL in

<footnote><sup>a</sup> Institute of Geography, Heidelberg University, Im Neuenheimer Feld 348, 69120, Heidelberg, Germany</footnote>

<footnote><sup>b</sup> Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100, Toruń, Poland</footnote>

<footnote><sup>c</sup> Independent researcher, 69120, Heidelberg, Germany</footnote>

<footnote><sup>d</sup> Institute of Nuclear Physics Polish Academy of Sciences, 31-342, Krakow, Poland</footnote>

<footnote>* Corresponding author. Institute of Geography, Heidelberg University, Im Neuenheimer Feld 348, 69120, Heidelberg, Germany.
E-mail address: magdalena.biernacka@uni-heidelberg.de (M. Biernacka).</footnote>
NaCl is comparatively stable (Bailey et al., 2000). A further practical limitation is the lack of dedicated, commercially available LL instrumentation. Earlier studies relied on laboratory-tailored detection systems, which hamper reproducibility and cross-laboratory comparison.

To address these issues, we introduce *LyoScope*, a compact, modular LL reader designed for reproducible measurements in both laboratory and (within limits) field settings. The system offers controlled solvent delivery and optical detection while remaining adaptable to diverse materials and solvents, allowing our LL reader to be used in various application scenarios.

## 2. *LyoScope* - design and performance

LL measurements require placing a specific amount of dry, solid crystalline material into a dry measurement chamber and initiating luminescence emission detection. A precisely known portion of the solvent is then injected into the sample chamber while the device captures the emitted light during dissolution, thus recording LL. After recording, the measured sample should be removable to be easily replaced with a new one.

The developed portable LL reader is exhibited in Fig. 1, while the general design scheme for such a system as a block diagram is shown in Fig. 2. We opted for a modular device configuration that facilitates the connection of a luminescence detector (here a photomultiplier tube, PMT) of choice in a vertical orientation. We tested two PMTs with comparable technical characteristics: an ET Enterprise PDMF9107-USB01 and a Hamamatsu H11870-01. Both devices have a built-in microcontroller and can be connected to a PC using a USB-A (ET Enterprise) or RS-232 (Hamamatsu) interface. To optimize the geometry and ensure high signal detection sensitivity, we minimized the distance between the sample and PMT, which shortens the optical path of the recorded LL signal. To protect the PMT from vapours emitted by the sample, a sealed, 1-mm-thick fused silica window was placed in front of the PMT. The solvent can be injected through a medical needle installed at the solvent inlet (shown in Fig. 3). The injection is achievable with a medical syringe, electronic repeater pipette, or programmable peristaltic pump connected to the needle. The advantage of using a pipette or pump over a syringe is the highly improved control over the volume and injection speed of the solvent, which ensures better repeatability and reproducibility of the obtained results. The detector housing and sample chamber are designed to be opaque, ensuring optimal light protection and making a shutter unnecessary to protect the PMT. Housing elements are printable, e.g., using a standard 3D printer with chosen filaments, e.g., PLA, ABS or PETG. Optionally, the device can be placed on a magnetic stirrer to enable consistent mixing during LL measurement (see Fig. 2).

The crucial component of *LyoScope* is the sample chamber (sample bowl). Only a sufficiently spacious (approximately volume of 9 ml), parabolically shaped bowl enables consistent LL results across a wide range of sample masses from as little as 1 mg to several hundred milligrams. The chamber shape ensures that the tested sample is always best centred and aligned with the PMT. Additionally, the shape of this element has been designed to maximise light collection. We constructed the bowl from high-gloss polished stainless steel, which provides a mirror-like surface that effectively reflects LL emission light and ensures chemical inertness with various solvents. As illustrated in Fig. 3, the green lines represent LL light rays emitted by point sources within the sample volume, while the blue lines depict their reflections. Based on our estimations, the reflective inner surface of the bowl, combined with the ~23 mm effective diameter of the one-inch photomultiplier window, allows for the detection of approximately half of the total LL emissions from a sample weighing several dozen milligrams dissolved in 5 ml of solvent. This could be further enhanced in the future through improvements in the reflective surface materials and further modifications to the edge geometry of the bowl.

All presented components are modular and reusable, and the material selection (e.g., PETG, Teflon, or stainless steel) is adaptable to the

user's needs. The dissolution solvent is stored in a closed container, while temperature, pressure, and humidity are controlled externally. We found that a temperature sensor is unnecessary, it can be included if wanted, although it requires a slight modification to the reader housing (not shown in the graphs).

We used PMTs that operate in continuous single-photon counting mode. Those PMTs only require a stable voltage of 5V in a current range available through standard USB ports of consumer PCs (please see the manufacturer's datasheet for more details). The ET Enterprise PMT is connected with a USB-A cable only and operated through photodetector module software that is freely available from the manufacturer. The Hamamatsu requires a simple wire connection to a 5V power supply and an RS-232 connection, for instance, through low-cost, commercially available USB to RS-232 adapters. To control the PMT in our experiments, we developed a basic R 'shiny' (Chang et al., 2025; R Core Team, 2024) based control software available open-access (Kreutzer and Colombo, 2024).

## 3. Sensitivity, repeatability, and stability in salt

For LL dose-response and stability (fading) experiments, a high-purity NaCl chemical reagent was used, prepared in grain size fractions of 125–212 µm and 90–125 µm, respectively, while repeatability tests were performed on natural blue halite from Morsleben (125–212 µm) without laboratory irradiation (natural LL signal). All samples were gently ground in a mortar, dried for ~16 h at 50 °C, and sieved to obtain sub-fractions stored in sealed lightproof containers. Laboratory irradiations were carried out in calibrated TL/OSL readers (Risø or Freiberg Instruments) equipped with ⁹⁰Sr/⁹⁰Y beta sources ensuring comparable dose delivery to quartz coarse-grain standards. Aliquots of typical mass ~5 mg were prepared by dispensing a thin layer of grains onto empty stainless-steel discs in the readers. After irradiation, aliquots were collected and stored in opaque containers until measurement. Each aliquot was weighed immediately prior to LL measurement and dissolved in a CuCl₂ solution (5·10⁻⁴ mol dm⁻³ cf. Biernacka et al., 2025) using solvent volumes of 5 ml or 1.5 ml in the stability test. A peristaltic pump in the *LyoScope* ensures a reproducible injection rate and dissolution of the material. Thus, “aliquots” denote independent subsamples prepared from the same homogenised sample fraction. No recrystallisation was performed, and each aliquot was measured only once. LL intensities were integrated over a fixed 30 s interval and normalized to the aliquot mass (counts·mg⁻¹). Instrumental background was regularly checked by measuring the empty *LyoScope* and with solvent alone; datasets affected by elevated background were discarded. All experiments were performed at room temperature, using subdued red light only for operation.

To estimate the lower determination limit (MDD) of the *LyoScope*, the LL dose-response was measured for NaCl after irradiation doses of 1, 10 and 50 Gy (dose rate: 0.244 ± 0.004 Gy s⁻¹) and stored in the dark at room temperature for 138 days to avoid the influence of unstable LL component. The dose-response data were fitted with a single-exponential function $y(D) = A \cdot (1 - \exp(-\frac{D}{D_0}))$ using weighted nonlinear least square fitting (weights = 1/σ²). Fig. 4 (log-log representation) illustrates the LL dose-response data, the best-fit single-exponential model, and the vertical line corresponding to $D_0$. The fit parameters are $A = (1.54 \pm 0.42) \times 10^5$ counts·mg⁻¹ and $D_0 = 21.0 \pm 7.8$ Gy (1σ). Here, $D_0$ represents the characteristic dose at which the LL signal reaches ~63% of its saturation value, which in principle provides a physically meaningful indicator of the useable dynamic range under ideal conditions and the given model. However, in the present case the obtained value of $D_0$ should be regarded as an approximate estimate, as the available dose range did not extend to full saturation. A more precise determination of $D_0$ will require additional regeneration dose points, which are planned in forthcoming studies.

The instrumental background of the PMT was characterised without
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Technical sketch of the elementary components of *LyoScope* based on the ET Enterprise model PDMF9107-USB-01 photomultiplier tube (CAD models of Parts 1–6 are available on Zenodo).</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Fig. 2. Block diagram of a generalised LL measurement system concept.</figcaption></figure>

a sample. The mean of three independent acquisitions was 185 counts, with a standard deviation (SD) of 6 counts for an integration range of 30 s. Following the standard definition, the determination threshold was taken as the mean plus three standard deviations (mean + 3·SD = 202 counts). Normalising this to a reference sample mass of 5.3 mg yields a threshold of 38.2 counts·mg⁻¹ (the horizontal line shown in Fig. 4). The intersection of this threshold with the single-exponential growth curve gives the minimum determination dose MDD = 5.22 ± 2.40 mGy (1σ), where the uncertainty reflects propagation of errors in A, D₀, and the background threshold. The corresponding 95 % confidence interval is ~2.0–9.6 mGy. The obtained MDD value is of the same order of magnitude as the one previously determined using OSL for NaCl (Ekendahl and Judas, 2011). This suggests that LL, under optimized conditions, can serve as a complementary technique to existing dosimetry methods.

Repeatability tests were conducted using a naturally occurring blue halite sample from Morsleben (Germany), which was also investigated earlier (see Biernacka et al., 2025). The relative variation in the LL signal among the nine measured aliquots was ~2.4 %, well within acceptable limits for heterogeneous natural materials. The experimental results on LL reproducibility are presented in Fig. 5. These findings highlight the robustness of *LyoScope* in delivering reproducible measurements, even for structurally heterogeneous materials such as natural halite.

Stability of the LL signal was investigated using NaCl irradiated with doses of 0.55 Gy, 5.46 Gy, and 54.61 Gy at a dose rate of 0.0546 ± 0.0013 Gy s⁻¹. Samples were stored in the dark at room temperature inside a desiccator for defined storage intervals (19, 78, 518, 859) h.

<figure><img src="image_5.png" /><figcaption>Fig. 4. LL dose-response of NaCl measured using *LyoScope* equipped with an ET Enterprise model PDMF9107-USB-01 photomultiplier tube. Data are shown as mass-normalized means ±1σ with a single-exponential fit. The dashed line marks the minimum determination dose (MDD) based on the PMT background + 3σ, and the vertical line corresponds to D₀. Both axes use logarithmic scales.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 5. Natural LL signals measured under identical conditions for aliquots of the blue halite sample bhS2, using *LyoScope* equipped with an ET Enterprise model PDMF9107-USB-01 photomultiplier tube (no laboratory irradiation of the aliquots). The mass-normalized LL corresponds to the entire integral of each LL curve.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 3. Cross-section of the sample chamber (bowl) in the *LyoScope* portable reader.</figcaption></figure>
Analysis of LL fading was performed by integrating the LL counts of each aliquot (three for each dose and storage interval), normalising them to the sample mass, and averaging the results for each dose and storage interval. The obtained mean values were further normalized to the mean intensity after 19 h of storage. The relative signal decrease over time was used to quantify fading. Background subtraction was not applied, as it remained negligible and stable throughout all measurements.

The fading results are summarised in Fig. 6, where the LL signal is plotted as a function of log-transformed storage time. The data follow an approximately linear decrease with $log_{10}(t/t_{19h})$, consistent with the empirical description of fading processes proposed by Huntley and Lamothe (2001). Across the dose range tested (0.55–54.61 Gy), ~35–40 % of the LL signal is lost within the first weeks of storage, after which the signal stabilises at ~35–60 % of its initial intensity. No systematic dose dependence was observed. This supports the interpretation that LL in NaCl comprises at least two components: a rapidly fading fraction and a more persistent residual signal. This indicates that 35–60 % of the LL signal originates from more stable defect centres that persist beyond several weeks of storage. Comparable behaviour was described by Atari and Ettinger (1975), who observed that after the rapid initial decay within 24 h, a residual fraction of the LL signal remained and decayed more slowly over months. It should be noted that the observed LL fading in NaCl differs from the so-called anomalous fading known from feldspars, where signal loss is unexpectedly fast compared to predictions from thermal stability. In contrast, OSL in NaCl has been shown to be stable without anomalous fading (Bailey et al., 2000), highlighting that LL measurements access a much less stable subset of traps. Additional storage-time points at 6 and 12 months are planned to evaluate longer-term stability; however, those experiments are beyond the scope of the present study.

## 4. LL visualization with an EM-CCD camera

The modular design of *LyoScope* facilitates the integration of alternative luminescence detectors, including high-sensitivity CCD imaging. To explore this capability, we adapted the system for LL visualization using an EM-CCD camera (ANDOR iXon Ultra 888) with a high-aperture lens (Navitar 25 mm F/0.95) attached to the 3D printed housing set elements. The setup enabled real-time imaging of LL emission during the dissolution of irradiated rock salt, confirming the presence of bright luminescent signals (Biernacka et al., 2025). In principle, the data acquired with the EM-CCD camera can be analysed in several steps, with

<figure><img src="image_8.png" /><figcaption>**Fig. 6.** Log-time representation of LL fading in NaCl for β doses of 0.55, 5.46, and 54.61 Gy at storage intervals of 19, 78, 518, and 859 h. Error bars include propagated uncertainty from the 19 h normalisation point. The lines indicate linear fits illustrating the approximately logarithmic fading behaviour over several weeks. Fit parameters (intercept, slope, R²) are given in the legend for each dose.</figcaption></figure>

intermediate results saved as TIFF images and further processed in ImageJ. Such a workflow may include: (1) raw data generation by the data acquisition software accompanying the EM-CCD camera (no median filters applied during analysis); (2) background subtraction using a pixel-by-pixel background image from the 2D signal image; and (3) summation of an active sample area with a central radius of 300 pixels for all LL images. Fig. 7 presents a representative LL image captured using the EM-CCD camera, illustrating the potential of this setup for visualising the spatial distribution of LL signals during sample dissolution. The recorded luminescence image is influenced by several factors, including optical effects of the measurement setup (lens aberrations, light scattering, and detector response) and sample-related properties such as grain size, homogeneity, and distribution of the material, as well as dynamic mixing during dissolution. In the present study, these images only illustrate hardware options and were not used for quantitative analysis, which was instead performed using the PMT setup.

## 5. Conclusions and future prospects

Our study presented a novel portable prototype device for measuring LL emissions. The device demonstrated reliable performance, as evidenced by repeatability tests, which achieved high precision for the natural LL signal of blue halite (~2.4 % variation). Sensitivity measurements using a pure NaCl detector yielded a minimum determination dose (MDD) of ~5 mGy, comparable to OSL-based dosimetry. Stability tests showed that ~35–40 % of the LL signal is lost within several weeks, after which 35–60 % of the signal persists as a stable residual fraction. Together, these findings provide the first quantitative evaluation of *LyoScope* performance and confirm its suitability for systematic LL studies.

*LyoScope*'s modular design allows adaptation to different luminescence detectors, including high-sensitivity CCD imaging, while providing a cost-effective and versatile solution for LL measurements. Its open-access construction expands the range of luminescence-based analytical techniques and radiation dosimetry tools and enables further development and customisation. Due to the easy accessibility of potential LL materials, starting from salt and other everyday-use materials such as sugars, the LL will have a valuable impact on personal, accident, environmental, or food monitoring dosimetry or wherever such applications are justified.

Beyond standard applications, LL has the potential to contribute to cutting-edge scientific fields. For instance, studies have proposed using halite as a natural archive for radiation events, including potential interactions with dark matter particles (Baum et al., 2023). Although definitive identification of the source, whether dark matter or another radiation type, may not yet be feasible, LL offers a promising method for qualitative, in-situ analysis of F-center concentration, even at the detection threshold level. Future improvements in detector sensitivity and material selection could expand *LyoScope*'s capabilities for ultra-low-dose detection and specialized research applications.

In the context of geological dating, LL offers specific advantages over conventional OSL/TL. It provides an additional means for dating of evaporite minerals such as halite, providing access to archives otherwise difficult to address with luminescence methods. With a minimum detectable dose of ~5 mGy, LL can resolve dose accumulations equivalent to only a few to several decades (depending on environmental dose rate). Based on a saturation parameter of $D_0 \approx 21$ Gy, the dose-response is quasi-linear up to ~5–7 Gy ($\approx 0.2–0.3 \cdot D_0$) and remains measurable – though non-linear – up to ~50 Gy, implying a potential dating range from decades to $>10^5$ years. This makes LL particularly valuable for reconstructing depositional and diagenetic histories of salt deposits. Such applications could extend LL-based dating into evaporite archives of palaeoenvironmental and climatic relevance. Although LL signal fading in halite remains a challenge, it may be mitigated by calibration procedures or by applying controlled storage conditions and correction factors. Furthermore, the portability of *LyoScope* opens perspectives for
<figure><img src="image_9.png" /><figcaption>Fig. 7. Sketch of the altered setup for retrieving the LL spatial light distribution. As a detector, we employed an ANDOR iXon Ultra 888 EM-CCD camera with a Navitar 25 mm F/0.95 lens. The sample bowl was made of Teflon, and the reconstructed LL signal was obtained using open-source software (μManager and ImageJ). The screen shows an example of the acquired LL signal during the dissolution of laboratory gamma-irradiated powdered rock salt (<63 µm, ~30 mg) in a copper chloride solution (~5 ml). An image clip and CAD model Part 3a are available in Zenodo.</figcaption></figure>

in situ LL measurements, which could minimise artefacts from sample storage and transport and preserve the geological context more faithfully. These features highlight LL additional tool to OSL, especially suited for materials and settings where other luminescence approaches are not applicable. When used alongside established OSL/TL methods, LL may thus provide complementary chronological information, particularly for materials that are otherwise unsuitable for optical or thermal stimulation, and the presented *LyoScope* enable such measurements.

### CRediT authorship contribution statement

**Magdalena Biernacka:** Writing – review & editing, Writing – original draft, Visualization, Validation, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.
**Krzysztof Maternicki:** Writing – review & editing, Writing – original draft, Visualization.
**Michał Sądel:** Writing – review & editing, Writing – original draft, Visualization, Investigation, Formal analysis.
**Sebastian Kreutzer:** Writing – review & editing, Writing – original draft, Validation, Supervision, Project administration, Methodology, Funding acquisition, Conceptualization.

### Funding

The research was financed by project #101107989 - Lyoluminescence - HORIZON-MSCA-2022-PF-01. SK was supported through the DFG Heisenberg programme (#505822867). MS was supported by the National Science Centre, Poland (grant No. 2021/43/D/ST5/03042).

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgements

We thank Clemens Theiler and Jannik Meyer for their input while testing the portable LL reader. We thank Professor Krzysztof Staniński from Adam Mickiewicz University in Poznań for his valuable contribution to optimizing the LL signal readout. We express our sincere gratitude to the scientific workshops (Zentralbereich Neuenheimer Feld,

Wissenschaftliche Werkstätten) at Heidelberg University for their invaluable service and unwavering support.

### Data availability

https://doi.org/10.5281/zenodo.15016847.

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