Laboratory Irradiation Research Articles

Mechanism and structure of micro-nanofluid directional heat conduction in asphalt pavement in plateau permafrost regions

Solar radiation in plateau permafrost regions is strong. The asphalt pavement strongly absorbs and slowly dissipates heat, leading to significant heat accumulation on the pavement. This accumulation disturbs the underlying permafrost and eventually causes serious pavement damage. To improve the heat resistance and dissipation capabilities of asphalt pavement, a nanofluid directional heat conduction structure (N-DHCS) was suggested and analyzed in this paper. The designed structure can resist heat in the daytime due to the low thermal conductivity of liquid and dissipates heat at night through natural convection. The finite element method and laboratory irradiation experiment were employed to performed thermal analyses of N-DHCS. The results demonstrated that establishing the N-DHCS in asphalt pavements can enhance active heat dissipation capacity, which is beneficial for protecting the frozen soil in plateau permafrost regions.

Development of a novel laboratory photodynamic therapy device: automated multi-mode LED system for optimum well-plate irradiation

HighlightsMulti-mode Automated Well-plate PDT LED Laboratory Irradiation System described.Automates and standardizes time-consuming experiments.LED wavelength and temperature stabilized for highly reproducible irradiations.Efficacy demonstrated in 5-aminolevulinic acid (5-ALA) treatments of HT-29 colon cancer cells and WI-38 human lung fibroblasts.

Assessing whether a thermoluminescence peak at ∼100 °C in calcitic opercula can be used to monitor thermal reproducibility

The opercula of the gastropod Bithynia tentaculata is composed of calcite and exhibits three main thermoluminescence peaks at ∼100, 280 and 360 °C when heated at 0.5 °C.s−1. The two higher temperature peaks can be used for geological and archaeological dating, whilst the lower temperature peak has a lifetime of hours and is only seen after laboratory irradiation. This study explores whether this lower temperature TL peak can be used to assess the reproducibility of laboratory heating of opercula. As found in previous studies, the TL peak at ∼100 °C is seen to consist of at least two signals which have different lifetimes at room temperature. By fixing the interval between irradiation and measurement of the TL signal, the impact of these different lifetimes on the temperature at which the TL peak occurs (Tm) can be reduced, and replicate measurements on a single operculum using the same radiation dose yield values of Tm within 1 °C. Comparison of different opercula shows variation in Tm of 9 °C when heating at 5 °C.s−1, interpreted as primarily arising from variation in thermal lag between the hotplate and the different samples assessed. Reducing the heating rate to 0.5 °C.s−1 reduces the variation in Tm between opercula to 2 °C. Imaging the TL emission from opercula using an EMCCD shows spatial variation in heating, and also demonstrates the reduction in variability that can be achieved by using a slower heating rate. Thus, monitoring the position of the TL peak at ∼100 °C can be used to assess thermal reproducibility of TL measurements on calcitic opercula.

Laboratory measurements underestimate persistence of the aquatic herbicide fluridone in lakes.

Fluridone is an aquatic herbicide commonly used to treat invasive freshwater plant species such as Eurasian watermilfoil, hydrilla, and curly-leaf pondweed. However, required exposures times are very long and often exceed 100 days. Thus, understanding the mechanisms that determine the fate of fluridone in lakes is critical for supporting effective herbicide treatments and minimizing impacts to non-target species. We use a combination of laboratory and field studies to quantify fluridone photodegradation, as well as sorption and microbial degradation in water and sediment microcosms. Laboratory irradiation studies demonstrate that fluridone is susceptible to direct photodegradation with negligible indirect photodegradation, with predicted half-lives in sunlight ranging from 2.3 days (1 cm path length) to 118 days (integrated over 1 meter). Biodegradation is attributable to microbes in sediment with an observed half-life of 57 days. Lastly, fluridone sorbs to sediments (Koc = 340 ± 28 L kg-1); sorption accounts for 16% of fluridone loss in the microcosm experiments. While the laboratory results indicate that all three loss pathways can influence fluridone fate, these controlled studies oversimplify herbicide behavior due to their inability to replicate field conditions. Fluridone concentration measurements in a lake following commercial application demonstrate a half-life of >150 days, indicating that the herbicide is very persistent in water. This study illustrates why caution should be used when relying on laboratory studies to predict the fate of pesticides and other polar organic compounds in the environment.

Transferring heat accumulated by asphalt pavement from inside to outside through carbon fibers

On the Qinghai-Tibet Plateau, intense solar irradiation will cause serious heat accumulation in asphalt pavement. Downward heat transfer will disturb the permafrost under subgrade, thus leading to a series of subgrade and pavement diseases. This makes construction of asphalt pavement in the permafrost regions of the Qinghai-Tibet Plateau a world-class challenge. This paper proposes for the first time a transversal heat transfer channel in asphalt pavement, which can quickly transfer heat accumulated in pavement to road shoulders. Finite element software ABAQUS was used to simulate the rutting plate with high axial thermal conductivity carbon fibers inserted transversely. Under the constant heat load of 500 W/m2, the heat flux near the carbon fibers showed the characteristic of convergence. The maximum transverse heat flux in the carbon fibers reached 4.97×107W/m2, which was 14 times that in the asphalt mixture. Meanwhile, the maximum vertical heat flux in the carbon fibers reduced to 2.62×106W/m2, which was 12 % less than the asphalt mixture. The effective thermal conductivity of composite specimens with different carbon fiber parameters was studied through control experiments. When the axial thermal conductivity, volume fraction and number of carbon fiber bundles increased to 100 W/m·°C, 10.72 % and 4 bundles respectively, the transverse ETC of composite specimens increased to 4.05 W/m·°C, 7.09 W/m·°C and 16.18 W/m·°C respectively. They were 3.12 times, 5.45 times and 12.45 times of the control group. The radial thermal conductivity of carbon fibers has a significant effect on the vertical ETC. When it decreased to 0.2 W/m·°C, the vertical ETC decreased by 6.15 % compared with the control group. The temperature variation trend of specimens were measured by a laboratory irradiation experiment. The maximum temperature difference between the control group and the experimental group at 0 mm was 5.81 °C, and the average temperature difference within 2 h was 5.14 °C. The maximum temperature difference at 50 mm was 3.84 °C and the average temperature difference within 2 h was 3.24 °C. The results showed that the transverse heat transfer channel can reduce downward heat transfer. The application of the channels will enhance transverse heat release and relieve heat accumulation of asphalt pavement. This can create a low temperature state for pavement structure and has a positive effect on maintaining the stability of the permafrost regions on the Qinghai-Tibet Plateau.

Space-occupied 3D structure improves distilled water collection at the solar interface distillation

Recently, solar-driven interfacial distillation has rapidly developed into an effective technology for unconventional water treatment. Solar evaporator as the central part of the system was extensively investigated and achieved high light-to-heat efficiencies. However, the combination of interfacial evaporators and solar still in the application was rarely studied, and the phenomena inside the device during evaporation have yet to be revealed. Here, we designed an interfacial evaporator with a conical solar still unit to study the enhancement of water collection. The physical changes inside the device during natural solar irradiation were also revealed. In addition, the COMSOL Multiphysics as simulation software was applied to reveal the temperature variation of the system during solar motion. As a result, the condensate collection of the space-occupied 3D system is 2.5 times that of the plant system in the actual solar irradiation, which is even larger than the laboratory irradiation process. In addition to more solar energy absorption during the solar movement, the faster saturation of the humidity (more than 90%) due to the space occupation is also an important factor for the higher water collection capacity of the 3D system. This discovery would provide a reference for the design of the interfacial evaporator and evaporation device in the future and promote its practical application.

Design and Experimental Evaluation of Composite Magnesium Phosphate Cement-Based Coating with High Cooling Effect

The application of surface heat reflective coatings is one of the effective measures to solve the temperature disease of concrete structures in sunlit environments. To achieve strong bonding, high durability, and good cooling characteristics, a novel inorganic reflective thermal insulation coating was prepared using magnesium phosphate cement (MPC) as the binder and reflective matrix, and titanium dioxide and glass beads as the reflective thermal insulation reinforcement functional additives. The optimum ratio of the new reflective thermal insulation coating was preferred through laboratory irradiation test, thermal conductivity test, and spectral reflectance test. The results show that MPC itself was a good reflection cooling material, and the surface and internal temperatures of concrete blocks were reduced by 7.6 °C and 6.6 °C, respectively, after using MPC as the cooling coating. When 2% titanium dioxide was added to MPC, the surface and internal temperatures were further reduced by 6.0 °C and 4.9 °C, respectively. On top of this, the surface and internal temperatures of the concrete were reduced by a further 3.9 °C and 2.2 °C when 8% glass beads were added. The bond strength of the MPCTG coating to the concrete matrix reached 2.1 MPa. Finally, the microscopic characteristics and the reflective thermal insulation mechanism of the MPCTG coating were investigated with the aid of SEM, thermo gravimetric analysis, and XRD analysis. The results show that the MPC in the MPCTG coating was well hydrated, and a large number of hydration products encapsulated the unreacted MgO particles, titanium dioxide, and glass beads, forming a dense whole with high reflection and low thermal conductivity, and the coating effectively prevented the entry of radiant heat. At the same time, the MPCTG coating was thermally stable below 70 °C. The magnesium phosphate cement-based reflective thermal insulation coating developed in this study has potential application prospects in concrete structure cooling coatings.

A Model Assessment of the Occurrence and Reactivity of the Nitrating/Nitrosating Agent Nitrogen Dioxide (•NO2) in Sunlit Natural Waters.

Nitrogen dioxide (•NO2) is produced in sunlit natural surface waters by the direct photolysis of nitrate, together with •OH, and upon the oxidation of nitrite by •OH itself. •NO2 is mainly scavenged by dissolved organic matter, and here, it is shown that •NO2 levels in sunlit surface waters are enhanced by high concentrations of nitrate and nitrite, and depressed by high values of the dissolved organic carbon. The dimer of nitrogen dioxide (N2O4) is also formed in the pathway of •NO2 hydrolysis, but with a very low concentration, i.e., several orders of magnitude below •NO2, and even below •OH. Therefore, at most, N2O4 would only be involved in the transformation (nitration/nitrosation) of electron-poor compounds, which would not react with •NO2. Although it is known that nitrite oxidation by CO3•− in high-alkalinity surface waters gives a minor-to-negligible contribution to •NO2 formation, it is shown here that NO2− oxidation by Br2•− can be a significant source of •NO2 in saline waters (saltwater, brackish waters, seawater, and brines), which offsets the scavenging of •OH by bromide. As an example, the anti-oxidant tripeptide glutathione undergoes nitrosation by •NO2 preferentially in saltwater, thanks to the inhibition of the degradation of glutathione itself by •OH, which is scavenged by bromide in saltwater. The enhancement of •NO2 reactions in saltwater could explain the literature findings, that several phenolic nitroderivatives are formed in shallow (i.e., thoroughly sunlit) and brackish lagoons in the Rhône river delta (S. France), and that the laboratory irradiation of phenol-spiked seawater yields nitrophenols in a significant amount.

Establish directional heat induced structure based on a grouting compound gradient thermal conductivity method

In order to control directional heat induced efficiency and reduce pavement temperature, a grouting compound directional heat induced structure (GC-DHIS) was proposed and analyzed in this paper. The structure was formed by pouring grout with different thermal conductivity successively into the same matrix asphalt mixture framework. According to the structural characteristics of grouting compound pavement and the principle of gradient thermal conductivity, the heat in the pavement could be quickly transferred down to the subgrade. The heat transfer performance and cooling effect of GC-DHIS were studied by finite element simulation, and the simulation results were verified by laboratory irradiation experiment. The results showed that the heat exchange between the designed structure and the atmosphere in the endothermic and exothermic periods was 7.10% and 7.98% less than that of the control structure, respectively. Moreover, the effective downward heat transfer rate of pavement throughout the day could be improved, and the maximum temperatures inside the pavement were reduced by 0.9 °C(2 cm), 1.9 °C(5 cm) and 0.8 °C(10 cm). The GC-DHIS with gradient high thermal conductivity grout increased the total downward heat transfer at the depth of 2 cm, 5 cm and 10 cm by 7.0%, 11.9% and 17.4% during the endothermic period. Meanwhile, the surface temperature of this structure in this period showed a slower rising trend. Therefore, it could be concluded that GC-DHIS is a promising pavement structure with the function of actively enhancing heat directional transfer and cooling pavement.

Response of the Ti and Al electron spin resonance signals in quartz to X-ray irradiation

Equivalent dose determination with electron spin resonance (ESR) involves laboratory irradiation of samples using a calibrated source. In this study, we investigated the response of the quartz ESR signals to irradiations from 50 kV or 200 kV X-ray sources by inter-comparison with 60Co gamma irradiation using seven quartz samples of different origins. For each sample, the equivalent X-ray irradiation time required to create the same concentration of defects as a known dose of 60Co gamma-ray was calculated. The effective dose rate was obtained from the given gamma dose (188 Gy) divided by the equivalent X-ray irradiation time; this is referred to as the ‘X-ray dose rate’ in this study. The X-ray dose rate estimates from different samples were relatively uniform. However, the dose rate calculated from the Al centre was on average ∼10% higher than that of the Ti centre, and more scattered among different samples especially for the low-energy X-ray source. The ratio of the dose rates, obtained from the two centres (Al/Ti) varied significantly between the samples; four sediment samples from Tajikistan, China, Chile and Greece yielded consistent dose rates from both centres for both sources, whereas the remaining three samples from Japan and Taiwan showed a dose rate up to 26% higher from the Al centre compared to the Ti centre. The cause of the higher effective dose rate for the Al centre for these three samples requires further investigations.

A performance analysis of a new secondary standard dosimetry laboratory irradiation system

This study reviews the performance analysis of a commercial 137Cs irradiation system that has recently been installed in the Secondary Standard Dosimetry Laboratory (SSDL) at the Soreq Nuclear Research Center (SNRC).The SSDL is responsible for calibrating calibration facilities and for calibrating most protection level radiation monitoring instruments used in medical, nuclear, industrial and academic settings in Israel. Until recently, these monitoring instruments have been calibrated by a 40-year-old irradiation system.At the end of 2018, a new Hopewell Designs Inc. ® irradiation system was installed at our SSDL. This system employs the most advanced radiation safety standards, along with 21st century source automation methods. In this work, we review the system’s performance. Our analysis shows excellent results in terms of repeatability, robustness, linearity, and beam uniformity. Additionally, the system accuracy was tested by participating in an international IAEA postal audit, and here too, excellent results were obtained.

EVALUATION OF THE DOSE LEVELS IN THE IRRADIATION CHANNELS OF PU-BE NEUTRON SOURCES STORAGE DEVICE BY USING NEUTRON ACTIVATION ANALYSIS AND MCNP6 MODELLING

PuBeneutrons sources of Educational Neutron Laboratory in the Center for Physical Sciences and Technology are used in several activities including neutron activation for educational purposes and laboratory irradiation experiments. In this work we address the dose rate estimation in the irradiation channels of reconstructed PuBe neutron sources storage device in the particular positions dedicated for neutron irradiation experiments using neutron activation analysis (NAA) and MCNP6 modelling.The results on neutron activation of V2O5, MnO2, Al and Na2CO3were analyzed and compared with MCNP6 model prediction results. The conclusions on the actual neutron flux energy distribution and model corrections are drawn. The absolute neutron intensity at dedicated irradiation points as well as neutron and gamma dose rates are obtained.

Solar Radiation as the Likely Cause of Acid-Soluble Rare-Earth Elements in Sediments of Fresh Water Humic Lakes

We studied photochemically induced precipitation of rare-earth elements (REEs) in water from a tributary to Plešné Lake and a tributary to Jiřická Pond, Czech Republic. Both tributaries had high concentrations of dissolved organic matter (∼1.8 mmol C L-1). Filtered (0.2 μm) samples were exposed to artificial solar radiation of 350 W m-2 for 48 to 96 h, corresponding to 3 to 6 days of natural solar radiation in summer at the sampling locations. Experiments were performed with altered and unaltered pH ranging from 3.8 to 6.0. The formation of particulate REEs occurred in all exposed samples with the fastest formation observed at the original pH. The formation of particulate metals continued in irradiated samples after the end of irradiation, suggesting that photochemically induced reactions and/or continuing precipitation continue in darkness or in deeper water due to mixing. Results were compared with paleolimnological records in the Plešné Lake sediment. At pH 5.0, the photochemically induced sediment flux was 3509 nmol m-2 y-1 for Ce, corresponding to 42% of the REEs' annual sediment flux in recent sediment layers. Combining the formation rates obtained in the laboratory irradiation experiments and known 1 day incident solar radiation enabled the estimation of a possible REE sediment flux. For Plešné Lake, the photochemically induced formation of particulate REEs explained 10-44% of the REE concentrations in the upper sediment layers. Observed photochemically induced sequestration of REEs into sediments can explain a significant part of the REEs' history in the Holocene sediment.

Dosimetry from OSL and Residual TL with TLD 400

The aim of this work is to propose a new methodological approach, using TLD400, to perform point dosimetry in medical physics applications. It investigates the possibility of using simultaneously the luminescence signals by optical stimulation with blue diode (OSL) and residual signals by thermal stimulation (ReTL), from TLD400, CaF2:Mn, for dosimetric purposes. Artificial irradiation was performed with 90Sr-90Y, calibrated beta sources delivering 6 Gy/min and integrated in the TL-DA-15 automated RisØ readers equipped with EMI 9235QA photomultipliers. In particular, for OSL measurements, to check the correct experimental conditions, the effect of the stimulation temperature during optical stimulation and the effect of the optical stimulation time were studied. For calibration curves from OSL and ReTL signals, a double Single Aliquot Regeneration (SAR) procedure was used, in which the “sensitivity-corrected” natural stimulated luminescence signal is compared with equivalent sensitivity-corrected signals regenerated by laboratory irradiation of the same aliquot. The double OSL and ReTL combined measurements allow to have a good accuracy coverage (⩽2%) in the whole dose range between 0 and 10 Gy.

Enhancing heat release of asphalt pavement by a gradient heat conduction channel

In order to enhance the heat transfer efficiency in asphalt pavement along a directional way, a gradient heat conduction channel structure (GHCC) was suggested and analyzed in this paper. The designed structure could gather heat from asphalt pavement into the channel and quickly transfer it to its subgrade along the axis of these channels in the pavement. Thermal analyses of GHCC were performed by a finite element method. The results showed that the maximum heat release of pavement with GHCC could be increased by 11.5 times. And the pavement temperatures at the upper surface and 4 cm were reduced by 2.1 °C and 6.1 °C, respectively. And the maximum downward heat transfer efficiency of the structure could be increased by 17.6 times. A strong horizontal heat flow was observed which was caused by a significant heat exchange between the channels and the surrounding asphalt mixtures. In order to verify the laboratory cooling effect of the structure, a laboratory irradiation experiment was also employed to verify the principles and models of the GHCC. All of these analytical tests showed that establishing the GHCC in asphalt pavements is a promising method to enhance heat release efficiency, endowing asphalt pavement with more active cooling function.

Radiolysis as a source of 13C depleted natural gases in the geosphere

Is natural radioactivity a significant agent of hydrocarbon gas generation from sedimentary organic matter? Laboratory gamma radiation of dead crude oil (no solution gas) yields wet hydrocarbon gases depleted in 13C: δ13C CH4 (−75‰ to −65‰), δ13C C2H6 (−52‰ to −45‰), δ13C C3H8 (−42‰ to −37‰) and δ13C n-C4H10 (−35‰ to −32‰). Although laboratory irradiation dose rates are orders of magnitude higher than those in geological settings, radiolytic transformations occur at total radiation doses equivalent to those in natural geological settings over many millions of years. Radiolysis generates wet gases with isotopic signatures that might be interpreted as “biogenic” if only the methane carbon isotope ratio is considered. We examine situations where such gases may be quantitatively significant.

Quartz natural and laboratory ESR dose response curves: A first attempt from Chinese loess

The natural electron spin resonance (ESR) dose response curve (DRC) of the Al and Ti centres was constructed for the first time using sand-sized quartz samples from Luochuan, Chinese Loess Plateau. The natural DRC of both centres showed an unexpected early saturation, with characteristic saturation dose (D0) values of ∼760 Gy for the Al centre and ∼650 Gy for the Ti centre, when fitted with a single saturating exponential function. This corresponds to an upper age limit of ∼500 ka (Al centre) and ∼400 ka (Ti centre), using the mean dose rate of 3 Gy/ka. The laboratory DRC of both centres showed much higher saturation dose, but both intensity and D0 value of the regenerated ESR signals decreased significantly with increasing preheat temperatures. The natural DRC had a better match with the laboratory DRC following higher temperature preheats, ∼210–240 °C for 4 min, suggesting the need for preheating after laboratory irradiation for quartz ESR dating. The results of isothermal heating tests revealed that the thermal lifetime at 10 °C at the studied site was ∼1.5 × 109 and ∼1.7 × 106 years for the Al and Ti centres. Although the thermal lifetime of these impurity centres could be sample dependent, the relatively short lifetime of the Ti centre contributed to the early saturation of the natural DRC of the Chinese loess. This highlights the importance of investigating the thermal lifetime of signals for dating older samples using ESR.

Photon energy (8–250 keV) response of optically stimulated luminescence: Implications for luminescence geochronology

Understanding the energy response of dosimeters and scintillators for measurements of ionising radiation is an important area in the field of solid state dosimetry. Such an understanding is particularly critical for source calibration and for quantifying effective dose (rates) in wide-energy mixed-radiation fields. While there have been several investigations on characterising the ionising- energy response of artificial dosimeters (e.g. LiF, Al2O3:C, etc.), there exist no studies on natural dosimeters such as quartz and feldspar which are extensively used in luminescence geochronology and retrospective dosimetry. Currently, luminescence geochronology assumes that all beta and gamma irradiations in nature (from the decay of K, the U and Th radioactive chains) are equivalent in terms of luminescence production per unit dose to each other, and to the laboratory 137Cs, 60Co (gamma) and 90Sr/90Y (beta) irradiations used for calibration and/or equivalent dose determination. In this study, we experimentally determine the quartz Optically Stimulated Luminescence (OSL) and feldspar Infra-Red Stimulated Luminescence (IRSL: IRSL at 50 °C and post-IR IRSL at 290 °C) response to irradiations with photons of in the energy range 8–250 keV. We show that microdosimetric effects lead to a steady, significant decrease in quartz OSL production efficiency for < 80 keV photons. Similar to quartz, the local saturation of the electron traps also leads to a systematic decrease in luminescence efficiency for < 120 keV photons in feldspar; however, this effect competes with an increase in recombination efficiency due an increased number density of hole centres in the vicinity of the trap, thus giving a peak-shaped IRSL efficiency response in the range of 250–8 keV. Our results suggest that dose-rate conversion factors, specific to radiation type and radioisotope, should be used for age calculation, and significant care should be taken for luminescence based calibration of the dose rate of the laboratory irradiation source.

LPHT annealing of brown-to-yellow type Ia diamonds

Low-pressure, high-temperature (LPHT) annealing of yellow-to-brown type Ia natural diamonds was performed to monitor its effects on optical centers within diamond, changes in the observed color, and to assess the process's viability as a commercial gem treatment.With LPHT annealing only, the mostly brown diamonds showed a shift towards yellow coloration; Vis-NIR absorption spectra showed this change was due to a modest increase in H3 intensity. Even at long annealing times (24h at 1800°C) or annealing at high temperatures (2000°C for five minutes), the diamonds did not significantly lose brown coloration. LPHT annealing showed itself as an ineffective means to break apart the vacancy clusters causing the brown color or causing nitrogen disaggregation, which resulted in only a small H3 generation.With LPHT annealing, “amber centers”—a group of several independent bands in the IR between 4200 and 4000cm−1 that disappear with HPHT annealing—were seen to anneal out gradually at various temperatures from 1700 to 2000°C.In contrast, high-pressure, high-temperature (HPHT) annealing effectively removes brown color at similar time/temperature conditions. Without the high stabilizing pressure provided by HPHT annealing techniques, the LPHT annealing showed pronounced damage on inclusions and dramatic surface etching.In subsequent experiments, LPHT annealing was used as a follow-up to laboratory irradiation. The irradiation-related vacancies created greater concentrations of H3 and the vacancy-assisted disaggregation of nitrogen created donors which led to a high concentration of H2 centers. This combination of defects resulted in a pronounced and favorable shift towards saleable yellow colors due to an increase in H3 and a dramatic increase in the H2 center, which led to the suppression of the remaining brownish component.The annealing characteristics for many centers detected by Vis-NIR absorption spectroscopy, FTIR absorption spectroscopy, and photoluminescence spectroscopy were chronicled throughout the study and compared with other LPHT annealing studies and HPHT annealing experiments.

Temporal changes in photoreactivity of dissolved organic carbon and implications for aquatic carbon fluxes from peatlands

Abstract. Aquatic systems draining peatland catchments receive a high loading of dissolved organic carbon (DOC) from the surrounding terrestrial environment. Whilst photo-processing is known to be an important process in the transformation of aquatic DOC, the drivers of temporal variability in this pathway are less well understood. In this study, 8 h laboratory irradiation experiments were conducted on water samples collected from two contrasting peatland aquatic systems in Scotland: a peatland stream and a reservoir in a catchment with high percentage peat cover. Samples were collected monthly at both sites from May 2014 to May 2015 and from the stream system during two rainfall events. DOC concentrations, absorbance properties and fluorescence characteristics were measured to investigate characteristics of the photochemically labile fraction of DOC. CO2 and CO produced by irradiation were also measured to determine gaseous photoproduction and intrinsic sample photoreactivity. Significant variation was seen in the photoreactivity of DOC between the two systems, with total irradiation-induced changes typically 2 orders of magnitude greater at the high-DOC stream site. This is attributed to longer water residence times in the reservoir rendering a higher proportion of the DOC recalcitrant to photo-processing. During the experimental irradiation, 7 % of DOC in the stream water samples was photochemically reactive and direct conversion to CO2 accounted for 46 % of the measured DOC loss. Rainfall events were identified as important in replenishing photoreactive material in the stream, with lignin phenol data indicating mobilisation of fresh DOC derived from woody vegetation in the upper catchment. This study shows that peatland catchments produce significant volumes of aromatic DOC and that photoreactivity of this DOC is greatest in headwater streams; however, an improved understanding of water residence times and DOC input–output along the source to sea aquatic pathway is required to determine the fate of peatland carbon.