Fluorescent Nuclear Track Detectors Research Articles

Evaluation and optimization of measurement conditions for heavy ions with fluorescent nuclear track detectors.

In applying fluorescent nuclear track detectors for heavy ion measurement, the fluorescence intensity directly influences linear energy transfer (LET) estimation. However, the conventional analysis highly depends on the analyzed depth and the reference frames from the optical readout. To improve the accuracy of measurements of heavy ions, the gradient of intensity and moving average fluorescence intensity were acquired and calculated to optimize the measurement conditions. The results indicate that the intensity gradient is an alternative quantity to discriminate ions with different LET, and the moving average fluorescence intensity is readily differentiated among individual ions without overlapping values in fluorescence intensity. The scanned range of 25-45μm is suggested to be the most suitable depth for measurement. To exclude the impact of the variation in fluorescence intensity on evaluation, it is recommended to use the quantities calculated in moving averages with depth in the future.

Isotopically Enriched Lithium Fluoride Crystals for Detection of Neutrons with the Fluorescent Track Technique.

In this work, the properties of LiF crystals grown using Li of different isotopic compositions are described from the standpoint of their application as fluorescent nuclear track detectors used in measurements in the neutron radiation fields. The crystals were grown using two techniques: the Czochralski method and the micro-pulling-down method. Three isotopic compositions of Li were studied: natural, highly enriched in 6Li, and highly enriched in 7Li. It was found that 6LiF detectors are about six times more sensitive to thermal (low energy) neutrons than natural LiF, which significantly decreases the lower detection limit. 7LiF detectors are insensitive to thermal neutrons, which makes it easier to detect tracks due to other radiation modalities, such as energetic ions or nuclei recoiled in collisions with high-energy neutrons. Besides the response to neutron radiation, no other significant differences in the crystal properties were identified, irrespective of the isotopic composition and crystal growth method employed.

3D track extraction from a fluorescent nuclear track detector via machine learning and an application to diagnostics of laser-driven ions.

We have developed an ion diagnostic method for laser-driven ion acceleration experiments that uses fluorescent nuclear track detectors (FNTDs). An FNTD records the particle tracks as color centers and does not require chemical etching, unlike CR-39 track detectors. The color centers are observed using a confocal laser microscope, and 3D particle tracks can be obtained by changing its focal position. The intensity of the color centers corresponds to the energy deposited by the ions. The nuclides of the ions can be determined from the intensity distribution of the color centers as a function of depth and the distance between the stopping point and the surface of the detector. To extract the intensity distribution, we must track the same ion tracks in the depth-layered microscopic images from the surface to the stopping point, even if they overlap with those of other ions. In addition, since an FNTD is sensitive not only to ions but also to electrons and photons, we must identify ion tracks among those from the latter particles. To analyze a statistical number of ion tracks, it is necessary to automate these processes. We have thus developed a method for automated ion detection and 3D tracking that relies on a support vector classifier and a kernelized correlation filter. This method was tested on a laser ion acceleration experiment performed using the J-KAREN-P laser. The method automatically detects ion tracks on FNTDs and tracks them in the depth direction. The training data are sampled from the Heavy-Ion Medical Accelerator in Chiba.

Assessment of fluence- and dose-averaged linear energy transfer with passive luminescence detectors in clinical proton beams

Objective. This work investigates the use of passive luminescence detectors to determine different types of averaged linear energy transfer ( LET― ) for the energies relevant to proton therapy. The experimental results are compared to reference values obtained from Monte Carlo simulations. Approach. Optically stimulated luminescence detectors (OSLDs), fluorescent nuclear track detectors (FNTDs), and two different groups of thermoluminescence detectors (TLDs) were irradiated at four different radiation qualities. For each irradiation, the fluence- ( LET―f ) and dose-averaged LET ( LET―d ) were determined. For both quantities, two sub-types of averages were calculated, either considering the contributions from primary and secondary protons or from all protons and heavier, charged particles. Both simulated and experimental data were used in combination with a phenomenological model to estimate the relative biological effectiveness (RBE). Main results. All types of LET― could be assessed with the luminescence detectors. The experimental determination of LET―f is in agreement with reference data obtained from simulations across all measurement techniques and types of averaging. On the other hand, LET―d can present challenges as a radiation quality metric to describe the detector response in mixed particle fields. However, excluding secondaries heavier than protons from the LET―d calculation, as their contribution to the luminescence is suppressed by ionization quenching, leads to equal accuracy between LET―f and LET―d . Assessment of RBE through the experimentally determined LET―d values agrees with independently acquired reference values, indicating that the investigated detectors can determine LET― with sufficient accuracy for proton therapy. Significance. OSLDs, TLDs, and FNTDs can be used to determine LET― and RBE in proton therapy. With the capability to determine dose through ionization quenching corrections derived from LET― , OSLDs and TLDs can simultaneously ascertain dose, LET― , and RBE. This makes passive detectors appealing for measurements in phantoms to facilitate validation of clinical treatment plans or experiments related to proton therapy.

Detection of fluorescent low-energy proton tracks in lithium fluoride crystals

The exploitation of visible radiophotoluminescence in lithium fluoride (LiF) crystals, due to local aggregate point defects produced by ionizing radiation in the crystal lattice, is demonstrated for fluorescent imaging of single tracks of protons at low energies. LiF crystals were irradiated perpendicularly with respect to nearly monochromatic, collimated proton beams at the energies of about 1 MeV in a fluence range from ∼5.8 × 105 p/cm2 up to ∼3.4 × 107 p/cm2 and of about 2.6 MeV in a fluence range from ∼9.6 × 105 p/cm2 up to ∼4.7 × 106 p/cm2. The fluence values were estimated by detecting and automatically counting the tracks on the images acquired with a fluorescence microscope at high magnification; they were found to be in agreement with those obtained using CR39 plastic detectors irradiated under the same experimental conditions. Despite the very short range in matter of these charged particles, by focusing the excitation blue light at discrete depths in the irradiated LiF crystals, an estimate of the proton energies was also obtained. These first results are encouraging for the utilization of LiF crystals as fluorescent nuclear track detectors under typical conditions employed in ion radiobiology.

Converter thickness optimisation using Monte Carlo simulations of Fluorescent Nuclear Track Detectors for neutron dosimetry

Secondary neutrons generated during ion beam radiotherapy present a concern due to the potential dose deposition beyond the treatment volume, thereby elevating the risk of inducing secondary tumours. These neutrons can possess energies comparable to those of the primary ions, reaching magnitudes of several hundred MeV, posing a challenge for neutron detectors. Fluorescent Nuclear Track Detectors (FNTDs) are promising detectors for high-energy neutron dosimetry given their capability to detect particles with a low linear energy transfer. In this work, the sensitivity of FNTDs to neutron energies reaching 20MeV was analysed by experiments and Monte Carlo (MC) simulations, quantifying the recoil proton yield of FNTDs combined with polyethylene (PE) converters of different thicknesses. The FNTDs were read out using a dedicated FNTD reader, demonstrating a reasonable uncertainty by analysing a detector area of 0.1mm2. Investigations of different converter thicknesses reveal optimal detector sensitivity between 0.5mm to 1.0mm for a 241AmBe source, yielding a maximum sensitivity of (22.7±3.4) tracksmSv-1mm-2. Similar converter-FNTD configurations were assessed through MC simulations using FLUKA, yielding a correlation between detector sensitivity and converter thickness. Furthermore, an enhanced detector sensitivity for neutron energies up to 20MeV was found for the PE converter thickness of 4.0mm. The MC simulations can be used to optimise FNTD detector configurations for measuring higher neutron energies by maximising the recoil proton yield.

Linear Energy Transfer Measurements and Estimation of Relative Biological Effectiveness in Proton and Helium Ion Beams Using Fluorescent Nuclear Track Detectors

PurposeTo develop a methodology for assessing the linear energy transfer (LET) and relative biological effectiveness (RBE) in clinical proton and helium-ion beams using fluorescent nuclear track detectors (FNTDs). Methods and materialsFNTDs were exposed behind solid water to proton and helium- (4He-) ion spread-out Bragg peaks (SOBPs). Detectors were imaged with a confocal microscope, and the LET spectra were derived from the fluorescence intensity. The track- and dose-averaged LET (LETF and LETD, respectively) were calculated from the LET spectra. LET measurements were used as input on RBE-models to estimate the RBE. Human alveolar adenocarcinoma cells (A549) were exposed at the same positions as the FNTDs. The RBE was calculated from the resulting survival curves. All measurements were compared with Monte Carlo simulations. ResultsFor protons, average relative differences between measurements and simulations were 6% and 19% for LETF and LETD, respectively. For helium ions the same differences were 11% for both quantities. The position of the experimental LET spectra primary peaks agreed with the simulations within 9% and 14% for protons and helium-ions, respectively. For the RBE-models using LETD as input, FNTD-based RBE values ranged from 1.02 ± 0.01 to 1.25 ± 0.04 and from 1.08 ± 0.09 to 2.68 ± 1.26 for protons and helium-ions, respectively. The average relative differences between these values and simulations were 2% and 4%. For A549 cells, the RBE ranged from 1.05 ± 0.07 to 1.47 ± 0.09 and from 0.89 ± 0.06 to 3.28 ± 0.20 for protons and helium-ions, respectively. Regarding the RBE-weighted dose (2.0 Gy at the SOBP), the differences between simulations and measurements were below 0.10 Gy. ConclusionThis study demonstrates for the first time that FNTDs can be used to perform direct LET measurements and to estimate the RBE in clinical proton and helium-ion beams.

Detection of proton tracks with LiF fluorescent nuclear track detectors

Fluorescent nuclear track detectors based on LiF crystals were successfully applied for detection of proton induced tracks. Irradiations were performed with protons with energy ranging from 1 MeV up to about 56 MeV and for all proton energies the fluorescent tracks were observed. The tracks are not continuous, but consist of a series of bright spots. The gaps between spots tend to narrow with decreasing proton energy (increasing ionization density). For the highest of the studied energies, the spots are scattered so sparsely, that it is not possible to link spots belonging to one track. The intensity (brightness) of the fluorescent tracks increases with the increasing LET and agrees well with the trend established earlier for various heavier ions.

Alpha particle spectrometry in fluorescent nuclear track detectors with an automatic 3D track reanalysis algorithm

The main obstacle to applying aluminum oxide doped with carbon and magnesium (Al2O3:C,Mg)-based fluorescent nuclear track detectors (FNTDs) in radionuclide therapy with alpha emitters is that it has not been known how to achieve an accurate and in situ dose assessment for in vitro cellular experiments. In this study, we developed an automatic 3D track reanalysis algorithm (ATRA) to analyze the alpha energy spectra in FNTDs. The algorithm provides an excellent track identification rate and an excellent track linking rate (0.961) without significant variations in various track densities. The algorithm also achieves a reliable track detection rate exceeding 0.927 for track densities at the level of in situ measurement, and it successfully measures the alpha energy spectra for obtaining the absorbed dose. We also confirmed that the track overlap clearly interferes with accurate track reconstruction for track densities beyond 1.5 × 106 tracks cm−2. We provided a correction equation that can be used to obtain the actual alpha tracks for high track densities; the equation may also correct estimations of absorbed doses due to alpha particles.

Correction method of the coloration in fluorescent nuclear track detector

A fluorescent nuclear track detector (FNTD) is a single crystal of aluminum oxide doped with carbon and magnesium (Al2O3:C,Mg). We report calibration method of difference in the fluorescence intensity depending on the color center concentration (coloration) using a confocal microscope. The fluorescence intensity ratio of 510–530 nm due to the excitation at 488 nm to the reflection intensity of 483–493 nm is used for the coloration correction. The fluorescence track intensity of alpha particles increases monotonically with the color center concentration. From the relation between values of coloration concentration and the fluorescence track intensity of alpha particles, we have made a correction function. Consequently, the standard deviation of the detection of alpha particles with the coloration correction becomes six times smaller than without it. Additionally, the track response curve is properly made in a wide LET range from 1 to 200 keV/μm.

Sensitivity correction of fluorescent nuclear track detectors using alpha particles: Determining LET spectra of light ions with enhanced accuracy.

Radiation fields encountered in proton therapy (PT) and ion-beam therapy (IBT) are characterized by a variable linear energy transfer (LET), which lead to a variation of relative biological effectiveness and also affect the response of certain dosimeters. Therefore, reliable tools to measure LET are advantageous to predict and correct LET effects. Fluorescent nuclear track detectors (FNTDs) are suitable to measure LET spectra within the range of interest for PT and IBT, but so far the accuracy and precision have been challenged by sensitivity variations between individual crystals. To develop a novel methodology to correct changes in the fluorescent intensity due to sensitivity variations among FNTDs. This methodology is based on exposing FNTDs to alpha particles in order to derive a detector-specific correction factor. This will allow us to improve the accuracy and precision of LET spectra measurements with FNTDs. FNTDs were exposed to alpha particles. Afterward, the detectors were irradiated to monoenergetic protons, 4 He-, 12 C-, and 16 O-ions. At each step, the detectors were imaged with a confocal laser scanning microscope. The tracks were reconstructed and analyzed using in-house developed tools. Alpha-particle tracks were used to derive a detector-specific sensitivity correction factor ( ). Proton, 4 He-, 12 C-, and 16 O-ion tracks were used to establish a traceable calibration curve that relates the fluorescence intensity with the LET in water ( ). FNTDs from a second batch were exposed and analyzed following the same procedures, to test if can be used to extend the applicability of the calibration curve to detectors from different batches. Finally, a set of blind tests was performed to assess the accuracy of the proposed methodology without user bias. Throughout all stages, the main sources of uncertainty were evaluated. Based on a sample of 100 FNTDs, our findings show a high sensitivity heterogeneity between FNTDs, with having values between 0.57 and 2.55. The fitting quality of the calibration curve, characterized by the mean absolute percentage residuals and correlation coefficient, was improved when was considered. Results for detectors from the second batch show that, if the fluorescence signal is corrected by , the differences in the predicted with respect to the reference set are reduced from 55%, 141%, 41%, and 186% to 4.2%, 6.5%, 5.0%, and 11.0%, for protons, 4 He-, 12 C-, and 16 O-ions, respectively. The blind tests showed that it is possible to measure the track- and dose-average with an accuracy of 0.3%, 16%, and 9.6% and 1.7%, 28%, and 30% for protons, 12 C-ions and mixed beams, respectively. On average, the combined uncertainty of the measured was 11%, 13%, 21%, and 26% for protons, 4 He-, 12 C-, and 16 O-ions, respectively. These values were increased by a mean factor of 2.0 when was not applied. We have demonstrated for the first time that alpha particles can be used to derive a detector-specific sensitivity correction factor. The proposed methodology allows us to measure LET spectra using FNTD-technology, with a degree of accuracy and precision unreachable before with sole experimental approaches.

Study on the reusability of fluorescent nuclear track detectors using optical bleaching

Fluorescent nuclear track detectors (FNTDs) based on Al2O3:C,Mg crystals are luminescent detectors that can be used for dosimetry and detection of charged particles and neutrons. These detectors can be utilized for imaging applications where a reasonably high track density, approximately of the order of 1×104 tracks in an area of 100 × 100 μm2, is required. To investigate the reusability of FNTDs for imaging applications, we present an approach to perform optical bleaching under the required track density conditions. The reusability was assessed through seven irradiation-bleaching cycles. For the irradiation, the studied FNTD was exposed to alpha-particles from an 241Am radioactive source. The optical bleaching was performed by means of ultraviolet laser light with a wavelength of 355 nm. Three dedicated regions on a single FNTD with different accumulated track densities and bleaching conditions were investigated. After every irradiation-bleaching cycle, signal-to-noise ratio was calculated to evaluate FNTD performance. It is concluded that FNTDs can be reused at least seven times for applications where accumulation of a high track density is required.

Thermal enhancement of the intensity of fluorescent nuclear tracks in lithium fluoride crystals

Lithium fluoride fluorescent nuclear track detectors (FNTD) irradiated with alpha-particles were subjected to annealing at temperatures ranging up to 400 °C. It was found that for the annealing temperatures between 200 °C and 300 °C the intensity of fluorescent tracks increases. The maximum enhancement factor of 2.5 is reached for a temperature of 290 °C. For temperatures exceeding 300 °C the intensity decreases and above 340 °C the tracks are not visible. The effect of track enhancement is permanent - no differences were observed for several weeks after the thermal treatment. An interesting phenomenon is the influence of the particle fluence: with increasing fluence the enhancement factor decreases and for the fluence around 2.9*107 cm−2, the intensity of light registered after heat treatment is lower than the initial one. It is still unclear what is the reason behind the observed effect. It however seems probable that the mechanism involves transforming part of F centers into F2 centers. Nevertheless, the effect is promising, as it may lead to signal-to-noise ratio improvement and improved measuring capabilities of LiF FNTDs.

Intensity threshold variation method in the post-irradiation analysis of Fluorescent Nuclear Track Detectors for neutron dosimetry

Fluorescent Nuclear Track Detectors (FNTDs) are biocompatible passive detectors and a promising tool for neutron dosimetry applications, such as in-phantom measurements within the scope of ion therapy. Sensitivity differences between individual detectors however complicate the post-irradiation analysis process, making detector comparability and consequently dose assessment challenging. Therefore, improvements in the analysis method are needed to account for the observed sensitivity effects. In this work, the FNTD technology was implemented for neutron dosimetry using a standard Am-241/Be neutron source for irradiation and a confocal laser scanning microscope for detector readout. Acquired images were evaluated in terms of the track number of recoil proton signals behind a polyethylene converter, which was found to be related to dose. This study presents a new methodology for the post-irradiation data analysis, based on the variation of the intensity threshold parameter during the proton track identification process. The procedure was tested within individual detectors in stepwise irradiation experiments, validating the consistency of the proposed methodology. The application of the method to an extended number of FNTDs was able to account for sensitivity impacts and enabled comparability between the different detectors. A calibration curve based on the observed linear relation between dose and the number of identify tracks was obtained, that can be used for future implementation of FNTDs in neutron dosimetry.

Estimation of biological effect of Cu-64 radiopharmaceuticals with Geant4-DNA simulation

The aim of this work is to estimate the biological effect of targeted radionuclide therapy using Cu-64, which is a well-known Auger electron emitter. To do so, we evaluate the absorbed dose of emitted particles from Cu-64 using the Geant4-DNA Monte Carlo simulation toolkit. The contribution of beta particles to the absorbed dose is higher than that of Auger electrons. The simulation result agrees with experimental ones evaluated using coumarin-3-carboxylic acid chemical dosimeter. The simulation result is also in good agreement with previous ones obtained using fluorescent nuclear track detector. From the results of present simulation (i.e., absorbed dose estimation) and previous biological experiments using two cell lines (i.e., evaluation of survival curves), we have estimated the relative biological effectiveness (RBE) of Cu-64 emitted particles on CHO wild-type cells and xrs5 cells. The RBE of xrs5 cells exposed to Cu-64 is almost equivalent to that with gamma rays and protons and C ions. This result indicates that the radiosensitivity of xrs5 cells is independent of LET. In comparison to this, the RBE on CHO wild-type cells exposed to Cu-64 is significantly higher than gamma rays and almost equivalent to that irradiated with C ions with a linear energy transfer of 70 keV/μm.

The kinetic parameters of the main thermoluminescence glow peak of Al2O3:C,Mg: A critical evaluation of different analytical methods

Carbon and magnesium co-doped aluminum oxide (Al2O3:C,Mg) is a highly sensitive luminescence dosimeter with promising use in a wide spectrum of radiation-related applications, including neutron dosimetry and as a fluorescent nuclear track detector (FNTD). The goal of this work is to critically evaluate diverse methods and approaches for the determination of the kinetic parameters using Al2O3:C, Mg as a case study. Al2O3:C, Mg was beta irradiated with doses from 0.1 to 0.6 Gy. Besides thermoluminescence (TL) peaks at 325, 350, and 375 K, the analysis of the activation energy, frequency factor and order of kinetics focused exclusively on the main TL peak at 450 K. Analysis by curve fittings used a number of freeware, namely, Glowfit, TLAnal, the Thermoluminescence Glow Curve Deconvolution (TGCD) package, and the spreadsheet TLDecoxcel. The results from the computational approaches were compared with results obtained by analyzing experimental data using conventional methods as initial-rise, whole glow peak, variable heating rate and peak shape. The performance of the computational methods is satisfactory as the values found are consistent with the ones determined by the methods listed above.

Measurement of the energy spectrum of laser-accelerated protons using FNTD: Development of an easy and quick method for energy spectrometry

This paper reports the derivation of energies of proton beams accelerated by an intense laser using a fluorescent nuclear track detector (FNTD), which is Al2O3 single crystal doped with C and Mg. Using the FNTD, we acquire 3D images of incoming tracks easily, consecutively and rapidly and we can follow the fluorescence intensity of the proton tracks towards their terminals. By counting the number of proton tracks that disappeared at a certain depth, we determine the range of the tracks. Then, we evaluate energies of incoming protons from the evaluated range. The maximum energy of accelerated proton is 3.3 MeV. The results obtained from FNTD measurements are in good agreement with those obtained from the relationship between the incident energy and the distance calculated from the spatial distribution of the magnetic field. The FNTD provides the energy spectrum quickly after the laser shot within few hours, much faster than conventional nuclear track detectors such as CR-39 plastic and nuclear emulsion detectors, which require several days due to the chemical treatments needed. The FNTD is a promising detector for the diagnosis of beams accelerated by an intense laser, which generates a complex mixed radiation field.

Correction Method of the Coloration in Fluorescent Nuclear Track Detector

Correction Method of the Coloration in Fluorescent Nuclear Track Detector

A Monte-Carlo study on the fluorescent nuclear track detector (FNTD) response to fast neutrons: Which information can be obtained by single layer and 3D track reconstruction analyses?

Fluorescence Nuclear Track Detectors (FNTDs) are part of a new technology developed for particle detection and applicable to personal neutron dosimetry. The objective of this study is to simulate the FNTD fast neutron response to: (i) assess and understand the performance of the existing neutron dosimeter design (Landauer Inc.) and its associated single layer track-spots analysis; and (ii) evaluate the potential information that can be obtained by the analysis of the 3D reconstructed recoil proton trajectories. To achieve that, a FLUKA Monte Carlo (MC) model of the current FNTD design was developed and the FNTD response was investigated for mono-energetic neutrons and the 252Cf and 241AmBe neutron sources. The investigation of the recoil proton densities behind the different converters showed that the single layer analysis and dose calculation algorithm, based on the comparison and subtraction of the track densities behind the different converters, works properly only up to neutron energies ~13 MeV. Above this neutron energies, recoil protons generated in the detector housing (PE) have a range larger than the thickness of the PTFE and 6Li-enriched glass, reaching the FTND and, therefore, adding to the signal in these detection regions and influencing the secondary electron discrimination and the energy determination algorithm. MC simulations show that the FNTD 3D reconstructed recoil proton tracks can provide estimates of the irradiation angles and average neutron energy. The results show that the angle or displacement (dX/dZ or dY/dZ) distributions of the recoil proton tracks can be used to obtain information on irradiation angle; the angle with the detector's normal (polar angle), the most important because of its influences on the FTND sensitivity, can be determined in laboratory and for irradiation angles < 60° with an 4° uncertainty already for doses > 4.5 mSv in the case of a214AmBe neutron irradiation. The neutron field mean energy can also be determined for normal irradiation by analysing the depth distribution of the recoil proton tracks already for a minimum of 150 tracks, or 2.5 mSv for 241AmBe, assuming a scanned area is ~2.0 mm2. Therefore, the present study contributes to understanding the performance of the current FNTD design and analysis for neutron dosimetry and investigates a new detector evaluation approach to gain additional information on the irradiation conditions.

Principal Component Analysis applied to neutron dosimetry based on PADC detectors and FNTDs

Solid State Nuclear Track Detectors (SSNTD) have been used as passive dosimeters for many decades. Fast neutron detection is performed by detecting recoil protons generated in a hydrogenous material (neutron converter). The dose is estimated by multiplying the recoil protons track-spots density present on the detector surface by a calibration coefficient obtained from reference irradiations. Therefore, one needs to automatically and reliably discriminate between the track-spots induced by recoil-protons and the spurious signal engendered either by material imperfections or by other ionising particles interactions. The objective of this work is to demonstrate and apply a method, based on the multivariate statistical tool named Principal Component Analysis (PCA), aiming at identifying and filtering out the spurious signal in track detectors. The advantage of this approach is that it can be applied to any type of SSNTD, provided apt definition of initial physical variables describing each track-spot. To show that, we applied the method to poly-allyl diglycol carbonate (PADC) detectors, to filter the signal generated by material imperfections, and to fluorescence nuclear track detectors (FNTDs), to remove the signal induced by other radiation field components. After filtering, dose assessments were compared with reference values of exposures, showing satisfactory agreement. In case of the FNTDs, the procedure proved to be effective regardless of the crystal colouration, which is known to affect signal-rejection techniques based on track-spots fluorescence intensity. The technique also offers the advantage of self-adjusting the filtering parameters based on the currently analysed detector set, as long as calibration and unirradiated detectors are included in the dataset.