Ionization Cluster Size Research Articles

Modification of Nafion membrane by polyaniline providing uniform polymer distribution throughout the membrane

Oxidative polymerization of aniline in the presence of Nafion membranes has been carried out in a water–isopropanol mixture after preliminary impregnation of the membrane with the monomer (aniline) in aqueous isopropanol. Uniform distribution of polyaniline (PANI) throughout whole membrane volume has been found. On the contrary, aniline polymerization in water, even after preliminary impregnation of the membrane with the monomer, has resulted in the formation of PANI thin layer only on the membrane surfaces but not inside the membrane. The polymerization in water–isopropanol mixture has not led to the change in the membrane surface properties but has induced the structural reorganization of Nafion membrane accompanied by the increase in the membrane ionic cluster size and the distance between the fluorocarbon crystallites. Modification by PANI carried out either in water or in aqueous isopropanol solution has resulted in the decrease in the membrane proton conductivity by 5–10 times.

Fast calculation of nanodosimetric quantities in treatment planning of proton and ion therapy

Details of the pattern of ionization formed by particle tracks extends knowledge of dose effects on the nanometer scale. Ionization detail (ID), frequently characterized by ionization cluster size distributions (ICSD), is obtained through time-consuming Monte Carlo (MC) track-structure simulations. In this work, TOPAS-nBio was used to generate a highly precise database of biologically significant ID quantities, sampled with randomly oriented 2.3 nm diameter cylinders, 3.4 nm (10 base pairs) long, inside a chromatin-size cylinder, irradiated by 1–1000 MeV/u ions of Z = 1–8. A macroscopic method developed to utilize the database using condensed-history MC was used to calculate distributions of the ICSD first moment and cumulative probability in a 20 × 20 × 40 cm3 water phantom irradiated with proton and carbon spread-out Bragg peak (SOBP) of 10.5 cm range, 2 cm width. Results were verified against detailed MC track-structure simulations using phase space scored at several depths. ID distributions were then obtained for intensity modulated proton and carbon radiotherapy plans in a digitized anthropomorphic phantom of a base of skull tumor to demonstrate clinical application of this approach.The database statistical uncertainties were 0.5% (3 standard deviations). Fluence-averaged ID as implemented proved unsuitable for macroscopic calculation. Edep-averaged ID agreed with track-structure results within 0.8% for protons. For carbon, maximum absolute differences of 2.9% ± 1.6% and 5.6% ± 1.9% for , 1.7% ± 0.8% and 1.9% ± 0.4% (1 standard deviation) for , were found in the plateau and SOBP, respectively, up to 11.5% ± 5.6% in the tail region. Macroscopic ID calculation was demonstrated for a realistic treatment plan. Computation times with or without ID calculation were comparable in all cases.Pre-calculated nanodosimetric data may be used for condensed-history MC for nanodosimetric ID-based treatment planning in ion radiotherapy in the future. The macroscopic approach developed has the calculation speed of condensed-history MC while approaching the accuracy of full track structure simulations.

ToF-SIMS analysis of an organic layer using toluene and its cluster ion beam projectiles generated by multiphoton ionization

Secondary ion mass spectrometry (SIMS) has become a powerful tool for a chemical imaging of surfaces. In particular, cluster ion beams have been widely implemented with SIMS using spatial distributions of molecules as an analysis and imaging method for a sample composed of organic molecules. In this study, we developed a home-built time-of-flight (ToF)-SIMS instrument and generated organic molecular cluster ion beams ionized by multiphoton ionization (MPI) as a primary ion beam. Further, the sample stage loaded with rhodamine 6G was bombarded with size-controlled toluene cluster ions to produce secondary ions. Mass spectra of rhodamine 6G were acquired as a function of the size of toluene cluster ions. We plotted the fragments-to-parent ion ratio against each size of cluster ion, and we found that an intact rhodamine 6G signal would be observed with less fragmentations using (Tol)n > 18+. We expect this combination of the organic molecular cluster ion beam generated by MPI and ToF-SIMS to greatly expand the field of surface analysis.

Spectral artefacts post sputter-etching and how to cope with them – A case study of XPS on nitride-based coatings using monoatomic and cluster ion beams

The issue of artefacts due to sputter-etching has been investigated for a group of AlN-based thin film materials with varying thermodynamical stability. Stability of the materials was controlled by alloying AlN with the group 14 elements Si, Ge or Sn in two different concentrations. The coatings were sputter-etched with monoatomic Ar+ with energies between 0.2 and 4.0 keV to study the sensitivity of the materials for sputter damage. The use of Arn+ clusters to remove an oxidised surface layer was also evaluated for a selected sample. The spectra were compared to pristine spectra obtained after in-vacuo sample transfer from the synthesis chamber to the analysis instrument. It was found that the all samples were affected by high energy (4 keV) Ar+ ions to varying degrees. The determining factors for the amount of observed damage were found to be the materials’ enthalpy of formation, where a threshold value seems to exist at approximately −1.25 eV/atom (∼−120 kJ/mol atoms). For each sample, the observed amount of damage was found to have a linear dependence to the energy deposited by the ion beam per volume removed material. Despite the occurrence of sputter-damage in all samples, etching settings that result in almost artefact-free spectral data were found; using either very low energy (i.e. 200 eV) monoatomic ions, or an appropriate combination of ion cluster size and energy. The present study underlines that analysis post sputter-etching must be carried out with an awareness of possible sputter-induced artefacts.

Poly (2,6-dimethyl-1,4-phenylene oxide)/ionic liquid functionalized graphene oxide anion exchange membranes for fuel cells

To improve the overall performance of anion exchange membranes (AEMs) for fuel cells, a series of composite AEMs was prepared via a facile approach using ionic liquid-functionalized graphene oxide (IL-GO) and imidazolium-functionalized poly (2,6-dimethyl-1,4-phenylene oxide) (ImPPO). The prepared ImPPO/IL-GO-0.5% (0.5% refers to the weight percentage of IL-GO) membranes with an ionic exchange capacity (IEC) of 1.9 meq g−1 achieved a hydroxide conductivity of 78.5 mS cm−1. The high conductivity of ImPPO/IL-GO-0.5% is due to the fact that the ionic cluster size of composite membranes (3.43–3.58 nm) is larger than that of the pristine membrane (3.30 nm). The ionic cluster morphology is confirmed by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). Moreover, the AEMs retained approximately 70% of their initial hydroxide conductivity after the alkaline stability test in a 2 M aqueous NaOH at 80 °C for 480 h, indicating a good alkaline stability. A single cell using ImPPO/IL-GO-0.5% exhibits a peak power density of 136 mW cm−2 at 60 °C under 100% related humidity, thereby having a great potential for fuel cells.

Influence of Dielectric Constant on Ionic Transport in Polyether-Based Electrolytes.

We use all-atom molecular dynamics simulations to study the effect of polymer polarity, as quantified by the dielectric constant, on the transport properties of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) doped polyethers. Our results indicate that increasing the host dielectric constant leads to a decrease in ionic cluster sizes and reduction in correlated motion of oppositely charged ions. This causes the ionic conductivity to more closely approach the Nernst-Einstein limit in which ionic conductivity is only limited by the diffusivities of Li+ and TFSI-. We compare our results to recent experimental observations which demonstrate similar qualitative trends in host polarity.

Measurement of track structure parameters of low and medium energy helium and carbon ions in nanometric volumes

Ionization cluster size distributions produced in the sensitive volume of an ion-counting wall-less nanodosimeter by monoenergetic carbon ions with energies between 45 MeV and 150 MeV were measured at the TANDEM-ALPI ion accelerator facility complex of the LNL-INFN in Legnaro. Those produced by monoenergetic helium ions with energies between 2 MeV and 20 MeV were measured at the accelerator facilities of PTB and with a 241Am alpha particle source. C3H8 was used as the target gas. The ionization cluster size distributions were measured in narrow beam geometry with the primary beam passing the target volume at specified distances from its centre, and in broad beam geometry with a fan-like primary beam. By applying a suitable drift time window, the effective size of the target volume was adjusted to match the size of a DNA segment. The measured data were compared with the results of simulations obtained with the PTB Monte Carlo code PTra. Before the comparison, the simulated cluster size distributions were corrected with respect to the background of additional ionizations produced in the transport system of the ionized target gas molecules. Measured and simulated characteristics of the particle track structure are in good agreement for both types of primary particles and for both types of the irradiation geometry. As the range in tissue of the ions investigated is within the typical extension of a spread-out Bragg peak, these data are useful for benchmarking not only ‘general purpose’ track structure simulation codes, but also treatment planning codes used in hadron therapy. Additionally, these data sets may serve as a data base for codes modelling the induction of radiation damages at the DNA-level as they almost completely characterize the ionization component of the nanometric track structure.

Clustered multi-imidazolium side chains functionalized alkaline anion exchange membranes for fuel cells

Clustered alkyl side chains bearing a string of three imidazolium cations with hexyl spacers are grafted to fluorene-based poly (arylene ether sulfone) successfully. Nanostructure is directly configured within the anion exchange membranes (AEMs) via the novel multi-cation side chains. As confirmed by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS), percolating OH– conducting channels with the size of ionic clusters nearly 20nm endow the trimPES-0.4 membrane with an excellent ion conductivity in excess of 120mScm–1 at 80°C. Because of the self-assembly of ionic groups, water molecules are compartmentalized into the hydrophilic side chain regions instead of backbones, resulting in advantageous over water management. Together with the lengthened hydrophobic segments, TrimPES-0.2 exhibits superior dimensional stability (12.0%, 30°C) to conventional mono-cation type AEMs. Furthermore, the novel multi-cation TrimPES-0.4 displays a peak power density of 134.4mWcm–2 at a current density of 280mAcm–2. Therefore, these findings suggest that by tuning the distribution of cations, AEMs with well-balanced performance can be made for fuel cell applications.

Sequential water molecule binding enthalpies for aqueous nanodrops containing a mono-, di- or trivalent ion and between 20 and 500 water molecules.

Sequential water molecule binding enthalpies, ΔHn,n-1, are important for a detailed understanding of competitive interactions between ions, water and solute molecules, and how these interactions affect physical properties of ion-containing nanodrops that are important in aerosol chemistry. Water molecule binding enthalpies have been measured for small clusters of many different ions, but these values for ion-containing nanodrops containing more than 20 water molecules are scarce. Here, ΔHn,n-1 values are deduced from high-precision ultraviolet photodissociation (UVPD) measurements as a function of ion identity, charge state and cluster size between 20-500 water molecules and for ions with +1, +2 and +3 charges. The ΔHn,n-1 values are obtained from the number of water molecules lost upon photoexcitation at a known wavelength, and modeling of the release of energy into the translational, rotational and vibrational motions of the products. The ΔHn,n-1 values range from 36.82 to 50.21 kJ mol-1. For clusters containing more than ∼250 water molecules, the binding enthalpies are between the bulk heat of vaporization (44.8 kJ mol-1) and the sublimation enthalpy of bulk ice (51.0 kJ mol-1). These values depend on ion charge state for clusters with fewer than 150 water molecules, but there is a negligible dependence at larger size. There is a minimum in the ΔHn,n-1 values that depends on the cluster size and ion charge state, which can be attributed to the competing effects of ion solvation and surface energy. The experimental ΔHn,n-1 values can be fit to the Thomson liquid drop model (TLDM) using bulk ice parameters. By optimizing the surface tension and temperature change of the logarithmic partial pressure for the TLDM, the experimental sequential water molecule binding enthalpies can be fit with an accuracy of ±3.3 kJ mol-1 over the entire range of cluster sizes.

Lipid specific molecular ion emission as a function of the primary ion characteristics in TOF-SIMS.

In the present work, the emission characteristics of lipids as a function of the primary ion cluster size and energy were studied using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Characteristic fragmentation patterns for common lipids are described, and changes in secondary ion (SI) yields using various primary ion beams are reported. In particular, emission characteristics were studied for pairs of small polyatomic and nanoparticle primary ion beams (e.g., Bi3+ versus Ar1000+ and Au3+ versus Au400+4) based on the secondary ion yield of characteristic fragment and intact molecular ions as a function of the lipid class. Detailed descriptions of the fragmentation patterns are shown for positive and negative mode TOF-SIMS. Results demonstrate that the lipid structure largely dictates the spectral presence of molecular and/or fragment ions in each ionization mode due to the localization of the charge carrier (head group or fatty acid chain). Our results suggest that the larger the energy per atom for small polyatomic projectiles (Bi3+ and Au3+), the larger the SI yield; in the case of nanoparticle projectiles, the SI increase with primary ion energy (200-500 keV range) for Au400+4 and with the decrease of the energy per atom (10-40 eV/atom range) for Arn=500-2000+ clusters. The secondary ion yield of the molecular ion of lipids from a single standard or from a mixture of lipids does not significantly change with the primary ion identity in the positive ion mode TOF-SIMS and slightly decreases in the negative ion mode TOF-SIMS.

Distributions of deposited energy and ionization clusters around ion tracks studied with Geant4 toolkit

The Geant4-based Monte Carlo model for Heavy-Ion Therapy (MCHIT) was extended to study the patterns of energy deposition at sub-micrometer distance from individual ion tracks. Dose distributions for low-energy 1H, 4He, 12C and 16O ions measured in several experiments are well described by the model in a broad range of radial distances, from 0.5 to 3000 nm. Despite the fact that such distributions are characterized by long tails, a dominant fraction of deposited energy (∼80%) is confined within a radius of about 10 nm. The probability distributions of clustered ionization events in nanoscale volumes of water traversed by 1H, 2H, 4He, 6Li, 7Li, and 12C ions are also calculated. A good agreement of calculated ionization cluster-size distributions with the corresponding experimental data suggests that the extended MCHIT can be used to characterize stochastic processes of energy deposition to sensitive cellular structures.

Changes in the molecular ion yield and fragmentation of peptides under various primary ions in ToF-SIMS and matrix-enhanced ToF-SIMS.

Time of flight secondary ion mass spectrometry (ToF-SIMS) is a powerful technique for the nanoanalysis of biological samples, but improvements in sensitivity are needed in order to detect large biomolecules, such as peptides, on the individual cell level at physiological concentrations. Two promising options to improve the sensitivity of SIMS to large peptides are the use of cluster primary ions to increase desorption of intact molecules or the use of matrix-assisted laser desorption/ionization (MALDI) matrices to increase the ionization probability. In this paper, the authors have combined these two approaches in order to improve understanding of the interaction between ionization and fragmentation processes. The peptides bradykinin and melittin were prepared as neat monolayers on silicon, in a Dextran-40 matrix and in two common MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxy cinnamic acid (HCCA). ToF-SIMS spectra of these samples were collected using a range of small Bi cluster primary ions and large Ar cluster primary ions. The trends observed in the molecular ion yield and the [M+H](+)/C4H8N(+) ratio with primary ion cluster size were sample system dependent. The molecular ion yield of the bradykinin was maximized by using 30 keV Bi3 (+) primary ions in a DHB matrix but in the HCCA matrix, the maximum molecular ion yield was obtained by using 30 keV Bi7 (+) primary ions. In contrast, the molecular ion yield for melittin in both matrices was greatest using 20 keV Ar2000 (+) primary ions. Improvements in the molecular ion yield were only loosely correlated with a decrease in small fragment ions. The data indicate a complex interplay between desorption processes and ion formation processes which mean that the optimal analytical conditions depend on both the target analyte and the matrix.

Local weighting of nanometric track structure properties in macroscopic voxel geometries for particle beam treatment planning

The research project BioQuaRT within the European Metrology Research Programme aimed at correlating ion track structure characteristics with the biological effects of radiation and developed measurement and simulation techniques for determining ion track structure on different length scales from about 2 nm to about 10 μm. Within this framework, we investigated methods to translate track-structure quantities derived on a nanometre scale to macroscopic dimensions. Here we make use of parameterizations that link the energy of the projectile to the ionization pattern of the track using nanodosimetric ionization cluster size distributions. They were defined with data generated by simulations of ion tracks in liquid water using the Geant4 Monte Carlo toolkit with the Geant4-DNA processes. For the clinical situation with a mixed radiation field, where particles of various energies hit a cell from several directions, we have to find macroscopic relevant mean values. They can be determined by appropriate local weighting functions for the identified parameterization. We show that a stopping power weighted mean value of the mentioned track structure properties can describe the overall track structure in a cell exposed to a mixed radiation field. The parameterization, together with the presented stopping power weighting approach, show how nanometric track structure properties could be integrated into treatment planning systems without the need to perform time consuming simulations on the nanometer level for each individual patient.

Influence of the geometrical detail in the description of DNA and the scoring method of ionization clustering on nanodosimetric parameters of track structure: a Monte Carlo study using Geant4-DNA

The aim of this study was to evaluate the influence of the geometrical detail of the DNA on nanodosimetric parameters of track structure induced by protons and alpha particles of different energies (LET values ranging from 1 to ) as calculated by Geant4-DNA Monte Carlo simulations.The first geometry considered consisted of a well-structured placement of a realistic description of the DNA double helix wrapped around cylindrical histones (GeomHist) forming a 18 kbp-long chromatin fiber. In the second geometry considered, the DNA was modeled as a total of 1800 ten bp-long homogeneous cylinders (2.3 nm diameter and 3.4 nm height) placed in random positions and orientations (GeomCyl). As for GeomHist, GeomCyl contained a DNA material equivalent to 18 kbp. Geant4-DNA track structure simulations were performed and ionizations were counted in the scoring volumes. For GeomCyl, clusters were defined as the number of ionizations (ν) scored in each 10 bp-long cylinder. For GeomHist, clusters of ionizations scored in the sugar-phosphate groups of the double-helix were revealed by the DBSCAN clustering algorithm according to a proximity criteria among ionizations separated by less than 10 bp. The topology of the ionization clusters formed using GeomHist and GeomCyl geometries were compared in terms of biologically relevant nanodosimetric quantities.The discontinuous modeling of the DNA for GeomCyl led to smaller cluster sizes than for GeomHist. The continuous modeling of the DNA molecule for GeomHist allowed the merging of ionization points by the DBSCAN algorithm giving rise to larger clusters, which were not detectable within the GeomCyl geometry. Mean cluster size (m1) was found to be of the order of 10% higher for GeomHist compared to GeomCyl for LET . For higher LETs, the difference increased with LET similarly for protons and alpha particles. Both geometries showed the same relationship between m1 and the cumulative relative frequency of clusters with (f3) within statistical variations, independently of particle type.In order to obtain ionization cluster size distributions relevant for biological DNA lesions, the complex DNA geometry and a scoring method without fixed boundaries should be preferred to the simple cylindrical geometry with a fixed scoring volume.

Secondary ionisations in a wall-less ion-counting nanodosimeter: quantitative analysis and the effect on the comparison of measured and simulated track structure parameters in nanometric volumes

The object of investigation in nanodosimetry is the physical characteristics of the microscopic structure of ionising particle tracks, i.e. the sequence of the interaction types and interaction sites of a primary particle and all its secondaries, which reflects the stochastic nature of the radiation interaction. In view of the upcoming radiation therapy with protons and carbon ions, the ionisation structure of the ion track is of particular interest. Owing to limitations in current detector technology, the only way to determine the ionisation cluster size distribution in a DNA segment is to simulate the particle track structure in condensed matter. This is done using dedicated computer programs based on Monte Carlo procedures simulating the interaction of the primary ions with the target. Hence, there is a need to benchmark these computer codes using suitable experimental data. Ionisation cluster size distributions produced in the nanodosimeter’s sensitive volume by monoenergetic protons and alpha particles (with energies between 0.1 MeV and 20 MeV) were measured at the PTB ion accelerator facilities. C3H8 and N2 were alternately used as the working gas. The measured data were compared with the simulation results obtained with the PTB Monte-Carlo code PTra [B. Grosswendt, Radiat. Environ. Biophys. 41, 103 (2002); M.U. Bug, E. Gargioni, H. Nettelbeck, W.Y. Baek, G. Hilgers, A.B. Rosenfeld, H. Rabus, Phys. Rev. E 88, 043308 (2013)]. Measured and simulated characteristics of the particle track structure are generally in good agreement for protons over the entire energy range investigated. For alpha particles with energies higher than the Bragg peak energy, a good agreement can also be seen, whereas for energies lower than the Bragg peak energy differences of as much as 25% occur. Significant deviations are only observed for large ionisation cluster sizes. These deviations can be explained by a background consisting of secondary ions. These ions are produced in the region downstream of the extraction aperture by electrons with a kinetic energy of about 2.5 keV, which are themselves released by ions of the “primary” ionisation cluster hitting an electrode in the ion transport system. Including this background of secondary ions in the simulated cluster size distributions leads to a significantly better agreement between measured and simulated data, especially for large ionisation clusters.

Energy dependent track structure parametrisations for protons and carbon ions based on nanometric simulations

The BioQuaRT project within the European Metrology Research Programme aims at correlating ion track structure characteristics with the biological effects of radiation and develops measurement and simulation techniques for determining ion track structure on different length scales from about 2 nm to about 10 μm. Within this framework, we investigate methods to translate track-structure quantities derived on a nanometre scale to macroscopic dimensions. Input data sets were generated by simulations of ion tracks of protons and carbon ions in liquid water using the Geant 4 Monte Carlo toolkit with the Geant4-DNA processes. Based on the energy transfer points — recorded with nanometre resolution — we investigated parametrisations of overall properties of ion track structure. Three different track structure parametrisations have been developed using the distances to the 10 next neighbouring ionisations, the radial energy distribution and ionisation cluster size distributions. These parametrisations of nanometric track structure build a basis for deriving biologically relevant mean values which are essential in the clinical situation where each voxel is exposed to a mixed radiation field.

Investigating ionisation cluster size distribution due to sub-1 keV electrons in view of Heisenberg's Uncertainty

As the wavelengths of low energy electrons become comparable with the length scale of the mean ionisation step size, each event particle should be treated with care as the condition outlined in Heisenberg's uncertainty principle (HUP) should also be satisfied. Within this quantum-classical regime, spatial delocalisations of individual ionisation event sites that are generated outside the target region are calculated, and particular attention is given to the validity of using classical transport methods in simulations of nanodosimetric parameters such as mean cluster size, first and second moments, variance and cumulative frequency of ionisation cluster-size probability distributions. This paper presents the comparison between conventionally calculated nanodosimetric quantities and the ones where interacting particles are treated semi-classically with spatial uncertainties satisfied by HUP. The simulated primary charged particles are electrons of energies between 100 eV and 1 keV in DNA equivalent target aqueous water volumes using GEANT4-DNA.

Removal of Organic Contamination from Graphene with a Controllable Mass-Selected Argon Gas Cluster Ion Beam

Since the discovery of graphene, organic surface contamination has posed difficulties both for accurate characterization of the material’s intrinsic properties and for development of graphene devices. In this study, we investigate the use of a mass-selected argon gas cluster ion beam for removing organic contaminants, such as residual poly(methyl methacrylate) (PMMA), from single-layer graphene. The influence of cluster ion size, energy, and ion dose has been investigated to identify the important factors for minimizing damage to the graphene layer during the cleaning process. Raman spectroscopy was used to analyze the variation in the D-peak and G-peak intensity ratio, an indicator of damage to the graphene lattice, as a function of ion beam dose and kinetic energy per atom (E/n) in the cluster ions. Using a mass-selected 5 keV Ar5000 beam with a dose of 5.0 ions/nm2, we were able to demonstrate removal of polymer residue and other carbonaceous material from single-layer chemical vapor deposition (CVD)-g...

Side-chain-type clustered sulfonated poly(arylene ether ketone)s prepared by click chemistry

A series of poly(arylene ether ketone)s containing azidomethylbenzoyl side chains were fabricated through a three-step process involving polymerization of methylated copolymers, followed by bromination and azido-functionalized with sodium azide. Click reaction was applied to introduce locally and densely populated sulfophenyl group into the aromatic copolymer backbone. Ion exchange capacity (IEC) was indirectly controlled by the contents of brominated methylene moieties as precursors for azido-functionalization. Structures of the copolymers were confirmed by FT-IR and 1H NMR. Transmission electron microscopy (TEM) showed good phase separated morphology with ionic cluster sizes in the range of 2–20 nm. Meanwhile, the sulfonated copolymers exhibited high proton conductivity in the range between 0.082 and 0.113 S cm−1 at 80 °C and 100% relative humidity (RH). The methanol permeability of these membranes was in the range between 4.07 × 10−7 and 10.00 × 10−7 cm2 s−1.

Nanodosimetry of electrons: analysis by experiment and modelling

Nanodosimetry experiments for high-energy electrons from a (131)I radioactive source interacting with gaseous nitrogen with sizes on a scale equivalent to the mass per area of a segment of DNA and nucleosome are described. The discrete ionisation cluster-size distributions were measured in experiments carried out with the Jet Counter. The experimental results were compared with those obtained by Monte Carlo modelling. The descriptors of radiation damages have been derived from the data obtained from ionisation cluster-size distributions.