Radiation chemical yields for loss of ether and carbonate ester bonds in PADC films exposed to proton and heavy ion beams

Chemical modification along ion tracks in PADC films has been studied by means of FT-IR spectrometry, which was exposed to proton and heavy ions of He, C, Ne, Ar, Fe, Kr and Xe with energies around the Bragg peaks. This study covers a wide region of the stopping power ranging from 10 to 10,000 keV/μm. Removal cross sections for the loss of ether and carbonate ester bonds are assessed for each ion, as a function of the stopping power. Chemical damage parameters like the damage density, the effective track core radius and the radiation chemical yields, G values (scissions/100 eV), for each bond are also derived. We have found anomalous dependence of these parameters on the stopping power. The G value for the loss of carbonate ester bond decreased from 20 for proton down to 5 for C and Ne ions, and then increased with atomic number of heavy ions up to 8 for Xe ion. Radial dose distribution for each ion has been also calculated. Results are discussed from the viewpoint of polymeric structure of PADC that consists of two parts with different radio-sensitivities.     

Vacuum effects on the radiation chemical yields in PADC films exposed to gamma rays and heavy ions

In order to understand the vacuum effects on the sensitivity of PADC detectors from the viewpoint of molecule structural modification along nuclear tracks, a series of FT-IR spectrometric studies has been made for PADC films exposed to He and C ions at energies below 6 MeV/n, as well as to gamma rays from an intense Co-60 source, under the both conditions of in air and in vacuum. The radiation chemical yields for the losses of ether and carbonate ester bonds are hardly affected by the environmental conditions in the cases of He and C ion irradiations. For gamma ray, the yields are about half in vacuum compared to those in air. The formation of OH groups is fairly suppressed in vacuum in all cases. Recombination of free radicals resulted in modified polymeric network formation would be enhanced in heavy ion irradiations rather than in that of gamma irradiations.     

On the mechanism of the sensitization of PADC (poly(allyl diglycol carbonate)) track detectors by carbon dioxide treatment

The sensitization effect of carbon dioxide treatments with 0.6 MPa on poly(allyl diglycol carbonate) (PADC) etched track detectors is confirmed for protons and He, C, and Fe ions, where the stopping powers range from 10 to 600 keV/μm. Based on the FT-IR study for the PADC films that were maintained at room temperature and at elevated temperatures, the diffusion coefficient of carbon dioxide, is determined as D = 14,670exp(−9030/T(K)) cm²/s. The sensitivity is enhanced when carbon dioxide is released toward the chemical etching solution that passes through the detector surface. Segmented PADC polymer chains are washed away by the flow of carbon dioxide along the latent tracks in PADC, which results in a higher track etch rate.     

Applicability of the polyimide films as an SSNTD material

Track registration properties in polyimide films, KAPTON, for heavy ions have been examined by means of FT-IR spectrometry and the chemical etching in sodium hypochlorite solution. The effective track core size for the loss of CO and C–N–C composing imide bonds, and diphenyl ethers of C–O–C have been evaluated under the irradiations by Ne, Fe and Xe ions at energies less than 6 MeV/n. On the other hand, the etching property of the polyimide films has been examined in the sodium hypochlorite solution at temperature of 55 °C. Before the etchings, the films were exposed to H, C, Ne, Fe and Xe ions, at incident energies below 6 MeV/n. The etch pits are found only on the films exposed to Fe and Xe ions, indicating significant difference on the etch pit size between them. This implies that the polyimide film has charge or energy resolution for these relatively heavy ions. The threshold level of the etchable track registration is inferred to be around 2500 keV/μm. The effective track core radius at this stopping power for the loss of diphenyl ether is 1.6 nm, which is equivalent to the length between the adjacent diphenyl ether bonds in the polyimide chains. Breakings at two adjacent diphenyl ethers in radial direction of latent tracks may produce etchable tracks in KAPTON.     

Impact of electron irradiation on particle track etching response in polyallyl diglycol carbonate (PADC)

In the present work, attempts have been made to investigate the modification in particle track etching response of polyallyl diglycol carbonate (PADC) due to impact of 2 MeV electrons. PADC samples pre-irradiated to 1, 10, 20, 40, 60, 80 and 100 Mrad doses of 2 MeV electrons were further exposed to 140 MeV²⁸ Si beam and dose-dependent track registration properties of PADC have been studied. Etch-rate values of the PADC irradiated to 100 Mrad dose electron was found to increase by nearly 4 times that of pristine PADC. The electron irradiation has promoted chain scissioning in PADC, thereby converting the polymer into an easily etchable polymer. Moreover, the etching response and the detection efficiency were found to improve by electron irradiation. Scanning electron microscopy of etched samples further revealed the surface damage in these irradiated PADCs.     

Modification induced by proton irradiation in polyallyldiglycol carbonate (PADC)

Swift heavy ions interact predominantly through inelastic scattering while traversing through any polymeric medium producing excited/ionised atoms. Beyond a certain threshold, they affect the lattice structure leading to remarkable flexibility in engineering many physical and mechanical properties of the polymer. Polyallyldiglycol carbonate (PADC) is a class of polymeric detectors which finds its applications in various fields. In the present work, PADC samples were irradiated by four different fluences (≈10¹²–10¹³ cm⁻²) of 62 MeV protons from heavy ion accelerator (ISL) at HMI, Berlin. The modifications in the proton irradiated polymers as a function of fluence have been studied through different characterisation techniques such as Fourier Transform IR, UV-Vis, Electron Spin resonance, Thermogravimetric analysis, Differential Scanning Calorimetry and Track studies. The optical band-gap was found to be constant while a decrease in transmittance of PADC was observed with the increase in proton fluence. The thermal stability of PADC was found to be an inverse function of fluence. Further, these proton irradiated PADCs were exposed to fission fragments from ²⁵²Cf source and the bulk etch-rate was improved with the increase in proton fluence and was found to be increased by 90% for the PADC irradiated at the highest fluence as compared to the pristine. Thus, proton irradiation has led to degradation of the polymer by chain scission converting it into an easily etchable material.     

Chemical cross sections induced by ions in solid organic detectors: Experimentation and simulation

Chemical ester bond scission induced by incoming ions in polyethylene terephthalate (PET), bisphenol A polycarbonate (PC), polyallyl diglycol carbonate (PADC), have been systematically determined by FT-IR transmission measurements. The studied ions (H, He, C, Ne, I, Ar, Fe, Kr, Xe) have LET ranging from 10 to 10 000 keV μm⁻¹. We discuss the opportunity to simulate the experimental chemical cross section obtained with an approach based on the dose deposited by the secondary electrons removed by the incoming ion. Such an approach has been already successfully applied for LR115.     

Different shapes of tracks in phlogopite, biotite and soda lime glass

Etched track opening geometries in Biotite, Phlogopite and soda-lime glass irradiated with swift heavy ions [¹⁹⁷Au(11.64 MeV/n), ¹³⁶Xe(11.56 MeV/n), ⁵⁸Ni(11.56 MeV/n)] at different angle of incidence have been studied using appropriate chemical etching technique. Different geometries (Hexagonal, irregular polygon, triangular in case of Biotite and Phlogopite, and circular & elliptical in case of soda lime glass detector) of heavy ion tracks are reported in the present investigations using optical microscope. The different shapes of these heavy ions track geometries are found to be related with various target-projectile parameters (viz: type of projectiles, energy, stopping power, angle of incidence of the projectile, density of defects and its reactivity with etchant, etching conditions and chemical structure of the detectors). The dependence of different shapes of heavy ion tracks in isotropic and anisotropic medium on the variation of radiation damage densities along the ion trajectories have also been discussed in the present paper.      

Modifications in track registration response of PADC detector by energetic protons

It has been well established that different ionising radiations modify the track registration properties of dielectric solids. In an effort to study the response of Polyallyl diglycol carbonate (PADC Homalite) detector towards fission fragment, PADC detectors were exposed to 10⁴ Gy dose of 62 MeV protons and then one set of samples were exposed to fission fragments from a ²⁵²Cf source. Two of these detectors were containing a thin layer of Buckminsterfullerene (C₆₀). The study of the etched tracks by Leitz Optical Microscope reveals that the track diameters are enhanced by more than 70% in the proton irradiated zone as compared to that in the unirradiated zone. Scanning Electron Microscopy was performed after etching the sample in 6 N NaOH at 55°C for different etching times, to study the details of the surface modifications due to proton irradiation of PADC detectors with and without C₆₀ layer. Our observations revealed that the diameters and density of proton tracks have increased with etching time on the surface facing the fullerene layer as well as the other surface. However, a relatively more open structure of the etched surface containing C₆₀ as compared to the bare one may be an indication of the extra damage caused by the energy released upon the destruction of C₆₀ molecules by energetic protons.     

Radiation chemical yield for loss of carbonate ester bonds in PADC films exposed to gamma ray

Radiation chemical yield, G value, for loss of carbonate ester bonds in PADC films, exposed to gamma ray from intense Co-60 source, has been determined by means of FT-IR spectrometry. The obtained value of 20 (scissions/100 eV) is fairly higher than that from heavy ion irradiations. It was found the density of hydroxide group in the film significantly increased by the exposure in air but hardly changed in vacuum.     

Spectrometry of linear energy transfer and its use in high-energy particle beams

A new method to determine the spectra of linear energy transfer (LET) based on track-etch detectors has been developed. It is based on chemically etched polyallyldiglycolcarbonate (PADC) track detector. LET spectra are calculated using the track parameters measured with an automatic optical image analyzer. This method has been recently improved; the calibration curves have been upgraded on the basis of evaluating the detectors exposed in heavier high-energy charged particle beams. The LET spectrometer has been used to determine LET spectra and integral dosimetry characteristics along the range of protons, resp. ¹²C ions with primary energies of 205 MeV, resp. about 480 MeV/amu; and to study the importance of the fragmentation and nuclear reactions in carbon and other heavier ion beams. The results obtained are analyzed and discussed; the possible advantages of this type of equipment are outlined. The text was submitted by the authors in English.     

Tracks of 18·56 MeV/u 40Ar ions in Lexan polycarbonate detector

Latent damage tracks of energetic⁴⁰Ar ions (18·56 MeV/u) have been recorded in Lexan polycarbonate detector. Bulk and track-etch parameters are evaluated under successive chemical etching. Our results show a linear correlation between the measured track-etch rate along the track and the corresponding total energy-loss rate and predict a threshold value of 5·0 MeV mg⁻¹ cm² for track registration. Maximum etchable track lengths of⁴⁰Ar ions as a function of energies have also been measured and compared with three different sets of theoretical ranges.     

Calibration of CR-39 with atomic force microscope for the measurement of short range tracks from proton-induced target fragmentation reactions

We studied the track response of CR-39 plastic nuclear track detectors (PNTD) for low (<6 MeV/n) and high (>100 MeV/n) energy heavy ions using the atomic force microscope (AFM). CR-39 PNTD was exposed to several heavy ion beams of different energy at HIMAC (Heavy Ion Medical Accelerator in Chiba). For AFM measurement, the amount of bulk etch was controlled to be ∼2 μm in order to avoid etching away of short range tracks. The response data obtained by AFM for ∼2 μm bulk etch was in good agreement with data obtained by the conventional optical microscope analysis for larger bulk etch. The response data from low energy beams (stopping near the surface) was also consistent with the data from high energy beams (penetrating the detector) as a function of REL (restricted energy loss) with the δ-ray cut off energy of ω₀ = 200 eV. We experimentally verified that REL (ω₀ = 200 eV) gives a universal function for wide energy range in CR-39 PNTD. This work has been done as part of a basic study in the measurement of secondary short range tracks produced by target fragmentation reactions in proton cancer therapy fields.     

Stopping powers of CR-39 nuclear track material for Z=1−14 ions with 0.25–2.8 MeV/u

Experimental studies of the slowing down of ¹H, ⁴He, ⁷Li, ¹¹B, ¹²C, ¹⁴N, ¹⁶O, ²³Na, ²⁷Al and ²⁸Si ions in CR-39 nuclear track etch material in the ion energy range 0.25–2.8 MeV/u are presented. The ion stopping powers obtained are compared to the predictions of two recent semiempirical models for calculating ion stopping powers. The predictions are found to clearly underestimate the observed stopping powers for ⁷Li, ¹¹B, ¹²C, ²³Na, ²⁷Al and ²⁸Si ions.     

Response of a track-etch-based LET-spectrometer to high-energy protons

The spectrometer of linear energy transfer (LET) was developed. It is based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector. LET spectra are estimated through track parameter determination and analysed by an automatic optical image analyser LUCIA G. Three PADC materials were used: 0.5 mm thick Page, 0.5 and 1 mm thick Tastrak; they were exposed to protons with energies up to 1000 MeV. Such energetic protons are generally not directly registrable in any of PADCs mentioned; the tracks observed correspond mostly to secondary particles created through nuclear interactions of primary protons. LET spectra permit to calculate the dose absorbed in the detector due to these secondary particles and to compare it with the ionization collision dose of primary protons. It is observed that the dose due to secondary particles represents a few percent of the ionization collision dose. Their ratio varies slightly with proton energy, and some differences between the three PADCs used were also observed. The importance of results obtained for on-board spacecraft dosimetry is analysed and discussed.     

Stopping power measurements of Si in polycarbonate detectors

The rate of energy loss of the impinging ion as it passes through succeeding layers of the target material gives information regarding the nature of the material and helps to calculate the range of the ions in a thick target in which the ions are stopped. In the present work, the range of 118 MeV ²⁸Si was measured in different types of polycarbonates, viz. Makrofol-N, Makrofol-G and Makrofol-KG, using the nuclear track technique. Polyallyldiglycol carbonate (PADC) was used as the backing detector. The experimental values of range and energy-loss rate are compared with the theoretical values obtained from different computer codes, viz. BENTON, HUBERT, RANGE, TRIM’98 and SRIM’03.     

Counting recoil proton tracks on PADC without a pre-etching step. A novel approach for neutron dosimeter application

At many laboratories involving in routine, individual neutron dosimetry, poly allyl diglycol carbonate (PADC) is utilized for particle registration. A pre-etching step is commonly applied in order to remove the alpha tracks of the environmental radon, so achieving the required lower limit of detection (LLD) performance. A novel approach is presented, which makes this pre-etching step unnecessary, but ensuring an excellent LLD performance, also providing a good throughput for a routine service. Exposing the PADC material to carbon dioxide atmosphere before the main etching step enhances the visibility of the microscopic track image. The enhancement is so efficient that the track size and image contrast between the alpha and the proton tracks are well distinctive. Customized image analyzer software is able to distinguish alpha and proton tracks, so providing the proton track density separately. A pilot study about the performance and potentials of this novel approach is presented. A complete application working with this approach was introduced to routine neutron dosimeter service 2 years ago and its good performance has been verified.     

The determination of the neutron component of cosmic radiation fields in spacecraft

Poly allyl diglycol carbonate (PADC or CR-39^®) etched track detectors may be used to estimate the neutron component of the cosmic radiation in spacecraft using simple techniques developed for neutron personal dosimetry. Electrochemically etched pits are identified and counted using fully automated read-out procedures. The neutron component of the radiation field at the location of the dosimeter will produce electrochemically etchable tracks, as will the proton and energetic heavy charged particle components, depending on particle type, energy and angle of incidence. The response to incident charged particles which produce tracks and are counted as if produced by a neutron, will lead to an over-estimate of the neutron component. A correction can be applied to take account of this, or an additional chemical etch carried out which allows discrimination. Recent results for exposures in low-Earth orbit are reported.     

The effect of different ion stopping models on calculated parameters of the radiation damage of materials

Direct numerical solution of the Boltzman transport equation for incident ions and knocked-off atoms of the target is applied for range and damage calculations. The influence of physical parameters in a model of ion stopping in matter on the obtained range and damage distribution is investigated in the range of ion energies from 1 KeV to 1 MeV. All the examined interatomic potentials give close values of mean depths and higher moments of range and damage distributions. The influence of differences in electronic stopping is also studied. The obtained results are compared with experimental data and the results of other calculations.     

Ultrahigh-intensity laser-produced plasmas as a compact heavy ioninjection source

The possibility of using high-intensity laser-produced plasmas as a source of energetic ions for heavy ion accelerators is addressed. Experiments have shown that neon ions greater than 6 MeV can be produced from gas jet plasmas, and well-collimated proton beams greater than 20 MeV have been produced from high intensity laser solid interactions. The proton beams from the back of thin targets appear to be more collimated and reproducible than are high-energy ions generated in the ablated plasma at the front of the target and may be more suitable for ion injection applications. Lead ions have been produced at energies up to 430 MeV