Method to measure composition modifications in polyethylene terephthalate during ion beam irradiation

Matter losses of polyethylene terephthalate (PET, Mylar) films induced by 1600 keV deuteron beams have been investigated in situ simultaneously by nuclear reaction analysis (NRA), deuteron forward elastic scattering (DFES) and hydrogen elastic recoil detection (HERD) in the fluence range from 1 × 10¹⁴ to 9 × 10¹⁶ cm⁻². Volatile degradation products escape from the polymeric film, mostly as hydrogen-, oxygen- and carbon-containing molecules. Appropriate experimental conditions for observing the composition and thickness changes during irradiation are determined. ¹⁶O(d,p₀)¹⁷O, ¹⁶O(d,p₁)¹⁷O and ¹²C(d,p₀)¹³C nuclear reactions were used to monitor the oxygen and carbon content as a function of deuteron fluence. Hydrogen release was determined simultaneously by H(d,d)H DFES and H(d,H)d HERD. Comparisons between NRA, DFES and HERD measurements show that the polymer carbonizes at high fluences because most of the oxygen and hydrogen depletion has already occured below a fluence of 3 × 10¹⁶ cm⁻². Release curves for each element are determined. Experimental results are consistent with the bulk molecular recombination (BMR) model.     

Temperature dependence of trapping and depth profiles of 6 to 15 kev deuterium in carbon

Depth profiles of 30 keV D⁺₂ and 20 keV D⁺₂ implanted into edge and basal-oriented pyrolytic graphite have been measured by means of the D(³He,α)H nuclear reaction in the temperature range of 300 to 800 K. At room temperature deuterium concentrations up to 30 at.% are found in a surface layer corresponding to the range of the ions. The measured depth profiles do not fully agree either with calculated range profiles or with the damage profiles, but are determined by the two together. At higher temperatures the deuterium concentrations decrease and the profiles broaden. At room temperature the amount of trapped deuterium increases linearly with dose below 10¹⁸ deuterons/cm². The trapping coefficient is roughly 60%. At 5 × 10¹⁸ deuterons/cm² the amount of trapped deuterium in the probed layer (~4000 Å) reaches saturation and the trapping coefficient becomes zero. The saturation value decreases with increasing temperature and increases with increasing energy.     

Irradiation damage induced on polyethylene terephtalate by 1.6 MeV deuteron ions

The irradiation damage caused on polyethylene terephtalate (Mylar, PET) samples by 1.6 MeV deuteron ions has been measured using simultaneously the nuclear reaction analysis (NRA) and the transmission energy loss (TEL) techniques. The irradiation was carried out at normal incidence relative to the target surface with the irradiation beam being used as the analysis beam. The evolution of the overall damage during irradiation was evaluated by measuring the variation of the energy loss of the deuteron beam passing through the target. For this purpose, a solid state Si detector placed at a forward angle of 30° relative to the incident beam direction was used. The NRA spectra recorded by a second Si detector located backward at 150° allowed the evaluation of the carbon and the oxygen depletion. The beam spot size was circular in shape and 1 mm in diameter and the beam current was set at 5 nA. The ion fluence was increased up to the value of 2.5 × 10¹⁶ deuterons/cm². It was observed that the target energy loss decreased steadily as the fluence increased and levelled off at high fluence. The ¹⁶O(d,p₀)¹⁷O, ¹⁶O(d,p₁)¹⁷O^* and ¹²C(d,p₀)¹³C reactions were used for monitoring the evolution of the oxygen and carbon content as a function of the deuteron fluence. A monotonic decrease of the oxygen content with the increase of ion fluence was observed. At the highest fluence the oxygen depletion reached a value of about 75%. For carbon, a weak depletion was observed at fluence ranging from 2.5 × 10¹⁵ d/cm² to 1.0 × 10¹⁶ d/cm² followed by a levelling-off with a total loss around 20%.     

Ion beam micro analysis of deposits at tokamak divertor surfaces

Cross sections of deposited layers in the Joint European Torus (JET) were analysed using the nuclear micro analysis at the Tandem Laboratory, Uppsala University. For deuterium and beryllium the nuclear reactions ²D(³He,p)⁴He and ⁹Be(³He,p_n)¹¹B were exploited for analysis. Typically the analyses have been made with 10 μm spatial resolution and a sensitivity of better than one atomic percent for beryllium or deuterium in carbon matrix. Comparing several different surface treatment techniques shows that polishing the sample surface give very good optical surface information but that some amount of deuterium and beryllium probably is removed. For good quantitative results the measurement can either be done on a rough surface or the top of the polished surface can be cut off.     

Flux and energy of deuterium incident on a limiter-like probe in PLT

Carbon samples were exposed to the plasma edge in the PLT tokamak at various distances from the plasma. The amount of deuterium retained was subsequently determined using nuclear reaction analysis. The deuterium retention was found to saturate with increasing exposure time. Values for the energies and fluxes of the deuterium incident on the samples were determined by comparing the observed retention behavior with a saturation model for the retention. The deuterium fluxes and energies were found to decrease from ø~4 × 10¹⁷ D/cm² s and kT~270 eV at the radius of the limiter to ø~0.8 × 10¹⁷ D/cm² s and kT~90 eV at the radius of the wall. At these energies the fraction of the incident deuterium directly reflected from carbon is predicted to be 30 to 40%. From the deuterium energies and fluxes, values for the power flux and erosion rates are estimated.     

A simple coincidence method of deuterium profiling using the DHe, α)H reaction

A simple standard coincidence arrangement is described for D(³He, α)H depth profiling experiments of deuterium in solids. Both reaction products are detected in coincidence, the high-energy protons being observed in transmission through a foil target. The energy of the α-particles is converted into the corresponding depth scale, whereas the local deuterium concentration is calculated from the yield of the α-particle spectrum. The measurement of α-particles in coincidence with protons allows a reduction of background arising from Rutherford scattering of ³He and other reaction products. For samples of deuterium implanted into Ta₂O₅ and Er, the method allows a reduction of the backscattering yield by a factor of more than 10³. The residual background is due to accidental coincidences. It can be even more reduced using an accurate experimental geometry. The background reduction is largest for samples with a low content of deuterium, allowing measurements of deuterium profiles of 9 × 10¹³ D⁺/cm² implanted into Ta₂O₅ at an energy of 8 keV. This corresponds to a maximum deuterium concentration of about 5 × 10⁻⁴ D per Ta₂O₅. This method is not restricted to thin films, but it allows measurements of deuterium profiles in a thick sample, e.g. of an implantation profile in a 0.4 mm silicon wafer.     

Plasma Focus Device as a Breeder of 14.66 MeV Protons to Produce Short-Lived Radioisotopes

In plasma focus devices filled deuterium gas with low pressure admixture gas, ³He, the deuterium creates high energy protons of 14.66 MeV through the ³He(d, p) ⁴He(Q = 18.35 MeV) fusion reaction. This reaction takes place due to the thermal and non-thermal (beam-target) mechanisms. The proton yield production for deuterium filling gas is determined by using the beam-target character of the pinched plasma and moving boiler model. If we use a low pressure admixture gas like ¹¹B, these high energy protons in turn, could generate short-lived radioisotopes like ¹¹C (used in positron emission tomography) via the ¹¹B(p, n)¹¹C reaction. Calculations indicate the influence of drive parameter to the final yield for a Mather type device.     

Differential cross-sections for nuclear reactions on Al and Si induced by deuterons at low energy (1-2 MeV)

Recent progress in thin film techniques has made possible the fabrication of stable and pollution-free reference standards. Thin Si₃N₄ film (thickness 70 nm) and thin Al foil (150 nm) were selected to measure the differential cross-sections of nuclear reactions induced by deuterons, from 1 to 2 MeV. The absence of oxygen and carbon in the standard, as well as the stoichiometry, were checked prior to measurement by RBS. The differential cross-sections of the ²⁷Al(d,p₀p₁)²⁸Al, ²⁷Al(d,p₂p₃)²⁸Al, ²⁷Al(d,p₅p₆)²⁸Al, ²⁷Al(d,p₉)²⁸Al, ²⁷Al(d,p₁₀)²⁸Al, ²⁷Al(d,p₁₁)²⁸Al, ²⁷Al(d,p₁₂)²⁸Al, ²⁷Al(d,α₀)²⁵Mg and ²⁷Al(d,α₂)²⁵Mg reactions for aluminium and ²⁸Si(d,p₀)²⁹Si- ²⁹Si(d,p₁)³⁰Si, ²⁸Si(d,p₁)²⁹Si- ²⁹Si(d,p₂)³⁰Si, ²⁸Si(d,p₂)²⁹Si, ²⁸Si(d,p₃)²⁹Si, ²⁸Si(d,p₉p₁₀)²⁹Si reactions for silicon were determined for a detector angle of 150°.     

Cross-section for D(p,p)D elastic scattering from 1.8 to 3.2 MeV at the laboratory angles of 155° and 165°

The D(p,p)D cross-sections for elastic scattering of proton on deuterium over incident proton energy range from 1.8 to 3.2 MeV at both laboratory angles of 155° and 165° were measured. A thin solid state target Ni/TiD_x/Ta/Al used for cross-section measurement was fabricated by firstly depositing layers of Ta, Ti and Ni film on the Al foil substrate of about 7 μm in turn using magnetron sputtering and then deuterating under the deuterium atmosphere. The areal density of metal element in each layer of film was measured with RBS analysis by using a 4.0 MeV ⁴He ion beam, while the areal density of the deuterium absorbed in the Ti film was measured with ERD analysis by using a 6.0 MeV ¹⁶O ion beam. The results show that the cross-sections of p-D scattering under this experimental circumstance were much enhanced over the Rutherford cross-section value. It was found that the enhancement increases linearly as the energy of the incident beam increases. The total uncertainty in the measurements was less than 7.5%.     

Ion beam studies of H and He in metals

The use of ion beams to study hydrogen and helium in metals is demonstrated. The ³He (d,p)⁴He nuclear reaction previously has been used together with ion channeling to determine the lattice locations of ion-implanted D and ³He in tungsten. Preliminary results applying these techniques to helium bubble and blister formation in tungsten are also presented and show that changes attributed to helium bubble formation are observed in tungsten at a He fluence as low as 6 × 10¹⁶ He/cm². The retention of ion-implanted deuterium in W, Au, and Pd surfaces is shown to be greatly enhanced by prior He ion-induced lattice damage. The amount of the damage trapping is also found to depend on whether the metal is in single crystal or polycrystalline form.     

Differential cross-section measurements for the C(d, p0)C reaction and applications to surface analysis of materials

This work involves surface analysis by nuclear techniques, which are non-destructive, and computer simulation. The “energy analysis” method for nuclear reaction analysis is used. Energy spectra are computer simulated and compared to experimental data, giving target composition and concentration profile information. Measured values are presented for the differential cross-section of the ¹²C(d, p₀)¹³C reaction in the deuteron energy range 0.81-2.07 MeV for laboratory detection angles of 165° and 135°, using self-supported two-layered targets consisting of high purity thin films of typically 13 μg/cm² natural carbon and 65 μg/cm² gold. The error in the absolute differential cross-section values is generally ∼6%. The method, using these values, is successfully applied to determination of uniform concentration profiles of ¹²C, along considerable depths, for a thick flat target of high purity pyrolitic graphite. It is characterised a thin surface film of carbon on a thick flat quartz target. Uniform concentration profiles of ¹⁶O are also obtained from (d, p) and (d, α) reactions.     

Studies on Ceramic Fuels with the Use of Fission Gas Release Loop, (III)

Flux monitoring in the specimen chamber of FGRL was carried out by directly and continuously reading with a γ-ray spectrometer the content of ¹⁶N in the primary cooling water produced by ¹⁶O(n,p)¹⁶N reaction within the cooling jacket of FGRL. 16N generation is not influenced by γ-ray build-up in the reactor nor by the temperature in the specimen chamber. The detector can be simply set outside the pipe through which the cooling water flows, because the high energy γ-rays (6.13 MeV) emitted during the ¹⁶N decay easily penetrate the pipe wall.     

Depth distribution profiling of deuterium and 3He

A technique using nuclear microanalysis has been developed to determine ²D an ³He concentrations versus depth profiles in the near surface regions (～2 μm) of solids. Ultimate near-surface depth resolutions of (≈100 Å) should be attainable by these techniques. A probing beam of ³He ions is used to analyze for the deuterium. By energy analyzing the emitted ⁴He ions from the reaction d(³He,p)⁴He and by simple computer analysis, deuterium concentration versus depth profiles are obtained. The same methods are applicable for ³He profiling except in that case a ²D probing beam is used. The techniques is currently being developed using Er hydride and Sc hydride films. It is particularly suited for the study of the transition metals with high hydrogen solubility such as Nb and V which are of interest for CTR reactor applications.     

Triton Emission Spectra in Some Target Nuclei Irradiated by Ultra-Fast Neutrons

High-current proton accelerator technologies make use of spallation neutrons produced in (p,xn) and (n,xn) nuclear reactions on high-Z targets. The produced neutrons are moderated by heavy water. These moderated neutrons are subsequently captured on ³He to produce tritium via the (n,p) reaction. Tritium self-sufficiency must be maintained for a commercial power plant. So, working out the systematics of (n,t) reaction cross sections and triton emission differential data are important for the given reaction taking place on various nuclei at different energies. In this study, triton emission spectra by using ultra-fast neutrons (incident neutron energy >50 MeV), the (n,xt) reactions for some target nuclei as ¹⁶O, ²⁷Al, ⁵⁶Fe, ⁵⁹Co, ²⁰⁸Pb and ²⁰⁹Bi have been investigated. In the calculations, the pre-equilibrium and equilibrium effects have been used. The calculated results have been compared with the experimental data taken from the literature.     

Oxidation resistance of Y-implanted steel using accelerator based techniques

The thermal oxidation behavior in air of Y-implanted (fluence 2 × 10¹⁷ ions/cm²) and non-implanted stainless steel AISI-321 samples was investigated using the ¹⁶O(d,p)¹⁷O nuclear reaction and Rutherford backscattering spectrometry (RBS). The oxidation temperature was 650 and 900 °C and the duration of the thermal treatment 48 hours. The influence of the implantation energy (40, 55 and 80 keV) on the oxidation behavior of stainless steel was also studied. An improvement of the oxidation resistance of the Y-implanted samples with increasing implantation energy was observed. Additional secondary ion mass spectroscopy (SIMS) measurements of the samples implanted by 40 keV Y-ions also indicated a slight chromium depletion of their near-surface layers. Mechanisms attempting to explain the experimental results are proposed.     

Research of Radioisotope Production with Fast Neutrons, (VII)

Production of radioisotopes of high specific activity was studied in the JRR-1 reactor using several (n,p) and (n,α) reactions, such as ²⁴Mg(n,p)²⁴Na, ²⁷A1(n,α)²⁴N_a, ³⁵Cl(n,p)³⁵S, ³⁵C1(n,α)³²P, ⁵⁸Ni(n,p)⁵⁸Co, ⁶⁴Z_n (n,p) ⁶⁴C_u and ⁶⁷Z_n(n,p) ⁶⁷Cu. The target materials for these reactions were irradiated in several experimental holes of JRR-1 and the radioisotopes formed in the target materials were separated. The amount of the radioisotopes produced and the specific activity were determined, and the possibility of producing high specific activity radioisotopes by these reactions was investigated. The specific activity of the radioisotopes produced by the (n,p) and (n,γ) reactions was more than several hundreds times higher than when produced by the corresponding (n,γ)reactions. Although the yield of the radioisotopes by the former two reactions was fairly small, practical production of high specific activity radioisotopes by this method was thought to be possible, at least for elements of lower atomic number such as those studied in the present work.

For each experimental hole, the thermal and the fast neutron fluxes were determined respectively by the reactions ¹⁹⁷Au(n,γ)¹⁹⁸Au and ⁵⁸Ni(n,p)⁵⁸Co. In order to apply these (n,p) and (n,α) reactions effectively to radioisotope production, such basic informations as the dependence of the reactions on neutron energy and the effect of irradiation position on the reaction yield were studied on the basis of the neutron flux distribution, and the cross section of the reactions for fast neutrons in JRR-1 was estimated.     

A rapid method for carbon and oxygen determination with external beam proton induced gamma-ray emission analysis

The applicability of the γ-rays from the reaction ¹²C(p, p′γ)¹²C and ¹⁶O(p, p′γ)¹⁶O for carbon and oxygen detection has been investigated. The optimum proton energy region for the analyses was determined. Various system construction materials were tested for obtaining a minimum background. Kapton, Havar and Ni exit foils were tested and the advantages of each are discussed. In the present external beam configuration the bombardments are carried out in a He atmosphere. By optimizing the method, carbon concentrations at the 100 ppm level and oxygen concentrations at the 300 ppm level are detectable.     

Laser annealing in combination with mass spectroscopy, a technique to study deuterium on tokamak carbon samples, a tool for detritiation

In this study, a method is presented based on mass spectroscopy to measure the areal density of deuterium on a graphite surface exposed to tokamak discharges. The studied sample was cut from a bumper limiter exposed in the TEXTOR tokamak and annealed by a 1 J Excimer laser (KrF). The energy used was 400 mJ cm⁻², which is below the threshold for ablation, 1 J cm⁻². The release of HD and D₂ was measured by a mass spectroscopy set-up and no other species released from the sample were detected in this experiment. The amount of D released from the sample after 20 laser pulses was measured to 7 × 10¹⁶ D atoms per cm⁻² (for this particular sample) and most of the hydrogen at the surface was released in the first pulse, as checked by nuclear reaction analysis (NRA) techniques, which gave changes of the amount of deuterium before and after laser annealing. The sensitivity in this experiment was 5 × 10¹⁴ atoms per cm⁻² for HD and 5 × 10¹³ atoms per cm⁻² for D₂.     

High energy primary knock-on process in metal-deuterium systems initiated by bombardment with noble gas ions

An experimental study confirms the possibility of nuclear fusion reactions initiating in metal-deuterium targets by bombarding them with ions that are not the reagents of the fusion reaction, in particular, with noble gas ions. The yields of (d,d) and (d,t) reactions were measured as functions of energy (0.4-3.2 MeV) and mass of incident ions (He⁺, Ne⁺, Ar⁺, Kr⁺ and Xe⁺). Irradiation by heavy ions produced a number of energetic deuterium atoms in the deuteride and deuterium + tritium metal targets. At ion energies of ∼0.1-1 MeV the d-d reaction yields are relatively high. A model of nuclear fusion reaction cross-sections in atomic collision cascades initiated by noble gas ion beam in metal-deuterium target is developed. The method for calculation tritium or deuterium recoil fluxes and the yield of d-d fusion reaction in subsequent collisions was proposed. It was shown that D(d,p)t and D(t,n)⁴He reactions mainly occur in energy region of the recoiled D-atom from 10 keV to 250 keV. The calculated probabilities of d-d and d-t fusion reactions were found to be in a good agreement with the experimental data.     

Nuclear micro-beam analysis of deuterium distribution in carbon fibre composites for controlled fusion devices

Probes made of carbon fibre composite NB41 were exposed to deuterium plasmas in the TEXTOR tokamak and in a simulator of plasma–wall interactions, PISCES. The aim was to assess the deuterium retention and its lateral and depth distribution. The analysis was performed by means of D(³He, p)⁴He and ¹²C(³He, p)¹⁴N nuclear reactions analysis using a standard (1 mm spot) and micro-beam (20 μm resolution). The measurements have revealed non uniform distribution of deuterium atoms in micro-regions: differences by a factor of 3 between the maximum and minimum deuterium concentrations. The differences were associated with the orientation and type of fibres for samples exposed in PICSES. For surface structure in the erosion zone of samples exposed to a tokamak plasma the micro-regions were more complex. Depth profiling has indicated migration of fuel into the bulk of materials.