Protactinium-231: A new radionuclide for AMS

For the first time, an AMS system was used to determine concentrations of the actinide Protactinium-231. ²³¹Pa has widespread applications in the earth sciences. It can be used for U-series disequilibrium dating, and ²³¹Pa is an important tracer in Paleoceanography. The Pa isotopes were measured with the compact ETH/PSI-AMS facility TANDY operating at about 300 kV. The linearity of the AMS is documented with two standard-dilution experiments and first measurements of natural samples from very different climate archives are presented. Our results show that it is possible to determine ²³¹Pa amounts in the lower femtogram (1 fg = 10⁻¹⁵ g) range with the TANDY. In natural samples, ²³¹Pa concentrations between 1 and 4 pg/g (1 pg = 10⁻¹² g) were measured with an average total error of 3% (one sigma). The average over all reproducibility of these first measurements was better than 2% with clear potential for improvement.     

Design study of a multibeam type IH-RFQ linac to accelerate high intensity and low energy heavy ion beams

A multibeam Radio Frequency Quadrupole (RFQ) linac with an Interdigital H-mode (IH) structure has been developed for high intensity heavy-ion beam acceleration. The defocusing force of space charge effect is proportional to the beam current and to the inverse square of the beam velocity. Therefore, multibeam acceleration is an attractive scheme to suppress this in the low energy region. The electromagnetic field distribution and the beam dynamics were studied for a prototype. We discuss the configuration of the multibeam IH-RFQ linac and the results of these simulations.     

Influence of some variable parameters on bremsstrahlung dosimetric characteristic for electron linac

The paper presents some important problems related to the practical aspect of employing the bremsstrahlung radiation generated by linear accelerators used in the irradiation technological processes, namely:

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The optimization of the electron-bremsstrahlung conversion output by optimizing the target thickness and

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the study on the influence of some variable parameters of the accelerator (i.e. the beam current, the magnetron frequency and the injection voltage) on the dosimeter characteristics of the bremsstrahlung radiation.

The measurements have been performed with the 3.5 and 10 MeV linear electron accelerators in NILPRP-Electron Accelerator Laboratory.     

Dynamic annealing study of SiC epilayers implanted with Ni ions at different temperatures

SiC epilayers grown on 4H-SiC single crystals were implanted with 850 keV Ni⁺ ions with fluences in the 0.5-9 × 10¹⁶ Ni⁺/cm² range. Most of the samples were implanted at 450 °C, but for comparison some implantations were performed at room temperature (RT). In addition, a post-implantation annealing was performed in N₂ at 1100 °C in order to recover the implantation-induced structural damage. The disorder produced by the implantation at 450 °C and the effect of the post-implantation annealing on the recrystallization of the substrates have been studied as a function of the fluence by Backscattering Spectrometry in channeling geometry (BS/C) with a 3.45 MeV He²⁺ beam. RT as-implanted samples showed a completely amorphous region which extends until the surface when irradiated with the highest dose, whereas in the case of 450 °C implantation amorphization does not occur. In general, partial recovery of the crystal lattice quality was found for the less damaged samples, and the dynamic recovery of the crystalline structure increases with the irradiation temperature.     

Accelerator mass spectrometry of strontium-90 for homeland security, environmental monitoring and human health

Strontium-90 is one of the most hazardous materials managed by agencies charged with protecting the public from radiation. Traditional radiometric methods have been limited by low sample throughput and slow turnaround times. Mass spectrometry offers the advantage of shorter analysis times and the ability to measure samples immediately after processing, however conventional mass spectrometric techniques are susceptible to molecular isobaric interferences that limit their overall sensitivity. In contrast, accelerator mass spectrometry is insensitive to molecular interferences and we have therefore begun developing a method for determination of ⁹⁰Sr by accelerator mass spectrometry. Despite a pervasive interference from ⁹⁰Zr, our initial development has yielded an instrumental background of ∼10⁸ atoms (75 mBq) per sample. Further refinement of our system (e.g. redesign of our detector, use of alternative target materials) is expected to push the background below 10⁶ atoms, close to the theoretical limit for AMS. Once we have refined our system and developed suitable sample preparation protocols, we will utilize our capability in applications to homeland security, environmental monitoring and human health.     

Determination of bulk etch rate for CR-39 nuclear track detectors using an X-ray fluorescence method

The thickness of a CR-39 detector is determined using an energy dispersive X-ray fluorescence (EDXRF) method of analysis. The method is based on exciting a suitable target and measuring the intensity of its fluorescence X-ray lines passing through the CR-39 sample in a fixed geometry. By properly selecting the target material, the method succeeds in assessing the thickness change of CR-39 detectors etched for different time intervals. The bulk etch rate (V_b) may thus be obtained, which is an important parameter for any solid state nuclear track detector. Application of the EDXRF method yielded a value of V_b = (2.01 ± 0.04) μm h⁻¹ for etching in a 6 N NaOH solution at 75 °C. This value agrees with the bulk etch rate of (1.90 ± 0.03) μm h⁻¹, obtained by the conventional mass-change method.     

Discriminative detection of deposited radon daughters on CR-39 track detectors using TRIAC II code

A method for detecting deposited ²¹⁸Po and ²¹⁴Po by a spectrometric study of CR-39 solid state nuclear track detectors is described. The method is based on the application of software imposed selection criteria, concerning the geometrical and optical properties of the tracks, which correspond to tracks created by alpha particles of specific energy falling on the detector at given angles of incidence. The selection criteria were based on a preliminary study of tracks’ parameters (major and minor axes and mean value of brightness), using the TRIAC II code. Since no linear relation was found between the energy and the geometric characteristics of the tracks (major and minor axes), we resorted to the use of an additional parameter in order to classify the tracks according to the particles’ energy. Since the brightness of tracks is associated with the tracks’ depth, the mean value of brightness was chosen as the parameter of choice. To reduce the energy of the particles, which are emitted by deposited ²¹⁸Po and ²¹⁴Po into a quantifiable range, the detectors were covered with an aluminum absorber material. In this way, the discrimination of radon’s daughters was finally accomplished by properly selecting amongst all registered tracks. This method could be applied as a low cost tool for the study of the radon’s daughters behavior in air.     

Innovative machine designs for radiation processing

In the 1990s Raychem Corporation established a program to investigate the commercialization of several promising applications involving the combined use of its core competencies in materials science, radiation chemistry and e-beam radiation technology. The applications investigated included those that would extend Raychem’s well known heat recoverable polymer and wire and cable product lines as well as new potential applications such as remediation of contaminated aqueous streams. A central part of the program was the development of new accelerator technology designed to improve quality, lower processing costs and efficiently process conformable materials such at liquids. A major emphasis with this new irradiation technology was to look at the accelerator and product handling systems as one integrated, not as two complimentary systems.     

Calculation and analysis of proton-induced reactions on Ni at incident energies from threshold to 200 MeV

Proton-induced reactions on ⁵⁸Ni have been studied in the energy range from threshold to 200 MeV. Based on experimental data of elastic scattering angular distributions and nonelastic cross section, an optimal set of proton optical potential parameters for ⁵⁸Ni has been obtained. All cross sections, elastic and inelastic scattering angular distributions, energy spectra and especially double differential cross sections for neutrons, protons, deuterons, tritons, helium particles and alpha particles emission have been calculated, using nuclear models theory. Theoretical calculations have been compared with existing experimental data, in most cases, the calculated results are in good agreement with the experimental data.     

Investigation of proton induced reactions on niobium at low and medium energies

Niobium is a metal with important technological applications: use as alloying element to increase strength of super alloys, as thin layer for tribological applications, as superconductive material, in high temperature engineering systems, etc. In the frame of a systematic study of activation cross-sections of charged particle induced reactions on structural materials proton induced excitation functions on Nb targets were determined with the aim of applications in accelerator and reactor technology and for thin layer activation (TLA). The charged particle activation cross-sections on this element are also important for yield calculation of medical isotope production (^88,89Zr, ^86,87,88Y) and for dose estimation in PET targetry. As niobium is a monoisotopic element it is an ideal target material to test nuclear reaction theories. We present here the experimental excitation functions of ⁹³Nb(p,x)^90,93mMo, ^92m,91m,90Nb, ^88,89Zr and ⁸⁸Y in the energy range 0-37 MeV.The results were compared with the theoretical cross-sections calculated by means of the code ALICE-IPPE, EMPIRE-3, TALYS and with the literature data. The theory reproduces the shape of the measured results well and magnitude is also acceptable.Thick target yields calculated from our fitted cross-section give reliable estimations for production of medically relevant radioisotopes and for dose estimation in accelerator technology.     

Analysis of C, N and O in aerosol collected on an organic backing using internal blank measurements and variable beam size

A method with low MDL (minimum detection limit) was developed for analysis of carbon (C), nitrogen (N) and oxygen (O) in aerosol samples collected on an organic backing. An accelerator-produced beam of protons interacting with the sample and the detection of elastically scattered protons (PESA; particle elastic scattering analysis) and emitted X-rays (PIXE; particle-induced X-ray emission) were the basic components of the setup. The method is based on measurement of internal blank concentrations, i.e. measurement of the blank concentration outside the aerosol deposit in each sample, and the use of two sizes of the beam in order to improve the MDL of the analysis. Large beam size covering the entire aerosol deposit was used to obtain quantitative analysis with PIXE. Small beam was used to obtain relative elemental concentrations with PESA and PIXE, which were transformed to absolute values by the aid of large-beam analysis. The small-size-beam served two purposes: to make internal blank measurements feasible and to improve the signal ratio of aerosol-deposit to backing. Compared with the traditional way of analysis, using a beam that is larger than the deposit and specially prepared blank samples, the new method reduced the MDL of C, N and O by a factor of 130, 70 and 90, respectively. The new method was applied to aerosol samples collected in the upper troposphere and the lowermost stratosphere from the CARIBIC platform. As far as the authors know, these measurements are the first quantitative determinations of C, N and O in the aerosol of this part of the atmosphere. The results show that these elements together with sulfur are major components of the aerosol.     

Gas phase chemical studies of superheavy elements using the Dubna gas-filled recoil separator - Stopping range determination

Currently, gas phase chemistry experiments with heaviest elements are usually performed with the gas-jet technique with the disadvantage that all reaction products are collected in a gas-filled thermalisation chamber adjacent to the target. The incorporation of a physical preseparation device between target and collection chamber opens up the perspective to perform new chemical studies. But this approach requires detailed knowledge of the stopping force (STF) of the heaviest elements in various materials. Measurements of the energy loss of mercury (Hg), radon (Rn), and nobelium (No) in Mylar and argon (Ar) were performed at low kinetic energies of around (40-270) keV per nucleon. The experimentally obtained values were compared with STF calculations of the commonly used program for calculating stopping and ranges of ions in matter (SRIM). Using the obtained data points an extrapolation of the STF up to element 114, eka-lead, in the same stopping media was carried out. These estimations were applied to design and to perform a first chemical experiment with a superheavy element behind a physical preseparator using the nuclear fusion reaction ²⁴⁴Pu(⁴⁸Ca; 3n)²⁸⁹114. One decay chain assigned to an atom of ²⁸⁵112, the α-decay product of ²⁸⁹114, was observed.     

Development of a novel reaction chamber for ion beam analysis of large samples

A novel vacuum chamber for ion beam analysis of large-size industrial samples - whose analysis are not feasible in conventional ion beam analysis reaction chambers - has been designed, fabricated and successfully tested. Using the newly developed chamber, both PIXE and RBS analyses could be carried out at the same time and on the same point of the samples. Ion beam analysis using this novel chamber lacks the disadvantages of external beam analysis and benefits the advantages of in-vacuum analysis. This has been achieved by designing a tiny open port in the wall of the reaction chamber to be sealed with a small flat area of sample body where its analysis is of interest. As a case study, two samples of gas turbine blades, a corroded one at highly corrosive environment and a refurbished one after application of certain coatings are analysed using the novel chamber. Experimental results confirm the performance and capability of the reaction chamber.     

Calculation and evaluation of cross-sections for p+Fe reactions up to 250 MeV

All cross-sections of proton-induced reactions, angular distributions and the energy spectra of neutron, proton, deuteron, triton, helium and alpha-particle emission are consistent calculated and analyzed for p+^{54,56,57,58,nat}Fe at incident proton energies below 250 MeV by using nuclear theoretical models which integrate the optical model, the intra-nuclear cascade model, direct, preequilibrium and equilibrium reaction theories. Especially, the cross-sections of the light composite particle (d, t, ³He and α) emissions are improved based on the exciton model including the pick-up mechanism. Theoretical calculated results are compared with existing experimental data.     

Study of Al measurement on the Shanghai Mini-cyclotron based AMS

We present a modification to the ¹⁴C-dedicated SMCAMS (Shanghai mini-cyclotron based AMS) system to allow the measurement of ²⁶Al for biomedical applications with the existing devices. This is accomplished by determining the turn number, harmonic number and RF frequency theoretically and then making the appropriate orbit programming and beam optics calculation and experimental adjustments. The tests were conducted using pencil graphite (for the carbon pilot beam), Al₂O₃ powder and metal aluminum to accelerate ions with mass number of 24, 25, 26 and 27. The frequency response curves for those ions are shown. Finally, the Al₂O₃ standard sample with a known isotope ratio of 1.0 × 10⁻¹⁰ is measured. The ²⁶Al⁻ ions are detected and its frequency response curve shows the peak of ²⁶Al⁻ though very weak is well separated from the most neighboring interfering molecular ions ²⁵MgH⁻.     

Light charged particle emission for p+Fe reactions

The energy spectra and double differential cross sections of nucleon and the light composite particle (d, t, ³He and α) emissions are studied based on the exciton model included the improved Iwamoto-Harada model. All cross sections of proton induced reactions, angular distributions and energy spectra are consistent calculated and analyzed for ^{54,56,57,58,nat}Fe at incident proton energies below 250 MeV by using nuclear theoretical models which integrate the optical model, the intra-nuclear cascade model, direct, pre-equilibrium and equilibrium reaction theories. Theoretical calculated results are compared with existing experimental data.     

An indirect method to measure the electric charge deposited on insulators during PIXE analysis

Total charge deposited by a proton beam in an insulator during PIXE analysis has been indirectly determined using a Mylar film coated with cobalt. Elemental concentrations in the samples, pieces of volcanic glass, were obtained and compared to concentrations determined by ICP OES on the same samples. The strong agreement between these results shows the accuracy of the charge determined by this method.     

Development of a fraction collector for coupling gas chromatography with an AMS facility

It has been shown that microscale ¹⁴C measurements are possible by using a gas handling system and a gas ion source [T. Uhl, W. Kretschmer, W. Luppold, A. Scharf, AMS measurements from microgram to milligram, Nucl. Instr. and Meth. (2005) 474 (240th ed.), T. Uhl, W. Luppold, A. Rottenbach, A. Scharf, K. Kritzler, W. Kretschmer, Development of an automatic gas handling system for microscale AMS (¹⁴C) measurements, Nucl. Instr. and Meth. (2007) 303 (259th ed.)]. In Erlangen a gas handling system was especially developed for environmental and biomedical investigations. For the separation of the compound of interest a standard gas chromatograph (GC) is used. To minimize the sample contamination and sample loss we have designed a fraction collector that connects a GC and an elemental analyzer (EA) directly. The selected compound is combusted in the EA and the resulting CO₂ is then transferred into the gas handling system for AMS measurements. From the beginning of GC preparation up to the AMS measurement the sample is in a closed line. All operations are fully automated, so no manual operations are necessary. This guarantees high cleanness and maximum sample yield. Preliminary measurements are done using modern and old ethyl alcohol (from fermentation and of petrochemical origin, respectively). The results are consistent with their expected values although cross contamination and background signal increased as the sample mass was decreased.     

Measurement of thermal neutron cross-section and resonance integral for the Yb(n,γ)Yb reaction by the cadmium ratio method

The thermal-neutron cross-section and the resonance integral for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction were measured by the activation method using a ⁵⁵Mn monitor as single comparator. Analytical grade MnO₂ and Yb₂O₃ powder samples with and without a cylindrical 1 mm Cd shield box were irradiated in an isotropic neutron field obtained from three ²⁴¹Am-Be neutron sources. The gamma-ray spectra from the activated samples were measured with a calibrated n-type high-purity Ge detector. The experimental results were corrected for the correction factors calculated for thermal and epithermal neutron self-shielding effects, epithermal neutron spectrum shape and gamma-ray self attenuation. Thus, the thermal neutron cross-section for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction is found to be 126.5 ± 6.6 b, relative to that of the ⁵⁵Mn monitor. The resonance integral value for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction is found to be 59.6 ± 8.5 b, at cadmium cut-off energy of a 0.55 eV. Using the measured cadmium ratios of ⁵⁵Mn and ¹⁷⁴Yb, the result for resonance integral of the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction has also been obtained relative to the reference value of the ⁵⁵Mn monitor. The present results for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction agree well only with the recent experimental ones obtained by Kafala et al. [1] and De Corte and Simonits [2] within uncertainty limits. However, the previously reported experimental data for the thermal neutron cross-section for this reaction are distributed between 24 and 141 b, and similarly the experimental values for the resonance integral value also show a large scatter in the range of 30-69 b.     

Measurement of thermal neutron cross-sections and resonance integrals for Hf(n,γ)Hf and Hf(n,γ)Hf reactions at the Pohang neutron facility

The thermal-neutron cross-sections and the resonance integrals for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been measured by the activation method. The high purity Hf and Au metallic foils within and without a Cd shield case were irradiated in a neutron field of the Pohang neutron facility. The gamma-ray spectra from the activated foils were measured with a calibrated p-type high-purity Ge detector.In the experimental procedure, the thermal neutron cross-sections, σ₀, and resonance integrals, I₀, for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been determined relative to the reference values of the ¹⁹⁷Au(n,γ)¹⁹⁸Au reaction, with σ₀ = 98.65 ± 0.09 barn and I₀ = 1550 ± 28 barn. In order to improve the accuracy of the experimental results, the interfering reactions and necessary correction factors were taken into account in the determinations. The obtained thermal neutron cross-sections and resonance integrals were σ₀ = 0.424 ± 0.018 barn and I₀ = 6.35 ± 0.45 barn for the ¹⁷⁹Hf(n,γ)^180mHf reaction, and σ₀ = 12.87 ± 0.52 barn and I₀ = 32.91 ± 2.38 barn for the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reaction. The present results are in good agreement with recent measurements.