Alpha Beam Research Articles

Electrochemical aspects of radiolytically enhanced UO2dissolution

SummaryExperiments were performed, irradiating UO2colloids of 3 nm diameter by a 5 MeV alpha beam of a cyclotron. Both the dissolution rate of these colloids and the production rate of hydrogen peroxide have been measured. The experimentally measured corrosion rate of these colloids is very similar to the corrosion rates measured for bulk UO2samples, indicating on the one hand that similar reaction mechanism prevail and on the other hand that the UO2colloids are well representative for bulk UO2. The results were compared with two current models for radiolytical dissolution of spent fuel. Additionally a new coupling between water radiolysis reactions and spent fuel dissolution has been established. The coupling is not anymore based on rate constants for direct reaction of oxidants with UO2, but on the electrochemical coupling of anodic dissolution reactions with cathodic reduction of molecular and radical radiolysis products. The model not only describes well the experimental data, it also allows to predict both the establishment of corrosion potentials and of fractional reaction orders with respect to oxidant concentrations. Model results can also be compared with experimental data (corrosion potential ...) using UO2as an electrode.

Dosimetric Aspects of tie Electron Microbeam irradiation System for Use in Low-Dose Radiation Effect Study

Microbeam experiment studies up to now have been performed with alpha and proton beams in major and with soft x-rays in minor. In this paper, the electron microbeam irradiation system under development in Korea is introduced with a focus on dosimetric aspects. The system consists of an electron gun, an electron transport chamber having the beam collimation of 5 urn in diameter and a biology stage automatically controlled. Dose distributions for the target layer in a cell dish have been investigated by Monte Carlo simulation for 25, 50, 75 and 100 keV electron source beams on the basis of the preliminary design specifications of the vacuum window, the cell dish bottom and the air gap in between. At the beam center, the average dose to the liquid water target layer in a cell dish was 0.078, 0.157, 0.179 and 0.194 cGy per single electron emission through a 5 um-dia. collimator with 25, 50, 75 and 100 keV electron source beam, respectively. With 25 keV electron beam, dose was reduced to 66.5, 28.7 and 2.10 percents at a 3, 5 and 10 jim distance, repectively, from the beam center. With 100 keV electron beam, on the other hand, the corresponding values were 46.1, 2.30 and 0.764 percent.

In1.08Gd0.92Ge2O7: A New Member of the Thortveitite Family.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Cross section measurements of the 102Pd(p, γ) 103Ag, 116Sn(p, γ) 117Sb, and 112Sn( α, γ) 116Te reactions relevant to the astrophysical rp- and γ-processes

Total cross section measurements for the 102Pd(p, γ) 103Ag and 116Sn(p, γ) 117Sb reactions have been performed in the proton energy range 2.6 to 4.25 MeV, and for the 112Sn( α, γ) 116Te reaction over the alpha beam energy range 7.0 to 10.5 MeV. An activation technique was used in which gamma rays from decays of the reaction products were detected off-line by two hyper-pure germanium detectors in a low background environment. Where possible, reaction rates are derived and the results compared to those of calculations generated by the NON-SMOKER and the MOST statistical model codes so as to judge their applicability for describing the cross sections needed for network calculations of nucleosynthesis in explosive astrophysical environments via the γ- and rp-processes.

Alpha beam monitoring via natCu + alpha processes in the energy range from 40 to 60 MeV

Excitation functions were measured using the stacked-foil method for alpha particle-induced nuclear reactions on natural copper leading to the formation of 61Cu, 66Ga and 67Ga in the energy range from 16 to 60 MeV. Extending the recommended database of the nat Cu( α, x) 66 Ga and nat Cu( α, x) 67 Ga processes with our new values, now the above processes can be used for alpha beam energy and intensity monitoring up to 60 MeV. On the basis of the present study it was found that the nat Cu( α, x) 61 Cu process is also a useful candidate for monitor purposes in the 40–60 MeV energy region.

Development of a single ion irradiation system at CENBG for applications in radiation biology

A single event facility is currently under development at CENBG for applications in radiation biology. The aim is to induce the response of living cells by hitting selected individual specimens or specific sub-cellular compartments with an exact number of light ions. In order to avoid the construction of a complete beam line, it was decided to adapt the existing microprobe system. The line has been equipped with a removable final irradiation stage constituting a versatile system working on demand either in external beam mode or classical analysis under vacuum. The beam blanking is ensured by particle detectors which have been specifically designed to control MeV proton or alpha beams in a single event mode. This paper presents the overall experimental setup and first in-air experimental tests.

Measurement of lateral straggling using a microbeam

An original method has been developed to measure the lateral straggling of sub-micron proton and alpha beams after passing through polymer foils of different thickness. For this purpose, the microbeam line at CENBG has been used in scanning transmission ion microscopy (STIM) configuration to deliver the ions in normal incidence on foils. The lateral spreading of the beam was measured using a collimated charged particle detector centred on the beam axis and placed 6.3 mm behind the foil. When the beam was horizontally scanned in front of the collimator, its lateral distribution was measured step by step detecting particles passing trough the small aperture. Regular gaussian shapes were obtained and data were compared to the result of simulations carried out using the SRIM Monte-Carlo code for 2.5 MeV protons and alphas in Mylar and Formvar thin films.

Evolution of nuclear spectroscopy at Saha Institute of Nuclear Physics

Experimental studies of nuclear excitations have been an important subject from the earliest days when the institute was established. The construction of 4 MeV proton cyclotron was mainly aimed to achieve this goal. Early experiments in nuclear spectroscopy were done with radioactive nuclei with the help of beta and gamma ray spectrometers. Small NaI(Tl) detectors were used for gamma-gamma coincidence, angular correlation and life time measurements. The excited states nuclear magnetic moments were measured in perturbed gamma-gamma angular correlation experiments. A high transmission magnetic beta ray spectrometer was used to measure internal conversion coefficients and beta-gamma coincidence studies. A large number of significant contributions were made during 1950–59 using these facilities. Proton beam in the cyclotron was made available in the late 1950’s and together with 14 MeV neutrons obtained from a C-W generator a large number of short-lived nuclei were investigated during 1960’s and 1970’s. The introduction of high resolution Ge gamma detectors and the improved electronics helped to extend the spectroscopic work which include on-line (p 7 p′γ) and (p 7 nγ) reaction studies. Nuclear spectroscopic studies entered a new phase in the 1980’s with the availability of 40–80 MeV alpha beam from the variable energy cyclotron at VECC, Calcutta. A number of experimental groups were formed in the institute to study nuclear level schemes with (α 7 xnγ) reactions. Initially only two unsuppressed Ge detectors were used for coincidence studies. Later in 1989 five Ge detectors with a large six segmented NaI(Tl) multiplicitysum detector system were successfully used to select various channels in (α 7 xnγ) reactions. From 1990 to date a variety of medium energy heavy ions were made available from the BARC-TIFR Pelletron and the Nuclear Science Centre Pelletron. The state of the art gamma detector arrays in these centres enabled the Saha Institute groups to undertake more sophisticated experiments. Front line nuclear spectroscopy works are now being done and new informations are obtained for a large number of nuclei over a wide mass range. Currently Saha Institute is building a multi-element gamma heavy ion neutron array detector (MEGHNAD), which will have six high efficiency clover Ge detector together with charged particle ball and other accessories. The system is expected to be usable in 2002 and will be used in experiments using high energy heavy ions from VECC.

Direct measurement of JET local deuteron densities by neural networkmodelling of Balmer alpha beam emission spectra

The analysis of Balmer alpha beam emission spectra represents a challengingtask, both in terms of the wealth of information hidden in them, and in termsof complex spectral features. The shape of a spectrum depends on many localplasma parameters, such as magnetic field strength and direction, beamdensity, effective charge and deuteron density. This paper is concerned withthe deduction of local plasma deuteron densities from Balmer alpha emissionfrom plasma atoms following charge exchange with the beam atoms. The model wewill use is statistical, and is based on multi-layer perceptron neuralnetworks (Hertz et al 1991, Bishop 1995). The use of neural networks makes thedeconvolution task fully automatic and fast enough for real-time calculationof complete deuteron density profiles. It is shown that the spectra themselvesand local electron densities are the only data necessary for accurateinference of local deuteron densities. This result is partly inferred from asensitivity analysis of dependences on different plasma parameters. Propererror bars for the model predictions will be derived using Bayesianprobability theory.

Optimisation of cyclotron production parameters for the 209Bi( α, 2n) 211At reaction related to biomedical use of 211At

The cyclotron alpha beam production of 211At and of the contaminant 210At related to beam energy were studied. Radiochemical purification of 211At from the other main contaminant, 210Po, by an extraction procedure was also evaluated. To avoid impurities 28 MeV has previously been considered as a maximum beam energy, but by using instead 29.1 MeV as a limit a large increase in EOB yield and sufficient radiochemical purity of extracted 211At were obtained. More cyclotrons could thereby deliver quantities useful for clinical cancer trials.

Alpha-radiolysis effects on UO 2 alteration in water

The behaviour of UO 2/water interface under irradiation has been investigated as a function of alpha flux using an alpha beam provided by a cyclotron. The effects of alpha-radiolysis on UO 2 alteration in aerated deionized water were studied by characterizing both the chemistry of irradiated aqueous solutions and the UO 2 surface. Uranium (as uranyl ion UO 2 2+) and hydrogen peroxide concentration (H 2O 2) increased whereas pH decreased in the irradiated solutions when alpha-beam flux increased. The formation of hydrated uranium peroxide (metastudtite UO 4 · 2H 2O) on UO 2 leached surface was identified by X-ray diffractometry. The production of metastudtite can be considered as a direct effect of water radiolysis due to the production of radiolytic species H 2O 2, since its formation is known to occur out of irradiation via a precipitation reaction between hydrogen peroxide and uranyl ion. From both these observations and literature about hydrated uranium peroxide occurrence, the possibility of metastudtite formation on nuclear spent fuel in storage conditions is discussed.

Energy resolution and energy–light response of CsI(Tl) scintillators for charged particle detection

This article describes the crystal selection and quality control utilized to develop and calibrate a high-resolution array of CsI(Tl) scintillator crystals for the detection of energetic charged particles. Alpha sources are used to test the light output variation due to thallium doping gradients. Selection of crystals with better than 1% non-uniformity in light output is accomplished using this method. Tests with a 240 MeV alpha beam reveal that local light output variations within each of the tested CsI(Tl) crystals limit the resolution to about 0.5%. Charge and mass dependences in the energy–light output relationship are determined by calibrating with energetic projectile fragmentation beams.

Systematic intensity errors and model imperfection as the consequence of spectral truncation

The wavelength dispersion delta lambda/lambda in a graphite (002) monochromated Mo K alpha beam was analyzed. A wavelength window was found with 0.68 < lambda < 0.79 A, i.e. delta lambda/lambda = 0.14. The very large dispersion leads to systematic errors in Iobserved(H) caused by scan-angle-induced spectral truncation. A limit on the scan angle during data collection is unavoidable, in order that an omega/2 theta measurement should not encompass neighboring reflections. The systematic intensity errors increase with the Bragg angle. Therefore they influence the refined X-ray structure by adding a truncational component to the temperature factor: B(X-ray) = B(true) + B(truncation). For an Mo tube at 50 kV, we find B(truncation) = 0.05 A2, whereas a value of 0.22 A2 applies to the same tube but operated at 25 kV. The values of B(truncation) are temperature independent. The model bias was verified via a series of experimental data collections on spherical crystals of nickel sulfate hexahydrate and ammonium hydrogen tartrate. Monochromatic reference structures were obtained via a synchrotron experiment and via a 'balanced' tube experiment.

Numerical Analysis of Ripple Loss in Reversed Shear Tokamak Operation.

Ripple loss of energetic alpha particles and neutral beam ions was calculated for reversed shear discharges in ITER-FDR(Final Design Report). The result indicates that, compared with normal operation with positive shear, reversed shear operation dramatically enhances the ripple loss. Ripple loss of alpha particles can reach 25 % with the maximum heat load of 3.7 MW/m2 on the outboard wall, while that of a 1 MeV negative ion source beam can be as high as 20 % as well. The heat load due to alpha particle loss is marginal in the light of a wall tolerance. The calculation suggests that the Toroidal Field (TF) ripple in a fusion reactor should be designed to be less than 0.6 % at the plasma surface so that ripple loss of alpha particles or beam ions can be acceptably low. Ferritic steel insert to the vacuum vessel, is a probable solution to reduce the ripple loss to an allowable level in the ITER-FDR design with the TF ripple reduction of by a factor of 0.4. With TF ripple reduction, ripple loss for alpha particles and beam ions is expected to decrease to 10 % and 4 %, respectively.

Thin synthetic windows for cryogenic targets

A liquid hydrogen/deuterium target with very thin windows made out of synthetic foils is described. The target has been used for nuclear physics experiments in medium-energy proton and alpha beams. Thin foils have been selected to allow low-energy particles to get out of the target and to have very little background from target-window material. The foils have been tested under different pressures and temperatures. The permeability of some of the foils was monitored with these variations. The foils were also tested for radiation resistance by placing them in the beam.

Beam bunching of the radioactive nuclear beam in a 6.4 GHz electron cyclotron resonance ion source

A single stage 6.4 GHz ECR ion source for an isotope separator on-line based radioactive nuclear beam facility at KEK-Tanashi, is under an on-line test for the effective production of Ne2+19 ions by using alpha beams from a cyclotron. Synchronized with the pulsed operation of heavy ion linacs, the millisecond beam bunching is now being performed to reduce the loss of radioactive ions in acceleration by using a pulsed-gating potential method. The highest beam intensity at 100 Hz and 20% duty factor reaches 60% of that obtained in a continuous-wave mode.

SSNTD and radiochemical studies on the transmutation of nuclei using relativistic ions

Extended targets were irradiated for transmutation studies with relativistic heavy ions. For this, a metal core was surrounded by a paraffin moderator. The metal is either copper or lead and it was irradiated with deuterium, alpha, or carbon beams of 1.5 or 3.7 GeV/u at the SYNCHROPHASOTRON, LHE, JINR, Dubna, Russia. During this irradiation copious amounts of secondary neutrons are produced and studied with SSNTD detectors and radiochemical sensors, for example 139La (n, γ) 140La→β − . The yield of reaction products allows an estimation of secondary neutron fluxes. The yields of all kinds of reactions produced with deuterium and alpha beams obey to some extent the law of “limiting fragmentation”, i.e. they show little influence on the energy and the kind of incoming particles. However, one observes with 44 GeV 12C ions always enhanced nuclear cross-sections induced by secondary particles. This behavior could not be confirmed with theoretical estimations based on the Dubna Cascade Model in its Cascade Evaporation Model version (DCM-CEM). Finally, some results for transmutation studies on 127I and Cu will be presented.

Production of short-lived positron sources for spin-polarized positron beams using a 35 MeV α-beam

Various short-lived positron sources for polarized positron beams have been on-line produced by irradiating nickel, aluminum, and silicon targets for the first time using a 35 MeV alpha beam from the RIKEN AVF cyclotron. The β + rays emitted from the targets with wide energy spread are converted to a monochromatic slow positron beam using a 10 μm tungsten polycrystalline moderator. In the current stage, ∼ 10 4 e +/(s μA) can be obtained from nickel and aluminum targets, which is in relatively good agreement with the calculated slow positron yield. For silicon, a relatively low slow-positron intensity, ∼ 10 3 e +/(s/μA) was obtained probably due to the charge up effect in the silicon surface during irradiation. For increasing the slow-positron yield loss of fast positrons in the material must be avoided, and as a new means for such improvement it is proposed to use gas targets.

Coincidence and correlation analysis for low spin states in 128Xe

Abstract Using the fusion evaporation reaction 125Te(α,n) 128Xe, low spin states of 128Xe have been investigated. The alpha beam at a beam energy of 16 MeV was supplied by the Cologne FN-tandem accelerator. Using the OSIRIS-6-Cube spectrometer we obtained both coincidence and singles data. We evaluated the γγ coincidence data, angular distributions and angular correlations. The technique of spin assignment by angular correlation analysis is discussed in some detail. We present an extended level scheme with 154 levels in the energy range up to 4 MeV and a spin range up to 10h. Two collective bands build up upon bandheads with spin I = 0 and I = 4, respectively, are established. Level energies and B(E2) values are compared to predictions of the IBM-1 near the O(6) dynamical symmetry and interpreted in the framework of the new Q phonon scheme.

Microstructures in an aluminum—silicon alloy analysed by means of a nuclear microprobe

An alloy consisting of a eutectic mix of aluminum and silicon to which traces of Sr and Mg have been added forms an important product of a major aluminum smelter (ALUSAF). Casts of this alloy, when cut and polished, display plate-like structures when viewed through an optical microscope. These structures are bound to have an effect on the physical properties of the alloy, for which strength is important. In this work we have used a nuclear microprobe to map areas of interest and determine the composition of the structures observed, using proton and alpha beams for proton-induced X-ray emission (PIXE) and Rutherford backscattering (RBS) analysis. The platelets were proved to be formed by the trace element strontium, a fact which has important metallurgical implications.