Stacked Foil Research Articles

/α, xn/ reactions on159Tb

Target foil stacks of terbium were bombarded with α-particles of incident energies ≤55 MeV. Excitation functions for the /α,xn/ x=2–5 reactions were determined. On the basis of the cross sections, the thick target yields of/163−x/Ho /x=2.5/ have been evaluated. Activation and stacked-foil techniques were applied.

Study of wear between piston ring and cylinder housing of an internal combustion engine by thin layer activation technique

The wear analysis of a compression ring and cylinder housing of an Internal Combustion Engine by thin layer activation (TLA) with 40 MeV α-particles from the Variable Energy Cyclotron at Calcutta is reported. The calibration curves have been obtained for Fe and Ni using stacked foil activation technique for determining the absolute wear in these machine parts. It has been possible to determine the pattern of wear on the points along the surface of machine components. The minimum detectable depth in this wear study has been estimated at 0.11 ± 0.04 μm.

Modifications induced in polyvinylidene fluoride by energetic ions

Modifications induced by energetic ions have been investigated in the regime of electronic stopping power by X-ray photoemission spectroscopy (XPS), infrared absorption spectroscopy (IRAS) and differential scanning calorimetry (DSC). Stacks of thin foils of polyvinylidene fluoride (PVDF) have been exposed to ion beams with energies ranging from 1 to 50 MeV/amu and with different atomic number Z ( 16 O, 84 Kr, 129 Xe) . XPS measurements provide information about the surface modifications of irradiated PVDF: (1) oxygen ions bombardment leads to the creation of cumulene compounds (CCC) n following hydrogen fluoride desorption, the intensity of which increases with the irradiation dose δE, the fluence φt of the ion and the energy loss ΔE in the polymer; (2) for krypton or xenon irradiation, no changes can be detected on the surface composition. Differential scanning calorimetry (DSC) performed on a pristine sample and on PVDF irradiated with xenon ions shows a decrease of the melting point T Fand of the enthalpy ΔH F with the irradiation dose δE. This behaviour is characteristic of a loss of crystallinity due to the internal reorganization of the polymer (creation of polyallenic compounds, chain scission, decrease of the molecular weight). Infrared transmission spectra (IRAS) and attenuated total reflexion spectroscopy (ATR) show that only surface modifications are induced by oxygen ions. For energetic heavy ions (Kr, Xe), the bulk of the polymer is loaded with unsaturated compounds like allenes (2038, 1720, 1610 and 1560 cm −1), and is depleted in fluorine atoms. On the other hand, the PVDF surface studied in ATR mode exibits a much smaller evolution. There results are consistent with XPS data. All these experimental data can be explained by gas formation and desorption, migration in the bulk of reactive species like free radicals and internal recombinations.

(α, αxn) and (α, 2pxn) reactions on93Nb

Target foil stacks of niobium were bombarded with beams of alpha particles at incident energies ranging from 0 to 90 MeV. Cumulative cross sections for the production of95(m+g)Nb,92mNb,91mNb and90(m+g)Nb were determined by semiconductor gamma-spectrometry of the residual activity of stacked foils. On the basis of the cumulative cross sections, the thick target yields and saturation production rates of niobium isotopes have been evaluated.

(α, αxn) and (α, 2pxn) reactions on107Ag and109Ag

Target foil stacks of silver were bombarded with beams of alpha particles at incident energies ≤90 MeV. Cumulative cross sections for the production of104(m+g)Ag,105(m+g)Ag,106mAg,108mAg,110mAg and111(m+g)Ag were determined by semiconductor gamma-spectrometry of the residual activity of stacked foils.

THEORETICAL CALCULATIONS OF THE QUANTUM DIFFERENTIAL SPECTRUM OF TRANSITION RADIATION FROM A STACK OF BERYLLIUM FOILS

In this paper, the formulas of quantum differential spectrum of the transition radiation, which are produced when a medium energy relativistic electron passes through a single foil or a stack of foils, are derived on the basis of the macroscopic pola rization theory of me-dium. Using these formulas, we calculate the spectra for a single beryllium foil and a stack of beryllium foils and obtain the results that agree with experiments.

Determination of the Excitation Functions for (d, xn)-Reactions on Natural Tellurium

Excitation functions for (d, n)- and (d, 2n)-reactions on natural unenriched tellurium has been measured simultaneously in the energy range between 5 and 13.7 MeV using stack foil technique. The maximum cross section for the 122-Te(d, n) 123-I reaction is 400 · 10−31 m2 (400 mb) at 9 MeV deuteron energy. The thick target yield for 123-I production via (d, n)-reaction on enriched 122-TeO2 was determined to be 55 M Bq/μAh. The main impurity is the 130-I produced in the (d, 2n)-reaction on 130-Te impurities in the target material.

Production cross section of radionuclides in (p, x) reactions at copper and nickel nuclei

The authors measured the cross sections of the production of radionuclides by 10-100-MeV protons in copper and nickel targets of the natural isotope composition. The currently available data on these target nuclei are basically limited to a proton energy of approx. 50 MeV and some of the information is even inconsistent. The experiment was made on the linear injector of the Institute of High-Energy Physics. The targets were irradiated with the extracted proton beam of the linear injector with a beam current of 97 mA, a current-pulse duration of 57 ..mu..sec, and a pulse-repetition frequency of 0.25 Hz. In order to calculate the proton energy after the passage through a stack of foils, data on the stopping power and the ranges of protons in aluminium were used. The proton flux was monitored via the nuclear reactions /sup 65/Cu(p,n)/sup 65/Zn in the proton energy range 10-40 MeV and /sup 27/Al(p,x)/sup 24/Na in the proton energy range 40-100 MeV.

Excitation functions of alpha particle induced reactions in cobalt in the energy range 10–120 MeV using variable energy cyclotrons

Alpha particle induced reactions on the target element cobalt were investigated from 10 to 120 MeV, using foil stack activation technique and the Ge(Li) gamma ray spectroscopy method. Ten excitation functions for reaction residues 51Cr, 52,54Mn, 56,57Ni, 59Fe and 56,57,58,60Co were measured, of which 59Co(α, p6n) 56Ni reaction was measured for the first time. A comparison with pre-equilibrium hybrid model was made using initial exciton number, n 0 = 4 (4pOh). It is observed that for ( α, xn ypz α) type reactions the agreement is within a factor of 2, while for ( α, xn yp) type the disagreement is generally by more than an order of magnitude.

Non-equilibrium effects in alpha-particle-induced reactions in light, medium and heavy nuclei up to 120 MeV

Alpha-particle-induced reactions on the target elements vanadium, niobium and holmium were investigated in the energy range from 10 to 120 MeV, using the foil stack activation technique and Ge(Li) gamma-ray spectroscopy. The excitation functions of six reactions of the ( alpha , xn) type were studied, of which three reactions 51V( alpha ,n)54Mn, 165Ho( alpha ,2n)167Tm and 165Ho( alpha ,4n)165Tm were measured for the first time in the energy range from 80 to 120 MeV. A preliminary theoretical comparison with the pre-equilibrium hybrid model was made using an initial exciton number of n0=4 (4p0h) and general agreement was found for all except the 51V( alpha ,n) and 93Nb( alpha ,n) reactions at high energies.

An improved tilted multifoil assembly for nuclear polarization

An improved tilted multifoil assembly for inducing nuclear polarization to high spin reaction products is described. The device is a stack of thin carbon foils, stretched between two bridges in such a way that two edges are free from support. The advantages of this new approach over earlier designs are discussed and the procedure for assembling the stack is laid out. The device was tested in an experiment on 138Ce (10 +) recoils exhibiting a nuclear polarization of 5.4(7)%.

Influence of Transition Radiation and Density Effect on Atomic K-Shell Excitation

A theoretical and experimental investigation is presented for the process of atomic K-shell excitation for GeV particles with special emphasis on the influence from the polarization of the surrounding target medium. It is shown that the transition radiation emitted upon entrance into the target compensates partly the reduction due to the density effect. In this way inner-shell excitation yields are obtained which depend on penetrated depth into the target, e.g., with the net result that polarization effects may be neglected for thin samples. A simple relation is constructed which explains all existing experimental data. The large spread in γ values (1-104) for a GeV secondary beam has been exploited to measure the above relativistic effects in one single experiment. Here the simple model has proven to stand all tests including variation of target thickness, comparison of X-ray yields from the front and back sides of the target, and inclusion of a stack of foils to produce extra transition radiation upstream with respect to the target.

Experimental measurement of particle deceleration and survival in multiple thin foil targets

Experimental results of deceleration of iron particles by means of a stack of thin Mylar foils are presented. The mass range of the iron particles is 3 × 10 −12 to 1 × 10 −108 the velocity ranges from 2.5 km/s to 5 km/s. Decelerations of up to ca. 70% were measured using 2 and 3 foils. The measured deceleration can be expressed over the whole velocity range studied as a function of the particle mass. Comparison with previous studies of thin foil penetration /1,2/ supports the approach to a scaling in terms of momentum conservation. We discuss limits for intact dust particle capture in space, and conclude that such techniques for deceleration and capture for comet flyby missions are effective. This is instanced already in Solar Max data where capture is effected at higher velocities and identifiable fragments of incident particles have been analysed.

Measurement of transition radiation from medium-energy electrons.

The absolute differential production efficiencies (photons/eV sr electron) for x rays emitted from each of three transition radiators were measured for incident electron-beam energies of 17.2, 25, and 54 MeV. The radiators were made of stacks of 1.0-..mu..m-thick foils: 18 foils of beryllium, 18 foils of carbon, and 30 foils of aluminum. The radiation spectra were most intense between 0.5 and 2.5 keV, peaking at 0.8, 1.3, and 1.3 keV, respectively. The angular distribution of the transition radiation from the beryllium-foil stack was measured for the three electron-beam energies and found to agree well with theoretical predictions. Owing to K-shell absorption, the photon-energy spectra from the carbon and aluminum stacks are narrowed. Theoretical calculations, which include both the two-surface interference and photon attenuation in the foil material, agree well with these data. A method of enhancing output using a split-foil stack is considered; cursory experiments with a split stack of Mylar foils showed enhanced emission. The use of transition radiation as a source of x rays for lithographic purposes may be practical.

Experimental study of the collective acceleration of deuterons

The collective acceleration of deuterons by an intense relativistic electron beam has been studied experimentally. The accelerated ion energy spectra for various different experimental configurations has been measured using stacked foil activation analysis. The spectra extend to energies below the injected electron beam energy, and thus allow estimates of the net efficiency of the acceleration process. The effect of variations in electron beam power and applied magnetic field on the acceleration process are also discussed.

Nuklidproduktionsfunktionen bei der Dünnschichtaktivierung von Eisen für Verschleißuntersuchungen

For wear measurements using thin layer activation information is necessary about the nuclide depth distribution in the activated materials. The nuclide concentration profiles as a result of iron activation by alphaparticles, deuterons, and protons have been determined at the Rossendorf cyclotron using iron foil stack.

Dynamic presure transfer through porous bodies

Calculation of dynamic pressures transmitted through porous specimens when the state in the medium ahead of the specimen and the compressibility of the porous material are known is a problem of scientific and technological importance. In the present study, experiments were carried out for the case of compressibility of the medium being less than that of the specimen. A vessel containing carbon tetrachloride was placed on top of the specimen, and the liquid's shock compression temperature was measured. Data were obtained for the conditions of a magnesium specimen placed on a copper screen, aluminum specimens placed on a copper screen, and each specimen placed on a screen of the same material. In addition, shock waves were transmitted through a series of foil stacks. This last permits correct prediction of the features of pressure transfer through pressed porous specimens.

A rotating wheel system for the detection of spontaneously fissioning nuclides from heavy ion reactions

A rotating wheel system for the detection of spontaneously fissioning reaction products from heavy ion reactions was developed. In this system products recoiling from a rotating target wheel are stopped in a catcher foil stack which can be rotated at various velocities up to 80 rotations per second. All products emitted within a wide emission cone are stopped in the catcher foils and are rotated into shielded positions with stationary fission-track detectors positioned on both sides of each rotating foil. This technique allows a sensitive detection of spontaneously fissioning nuclides over a broad range of half-lives from 1 ms to about 1 d. By post-bombardment exposure of the catchers to new fission-track detectors, the half-lives covered can be extended to about 1 y. From their range and angular distributions within the catcher foils, heavy-ion fusion products can be distinguished from nuclides produced in damped collisions, and excitation functions can be extracted.

Accelerator mass spectrometry and radioisotope detection at the Argonne FN tandem facility

The Argonne FN tandem accelerator and standard components of its experimental heavy-ion research facility have been used as a highly-sensitive mass spectrometer to detect several long-lived radioisotopes and measure their concentrations by counting accelerated ions. Background beams from isobaric nuclei have been eliminated by combining the dispersion from the energy loss in a uniform Al foil stack with the momentum resolution of an Enge split-pole magnetic spectrograph. Radioisotope concentrations in the following ranges have been measured: 14C/ 12C = 10 −12 to 10 −13, 26Al/ 27Al = 10 −10 to 10 −12, 32Si/Si = 10 −8 to 10 −14, 36Cl/Cl = 10 −10 to 10 −11. Particular emphasis was placed on exploring to what extent the technique of identifying and counting individual ions in an accelerator beam can be conveniently used to determine nuclear quantities of interest when the measurement involves very low radioisotope concentrations. We are able to demonstrate the usefulness of this method by measuring the 26Mg(p, n) 26 Al(7.2 × 10 5 yr) cross section at proton energies in the astrophysically interesting range just above threshold, and by accurately determining the previously poorly known half-life of 32Si.

Alpha particle induced reactions on zirconium

Target foil stacks of zirconium were bombarded with beams of alpha particles at incident energies ≤55.0 MeV. Excitation functions for the production of99mMo,90Mo,97gNb,90Nb,95Zr,92Y,90mY and86Y were determined. On the basis of the cross sections, the thick target yields and saturation production rates of95Zr have been evaluated.