Thick-target Measurements Research Articles

Nuclear Astrophysics with Exotic Beam; Thick-target Measurements at CRIB

Nuclear Astrophysics with Exotic Beam; Thick-target Measurements at CRIB

Measurement of the B10(α,n0)13N cross section for 2.2<Eα<4.9MeV and its application as a diagnostic at the National Ignition Facility

The National Ignition Facility (NIF) provides the opportunity to study nuclear reactions under controlled conditions at high temperatures and pressures at a level never before achieved. However, the timescale of the deuterium-tritium (DT) implosion is only a few nanoseconds, making data collection and diagnostics very challenging. One method that has been proposed for obtaining additional information about the conditions of the implosion is to activate a dopant material using the $\ensuremath{\alpha}$ particles produced from the DT fuel as a diagnostic. The yield of the activated material can give a measure of the mixing that occurs in the capsule. One of the reactions that has been proposed is $^{10}\mathrm{B}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{13}\mathrm{N}$ as it produces a radioactive reactant product with a convenient half-life of $\ensuremath{\approx}10\phantom{\rule{0.16em}{0ex}}\mathrm{min}$. Although this reaction has several advantages for the application at hand, it has not seen much study in the present literature, resulting in large uncertainties in the cross section. Furthermore, for the current application, the cross section must be well characterized. With this motivation, the $^{10}\mathrm{B}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{13}\mathrm{N}$ cross section has been remeasured for $2.2<{E}_{\ensuremath{\alpha}}<4.9\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ with the angle-integrated ground-state cross section reported for the first time. The present results, combined with previous measurements, allow for a determination of the cross section to a significantly higher degree of accuracy and precision than obtained previously and are shown to be consistent with thick-target measurements. Preliminary calculations are performed to test the feasibility of this reaction as a diagnostic for a NIF implosion.

PIGE related differential cross-section measurements of the 25Mg(p,p′γ)25Mg reaction

The differential cross sections of the 25Mg(p,p′γ)25Mg reaction, critical for the quantitative determination of magnesium in complex matrices using the PIGE technique, were measured at two (2) angles, 55° and 90°, and at proton energies from 2420 to 4550keV, by detecting the 390, 585 and 975keV γ-rays emitted. The experimental setup consisted of two 100% relative efficiency HPGe detectors. The results are compared to those already present in literature and an attempt is made to explain the existing discrepancies. The obtained results from the present work are validated via thick-target measurements.

Study of the [formula omitted] reaction for PIGE applications

The differential cross sections of the 2125keV γ-ray, emitted by the 11B(p,p′γ)11B reaction were measured at six (6) angles and at proton energies from 2.5 to 5.0MeV. The experimental setup consisted of three (3) 100% relative efficiency HPGe detectors placed on a motorized turntable. The comparison between the present measurements, which have an overall uncertainty of ∼8%, and previous ones from literature gives contradictory results. While there are large differences with previous differential cross-section measurements from literature, there is good agreement with previous thick-target yield ones. Additional thick-target measurements were performed in an effort to explain the observed discrepancies.

The density and tube energy dependency of cobalt Kα/Kβ in x‐ray fluorescence spectrometryfor thick target measurements

AbstractThe relative intensity of Kα/Kβ for cobalt in thick targets with cobalt mass densities from 0.51 to 22.49% has been measured by the wavelength dispersive x‐ray fluorescence (XRF) spectrometer. The measuring conditions are: tube current ranging from 10 to 60 mA and voltages ranging from 20 to 60 kV. We plotted the Kα/Kβ ratio vs Co densities for different tube voltages and currents. Our study shows that the Kα/Kβ ratio is below the theoretical value for low Co densities and it increases with increasing Co density. For higher x‐ray energies, the Kα/Kβ ratio shows a sharp growth at the special density and then reaches a nearly constant value. However, Kα/Kβ ratio is theoretically constant and independent of energy in thin target measurements. The changes of this ratio according to the x‐ray energy and the element density have been studied in thick target measurements. The results provide experimental evidence to suggest that exciting energy and element density can indeed affect the Kα/Kβ ratio. Copyright © 2008 John Wiley & Sons, Ltd.

Elastic ?+28Si scattering ? thick target measurements and results

Excitation functions for elastic α-particle scattering from a thick target have been measured. The formalism developed for elemental analysis has been adopted to calculate cross sections. Results from α+28Si elastic scattering, E α = 6.5−19 MeV, are presented. Spins have been deduced from angular distributions and are shown to form a rotational band with odd and even parities. This result is compared to an old GCM phase shift prediction taken from literature.

Level density of 57Co.

Levels in [sup 57]Co have been studied in the region of resolved levels ([ital E][lt]5.5 MeV) with measurements of the [sup 57]Fe([ital p],[ital n])[sup 57]Co neutron spectrum with resolution [Delta][ital E][similar to]5 keV. Seventeen previously unknown levels are located. Level density parameters in the continuum region are deduced from thick target measurements of the same reaction and additional level density information is deduced from Ericson fluctuation studies of the reaction [sup 56]Fe([ital p],[ital n])[sup 56]Co. A set of level density parameters is found which describes the level density of [sup 57]Co at energies up to 14 MeV. Efforts to obtain level density information from the [sup 56]Fe([ital d],[ital n])[sup 57]Co reaction were unsuccessful, but estimates of the fraction of the deuteron absorption cross section corresponding to compound nucleus formation are obtained.

Trace element analysis of steel samples by particle induced X-ray emission

Absolute concentrations of trace elements in steel samples obtained from Texas Utilities power plants have been determined by computer analysis of PIXE spectra produced by 1–2 MeV protons. The X-ray spectra were measured with a windowless Si(Li) detector that is mounted on the 55 ° beam line of the 3 MV NEC 9SDH-2 tandem accelerator at UNT. The peak areas were obtained by fitting a theoretical spectrum of known elemental concentration to the filtered data using the Guelph PIXE Analysis Code [J.A. Maxwell et al., Nucl. Instr. and Meth. B43 (1989) 218]. Absolute concentrations were derived from the peak areas by comparison to spectra of steel standards of known composition from NIST and secondary standards. Thin samples approximately 10 smg/cm 2 thick were also prepared by evaporation onto thin carbon foils. The purpose of the thin sample preparation was to determine which elements evaporated stoichiometrically from the thick samples. In addition, the PIXE results for percentage Fe were checked with the results of Rutherford backscattering. These two thin sample comparisons gave results that were in agreement to ± 5% which gives additional support to the value quoted from the thick target measurements. Concentrations as low as 54 ppm were observed and, for statistically significant peaks, fitting errors were under 5%. These measurements are being made in an attempt to understand the role of impurities in failed electrical power plant components.

Cross sections and astrophysical [formula omitted] factor for the 7Li(p, α) reaction at low energies

The energy dependence of the total cross section and the astrophysical S ̃ factor down to 20 keV are presented for the 7Li(p, α) reaction. The results were obtained by using the known S ̃ factor for the 6Li(p, α) reaction and the slopes of thick target yield vs energy for the two reactions. This relative method avoids several major difficulties with thick target measurements at low energies. Good agreement is obtained with the higher energy results of Spinka, Tombrello, and Winkler and the results of Rolfs and Kavanagh.

Thick-target Ti and Fe K X-ray production cross sections from D, He, C, N and O bombardment

Deuteron-, alpha-particle-, carbon-, nitrogen- and oxygen-induced K-shell X-ray production cross sections for Ti and Fe were obtained from thick-target measurements for low impact velocities. The D and He data agree well with results found in the literature but C, N and O data are reported for the first time. The experimental results were compared with the ECPSSR model and with calculations developed in the authors' laboratory. The data concerning the heavier projectiles allow one to distinguish between the two sets of calculations.

On the depth dependence of spallation reactions in a spherical thick diorite target homogeneously irradiated by 600 MeV protons: Simulation of production of cosmogenic nuclides in small meteorites

An artificial meteorite made out of diorite with a radius of 5 cm was irradiated isotropically with 600 MeV protons in order to simulate the production of cosmogenic nuclides in small meteorites by galactic cosmic ray protons. The primary proton dose of 4.82 × 10 15 cm −2 is equivalent to a some 50 Ma of cosmic ray exposure. The depth dependent production of a wide range of radionuclides from target elements O, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Ba, and Lu was measured. Furthermore, the production of He and Ne isotopes from Al, Mg, Si, as well as from glass and meteoritic material was determined. Thick-target data are compared with thin-target production rates measured simultaneously, thus allowing to separate the contribution of secondary protons and neutrons. The results demonstrate that, in contrast to present presumptions, even in small meteorites secondary particles have to be considered and that the depth profiles show differences in production of up to 30% between surface and center. The experimental data are discussed with respect to cosmic irradiation conditions of real meteorites. Using Monte Carlo techniques depth dependent nucleon spectra were calculated. On the basis of these spectra and of thin-target excitation functions theoretical production rates were derived and compared with the experimental ones. This comparison shows that it is possible to reproduce the experimental depth profiles quite well by thin-target calculations provided reliable excitation functions are at hand. The thick-target measurements and the thin-target calculations provide a basis for an advanced modelling of the production of cosmogenic nuclides in small meteorites, which strictly differentiates between all contributing production modes.

Deuteron- and alpha-particle-induced K-shell ionisation of W and Au atoms

Deuteron- and alpha-particle-induced K-shell ionisation cross sections for W and Au were obtained from thick target measurements for low impact velocities. They were compared with proton-induced cross sections in the same range of velocities. Equal velocity cross section ratios are a very stringent test of the corrections incorporated in the PWBA calculations. The sigma d/ sigma p data presented in this paper shed some light on the Coulomb deflection corrections discussed in the literature. The consequences of the inelastic character of the ionisation process are thoroughly examined.

Production of thick elemental low-oxygen content nat,26Mg from nat,26MgO

The results of thick target (p, n) and (α, n) yield measurements are relevant to current problems in nuclear astrophysics or nuclear reactor operations. The large neutron detection system recently built in our Laboratory for these measurements requires that the beam be stopped in the target, thus necessitating very thick targets. Targets of thicknesses from 39 mg/cm 2 to 100 mg/cm 2 of elemental magnesium ( nat,26Mg) with an oxygen content of less than 7% for 26Mg and less than 1% for natMg, have been successfully made by high-vacuum reduction evaporation from their respective oxides onto a water-cooled 0.05 mm tantalum sheet. Very short duration (5 s) pulsed heating during reduction evaporation insures that the oxide formation remains low. The final desired thickness is produced by pressing the elemental magnesium in a die of the appropriate size. An analysis of the carbon content in the final elemental 26Mg showed it to be 1.4% of the carbon content present in the 26MgO from which it was derived.

K-shell ionisation cross sections for W, Au and U by low-velocity protons

Proton-induced K-shell ionisation cross sections for W, Au and U by low-velocity protons were obtained from thick-target measurements. For the first time the lowest incident energy reached a value less than ten times the binding energy of the K-shell electron (less than nine times in the case of Au). Possible sources of error are thoroughly examined and a comparison with other available experimental results and theoretical values is presented and discussed.

Levels in 23Na excited by the [formula omitted], [formula omitted] and 19F( α, p) 22Ne reactions

Excitation functions have been measured at five angles for the 19F(α, α) 19F scattering process up to E α = 3.7 MeV. The yield curves for the 19F(α, γ) 23Na , 19F(α, p 0) 22Ne and 19F(α, p 1γ) 22Ne reactions were also obtained in simultaneous measurements. A multi-level R-matrix calculation was used to analyse the elastic scattering data, yielding parameters for 16 resonances. Sixty resonances corresponding to levels in 23Na were seen in the different reactions. A comparison of resonance energy and total width data is given. The 19F(α, γ) 23Na reaction below E α = 2.3 MeV was studied also with thick-target measurements. Decay schemes are given for two resonances. The α-particle strength is discussed.

Electron Double Ionization Cross Section in Sodium Obtained from Kαh Hypersatellite Spectra

The Kαh hypersatellite spectrum of Na metal has been measured in electron excitation with voltages from 4 to 25 kV. The spectrum shows lines with initial K-2 (Kα2h) and K-2 L-1 holes. The energies of these lines as well as the K2 binding energy have been determined and compared with theoretical calculations. The intensity of the line group with K-2 L-1 initial configuration relative to the K-2 group has been measured and found to be in agreement with simple shake-off calculation. The electron double ionization cross section (EDC) of the K-shell has been determined from both thick and thin target measurements using the method developed by Saijonmaa and Keski-Rahkonen, and found to yield equivalent results. The EDC has also been calculated theoretically using classical and quantum mechanical binary encounter approximations as devised by Saijonmaa. Theory reproduces fairly well the magnitude and the atomic number dependence of the EDC whereas the shape of the EDC-curve as function of energy deviates clearly from observed values.

Calculation of X-ray bremsstrahlung and characteristic line emission produced by a Maxwellian electron distribution

Using power-law least-squares fits to thick-target measurements of X-ray bremsstrahlung and characteristic line emission, analytic expressions for spectra and emission efficiencies of X-rays produced by a Maxwellian electron distribution were calculated. These expressions are particularly useful for the analysis of X-ray spectra produced by hot electrons in laser-produced plasma. The effect of self-absorption on the analysis of these spectra is estimated. It is shown that both the spectral shape and the adsorption effects dictate that bremsstrahlung measurements of plasma temperature should be made at photon energies greater than kT.

Kαh Hypersatellite Spectrum and Electron Double Ionization Cross Section of the K-Shell in Magnesium

The Kαh hypersatellite spectrum of Mg metal has been measured in electron excitation with excitation voltages from 4 to 32 kV. The spectrum shows lines with initial K-2(Kαh2) and K-2L-1 holes. The energies of these lines as well as the K-2 binding energy have been determined and compared with theoretical calculations. The intensity of the line group with K-2L-1 initial states relative to the Kαh2 line has been measured and found to be in good agreement with simple shake-off calculation. The electron double ionization cross section (EDC) of the K- shell has been determined from these thick target measurements using the method developed by Saijonmaa and Keski-Rahkonen. The EDC has also been calculated theoretically using classical and quantum mechanical binary encounter approximations as devised by Saijonmaa. Theory reproduces fairly well the magnitude but not the shape of the EDC-curve as a function of energy.

Comment on Biological Effect of Elastic Nuclear Collisions

Existing evidence in favor of a biological effect of elastic nuclear collisions (inactivation of RNase) is examined. A general scheme is outlined for extraction of inactivation cross sections from thick-target measurements. The importance of ion reflection from the backing material in thin-target measurements is pointed out. Experimental inactivation yields are examined together with estimated energy-loss curves for hydrogen, helium, and nitrogen bombardment at energies in the 0.1-10-keV range. It is concluded, with some precautions with regard to experimental accuracy, that neither hydrogen nor helium bombardments present compelling evidence for a significant inactivation effect of elastic nuclear collisions. Results for nitrogen bombardment are ambiguous because of very high density of both elastic and electronic energy deposition.

Comparisons of thick and thin target methods for obtaining X-ray production cross sections for fast ion impact

Comparisons of X-ray production cross sections obtained from thick and thin target measurements for α-particle and neon ion impact show reliable cross sections may be obtained for K and L X-rays for α-particle bombardment by using thick target techniques. Because of large self-absorption corrections, M X-ray cross sections have large uncertainties. Similar comparisons for neon ion impact show significant differences between thick and thin target measurements.