Absolute Energy Measurements Research Articles

Absolute measurement of the GANIL beam energy

The energy of the GANIL cyclotron beam was measured on-line during the 208Pb + 208Pb elastic scattering experiment “Search for Color van der Waals Force in the 208Pb + 208Pb Mott scattering” with an absolute precision of 7 × 10−5 at ∼ 1.0 GeV, which represents an improvement of one order of magnitude over previous absolute energy measurements. The energy was deduced from the time of flight between two beam-scanners, which only partially intercept the beam, situated on a straight line and separated by ∼ 48.0 m. It was found that the nominal beam energy was in good agreement with the present results.

Local electric fields at individual atomic surface sites: field ion appearance energy measurements

A new method of determining local electric fields is reported. Under conditions of highest field ion image contrast, absolute appearance energy measurements were carried out at a weakly corrugated step of a Rh(001) plane and at strongly corrugated step across the atom rows of a Rh(113) facet. Data of local fields, F hkl loc , are derived from appearance energies. A comparison is made with external electric field strengths, F hkl 0 , determined by electron energy spectroscopy and i- V (Fowler-Nordheim) measurements. Significantly different enhancement factors, F hkl loc / F hkl 0 , were found, 1.27 for steps at the (001) plane, and 1.54 for steps across the rows of Rh(113). In both cases the step-site atoms were covered with field-adsorbed Ne. The experimental results are discussed in view of recent self-consistent calculations of local-field distributions in the proximity of protruding surface atoms. The occurence of field ionization of image gas atoms, released from field-adsorbed states at step sites by atom-collision processes, is in accord with the present observations.

Absolute energy measurement of heavy ion beams using a resonant time-of-flight system

A resonant time-of-flight measurement system has been put into operation at the ATLAS facility for the determination of the energy of heavy ion beams. The system provides continuous, nondestructive monitoring of the beam energy. The system provides relative energy determination with a precision of ΔE E ⋍ 10 −4 . Absolute energy is determined to an accuracy of 10 −3. A variety of beam tests have been performed to study the properties of the system.

Absolute measurement of the energies of alpha-particles emitted by sources of 252Cf and 227Ac

Absolute energy measurements of α-particles from sources of 252Cf and 227Ac by magnetic spectrometry are described. The sources were prepared at AERE, Harwell and measurements carried out using the 180° uniform-field spectrometer at BIPM followed the well-established technique applying cellulose-nitrate films (Kodak LR115) for track detection. The following values and uncertainties were obtained: 252 Cf: E α 0 = (6118.24±0.04) keV, E α 43 = (6075.77±0.11) keV; 250 Cf: E α 0 = (6030.35±0.20) keV; 227 Ac: E α 0 = (4953.37±0.14) kev, E α 13 = (4940.8±0.8) keV .

Absolute determination of the energies of alpha particles emitted by 236Pu

The only two previous measurements of the energies of alpha particles emitted by 236Pu were relative determinations. They were in fair agreement with each other, except for the intensity ratios of the two strong lines. We now report an absolute energy measurement which was carried out using the 180° uniform-field magnetic spectrometer at BIPM on four sources prepared at AERE, Harwell with material formed by the reaction 238 U( p, 3 n) 236 Np a ̊ 236 Np a ̊ 236Pu . The alpha particles were detected with aid of Kodak LR 115 (Type 2) cellulose-nitrate films which had considerable advantages over nuclear-track plates. Etching for seven hours in dilute NaOH at 40°C produced only weak and sufficiently reproducible distortions of the films reducing uncertainties to at most 50 eV. From six spectra the following mean values of particle energy E α and relative intensity I α were obtained: E α = (5767.66±0.08) keV, I α = (69.26±0.45) %; E α = (5721000±0.10) keV, I α = (30.56±0.45) %.

The differential cross section of the reaction pp → πd for proton energies between 500 and 600 MeV

The differential cross section of the pp → πd reaction was measured for seven energies between 516 and 582 MeV with an overall absolute precision better than 2%. Pions and deuterons were detected in coincidence with scintillation detectors, using time-of-flight techniques for event identification. Experimental techniques for absolute energy calibration, normalization and measurement of relative distributions are described. Detailed corrections have been applied to the data, which have been fit with Legendre polynomials. An upper limit of 50 μb for a sixth-order term is obtained. The results are compared with those of a recent precision experiment for the inverse reaction, and with theoretical predictions.

Limb darkening in the solar ultraviolet

New photoelectric limb-darkening data are given for 38 of the windows in the UV solar spectrum in which Houtgast has supplied absolute energy measurements. The region, 4000 A to 3000 A, is marked by unaccounted opacity. Results are given also for 13 longer wavelengths. The measurements are fully corrected for atmospheric seeing and scattering. The corrected drift curves exhibit a quasi-periodic character suggestive of the supergranulation.

Absolute reference calorimeter for measuring high power laser pulses

A calorimeter for making absolute energy measurements of high power laser pulses is described. The calorimeter, based on volume absorption in a solid, is calibrated electrically and requires no window or vacuum environment. An error analysis is included giving the systematic and random errors of the instrument for a laser measurement. Briefly, the following performance is typical of the 32-mm x 32-mm aperture calorimeter: range 0.4-15-J; random error +/-0.2% (one standard deviation); systematic error +/-2.3%; and an upper operational limit of 3 J/cm(2). Most of the volume absorber documentation is applicable for 1.06 microm; however, the calorimeter should be useful from the near ir through the visible. Absorbers for use with CO(2) lasers in the 9-11-microm range are also discussed.

Reference levels in photoelectron spectroscopy

Experimental results and theoretical argument show that the Fermi level of a conducting sample is an appropriate reference in the measurement of absolute binding energies by photoelectron spectroscopy. The work function of the sample is shown to be irrelevant.

Alpha-particle energy standards

Since absolute energy measurements are not possible with doubly focussing magnetic spectrometers, most α-spectroscopists relied largely on a few standard energies determined by Rosenblum and Dupouy and by Briggs. Although more absolute results became available later, some major inconsistencies remained and caused difficulties in interpreting α-ray spectra. Since 1969, 22 α-emitters and 35 lines have been measured in the absolute magnetic spectrograph of the BIPM. The results are compared with the values found in the most commonly used compilations. They are useful in calibrating various types of spectrometers and in atomic mass calculations. A new compilation of α-energy data is now in preparation.

Measurement of absolute interfacial free energies in a NiCr alloy

The method of zero creep utilizing the concept of balance of surface tension in thin wires, and the observation of twin boundary-grain boundary intersections in thin foils have been combined in a simultaneous measurement of absolute (average) interfacial free energies in 80 20 NiCr (Chromel-A) at 1060 °C. Using optical microscopy and scanning electron microscopy to measure and identify equilibrium grain lengths and wire diameters, and transmission electron (projection shadowgraph) microscopy to accurately determine the dihedral angles at the intersection of grain boundaries with the wire surface, the surface and grain boundary free energies were measured to be 1960 and 680 erg cm 2 respectively. From measurements of a representative number of low-torque twin-grain boundary inter sections in thin foils by transmission electron microscopy, the twin boundary free energy was calculated to be 17 erg cm 2 from a relative twin/grain boundary free energy ratio of 0.025.

Absolute Measurements of α-ray Energies

New absolute energy measurements of α-particles from 20 natural and artificial emitters are reported, some of which are first absolute values. The uniform field 180° magnetic spectrograph is described in detail. Accurate length and field measurements and line shape extrapolations have been given special attention. A detailed error analysis is presented.

Experimental Test of the Franck-Condon Principle: Double Ionization of Molecular Hydrogen

The double ionization of molecular hydrogen by electron impact has been observed by coincidence detection of the resulting proton pairs in a system especially designed for absolute kinetic energy measurements. Monte Carlo calculations provided an accurate knowledge of the resolution with which the kinetic energy measurements were made. Experimental results agree closely with predictions based on accurate Franck-Condon overlap integrals for a model involving Morse oscillator wavefunctions for the molecule and Coulomb wavefunctions for the ion. In contrast, the reflection approximation and the harmonic oscillator approximation for molecular vibration, two approximations frequently made in such Franck-Condon calculations, do not agree well either with experiment or accurate calculations. Observations at electron energies of 0.5, 0.75, and 1 keV show that the kinetic energy distribution is independent of electron energy and suggest that the double ionization cross section is inversely proportional to electron energy in this range. These results are to be expected for a direct two-electron ejection mechanism for double ionization of H2.

1.7-MeV Anomaly in theC12(p, p)C12Reaction

The ${\mathrm{C}}^{12}(p, p){\mathrm{C}}^{12}$ reaction cross section has been measured for laboratory proton energies from 1.48 to 2.02 MeV at center-of-mass scattering angles of 25\ifmmode^\circ\else\textdegree\fi{}, 35\ifmmode^\circ\else\textdegree\fi{}, 45\ifmmode^\circ\else\textdegree\fi{}, 54.7\ifmmode^\circ\else\textdegree\fi{}, 70\ifmmode^\circ\else\textdegree\fi{}, 80\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, and 125.2\ifmmode^\circ\else\textdegree\fi{}. Thin self-supporting carbon films were used as targets and the scattered protons were analyzed with a double-focusing magnetic spectrometer. The data were fitted with a theoretical one-level formula. Resonances included in the theoretical expression were the ${\mathrm{J}}^{\ensuremath{\pi}}={\frac{1}{2}}^{+}$, ${\mathrm{E}}_{\mathrm{p}}$=0.461-MeV resonance (unobserved in this experiment) and the ${\mathrm{J}}^{\ensuremath{\pi}}={\frac{3}{2}}^{\ensuremath{-}} \mathrm{and} {\frac{5}{2}}^{+}$ resonances associated with the 1.7-MeV anomaly. Parameters for the ${\mathrm{J}}^{\ensuremath{\pi}}={\frac{1}{2}}^{+}$ resonance were taken from previous experiments, and parameters for the ${\mathrm{J}}^{\ensuremath{\pi}}={\frac{3}{2}}^{\ensuremath{-}} \mathrm{and} {\frac{5}{2}}^{+}$ resonances were varied to obtain a best fit to the data. The final parameter values are: ${\mathrm{E}}_{\mathrm{p}}$=1686\ifmmode\pm\else\textpm\fi{}6 keV, ${\ensuremath{\gamma}}^{2}=(0.515\ifmmode\pm\else\textpm\fi{}0.02)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ MeV cm for the ${\mathrm{J}}^{\ensuremath{\pi}}={\frac{3}{2}}^{\ensuremath{-}}$ level, and ${\mathrm{E}}_{\mathrm{p}}$=1734\ifmmode\pm\else\textpm\fi{}6 keV, ${\ensuremath{\gamma}}^{2}=(3.55\ifmmode\pm\else\textpm\fi{}0.18)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ MeV cm for the ${\mathrm{J}}^{\ensuremath{\pi}}={\frac{5}{2}}^{+}$ level. These reduced-width values are approximately 20% larger than those previously measured. Although the error in the absolute energy measurements is 6 keV, the errors in energy differences are smaller and the measured difference ${\mathrm{E}}_{\mathrm{p}}$ values for the ${\frac{3}{2}}^{\ensuremath{-}}$ and ${\frac{5}{2}}^{+}$ levels is 48\ifmmode\pm\else\textpm\fi{}2 keV.

Three absolute energy calibration points for protons below 3 MeV

An electrostatic beam-energy analyser has been used to make absolute energy measurements of the following resonances and threshold: Be 9(p, γ)B 10, 1083.2±0.4 keV; N 15(p, αγ)C 12, 897.37±0.29 keV; and O 18(p, n)F 18, 2576.72±0.77 keV. The widths of the two resonances were measured to be 3.25±0.33 keV and 1.5±0.3 keV, respectively. For calibration purposes, the peak of a thin-target resonance yield curve, the midpoint of the rise of a thick-target resonance yield curve, and the intercept of the extrapolated threshold yield curve do not correspond precisely to the above values, but corrections are given to enable such yield curves to be used directly for energy calibration of proton beam-energy analysers.

Luminescence of Solids Excited by Surface Recombination of Atoms. III. Measurement of Absolute Energies Released as Luminescence and Heat

The absolute energies of luminescence and heat produced by heterogeneous nitrogen atom recombination on CaO were measured by actinometry and calorimetry, respectively. The heat energy produced on MgO was also measured, and the luminescence energy was estimated from its luminescence intensity relative to CaO. The ratio of energy released as luminescence to that as heat is about 2×10—3 for CaO, and about 8×10—5 for MgO. The rate of heat production in CaO and MgO may be explained in terms of heterogeneous atom recombination.

A Comparison of Several Nuclear Absolute Voltage Determinations

An evaluation of the consistency between the absolute voltage determination of the threshold energy of the ${\mathrm{Li}}^{7}(p,n){\mathrm{Be}}^{7}$ reaction as measured by Herb, Snowdon, and Sala and earlier independent absolute alphaparticle energy measurements has been made. The experimental comparison was affected by employing the natural alpha-particles from polonium and radium C\ensuremath{'}, the energy of which has been measured absolutely by several authors using magnetic deflection methods. In this experiment the alpha-particles from these substances have been electrostatically deflected in the 90\ifmmode^\circ\else\textdegree\fi{} cylindrical electrostatic analyzer at the University of Wisconsin. Alpha-particle line measurements were analyzed by numerical integration of resolution and source functions and in themselves contributed negligibly to the uncertainties of the comparison. The resulting alpha-particle energies, evaluated by comparison with the energy of the ${\mathrm{Li}}^{7}(p,n){\mathrm{Be}}^{7}$ threshold, agree with earlier measurements, and indicate that within the limits of accuracy of the experiments, all determinations give identical results.

The experimental determination by ionization methods of the rate of emission of beta- and gamma-ray energy by radioactive substances; the isotopes Na24, P32, Co60 and I131.

The known relation between the ionization in cavity type ionization chambers and the γ-ray energy absorbed per unit mass of the wall material has been employed for the absolute determination of the rate of emission of γ-ray energy by samples of the isotopes Na24, Co60, and I131. When the rate of emission of quanta by the sample has been determined by counting procedures, the measured rate of emission of γ-ray energy agrees well with expectation based on the accepted decay schemes of Na24 and Co60, and the Metzger Deutsch scheme for I131. In principle an analogous method may be used to measure the absolute rate of emission of β-ray energy by a sample of isotope uniformly incorporated in the walls of a cavity type ionization chamber. Measurements of the rate of emission of β-ray energy by Na24, P32, Co60 and I131, have been made by means of ionization chambers lined with gelatine containing these isotopes. By comparing the results with the rate of emission of γ-ray energy from the same sample of isotope, the following values have been obtained for the ratio of the mean β-ray energy to the γ-ray energy emitted per disintegration: Na24 = 0·139 ± 0·007, Co60 = 0·043 ± 0·002, I131 = 0·505 ± 0·025. These figures are in satisfactory agreement with the accepted decay schemes for Na24 and Co60, and the Metzger Deutsch scheme for I131. The principles of the method and the factors which limit accuracy are discussed in some detail. In the case of the β-ray measurements, errors arising from the finite size of the chamber and the use of gelatine linings of thickness less than the maximum β-ray range of the isotope under investigation are evaluated experimentally. It is concluded that when all sources of error are taken into account absolute γ-ray energy measurements may be considered reliable to about 4 per cent., β-ray measurements to about 6 per cent., and the ratio of β- to γ-ray energy to about 5 per cent. for the isotopes studied.