John O. Stoner

Line shapes and charge identification

Abstract We present results of theoretical calculations and supporting experiments which determine optimum settings for spectrometers used in the “side-on” viewing mode to observe spectral lines emitted by fast-beam sources. These results establish the validity of the refocusing procedure. We report the expressions obtained for the refocus distance (D), the entrance slitwidth (wsopt) and exit slitwidth (wdopt) that cause the ratio of peak intensity to recorded linewidth to be maximum, and report the expression for the corresponding recorded linewidth (Δλ 1 2 opt ) . These expressions are: D ≐ (ν/c) (λ 0 /K); w sopt ≐ 1.45 λ 0 (ν/cK) 1 2 ; w dopt Δ 0.48λ 0 (ν/cK) 1 2 ; Δλ 1 2 opt ≐ 0.74 (νK/c) 1 2 s , where λ0 = the wavelength of the spectral line in the rest frame of the beam particles, ν = the speed of the excited beam (ν〈c), c = the speed of light and K is the inverse linear dispersion (plate factor) of the spectrometer. We also show that a refocused spectrometer may be profitably used with a particular method for identifying the charge of the emitting particle.

Properties of axicon systems for collecting foil-excited accelerator beam spectra

We describe properties of a particular kind of light-collecting system used for spectroscopy of light emitted by foil-excited accelerator beams. This system, built to test the possibility of obtaining narrow lines from such sources, has as its basic optical element an axicon, a conical reflector with its axis coincident with that of the accelerator beam. We consider the properties of an axicon followed by a lens and aperture and point out some criteria that are appropriate to the design of optical systems using such devices. Experimentally we find that scattering of the accelerator beam by the foil contributes significantly to spectral linewidths.

Spectral linewidth limitations set by ion-foil interactions☆

Abstract We show experimentally and theoretically that beam-foil spectral linewidths due to scattering of the ion beam in carbon exciter foils are of the order of 1–2 A for typical ion energies in the visible spectrum. The empirical relationship θ 2 = 2(m 2 /m 1 ) (ΔE v /E) , θ = rms total scattering angle, m 2 = foil atom mass, m 1 = incident ion mass, ΔE ν = ion energy loss due to nuclear collisi ns in the foil, E = incident ion laboratory energy, fits linewidth data for H, O, Ar, Xe, in the range 0.08–1.5 MeV.

Cross sections for 170.5° backscattering of 4He by the isotopes of boron for 4He energies between 1.0 and 3.3 MeV

Elastic scattering cross sections for 4He on both isotopes of boron have been measured at a laboratory angle of 170.5° in the energy range 1–3.3 MeV to an accuracy of about 7%. Self-supporting targets of natural boron (18μgcm2) and 99% enriched 10B (6μgcm2) were used. The scattering was observed to be Rutherford between 1 and 1.3 MeV for both isotopes. Previously unreported elastic scattering anomalies were observed in 10B near 1.5 and 1.65 MeV and in 11B near 1.5 and 2.05 MeV. Results above 2.1 MeV are compared to previous measurements; discrepancies of up to 50% are noted. The major features in the cross sections above 2.1 MeV are broad resonances near 2.4 MeV in 10B and near 2.6 MeV in 11B. The cross section is found to be smooth and approximately Rutherford for 11B in the energy range 2.2 to 2.5 MeV.

Casting thin films of cellulose nitrate, polycarbonate, and polypropylene

Abstract Plastic films of cellulose nitrate (collodion), polycarbonate (Lexan ™ ), and polypropylene have many uses in the production of nuclear targets, as well as in other research areas. The uses and properties of these films are summarized, and techniques for producing them by casting onto glass and other surfaces in controlled thicknesses are described. Special apparatus and precautions for producing such films in the thickness range from 0.04 μm to 10 μm, and in sizes up to 100 mm × 125 mm have been developed.

Quantification of beryllium in thin films using proton backscattering

Abstract The strong resonance in the 1H-9Be backscattering cross section near 1H laboratory energy 2525 keV has been used to determine 9Be areal densities in thin films with accuracies of about 6%. We report measured cross sections (for a 170.5° laboratory backscattering angle) for 1H on 9Be for 1H energies from 2400 to 2700 keV. The areal densities of the self-supporting Be foils used for the 1H-9Be measurements were determined from 4He-9Be backscattering measurements. We also report measured cross sections for 170.5° backscattering of 4He by 9Be for 4He laboratory energies of 500 to 4200 keV. Results of channeling measurements in epitaxial Be films on crystalline substrates are also discussed.

Determination of boron using the B(α,p)C nuclear reaction at incident energies near 3 MeV

Abstract A technique for determining boron content of thin films using the B(α,p)C reaction on both isotopes of boron is described. An incident alpha energy near 3 MeV is used and emitted protons are detected at 135° lab angle. A thin film containing a known areal density of boron is required for calibration. A comparison is made between this method and conventional elastic scattering of 4 He + ions for boron determination in thin films containing heavy elements or backings. We also present relative yield data on protons from the 10 B(α,p) 13 C and 11 B(α,p) 14 C reactinos at 135° lab angle between 1.4 and 3.3 MeV.

Lifetimes of levels in neutral strontium (Sr i)

We have measured mean lives of five levels in three different configurations in Sr i by exciting them selectively in fast beams of neutralized ions by light from an argon-ion laser, and following their time-resolved decay downstream. The mean lives of these levels are 5s5d3D3, 16.29 ± 0.24 ns; 5s5d3D2, 16.34 ± 0.13 ns; 5s5d3D1, 16.49 ± 0.10 ns; 5p2 3P2, 7.89 ± 0.05 ns; and 5s4f F13°, 34.2 ± 0.4 ns.

Collodion-reinforcement and plasma-cleaning of target foils

The preparation of evaporated target foils can often be facilitated by use of collodion coatings either on the substrate sides or on the exterior surfaces of the foils. Later, such coatings must usually be removed. Cleaning of a foil is necessary if thin layers of adhesives have crept onto the foil. Removal and/or cleaning can often be done satisfactorily with an oxygen plasma. Apparatus and procedures used for this are described. Foils that were cleaned successfully, and some that were incompatible with the cleaning process are listed.

A facility for production of improved carbon foils

Abstract Tests of an apparatus intended for the production of cracked-hydrocarbon foils have begun. Such foils are used for strippers, windows, and filters for both soft X-rays and the near infrared. Thus far, pilot quantities of such foils have been produced with various substrate materials; full-scale operation is expected by late 1984.