J.M. Lambert

Two-spectator quasifree processes

Abstract Two-spectator quasifree processes (graphs with two spectator particles) for the 3 He( 3 He, dd)pp reaction at the symmetric angle pairs θ = 30.1° at E 3 He = 50 MeV and θ = 37° at E 3 He = 78 MeV are investigated. The theoretical cross sections are calculated with the PWIA model. The measured cross sections are smaller but have shapes which are in good agreement with the calculation. The ratio N = experiment/theory is approximately 0.05 at 50 MeV and 0.1 at 78 MeV. The reaction 2 H(d, pp)nn also was studied at the symmetric angle pair θ = 34.8° and E 2 H = 34.7 MeV and the ratio is about 0.14.

Sputtering Analysis with PIXE

The applicability of the particle induced x-ray emission (PIXE) in the determination of sputtering distributions and yields was studied. Sputtered particles were caught on foils for the 45 keV to 125 keV self sputtering of Fe, Ni, Cu, Ti, Mo and Au and for the 90 keV sputtering of both target and implanted particles of Ni+ + Cu, Cu+ + Ni, Ni+ + Fe, and As+ + Ag, and for the target particles of Ar+ + Au. Sputtered particles were collected in an ultra high vacuum (UHV) and in a poorer vacuum system with 99.99% pure Al catcher foils. PIXE data, the x-ray yields from 1 MeV proton and 2 MeV alpha particle beam bombardments, were used to determine the angular distribution of the sputtered products. The sputtering yield was calculated from the angular disbution data by integration over a hemisphere assuming azimuthal symmetry. The efficiency of the PIXE systems was calibrated with a standardized target such as 18 ¿g/cm2 Fe on the same 99.99% Al foil material. The Al x-ray yield of the catcher foils provided a normalization of all data from a given catcher foil. For a number of samples studied, we have been able to compare the distribution and yields obtained with PIXE to those measured by the Rutherford backscattering (RBS) technique. Also separate RBS analysis of Xe markers in the sputtering targets provided yield values. Comparision of the PIXE and RBS results indicate that the PIXE sputtering distribution and yield measurements are comparable.

Effects of non-normal incidence on the implantation of copper with gold and tantalum

Abstract Copper targets were implanted with 125 keV gold and tantalum ions at selected incident angles of the beam relative to the target normal to examine the effect of the incident angle on the sputtering yields, the dose retained in the modified layer, and the atomic surface fractions. Sputtered particles were collected on aluminum foils to measure the angular distribution of the sputtered particles and to determine the partial sputtering yields of the beam and target species. A 1.5 MeV xenon beam implanted markers into the copper targets to determine the average sputtering yield for the surface during the implantation. Theoretical predictions from a surface binding energy correction model were compared with the experimental results. Although the predictions from the model were not exact, the trends of the data were in agreement with the model. The measured total sputtering yield increases with increasing incident beam angle, and, correspondingly, the fluence retained decreases with incident beam angle.

Sequential decay in the 7Li(α, t)8Be(α)4He and 7Li(α, α')7Li∗(t)4He reactions at Eα = 50 MeV

Abstract The 7 Li (α, t) 8 Be (α) 4 He and 7 Li (α, α) 7 Li ∗ ( t ) 4 He reactions have been observed in a kinematically complete experiment with E α = 50 MeV, particle identification, and on-line computer coincidence electronics. Sequential decay through the ground, 2.9, 11.4, 16.6 and 16.9, and 19.9 MeV states of 8 Be and the 4.63 and 7.48 MeV states of 7 Li has been observed. Triton angular distributions for the decay through the ground state of 8 Be were obtained with and without coincidence requirements. Agreement of these distributions implies isotropic decay in the c.m. of the 8 Be ground state. The contribution of quasi-elastic processes is small due to the specific limited portion of phase space observed.

Quasifree processes in the3He+3Hand3He+3He interactions

Abstract Quasifree scattering and quasifree reaction processes have been examined in ten 3 H + 3 He and 3 He + 3 He reactions with at least two of the three or more final state particles being charged. Beam energies of 50, 65 and 78 MeV were used. The experimental results are compared with PWIA predictions and Fourier transforms of the wave functions are extracted. The quasifree processes are described in a consistent, but qualitative, manner by the PWIA; distortion in the intial state appears to be the cause of the consistent deviation of the data from the PWIA predictions. Extracted values for the 3 H(d, 3 He)2n cross section are given.

Doppler-shift attenuation measurements on 24Mg by (α, α') and (p, p') reactions

Abstract The (α, α) and (p, p) reactions have been used to populate states in 24 Mg in order to measure lifetimes of ten states by the Doppler-shift attenuation method. The shifted γ-rays were observed by a planar 5.6 cm 3 Ge(Li) detector at 90° to the beam at the target in coincidence with the scattered particles observed in either of two particle detectors located symmetrically with respect to the beam. A computer coupled dual two-parameter arrangement permitted concurrent measurements for all states appreciably populated. The present measured transition probabilities are compared with predictions from a truncated j - j coupling shell-model calculation.

Sputtering from Binary Alloys - A Technique for Evaluating Change in Surface Binding Energy

In recent years computer simulations, experimental observations and analyses of the collected sputtered products from the interaction of ion beams on solid materials have demonstrated the sensitivity of the sputtering process to the surface characteristics of the material being investigated or modified. The usual characterization of the target material has been a post bombardment analysis of the surface for the relative concentration of the implanted atoms compared with the initial target components coupled with an examination of the profile of the implanted atoms in the surface region. Recent experiments have collected sputtered products during ion implantation and have compared the distribution of sputtered particles with theory. Techniques have been developed to measure the partial and net sputtering yields from the amount of material collected on the foils in these experiments. Typically the evaluation of the target material and the collected sputtered products has been reported for the steady state conditions during ion implantation. Our experimental group has chosen to evaluate the sputtering process from the onset of ion bombardment through the steady state condition. From these experiments models have been proposed for the behavior of the surface composition and the sputtering yields. Techniques developed for monitoring of the surface have provided data supporting the concept that the average surface binding energy of the bombarded target material is sensitive to the sputtering process. Calculating the manner in which the surface binding energy will change with the developing atomic surface fraction can qualitatively lead to more precise prediction of implantation requirements.

Single Surface Barrier Detectors for Neutron Dosimetry and Associated Light-Ion Fluxes

Surface barrier detectors can measure the characteristics of neutron fields and related light-ion fluxes (LIF). Some of us have shown that a photodiode, with a suitably chosen radiator, can measure fluences of monoenergetic neutrons and have studied the shapes of a few continuous neutron spectra. Others have used silicon detectors to measure the energy of neutrons from reactions. We have attempted to perfect a simple, compact and inexpensive single surface barrier detection system to measure both the intensities and approximate spectral shape of continuous neutron and LIFs. We have measured such fluxes for three known collimated and uncollimated neutron beams with two geometrical configurations and with at least two different thicknesses of CH2 and CD2 radiators. All neutron flux data were obtained with a Au shield in front of the detector; this was removed for LIF measurements. The known shapes of the impinging neutron beams were used to calculate the expected recoil-particle spectra and such predictions have been compared with the experimental data. Also, data have been obtained with telescopes, with carbon foil and thin detector-grade silicon foil radiators. These data allow us to estimate contributions to the higher-energy portion of the recoil-particle spectra from reactions due to the carbon in the CH2 and CD2 radiators and due to the silicon in the detector. Corrections for rim effects in the detector and multiple scattering in the radiator are calculable.

Neutron Damage to Commercial GaAsP LED Devices

On-line measurement of the degradation of a small set of commercial LED devices bombarded with a 15 MeV median energy neutron beam has been obtained. During irradiation the light output of an LED was recorded via a fiber optic link to an external area free of radiation where a photodiode detector viewed the fiber optic signal. All data were recorded on DVMs, on chart recorders and on magnetic tape with an on-line computer. The data for each LED can be described by one primary damage function and the amount of damage is rather strongly dependent on the amount of phosphorous in the GaAsP LEDs studied. The neutron energy distribution and intensity are well known from previous dosimetry measurements. Radiographic data determined that a homogeneous spatial distribution of neutron flux is used. The neutron beam was uniform over the dimension of the samples and 2 × 1010 neutrons/cm2/sec are easy to obtain.

QUASIFREE PROCESSES IN THE 2H + 3He REACTIONS

This chapter discusses quasi-free processes in the 2 H+ 3 He reactions. In the interaction between 3 He and 2 H, there are several three-particle breakup combinations possible. Kinematically, complete measurements were obtained with 2 H beam energies of 22.3 and 35 MeV and 3 He beam energies of 30.0, 33·4, and 52.5 MeV. Charged particle pairs were detected with conditions favoring the observation of quasi-free processes, both quasi-free scattering (QFS) and quasi-free reactions (QFR). The d + d, p + d, and 3 He + p QFS interactions and the 3 He + n→ p + t, d + d → p + t, and 3 He + n → d + d QFR interactions were observed. The chapter presents the analysis of data for a given interaction and comparison of a plane-wave-impulse-approximation prediction. The momentum wave function is extracted for small values of spectator momentum. Data were acquired primarily with a gas cell target having either 2 H or 3 He gas and fixed detector-aperture geometry. The results indicate that there is little difference in d 3 σ (exper)/d 3 σ (PWIA) as a function of beam energy (incoming channel CM energy), and this ratio does not depend on whether the spectator is in the projectile or in the target.