N. R. Fletcher

Elastic scattering of 4He from 6Li and 7Li at 12.0 to 18.5 MeV

Abstract An optical model analysis has been applied to measured angular distributions of elastic scattering of α-particles by 6 Li and 7 Li at several bombarding energies between 12.0 and 18.5 MeV. The optical model gives a good representation of the data when a target spin-orbit, V I · l , potential is included. With V I · l ≠ 0 , a large interaction radius, ≈ 3.5 fm, for the real potential is preferred over a smaller radius, ≈ 2.5 fm.

Elastic scattering of deuterons by 6Li and 7Li at 8.0–12.0 MeV

Abstract Absolute differential cross sections for the elastic scattering of protons and deuterons by 6 Li and 7 Li have been measured with an error of ≈ 2% at selected angles and bombarding energies. The optical model is used to describe the angular distributions of the deuteron scattering at E d = 8.0, 10.0 and 12.0 MeV. The model parameters found when one uses a real potential radius between 3 fm and 4 fm are more nearly constant with changes in bombarding energy than are those obtained using a value ≈ 2 fm. The two sets of parameters represent a phase equivalent ambiguity.

The Florida State University quadrupole spectrometer

Abstract A quadrupole doublet lens refocuses particles of rigidities up to 400 MeV/c per unit charge scattered within an angular range of −15° to +140° from a 30 cm chamber onto a detection surface 3.0 m removed from the target. This system, herein to be called the quadrupole spectrometer, has been developed for the purpose of (1) reduction of noise and background during detection of charged particles, (2) magnetic rigidity band pass filtering and reduction of unwanted or overprolific beam species, (3) small-angle cross section measurements, (4) charge state determinations, and (5) time-of-flight measurements. A general description of the quadrupole spectrometer, discussion of its intended uses and examples of data obtained are presented.

The use of PIXE in generating evidence for primordial superheavy elements

Abstract The physical and chemical nature of the monazite inclusions studied through PIXE in the search for superheavy elements sharply constrained the nature of the analysis and set strict limits on the nature fo the ion beam and X-ray detection techniques.

A new Jπ = 12 + resonance in the 12C + 16O system☆

Abstract The resonance in 28Si formed in the 12C+16O system at Ec.m. = 19.7 MeV is well known and has been assigned a Jπ value of 14+. We propose that the variation in energy reported for this resonance in a number of exit channels is due to different relative contributions of the 14+ resonance and a new 12+ resonance at Ec.m. = 19.92 MeV.

Cross Section Measurements for the Forward Elastic Scattering of 13 MeV 6,7 Li and 24 MeV 16 O from 9 Be, 12 C, 16 O and 28 Si

Absolute elastic cross sections have been measured at 12.45°, 16.45°, 20.45° and 28.0° for targets of 9Be, 12C, 16O, 28Si and 197Au being bombarded by beams of 13 MeV 6,7Li and 24 MeV 16O. The reliability of a method previously proposed for low mass multielemental analysis [1,2] depends to some extent on the precision and accuracy of the cross sections reported here. The 16O-beam reactions, except the 16O + 9Be reaction, are found to be consistent with the Rutherford predictions. This allows us to obtain target thickness independent cross sections with uncertainties of approximately 7% for the reactions initiated with 6,7Li beams. Most of these cross sections are found to be non-Rutherford. Comparisons made with previous investigations give strong support to the cross section values obtained in this work.

Measurement and direct reaction analysis of the reactions 7Li(d, t)6Li and 7Li(τ, α)6Li

Abstract Angular distributions for the reactions 7 Li(d, t) 6 Li and 7 Li(τ, α) 6 Li were measured and analyzed in an energy region shown to be relatively free of compound nucleus resonance structure. Both front and back angle maxima in the measured angular distributions have been reproduced by the conventional DWBA without the inclusion of exchange effects. The zero-range DWBA calculation is a factor of 25 smaller than the 7 Li(τ, α) 6 Li cross section and a factor of 2.5 to 4.5 smaller than the 7 Li(d, t) 6 Li cross section. In a true finite-range calculation the large renormalization of the DWBA calculation is no longer necessary.

Assignment of Jπ = 6+ to two states of 16O via the 12C(α, 8Be)8Be reaction☆

Abstract Excitation functions of the reaction 12 C(α, 8 Be) 8 Be have been measured for approximate c.m. angles of 90°, 69°, and 48°, the latter two angles corresponding to P 4 ( cos θ c . m ) ≈ 0 and P 6 ( cos θ c . m . ) ≈ 0. Angular distributions were measured at bombarding energies corresponding to the two prominent resonances in 16 O at E α = 21.3 and 22.31 MeV. A J π assignment of 6 + is made for each of these states.

Investigation of lithium forward scattering for the analysis of carbon and oxygen in human amniotic fluid

Lithium forward elastic scattering is investigated as an additional method for Z<11 multielemental analysis in human amniotic fluid (AF). Concentrations of C and O are obtained from the analysis of an AF sample that is diluted with distilled water, deposited on a formvar backing and dried naturally. Solid residues of this diluted sample are bombarded with 13 MeV 6,7Li beams and the elastically scattered beam is detected at 16.45o, 20.45o and 28.0o simultaneously. The quality of elastic spectra improves with sample dilution. The content of C and O in the backing is subtracted. Carbon and oxygen concentrations of the non-diluted AF sample are determined by assuming that elemental concentration varies linearly with dilution.

Use of Rutherford forward scattering for the elemental analysis of evaporated liquid samples

Multielemental analysis of evaporated liquid samples is possible by irradiating the samples with a 16 MeV 7Li beam and detecting the elastically scattered ions at 28°. The method is easily applied when Rutherford scattering dominates. To prepare the targets, the liquid sample is deposited on a formvar backing and dried with vacuum. Preliminary results indicate a possible relationship between sample concentration, uniformity and spectrum energy resolution. Details on the spectrum analysis will be given. The method is mainly useful for multielemental quantification in the low mass region from lithium to fluorine where standard techniques such as PIXE and TXRF are useless.