C. F. Moore

On the structure of the first three excited states in 208Pb

Abstract The nuclear structure of the first three excited states in 208 Pb is studied using inelastic proton scattering on 208 Pb at proton energies corresponding to isobaric analogue resonances in 209 Bi.

THE PROTON DECAY OF THE g/sub 9/2/ ANALOGUE RESONANCE IN

Abstract Angular distributions for the inelastic proton decay of the g 9 2 isobaric analogue resonance in 207 Bi have been measured. A characteristic group of levels in 206 Pb is found to be strongly excited in the resonance and these levels are interpreted as neutron particle-hole states with a g 9 2 particle. The levels in the group were very close lying and the detector resolution of about 15 keV was not always sufficient to separate the levels. The separation was, however, very much improved with the help of a spectrum unfolding program. Most of the angular distributions are symmetrical about 90° and they were fitted with a series of Legendre polynomials and integrated widths Γ( g 9 2 → I) for the decay of the g 9 2 resonance to these levels were deduced.

sup 207

The double isovector giant-dipolar state has been observed in the ({pi}{sup {minus}},{pi}{sup +}) {Delta}{ital T}{sub {ital z}}=+2 and ({pi}{sup +},{pi}{sup {minus}}) {Delta}{ital T}{sub {ital z}}={minus}2 double-charge-exchange reactions on {sup 40}Ca and {sup 27}Al. The resonances observed in the ({pi}{sup {minus}},{pi}{sup +}) reaction are closely related via Coulomb energy and isospin symmetry to the resonances measured in the inverse ({pi}{sup +},{pi}{sup {minus}}) reaction on the same nuclei. The new observations provide strong support for the identification of the double giant-dipole state in nuclei. The differences between the self-conjugate and non-self-conjugate cases are outlined.

Bi.

Cross sections at theta = 5/sup 0/ (lab) were obtained at seven energies for /sup 14/C(..pi../sup +/,..pi../sup -/) /sup 14/ O(g.s.) and at four energies for /sup 26/Mg(..pi../sup +/,..pi../sup -/) /sup 26/ Si(g.s.). Angular distributions have been measured for both reactions at energies of 140 and 200 MeV. The results are compared to previous angular distributions at other energies on these two nuclei, and to a series of angular distributions measured for /sup 18/O(..pi../sup +/,..pi../sup -/).

Comparison of the double giant-dipole states observed in (. pi. sup minus ,. pi. sup + ) and (. pi. sup + ,. pi. sup minus ) reactions on sup 40 Ca and sup 27 Al

Two delay-line readout drift chambers with an active area of 90 cm by 7 cm are now in use as focal plane detectors at the high resolution spectrometer Big Karl. The position resolution is better than 0.2 mm fwhm with detector efficiencies exceeding 99.5% for 45 MeV deuterons. Light ions such as protons, deuterons, alphas and others up to 6He have been measured at energies between 15 and 45 Mev per nucleon. The new detector offers a significantly higher focal plane acceptance with improved background suppression and correction capabilities.

Angular distributions for /sup 14/C,/sup 26/Mg(. pi. /sup +/,. pi. /sup -/)

The 164-MeV angular distribution for the non-analog double charge exchange reaction /sup 16/O(..pi../sup +/, ..pi../sup -/)/sup 16/Ne(g.s.) has been measured and is found to be basically diffractive. This is contrasted with the previously measured analog distribution /sup 18/O(..pi../sup +/, ..pi../sup -/)/sup 18/Ne (double isobaric analog) which is not diffractive.

The new focal plane detector for the magnet spectrometer Big Karl

Abstract A singles measurement of the quasielastic scattering of 255 MeV pions by 27 Al and 208 Pb has been made. The measured values for the ratio R of π + and π − induced cross section, averaged over all measured angles of 2.2 ± 0.2 and 1.5 ± 0.1 for 27 Al and 208 Pb respectively are substantially below the classical impulse approximation value of 11. A semiclassical nucleon charge exchange model is described for singles and coincidence measurements and is compared with the measured proton spectra. The comparison indicates that the singles proton spectra are dominated by events other than the quasielastic process whereas the coincidence data reported earlier and compared with the present calculations support the quasielastic interpretation. A strongly decreasing dependence of R on A for coincidence measurements may be interpreted as supporting the view that recoil nucleon charge exchange plays an important role in the quasielastic knockout process.

Diffractive angular distribution for /sup 16/O(. pi. /sup +/,. pi. /sup -/)/sup 16/Ne(g. s. )

Pion-nucleus elastic scattering at energies above the Delta(1232) resonance is studied using both pi+ and pi- beams on 12C, 40Ca, 90Zr, and 208Pb. The present data provide an opportunity to study the interaction of pions with nuclei at energies where second-order corrections to impulse approximation calculations should be small. The results are compared with other data sets at similar energies, and with four different first-order impulse approximation calculations. Significant disagreement exists between the calculations and the data from this experiment.

Proton yields from quasielastic pion scattering on 27Al and 208Pb

Analyzing powers [ital A][sub [ital y]] were measured for [pi][sup +] and [pi][sup [minus]] elastic scattering from polarized [sup 13]C at incident pion energies [ital T][sub [pi]] near the [ital P][sub 33] [pi]-nucleon resonance. At [ital T][sub [pi]]=130 MeV, the values of [ital A][sub [ital y]] are significantly different from zero for [pi][sup [minus]] scattering. For [pi][sup +] at [ital T][sub [pi]]=130 MeV and for both [pi][sup [minus]] and [pi][sup +] at all other energies, the [ital A][sub [ital y]] are mostly consistent with zero. Elastic differential cross sections were measured using an unpolarized [sup 13]C target. Both the analyzing-power and cross-section data were compared with predictions using a variety of nuclear structure and reaction models. The analyzing power was found to be strongly sensitive to the quadrupole spin-flip part of the transition. The data of this work complement measurements of the magnetic form factor by electron scattering. The pion [ital A][sub [ital y]] data are not reproduced by calculations using wave functions that fit the magnetic form factor at low momentum transfers.

Pion-nucleus elastic scattering on {sup 12}C, {sup 40}Ca, {sup 90}Zr, and {sup 208}Pb at 400 and 500 MeV

Analyzing powers [ital A][sub [ital y]] were measured for [pi][sup +] and [pi][sup [minus]] elastic scattering from polarized [sup 13]C at incident pion energies [ital T][sub [pi]] near the [ital P][sub 33] [pi]-nucleon resonance. At [ital T][sub [pi]]=130 MeV, the values of [ital A][sub [ital y]] are significantly different from zero for [pi][sup [minus]] scattering. For [pi][sup +] at [ital T][sub [pi]]=130 MeV and for both [pi][sup [minus]] and [pi][sup +] at all other energies, the [ital A][sub [ital y]] are mostly consistent with zero. Elastic differential cross sections were measured using an unpolarized [sup 13]C target. Both the analyzing-power and cross-section data were compared with predictions using a variety of nuclear structure and reaction models. The analyzing power was found to be strongly sensitive to the quadrupole spin-flip part of the transition. The data of this work complement measurements of the magnetic form factor by electron scattering. The pion [ital A][sub [ital y]] data are not reproduced by calculations using wave functions that fit the magnetic form factor at low momentum transfers.