Search

The design, construction, and performance of a segmented-target, cathode-strip, tracking-detector is discussed. The chamber was made of low- Z materials in order to allow photons to leave the target region. It was used to determine the reaction vertex of stopping kaons, and was successfully operated in a high-intensity kaon beamline at the Alternating Gradient Synchrotron at Brookhaven National Laboratory. The vertical and horizontal resolutions of the stopping kaon reaction positions were σ X ∼0.454 mm and σ Y ∼1.180 mm , respectively. The uncertainty in the longitudinal ( Z ) direction is given by one-half the thickness of a target segment.

π + and π − production cross sections for 800-MeV protons on C and Cu have been measured at laboratory angles of 0°, 3°, 5°, 7°, 10°, 15°, and 20°. Pions were analyzed using the High Resolution Proton Spectrometer (HRS) facility for momenta from 364 to 675 MeV/ c . Particle identification was made utilizing a time-of-flight method. We estimate the total systematic and statistical error to be ±15% for measurements at 0° and 3° and ±10% at other angles. These data have been used to determine the optimum energy and pion production angle for injection into a proposed superconducting accelerator for pions. Protons are the main source of contamination for a π + beam. Proton-to-pion ratios are given for laboratory angles of 5° and larger.

A fast instability with beam loss is observed in the Los Alamos Proton Storage Ring (PSR) when the injected beam current exceeds a threshold value, with both bunched and unbunched beams. Large coherent transverse oscillations occur prior to and during beam loss. The threshold depends strongly on rf voltage, beam-pulse shape, beam size, nonlinear fields, and beam environmental. Results of recent observations of the instability are reported; possible causes of the instability are discussed. Recent measurements and calculations indicate that the instability is an “e-p”-type instability, driven by coupled oscillations with electrons trapped within the proton beam. Future experiments toward further understanding of the instability are discussed, and methods of increasing PSR beam storage are suggested.

A design study for a Pion Linac (PILAC) at LAMPF is underway at Los Alamos. We present here a reference design for a system of pion source, linac, and high-resolution beam line and spectrometer that will provide 10 9 pions per second on target and 200-keV resolution for the ( π + , K + ) reaction at 0.92 GeV. A general-purpose beam line that delivers both positive and negative pions in the energy range 0.4–1.1 GeV is included, thus opening up the possibility of a broad experimental program as is discussed in this report. A kicker-based beam sharing system allows delivery of beam to both beamlines simultaneously with independent sign and energy contro. Because the pion linac acts like an rf particle separator, all beams produced by PILAC will be free of electron (or positron) and proton contamination.

A design study for a Pion Linac (PILAC) at LAMPF is under way at Los Alamos. We present here a reference design for a system of pion source, linac, and high-resolution beam line and spectrometer that will provide 109 pions per second on target and 200-keV resolution for the (π +, K+) reaction at 0.92 GeV. A general-purpose beam line that delivers both positive and negative pions in the energy range 0.4–1.1 GeV is included, thus opening up the possibility of a broad experimental program as is discussed in this report. A kicker-based beam sharing system allows delivery of beam to both beam lines simultaneously with independent sign and energy control. Because the pion linac acts like an rf particle separator, all beams produced by PILAC will be free of electron (or positron) and proton contamination.

A particle-tracking program has been written for simulating the acceleration cycle of a rapid-cycling proton synchrotron. A lattice can consist of up to 100 cells and rf cavities. Transport of the beam in six dimensions includes all second-order optical terms. The rf field and proton velocity are treated exactly. Longitudinal space charge is handled in a self-consistent manner. The fluctuations due to the finite number of particles are handled by a Gaussian smoothing algorithm. The program runs on a VAX 11/780 and can track 100 particles without space charge through the full acceleration cycle from 0.8 to 32 GeV in 49 minutes. A thousand particles with space charge takes about ten hours of computer time.

Protons are accumulated into the low-energy booster of the SSC (Superconducting Super Collider) by utilizing H/sup -/ to H/sup +/ conversion in a 225- mu g/cm/sup 2/ carbon stripping foil. Synchronous injection is performed for 26 turns into stationary RF buckets, thereby allowing operation with variable bunch spacing. By injecting the beam offset in x and y, the required RMS normalized transverse emittance area of 0.75 pi mm-mr is obtained. Similarly, the required RMS longitudinal emittance area of 1.75 mu *10/sup -3/ eVs is obtained by injecting single linac micropulses, centered at phi =0 and dp/p=+0.12%, into each 49.9-MHz RF bucket formed with an RF voltage of 350 kV. The transverse space-charge tune shift is -0.17 for 10/sup 10/ protons/bunch accumulated at 600 MeV. >

Proposed designs for kaon factory accelerators require that the RF cavities support beam currents of the order of several amperes. The beam current has Fourier components at all multiples of the RF frequency. Empty RF buckets produce additional components at all multiples of the revolution frequency. If a Fourier component of the beam coincides with the resonant frequency of a higher-order mode of the cavity, which is inevitable if the cavity has a large frequency swing, significant excitation of this mode can occur. The induced voltage may then excite coupled bunch mode instabilities. Effective means are required to damp higher modes without significantly affecting the fundamental mode. A mode damping scheme based on coupled transmission lines has been investigated and is reported. Theoretical analysis and measurement indicate that this scheme is effective for damping higher-order TEM (transverse electromagnetic) modes without significantly affecting the fundamental mode. >

A method for measuring the response of a beam current monitor is described, and response and impedance measurement results for a Proton Storage Ring (PSR) wall current monitor are reported. The through-short-delay calibration method (TSD) is extended to measure the response of a current monitor embedded within hardware that interfaces to a network analyzer. Error correction parameters generated with the TSD-calibration are used to calculate the actual current present at the current monitor. The results show a marked increase in impedance due to the cables and combiners. >

The beam diagnostics for the Los Alamos Proton Storage Ring (PSR) are being upgraded in several areas, including the closed-orbit beam-position system, the high-frequency longitudinal and transverse beam diagnostics, and the extraction-line beam-position monitoring system. The closed-orbit beam-position measuring system is based on detecting the 201 MHz modulation on the injected beam, which disappears in about 10 mu s, due primarily to the beam's momentum spread (about +or-0.1%), and the consequent spread in the revolution frequencies. Thus, although the first few turns of the injected beam are monitored with the system, the main body of the stored beam, which has lost its 201 MHz component, is not. In order to monitor the position of the stored beam, the ring beam-position system is being redesigned to operate at the revolution frequency, 2.8 MHz. >

A prototype RF cavity and RF drive system for a hadron facility main ring has been designed and is tested in the Proton Storage Ring (PSR) at Los Alamos National Laboratory (LANL) as part of a collaborative effort between LANL and TRIUMF. The cavity uses an orthogonally biased ferrite tuner. The design provides for accelerating gap voltages up to 200 kV for the 49.3-50.8-MHz range. Progress on the cavity construction and testing is described. >

In the high-intensity unbunched-beam experiments carried out in the Proton Storage Ring (PSR) at Los Alamos National Laboratory, the threshold current of the vertical transverse instability showed pronounced differences when the betatron tune varied across an integer. Experimental observations are presented, and the possible relations between the threshold current and the machine impedance are discussed. The possible effects related to the distorted closed orbit are also discussed. It was found that the behavior of the threshold current for vertical tune near the integers 2 and 3 could be related to the resistive-wall-type instability of modes n=2 to 4 together with the space-charge effect. It is conjectured that the closed-orbit distortion and a nonuniformly distributed asymmetric transverse impedance may contribute to some degree to the discontinuity of the threshold current when the vertical tune crosses an integer. >

The study of a possible chopping system for the Advanced Hadron Facility (AHF) and the Superconducting Super Collider (SSC) is presented. A 200 MHz RFQ (radio-frequency quadrupole accelerator) may be preferable to lower-frequency structures for the injection linacs of the AHF and SSC. To achieve a pulse frequency of 50 MHz, a chopper must be developed to eliminate three out of four bunches at the tenth of a percent level. Conventional choppers suffer from risetime limitations due to the finite separation of the deflecting plates. One alternative is a spectrometer chopper which modulates the energy of each bunch and then separates the bunches with a spectrometer transport. Initial design studies are presented for this concept. >

The Superconducting RF Cavity Development Program at Los Alamos has designed, fabricated, and tested single-cell niobium cavities at 3 GHz and 805 MHz. This work is being done in preparation for procuring and testing a multicell niobium cavity. The multicell cavity is designed to accelerate protons at /spl beta/=0.9; initial tests will be without beam. Programmatic changes have required us to modify our plans to install a 6800 litre helium cryostat and a 12.8 g/s helium pump. We will use an installed cryostat to test the multicell cavity. Also, the cavity will be modified from a seven-cell to a four-cell structure to match the dimensions of the installed cryostat. Previous reports concentrated on 3 GHz results. In this paper, some of the latest results of the 805 MHz cavity tests are presented. Modifications to allow high pulsed power testing on 805 MHz single- and four-cell cavities are proceeding. Glow discharge cleaning of an 805 MHz niobium cavity resulted in a decrease in cavity performance. The cavity was restored to previous performance levels with buffered chemical polishing. Initial results with high-pressure water cleaning show the process is useful in restoring cavity performance. >

Developers at the Proton Storage Ring have long desired a modulator and electrode combination capable of kicking the 800 MeV proton beam enough to conduct tune measurements with full intensity beams. To provide tune data at any time throughout the accumulation cycle, a pinger system has been developed. In addition, to tune data the system described here can provide a series of kicks synchronized with the area between bunches. A 4 m electrode has been designed and constructed for this purpose. The design is flexible in that the electrode may be split in the center and rotated in order to provide vertical and horizontal electrodes each 2 m long. In addition, two solid-state pulse modulators that can provide 10 kV in burst mode at up to 700 kHz have been purchased. This hardware and its intended use are described. >

In recent operation of the Los Alamos Proton Storage Ring (PSR), the vertical and horizontal tunes have been moved closer to the integers ( nu /sub y/=2.12, nu /sub x/=3.17) to enlarge the low-loss working region. In this region, the beam can be significantly affected by space charge. The first observed effects are a nondestructive distortion of the beam profile and vertical growth of beam size sufficient to keep the shifted tunes from crossing the integer, but without large beam loss. At higher intensities, or with tunes closer to the integer, beam blow-up, accompanied by beam losses, can occur. A report is presented on recent observations of this intensity-dependent effect and implications for future PSR operation are discussed. >

A pion linear accelerator (PILAC) is being designed as a new experimental facility for the Los Alamos Meson Physics Facility (LAMPF). The design goal is a flux of 10/sup 9/ pions per second at an energy of 920 MeV into a spectrometer having a resolution of 200 keV. To meet this design goal, the system will have to accept a large phase space of particles which, in turn, implies that higher-order aberrations will be significant and have to be corrected. The computer program MOTER is being used to investigate the size of the aberrations and their effect on the resolution of the system. To meet this challenge a number of improvements were made to MOTER. This work describes those improvements, shows how MOTER can be used to design the high-resolution channel, and indicates the direction that future developments of this program will take. >

The peak intensity of the PSR is limited by a fast transverse instability. In 1996 we started a project to upgrade the PSR to 200 /spl mu/A at 30 Hz, which requires operation above the instability threshold achieved with our present RF system. We have, therefore, resumed our experimental program to understand and control the instability. In this paper we will present our latest data.

The ability to model and simulate beam behavior in the Proton Storage Ring (PSR) of the Los Alamos Neutron Science Center (LANSCE) is an important diagnostic and predictive tool. This paper gives the results of an effort to model the ring apertures and lattice and use beam simulation programs to track the beam. The results are then compared to measured activation levels from beam loss in the ring. The success of the method determines its usefulness in evaluating the effects of planned upgrades to the Proton Storage Ring.

An upgrade is in progress to the Los Alamos Proton Storage Ring (PSR) to allow direct injection of the H/sup -/ beam into the ring and provide a beam bump system to move the circulating beam off the stripper foil. The primary benefits of this upgrade are matching the transverse phase space of the injected beam to the PSR acceptance and reduction of foil hits by the circulating beam by a factor of ten. Foil thickness is optimized to minimize the combination of circulating-beam losses plus losses due to excited H/sup 0/ states produced at injection. An overall factor of five reduction in losses is expected. The project comprises extensive modifications of the injection line, the injection section of the ring, and the waste-beam transport line. We will discuss the goals of the project, present an overview of the technical design, and describe the status of the implementation plan.

In Proton Radiography, one of the goals is a motion picture of a rapidly moving object. The Los Alamos Proton Storage Ring (PSR) in its normal operating mode, delivers a single pulse approximately 120 ns wide (fwhm). In development runs at the PSR, we successfully demonstrated operation of a technique to deliver two pulses, each 40 nsec wide, with adjustable spacing.

A design study for a Pion Linac (PILAC) at LAMPF is under way at Los Alamos National Laboratory. The reference design for a system of pion source, linac, and high-resolution beam line and spectrometer that will provide 10/sup 9/ pions/s on target and 200-keV resolution for the ( pi /sup +/, K/sup +/) reaction at 0.92 GeV is presented. A general-purpose beam line that delivers both positive and negative pions in the energy range of 0.4-1.1 GeV is included, thus opening up the possibility of a broad experimental program. A kicker-based beam sharing system allows delivery of beam to both beam lines simultaneously with independent sign and energy control. Because the pion linac acts like an RF particle separator, all beams produced by PILAC will be free of electron (or positron) and proton contamination. >

A Pion Linac (PILAC) is being designed for LAMPF. Together with its high resolution beam line and spectrometer, the system is optimized to provide 109 pions per second on target and 200‐keV resolution for the (π+, K+) reaction at 920 MeV. There will also be an achromatic beam line capable of utilizing the maximum energy available, thus opening up the possibility of a broad experimental program as is being discussed at this workshop.

A beam of 2 × 1010 protons/s was focused onto a small area on the high-field iris of a superconducting cavity operating at the resonance frequency. The input, reflected, and stored power were monitored. The cavity remained in steady state during this test. We conclude that such superconducting cavities will remain viable in the high-proton-flux environments proposed in the design of a superconducting accelerator for pions (PILAC).

A distorted-wave impulse-approximation analysis of 180-MeV ..pi../sup + -/ inelastic-scattering data to the 2/sup +//sub 1/ and 3/sup -//sub 1/ states in /sup 42,44,48/Ca is used to extract the neutron and proton (alternatively, isovector and isoscalar) multipole matrix elements for exciting these states. Model-dependent errors are examined by comparing results of calculations using collective-model form factors with those using form factors fitted to electron inelastic-scattering data.

Differential cross sections for elastic and inelastic scattering of 800 MeV protons from 58 Ni have been measured to momentum transfers of 4 fm −1 . The elastic scattering data were fit using a phenomenological optical model potential. The inelastic scattering was analyzed in the distorted wave Born approximation (DWBA) to obtain deformation lengths.

Angular distributions for the elastic and inelastic scattering of 0.8 GeV protons from /sup 12/C, /sup 13/C, and /sup 208/Pb have been measured. Reported are data for the ground, 4.4 MeV 2/sup +/, 7.6 MeV 0/sup +/, 9.6 MeV 3/sup -/, and 14.1 MeV 4/sup +/ states of /sup 12/C; the ground, 3.1 MeV 1/2/sup +/, 3.7 MeV 3/2/sup -/, 6.9 MeV 5/2/sup +/, 7.6 MeV 5/2/sup -/, and 11.9 MeV () states of /sup 13/C; and the ground, 2.6 MeV 3/sup -/, and 3.2 MeV 5/sup -/ states of /sup 208/Pb. Analyses of the elastic angular distributions are made using the partial wave formalism and the Kerman-McManus-Thaler approach to the nucleon-nucleus optical potential; a realistic spin-orbit term is included. The inelastic transitions are analyzed within the framework of the distorted-wave Born-approximation, using transition strengths consistent with previous low-energy studies of inelastic scattering. A simple single-particle-plus-excited-core model is used for /sup 13/C. In terms of this analysis, an assignment of J/sup ..pi../ = (5/2,7/2)/sup +/ is made for the 11.9 MeV state in /sup 13/C.

Differential cross sections for the inelastic excitation of /sup 12/C by protons have been measured at 0.8 GeV; the range of the angular distribution corresponds to momentum transfers of 0.7--2.4 fm/sup -1/ (1--3.3 m/sub ..pi../). Data for the 1/sup +/(T = 0), 1/sup +/(T = 1), 2/sup +/(T = 1), and the 2/sup -/(T = 1) states at 12.71, 15.11, 16.11, and 16.58 MeV, respectively, have been obtained. These states, as well as the 2/sup +/(T = 0) state at 4.44 MeV, provide a sensitive test of different parts of the effective N-N interaction at 0.8 GeV. We conclude that the differential cross sections for the /sup 12/C excitations can be adequately described in the distorted-wave impulse approximation using a recently published t-matrix interaction.

The pion double-charge exchange reaction (${\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}}$) has been used to measure the ground-state masses of $^{12}\mathrm{O}$, $^{16}\mathrm{Ne}$, $^{24}\mathrm{Si}$, and $^{32}\mathrm{Ar}$. The mass excesses were found to be 32.059(48), 24.051(45), 10.682(52), and - 2.181(50) MeV, respectively. These are the first reported measurements of the masses of $^{24}\mathrm{Si}$ and $^{32}\mathrm{Ar}$ and the values for $^{12}\mathrm{O}$ and $^{16}\mathrm{Ne}$ are improved over previous results. Good agreement with the isobaric multiplet mass equation $M=a+b{T}_{z}+c{{T}_{z}}^{2}$ is obtained for the known members of all four quintets.NUCLEAR REACTIONS Pion double-charge exchange, $^{9}\mathrm{Be}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{9}\mathrm{C}$, $^{12}\mathrm{C}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{12}\mathrm{O}$, $^{13}\mathrm{C}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{13}\mathrm{O}$, $^{16}\mathrm{O}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{16}\mathrm{Ne}$, $^{24}\mathrm{Mg}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{24}\mathrm{Si}$, $^{32}\mathrm{S}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{32}\mathrm{Ar}$, $E=180$ MeV, measured $Q$ and $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$ (5\ifmmode^\circ\else\textdegree\fi{}).

The first angular distributions for pion double charge exchange to discrete nuclear states are reported. The analog and nonanalog states are found to be equally strongly populated. The-direct, surface dominated nature of the reaction is clearly demonstrated by the angular distribution shapes. It is shown that in order to produce detailed agreement with the data, the present ideas for the pion charge-exchange form factors may need to be drastically revised.

Differential cross sections ${\ensuremath{\sigma}}_{{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}}(\ensuremath{\theta})$ for elastic and inelastic scattering of 162-MeV pions from $^{13}\mathrm{C}$ were measured at momentum transfers between 0.6 and 2.1 \ensuremath{\Elzxh} \ifmmode\cdot\else\textperiodcentered\fi{} ${\mathrm{fm}}^{\ensuremath{-}1}$. For two inelastic transitions, enhancement of ${\ensuremath{\sigma}}_{{\ensuremath{\pi}}^{\ensuremath{-}}}$ over ${\ensuremath{\sigma}}_{{\ensuremath{\pi}}^{+}}$ and of ${\ensuremath{\sigma}}_{{\ensuremath{\pi}}^{+}}$ over ${\ensuremath{\sigma}}_{{\ensuremath{\pi}}^{\ensuremath{-}}}$ were observed which are consistent with the values for pion scattering from free nucleons. The results are discussed qualitatively in terms of simple shell-model and weak-coupling-model configurations.

The differential cross section for the reaction /sup 12/C(p,p')/sup 12/C* (15.11 MeV, 1/sup +/, T=1) has been measured at 800 MeV; the range of the angular distribution corresponds to momentum transfers of 0.7--2.4 fm/sup -1/ ((1-3.3)m/sub ..pi../). The cross section decreases almost exponentially at large angles; no maximum is observed in the region where nuclear critical opalescence might be expected.

Simple delay lines have been developed for reading out active anode wire locations in multiwire proportional chambers. Anode wire positions are read out using commercial fast logic and time digitization apparatus with no special electronics required.

Elastic scattering analyzing powers and differential cross sections for 800 MeV → p + 54Fe, 58,64Ni are reported. An approximately mode-independent technique is used to extract information concerning the neutron density distributions of these nuclei.

Calculations indicate that a single-cell superconducting rf cavity can be used to reduce the energy spread of a secondary pion beam. Such a device would increase the pion flux in a small energy spread pion beam at the Low Energy Pion channel at LAMPF by more than a factor of 5.

The first elastic-scattering analyzing-power (${A}_{y}$) data at 0.8 GeV are presented and discussed. Angular distributions of ${A}_{y}$ over the range 2\ifmmode^\circ\else\textdegree\fi{} to 20\ifmmode^\circ\else\textdegree\fi{} (30\ifmmode^\circ\else\textdegree\fi{} for $^{12}\mathrm{C}$) have been obtained for $^{12}\mathrm{C}$, $^{58}\mathrm{Ni}$, $^{90}\mathrm{Zr}$, and $^{208}\mathrm{Pb}$ using the high-resolution spectrometer at the Clinton P. Anderson Meson Physics Facility. The analyzing powers oscillate sharply over positive values in qualitiative agreement with expectations.

Differential cross sections for the (..pi../sup -/,n) reactions in /sup 3/He and /sup 4/He have been measured at energies of 100, 200, and 290 MeV. The angular distributions for /sup 3/He and /sup 4/He are different, with the /sup 4/He characterized by an oscillatory pattern with a dip at a fixed angle of approx. = 70/sup 0/. The forward-angle cross sections show a simple dependence upon momentum transfer for both /sup 3/He and /sup 4/He. These results are discussed in the context of single-nucleon and multinucleon reaction diagrams.

Differential cross sections for the reaction /sup 3/He(..pi../sup -/,..pi../sup 0/)/sup 3/H at energies of 200, 250, 275, and 290 MeV over the angular region 80 /sup 0/ < or approx. = theta/sub c.m./ < or approx. = 150/sup 0/ are presented. Comparison is made with theoretical predictions based on Glauber theory and optical-potential calculations. Neither approach gives a satisfactory description on the data; in particular, the observed energy dependence is much smaller than the theoretical predictions.

Angular distributions for the elastic and inelastic scattering of 162 MeV ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ by Si, $^{58}\mathrm{Ni}$, and $^{208}\mathrm{Pb}$ have been measured. The elastic scattering data are fitted with optical model calculations in configuration space. Momentum-space optical-model calculations qualitatively reproduce the elastic scattering data, but substantially better agreement can be obtained if suitable modifications to the model are made. Distorted-wave impulse approximation calculations of the inelastic scattering, using both configuration-space and momentum-space models, generally reproduce the experimental data.NUCLEAR REACTIONS $^{28}\mathrm{Si}(\ensuremath{\pi},{\ensuremath{\pi}}^{\ensuremath{'}})$, $^{58}\mathrm{Ni}(\ensuremath{\pi},{\ensuremath{\pi}}^{\ensuremath{'}})$, $^{208}\mathrm{Pb}(\ensuremath{\pi},{\ensuremath{\pi}}^{\ensuremath{'}})$, $E=162$ MeV, measured $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$; optical potential and DWIA collective model analyses.

Angular distributions for elastic and inelastic scattering of approx. 50 MeV ..pi../sup +/ projectiles from targets of /sup 12/C, /sup 16/O, Si, and Fe are reported. Systematic differences between the experimental results and predictions of some first-order theories constructed from free ..pi..-N amplitudes are observed for all cases studied. These discrepancies are similar to those reported earlier. Although several improved optical models exist which take into account better treatments of the first-order potential as well as some second-order effects such as ..pi.. absorption and the Lorentz-Lorentz effect, good agreement with the data cannot be achieved without a phenomenological adjustment of the potential parameters. A purely phenomenological Kisslinger potential when used to fit the data yields potential parameters which are independent of mass number over the A region studied. The resulting p-wave parameter b/sub 1/ is close to the value predicted from free ..pi..N models, while the s-wave parameter b/sub 0/ requires severe adjustment of both real and imaginary parts from the value predicted from free ..pi..N models. The inelastic results are compared to distorted-wave Born-approximation calculations, which are seen to manifest characteristics similar to those seen in the elastic channel. A common optical potential is found to provide a goodmore » description of both elastic and inelastic scattering.« less

New differential cross sections for 0.8 GeV proton inelastic excitation of the first 2+ and 4+ states in 58Ni are compared with distorted wave Born approximation and coupled-channels predictions. Multistep processes and multi-phonon mixing are both shown to be important in describing the excitation of the 4+ state.

Energy spectra of Λ 12 C and Λ 56 Fe have been measured by means of (π+, K+) reactions at the KEK 12 GeV PS. The spectrometer PIK, which has large angular and momentum acceptance and medium energy resolution, has been constructed to study the reaction. The differential cross-section of the (π+, K+) reaction at forward angles θK∼(0÷6)o for the ground state of Λ 12 C and that for the effectively Λ-bound region of Λ 56 Fe agree well with the DWIA calculation using single-particle Λ wave functions obtained from a Woods-Saxon potential. The spectrum of Λ 56 Fe is consistent with the DWIA calculation using the realistic distribution of the hole-state strengths in55Fe.

The initial results of a systematic investigation into pion-double-charge-exchange reactions are reported. Data consisting of angular distributions and excitation functions have been measured in an effort to determine the reaction mechanism and understand its implications for nuclear physics. Cross sections are presented for (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{\ensuremath{-}}$) reactions on $^{9}\mathrm{Be}$ $^{12,13}\mathrm{C}$, $^{16,18}\mathrm{O}$, $^{24,26}\mathrm{Mg}$, $^{32}\mathrm{S}$, and $^{209}\mathrm{Bi}$. Surprising systematics of the reaction as functions of pion scattering angle and energy, as well as target mass and isospin, are revealed. The data are discussed in terms of two reaction models, one involving a higher-order optical potential and the other involving multiple reaction amplitudes.

The data acquisition and analysis system for LAMPF'S high resolution magnetic spectrometers, HRS and EPICS, consists of two on-line PDP-11/45 computers and an off-line PDP-11/60 for analysis of taped data. Each system has 124K words of memory and runs under DEC's RSX-11D operating system. The on-line computers are interfaced to several CAMAC crates through a Microprogrammable Branch Driver (MBD). Each system is also equipped with two Tektronix 4010 terminals, a Versatec printer/plotter, at least one RK05 disk drive, a 9 track 75 IPS 800/1600 BPI Kennedy tape drive, and a 40MB Diva/Calcomp disk drive system which is compatible with DEC software for their RP03. The software developed for these systems was designed to meet the goals of flexibility and speed of analysis for multiparameter data (20-100 words/event). The LAMPF standard data aquisition package "O" and its associated routines for histogram management are used as the basis of the system. A number of additional features have been added whose usefulness appears to he common to most experiments of this type.

The observation of $\ensuremath{\Lambda}$-hypernuclear levels in $_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ by associated production through the (${\ensuremath{\pi}}^{+}, {K}^{+}$) reaction is reported. The $_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ excitation-energy spectra were recorded at laboratory scattering angles of 5.6\ifmmode^\circ\else\textdegree\fi{}, 10.3\ifmmode^\circ\else\textdegree\fi{}, and 15.2\ifmmode^\circ\else\textdegree\fi{}. They show two major peaks---one attributed to the ground state, and one about 11 MeV higher. These results are compared to the strangeness-exchanging (${K}^{\ensuremath{-}}, {\ensuremath{\pi}}^{\ensuremath{-}}$) reaction. The measured cross sections are compared to relativistic distorted-wave Born-approximation calculations.

π+ and π− elastic and inelastic scattering from 18O have been measured at T(π)=164 MeV. Consistent with the results at 230 MeV, it is found that the ratio σ(π − ) σ(π + ) for the 21+ state is 1.86(16), while for the 31− state it is 0.89(6). These results are interpreted as indicating differences in neutron and proton deformations characterizing the 21+ transition and partial neutron blocking for the 31− transition. Optical model analysis of elastic scattering leads to the conclusion that 〈r n 2 〉 1 2 −〈r p 2 〉 1 2 =0.03(3) fm .