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Inclusive inelastic electron scattering cross sections for {sup 3}H and {sup 3}He were measured for excitation energies below 18 MeV. Longitudinal and transverse response functions were determined from these cross sections for six values of the three-momentum transfer {ital q} in the range 0.88 {lt}{ital q}{lt}2.87 fm{sup {minus}1}. A previously observed {ital C}0 multipole enhancement near threshold in the two-body channel for {sup 3}He is confirmed but is not observed for {sup 3}H. The experimental data are found to be in good agreement with two recent calculations of the longitudinal and transverse response functions. The first uses variational ground-state wave functions and the orthogonal correlated states method to describe the two- and three-body breakup channels. The second uses bound and continuum Faddeev wave functions obtained for a simple central potential. Agreement with the data is good for the first model and better for the second. The inclusion of final-state interactions (FSI) in the Faddeev continuum is found to be very important in these threshold breakup kinematics; in many cases inclusion of FSI changes the response functions by factors of two or three giving excellent agreement with the data. The transverse response functions are well reproduced, even though neither model includesmore » meson exchange currents. Ratios of the response functions for the two nuclei are also well described.« less

We have measured the [sup 12]C([gamma][sup *],[pi][sup [minus]][ital p])[sup 11]C[sub g.s.] cross section using virtual bremsstrahlung at three points at invariant masses of 1444 and 1530 MeV. At low neutron initial momentum ([ital p][sub [ital m]][approx]60 MeV/[ital c]) and large [ital N][sup *] momentum ([ital p][sub [ital N]][sup *][approx]750 MeV/[ital c]) the measured cross section is at or below the distorted wave impulse approximation (DWIA) calculation. At larger initial momentum ([ital p][sub [ital m]][approx]220 MeV/[ital c]) and smaller [ital N][sup *] momentum ([ital p][sub [ital N]][sup *][approx]500 MeV/[ital c]), the measured cross section is almost twice as large as the DWIA calculation. This discrepancy might be due to [ital N][sup *]-nucleus interactions.

Form-factor measurements in the momentum-transfer range 0.6{le}{ital q}{le}2.7 fm{sup {minus}1} are presented for the 1{sup {minus}} levels in {sup 18}O at 4.46, 6.20, 7.62, and 8.04 MeV, the 3{sup {minus}} levels at 5.10, 6.40, and 8.29 MeV, and the 5{sup {minus}} levels at 7.86 and 8.13 MeV. These are the first measurements of the 5{sup {minus}} states by inelastic scattering and the first electron-scattering measurements of the higher 1{sup {minus}} and 3{sup {minus}} states. A Rosenbluth separation of the longitudinal and transverse form factors was performed by fitting the data with a phenomenological polynomial-times-Gaussian parametrization motivated by the form of theoretical form factors when harmonic-oscillator wave functions are used. Comparisons are made with structure models. The Coulomb form factors of several levels indicate the significance of small admixtures of 3{h bar}{omega} components in the negative-parity wave functions.

We have measured missing-energy spectra for the reaction {sup 12}C({ital e},{ital e}{prime}{ital p}) in the quasielastic region in parallel kinematics at momentum transfers {ital q} of 585, 775, and 827 MeV/{ital c}. We observed {sup 1}{ital p} and {sup 1}{ital s} single-proton knockout peaks and large broad strength attributed to multinucleon knockout. We saw no increase in strength at pion threshold. The ratio of single-particle knockout to a distorted-wave impulse-approximation calculation is approximately constant with {ital q}. Multinucleon knockout is 25%--40% of the total cross section; it increases with {ital q}. This quasielastic non-single-nucleon knockout is much stronger than previously observed.

Double differential cross sections for inelastic electron scattering from {sup 4}He have been measured at bombarding energies between 279 and 725 MeV. The longitudinal and transverse response functions were obtained for constant momentum transfer between 300 and 500 MeV/{ital c}. Plane-wave impulse approximation calculations overestimate the longitudinal response and produce fair agreement with the transverse part. The Coulomb sum is determined and compared with exact calculations. Within the experimental error the data exhaust the sum rule; this provides a first measurement of ground-state correlations.

The fourth 2{sup +} state in {sup 18}O at an excitation energy of 8.21 MeV has been studied by high-resolution electron scattering. The Coulomb form factor for this state was measured in the momentum-transfer range 0.9{le}{ital q}{le}2.1 fm{sup {minus}1} and the extracted {ital B}({ital C}2){up arrow} value was determined to be 7.3{plus minus}4.2 {ital e}{sup 2}fm{sup 4}. The level at 8.21 MeV is identified as a four-particle, two-hole (4p2h) state of the type {ital p}{sup {minus}2}(sd){sup 4}. Form-factor measurements in the range 1.0{le}{ital q}{le}1.9 fm{sup {minus}1} are also presented for a strongly excited normal-parity state at 9.36 MeV. Preliminary measurements of the differential cross section for exciting this state by 135-MeV protons suggest a 2{sup +} assignment; the measured Coulomb form factor of this state allows it to be identified as the best experimental candidate for a predicted {ital K}=2 4p2h state with the four {ital sd}-shell nucleons coupled to {ital T}=0. The excitation of these states and other members of rotational bands in {sup 18}O are discussed within the framework of structure models. Shell-model calculations for the {ital C}4 form factors of the first three 4{sup +} states in {sup 18}O are compared to existing data.

From natSi (e, e′) spectra taken at 90° and 160°, we present evidence for fragmented 6− T=1 strength in 28Si. A narrow peak at 17.35±0.10 MeV excitation is shown to be consistent with 6− T=1 strength.

Inclusive inelastic electron scattering cross sections for 3H and 3He were measured for excitation energies below 18 MeV. For six values of the three-momentum transfer q in the range 0.88 < q < 2.87 fm−1, longitudinal and transverse response functions were determined. The experimental data are in good agreement with two recent calculations. One uses variational ground-state wave functions and the orthogonal correlated states method to describe the two- and three-body breakup channels. The other uses bound and continuum Faddeev wave functions for a simple central potential. The inclusion of final-state interactions (FSI) in the Faddeev continuum is found to be very important; inclusion of FSI changes the response functions in the threshold kinematics by a large amount, yielding excellent agreement with the data.

Transverse form factors have been extracted for the low-lying neutron hole (particle) states of /sup 207/Pb from inelastic-electron-scattering data. A systematic, multipolarity-and momentum-transfer-independent quenching of approx.55% in the transverse amplitude is observed when compared with single particle predictions for both electric and magnetic transitions. The magnitude of the observed effect is not readily explained by our present theoretical understanding of this nucleus.

Elastic electron scattering has been used to determine the transverse form factor of the /sup 17/O ground state in the effective momentum-transfer range 0.55 < or = q/sub epsilon/ < or = 2.8 fm/sup -1/. The data show considerable deviation from single-particle predictions; in particular, a sizable suppression of the M3 and an enhancement of the high-q side of the M5. Recent shell-model, core-polarization, and meson-exchange calculations are not adequate to explain these effects.

The /sup 12/C(e,e'p) reaction at the delta resonance has been measured for protons detected parallel to the momentum transfer at two kinematical situations: at the maximum and the low-energy-loss side of the peak. The cross section was measured for missing energies up to 320 and 220 MeV, respectively. In the missing energy spectrum two distinct structures are observed, which correspond to multinucleon knockout and quasifree pion production processes. In addition, there is a remnant of the quasifree knockout process.

Natural-parity high-spin states of J/sup ..pi../=12/sup +/ (6.10 MeV) and 10/sup +/ (4.89, 5.07, and 5.92 MeV) were observed and identified via inelastic electron scattering. Dominant single-particle--hole configurations in these excitations were deduced. The measured cross sections indicate a reduction of the transverse transition amplitude to 65% of the shell-model prediction, and the absence of an effective charge for the neutron.

The differential cross section for the /sup 16/O(..gamma..,p)/sup 15/N process has been measured in the energy range E/sub ..gamma../ = 100--400 MeV at laboratory angles of 45/sup 0/, 90/sup 0/, and 135/sup 0/. The cross sections for the (..gamma..,p) reaction leaving /sup 15/N in its ground state, in its first and second excited states at E/sub x/roughly-equal5.3 MeV, and in its third excited state at E/sub x/ = 6.3 MeV were extracted from the tip region of the proton spectra measured at a series of bremsstrahlung end point energies. The data are compared with calculations based on a direct, single-particle knockout mechanism and on mechanisms involving two particles in an intermediate state.

The $^{3}\mathrm{He}$ magnetic form factor has been measured for momentum transfers between 0.7 and 11 ${\mathrm{fm}}^{\ensuremath{-}2}$ with improved precision over previous measurements. The charge form factor has been measured for momentum transfers less than 1 ${\mathrm{fm}}^{\ensuremath{-}2}$. The charge radius was determined to be 1.935\ifmmode\pm\else\textpm\fi{}0.03 fm, and the magnetic radius 1.935\ifmmode\pm\else\textpm\fi{}0.04 fm. Comparisons are made with calculations which include meson exchange corrections and reasonable agreement is found.NUCLEAR REACTIONS $d(e, {e}^{\ensuremath{'}})d$, ${q}^{2}=0.7 \mathrm{to} 11$ ${\mathrm{fm}}^{\ensuremath{-}2}$, $\ensuremath{\theta}=160\ifmmode^\circ\else\textdegree\fi{}$, measured magnetic form factor; ${q}^{2}l1$ ${\mathrm{fm}}^{\ensuremath{-}2}$, $\ensuremath{\theta}=60\ifmmode^\circ\else\textdegree\fi{}$, measured charge radius.

We report high resolution measurements of inelastic electron scattering to all narrow normal-parity states of $^{16}\mathrm{O}$ up to 12.05 MeV, which include states with ${J}_{n}^{\ensuremath{\pi}}$(${E}_{x}$ MeV): ${0}_{2}^{+}$(6.049), ${0}_{3}^{+}$(12.049), ${1}_{1}^{\mathrm{\ensuremath{-}}}$(7.117), ${2}_{1}^{+}$(6.917), ${2}_{2}^{+}$(9.845), ${2}_{3}^{+}$(11.52), ${3}_{1}^{\mathrm{\ensuremath{-}}}$(6.130), ${4}_{1}^{+}$(10.356), and ${4}_{2}^{+}$(11.097). The measurements were performed primarily at 90\ifmmode^\circ\else\textdegree\fi{} and 160\ifmmode^\circ\else\textdegree\fi{} and span momentum transfers between 0.6 and 2.6 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. Improved line shape fitting techniques have been developed. These are the first electron scattering measurements for the ${4}_{2}^{+}$ state and of second form-factor maxima for several states. The form factor for excitation of the ${2}_{2}^{+}$ state is strikingly different from that of the other ${2}^{+}$ states and indicates a transition density peaked in the interior. Transition charge densities were extracted from a combined data set that includes earlier electron scattering data renormalized to a recent analysis of elastic scattering from $^{16}\mathrm{O}$. Comparisons have been made with several structure models, including the Brown-Green model, the weak-coupling model, a 2\ensuremath{\Elzxh}\ensuremath{\omega} shell model, and the tetrahedral alpha-cluster model.

The elastic magnetic form factor of $^{17}\mathrm{O}$ has been measured for effective momentum transfers 2.47\ensuremath{\le}${\mathrm{q}}_{\mathrm{eff}}$\ensuremath{\le}3.65 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$ by electron scattering. The form factor drops by almost three decades in this range. The data follow an extreme single-particle Woods-Saxon shell-model calculation. Many-body effects such as meson-exchange currents or core polarization do not seem to play a significant role in the q range of this experiment.

Transverse electron scattering form factors from the ground-state rotational band of /sup 181/Ta have been measured to study the single-particle contribution to the magnetization current density. The data are compared with a Hartree-Fock calculation by use of density matrix expansion with filling approximation.

The charge form factors of 17O and 18O have been measured by electron scattering, and the charge-distribution differences between these nuclei and 16O have been extracted. The spherical part of the 17O distribution is very close to that of 16O while the 18O distribution is substantially different.

We report the results of a study of high-resolution inelastic electron scattering from /sup 17/O and /sup 18/O at excitation energies between 15 and 23 MeV. Measurements were performed at 90/sup 0/ for momentum transfers of 1.4, 1.5, 1.7, and 1.9 fm/sup -1/ and at 160/sup 0/ for a momentum transfer of 1.7 fm/sup -1/. Several prominent narrow peaks were observed in the spectra of both nuclei. The measured form factors for levels in /sup 17/O at 15.78, 17.06, 20.14, and 20.70 MeV and in /sup 18/O at 18.70, 20.36, and 22.39 MeV are, within experimental uncertainties, completely transverse. These strongly excited states are assumed to arise from isovector M4 transitions of the type 1p/sub 3/2/..-->..1d/sub 5/2/. A simple weak-coupling model is used to assign spins to the levels in /sup 17/O. Finally, we also report measurements for several narrow states in both nuclei, for which the spins and parities have not yet been identified.

New electron scattering data are presented for levels of 154 Gd. The study includes the three lowest-lying 2 + levels at 0.123, 0.816, and 0.996 MeV excitation energies. These data provide a test of the Interacting Boson Approximation (IBA) prediction that three electric quadrupole transition charge densities are clearly dependent. Deviation of the experimental densities from linear dependence is presented and discussed.

High-resolution (e,e′) was used to measure the form factor of the 6−, T=1 resonance in 28Si. The results disagree with previous experimental results and with theoretical calculations. The role of meson-exchange currents in producing the observed quenching of magnetic strength, and the relevance of (e,e′) to other reactions are briefly discussed.

Differential cross sections for elastic and inelastic scattering of electrons by /sup 154/Gd have been measured for states below 1 MeV of excitation. Levels of three major collective bands are studied: the 0/sup +/, 2/sup +/, 4/sup +/, and 6/sup +/ rotational states; the 2/sup +/ gamma vibration; and the 0/sup +/ and 2/sup +/ beta vibrational levels. This study includes the first electron scattering measurements of a beta vibration. Extraction of these small inelastic cross sections required improvements in momentum resolution and detector response uniformity. Data from the rotational band are compared with axially symmetric Hartree-Fock predictions. Disagreement between the measurements and Legendre projections of the calculated density, particularly for higher multipolarity states, indicates a breakdown in the Hartree-Fock approximation or the rotational model. Small amplitude vibrations of the nuclear shape derived from the measured rotational densities agree well in shape when independently normalized to the cross section strength for both the beta and gamma 2/sup +/ vibrations, substantiating their geometrical interpretations. Once transition strength of the beta band is set, however, the strength and shape of the 0/sup +/ beta is not correctly predicted, indicating a more complicated configuration.

A focal plane system has been developed for the MIT energy-loss magnetic spectrometer. The arrival time information from adjacent wires of one MWPC (s = 2 mm), is used to trace particle trajectories with a position resolution of 120 μm (2σ) and an angular resolution of less than 17 mrad (2σ). The tracks are inclined to the MWPC at about 45°. The readout uses 3 delay lines connected to successive sence wires in a cyclical pattern. Coarse wire positions are determined by differences and drift times by sums of signal arrival times at the ends of the delay lines. A Cherenkov counter provides a fiducial signal. Interpolation is independent of drift velocity since the drift is normal to the sense plane. A similar readout with a second chamber provides position information perpendicular to momentum plane. This information is used to correct on-line for focal plane curvatures and other spectrometer aberrations. Final momentum resolution is about 10−4.

Electron scattering form factors have been measured for the first six excited states in $^{14}\mathrm{N}$ and for the 2.429-MeV (${\frac{5}{2}}^{\ensuremath{-}}$) level in $^{9}\mathrm{Be}$. The form factors for the lowest $T=1$ level in $^{14}\mathrm{N}$ along with the previously measured ground-state magnetic moment are used to specify the $T=0$ and $T=1$ wave functions for the mass-14 system assuming two $p$-shell valence particles in an $\mathrm{LS}$-coupling basis. The amplitudes of the various configurations so derived are generally in poor agreement with previous determinations, although the present wave functions yield values of the lifetime of the first $T=0$ state in $^{14}\mathrm{N}$ and of the $^{14}\mathrm{N}$ ground-state quadrupole moment that are in excellent agreement with previous measurements. The present data are not sufficiently precise to allow a direct separation of the $T=0$ and $T=1$ components for the first four negative-parity excited states. However, for two of these states which are excited primarily by $C1$ transitions, a comparison of the radiative strengths determined in this experiment with previous lifetime measurements sets a lower limit of 2% for the $T=1$ admixture.

In this article we discuss high-precision, high-resolution magnetic spectrometry as applied to electron scattering at intermediate energies (⩽1 GeV). Beginning with a brief summary of some aspects of the electron-scattering process, we develop the specifications for systems capable of achieving precision of about 1% in cross-section and 10 −4 in momentum resolution. Following a brief outline of the general formalism of magnetic optics, we describe in considerable detail the MIT DD electron energy-loss spectrometer including: (1) general optical specifications, (2) mechanical construction methods and special features, (3) focal plane instrumentation, and (4) examples of performance to date. In a concluding section we make some comparisons with more recent systems and indicate where further improvements in the MIT system may possibly be achieved.

Excited states of $^{17}\mathrm{O}$ up to an excitation energy of 15 MeV have been studied by high-resolution electron scattering for momentum transfers between 0.8 and 2.6 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. Previous electron-scattering measurements in this excitation region were confined to momentum transfers below 1.1 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$ and were of lower resolution. Form factors were measured and reduced transition probabilities determined for most excited states below 9.5 MeV. The present data are interpreted within the framework of weak-coupling models to facilitate a simple description of the observed spectrum. Particular emphasis is placed upon understanding states that are excited strongly by electric quadrupole or octupole transitions. Spins and parities have been assigned for several levels that have very narrow widths and, hence, are not amenable to partial-wave analyses involving the $^{16}$O+n and $^{13}$C+\ensuremath{\alpha} reactions. Levels at 5.87 MeV (${(3/2}^{+}$), 6.86 MeV (${(5/2}^{+}$), 7.58 MeV (${(7/2}^{+}$), and 8.47 MeV (${(9/2}^{+}$) are suggested as candidates for predominantly 5p-4h members of a ${K}^{\ensuremath{\pi}}$${=(3/2}^{+}$ rotational band. A narrow state (\ensuremath{\Gamma}\ensuremath{\le}20 keV) at 12.22\ifmmode\pm\else\textpm\fi{}0.02 MeV was observed for the first time and the existence of narrow states at 8.90\ifmmode\pm\else\textpm\fi{}0.02 and 14.72\ifmmode\pm\else\textpm\fi{}0.02 MeV was confirmed.

An effective momentum distribution in the region from about 300 to 900 MeV/c has been obtained from recent high-energy 16O(γ, p0) data. The result is compared with two different interpretations of other experimental data and with theoretical momentum distributions.

States at 6.42-, 6.75-, and 706-MeV excitation have been observed in electron scattering on /sup 2/08Pb. The transverse character of the excitation cross sections has been established. The states have been interpreted as the v (i/sub 13/2//sup -/1j/sub 15/2/)/sub 12hyphen/,/sup 14hyphen/ and the ..pi.. (h/sub 11/2//sup -/1i/sub 13/2/)/sub 12hyphen/ single-particle hole excitations of the /sup 2/08Pb ground state, on the basis of the measured momentum-transfer dependence and the magnitude of the cross section.

The electromagnetic form factors for the stronger transitions to negative parity states in /sup 24/Mg were measured for electron energies 90--280 MeV and scattering angles of 90/sup 0/ and 160/sup 0/. The isoscalar K/sup ..pi../ = 0/sup -/ and 3/sup -/ bands show form factors in agreement with open-shell random-phase approximation calculations, even though the parentages of these two bands are radically different. For the isovector negative parity states, a quenching of magnetic strength is observed; its origins are discussed.

The unique high-resolution and high-energy features of the electron-scattering facility at the MIT-Bates Accelerator were used to locate a dominant narrow resonance at 15.045 +- 0.035 MeV in /sup 24/Mg. A spin-parity assignment of 6/sup -/ and an isospin T=1 assignment were made. The M6 form factor was measured and compared to the prediction of a theoretical calculation which uses the open-shell random-phase approximation on a shell-model ground state for /sup 24/Mg.

Electron scattering cross section measurements on $^{32}\mathrm{S}$ have been made at incident electron energies between 34 and 74 MeV and at scattering angles of 162.4\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{}. Form factors were deduced for transitions to states at 8.11, 9.68, 10.05, 10.78, 11.12, and 11.63 MeV. Additional peaks at 7.12, 12.02, and 13.36 MeV were observed in some spectra. Comparisons of cross sections at different angles show that the above six transitions are transverse. Comparison of the experimental form factors with those calculated using an oscillator shell model indicate that the 8.11, 9.68, 11.12, and 11.63 MeV transitions are $M1$. Transition probabilities $B(M1)\ensuremath{\uparrow}=1.14\ifmmode\pm\else\textpm\fi{}0.18$, $0.69\ifmmode\pm\else\textpm\fi{}0.20$, $2.40\ifmmode\pm\else\textpm\fi{}0.22$, and $1.26\ifmmode\pm\else\textpm\fi{}0.20 {\ensuremath{\mu}}_{0}^{2}$, respectively, were determined for these four transitions. The $M1$ form factors and transition probabilities are also compared with other theoretical shell model calculations. The transition at 10.78 MeV is probably $M2$, or a mixture of $M2$ and transverse $E2$ transitions to unresolved states at about that energy.

We report electron scattering form factors for known 4/sup -/ states in /sup 16/O at 17.79 and 18.98 MeV. We also report statistical upper bounds for the 4/sup -/ state at 19.80 MeV. The ratios of these form factors are consistent with the isospin amplitudes derived from pion scattering data. The form factors of levels observed in (e,e') at 17.880 +- 0.015, 18.635 +- 0.020, and 20.510 +- 0.025 MeV are compatible with 4/sup -/ T = 1 assignments. Existing (..pi..,..pi..') and (p,p') spectra do not contradict these identifications. The 4/sup -/ form factors are well described by a harmonic-oscillator density with oscillator length b = 1.58 fm. This value is substantially smaller than the value of 1.77 fm obtained from the ground state charge density. The form factor of the 18.98 MeV state can also be fitted by a Woods-Saxon transition density, with parameters fitted to the elastic M5 multipole of /sup 17/O. The fit is improved by inclusion of meson-exchange currents. However, the isoscalar-isovector differences in the Woods-Saxon plus meson-exchange current form factors result in a poor fit to the 17.79 MeV state. The total isovector and isoscalar strengths observed for the established 4/sup -/ states are 41%more » and 23%, respectively, of a pure single-particle prediction.« less

Inelastic electron scattering from the low-lying even-parity states of $^{18}\mathrm{O}$ has been performed. The measurements span a range in momentum transfer from 0.6 to 2.7 ${\mathrm{fm}}^{\ensuremath{-}1}$. Form factors have been determined for the two lowest ${0}^{+}$ excitations, the three lowest ${2}^{+}$ excitations, and the three lowest ${4}^{+}$ excitations. Transition densities for the ${2}^{+}$ and ${4}^{+}$ excitations have been obtained from a Fourier-Bessel analysis of these data. Comparisons were made with the predictions of various theoretical calculations and the agreement was found generally to be poor. A coexistence model was used to decompose the measured form factors into their single-particle and collective components, which in turn were compared with their counterparts in $^{16}\mathrm{O}$ and $^{17}\mathrm{O}$. The results indicate that this model provides a useful framework within which to understand the structure of the oxygen isotopes. Transition densities also were obtained within the context of this model.NUCLEAR REACTIONS $^{18}\mathrm{O}$($e$,${e}^{\ensuremath{'}}$) low-lying even-parity excited states; measured form factors at 90\ifmmode^\circ\else\textdegree\fi{} and 160\ifmmode^\circ\else\textdegree\fi{}, $0.6\ensuremath{\le}q\ensuremath{\le}2.7$ ${\mathrm{fm}}^{\ensuremath{-}1}$; comparison to shell and coexistence models; transition densities extracted.

The high-resolution electron scattering facility at the MIT-Bates accelarator was used to resolve the 4 + 1 4.12 MeV and 2 + 2 4.24 MeV levels in 24 Mg. The respective E2 and E4 Coulomb form factors were measured and compared to form factors calculated theoretically; the 4 + 1 form factor exhibits a momentum-transfer dependence which strongly suggests that K is a good quantum number in 24 Mg.

The design and performance of a highly achromatic and isochronous system of magnets which transport a pulsed electron beam for the purpose of beam recirculation is described. The beam energy capability of the Bates electron linear accelerator has been increased from 400 to 750 MeV by the addition of this system. The isochronicity is achieved by the use of reverse bends and dipole pole edge rotations. A high degree of symmetry in the optical design and the use of sextuple corrections allow an energy band pass of 6%. The system has been used to supply beam for nuclear physics experiments with average currents of over 30 μA.

The past year has seen the completion of a major expansion of the Bates Accelerator Laboratory. A second experimental hall, South Hall, and several magnetic spectrometers have been constructed. The accelerator's maximum energy has been raised from 400 to 750 MeV by means of beam recirculation. A current two-year project for the fabrication of an additional RF transmitter plus a 30% increase in RF peak power capability will increase energy further to ca. 1 GeV. During the same period pulse-to-pulse beam sharing between the high-resolution spectrometer area and South Hall will become available. In January 1981 the Laboratory submitted their ''Proposal for a Long-Range Expansion Program'' to DOE-NSF. The proposed development consists of three stages. Stage I calls for the addition of a pulse stretcher ring to furnish a CW beam to the South Hall beam lines. Additional experimental space for internal target experiments and photon tagging research are also included. Stage II increases the accelerator energy to 2.1 GeV (at 140 microamps) by means of a five-pass head-to-tail recirculator. Stage III is, at this time, a plan rather than a proposal. It increases accelerator energy to 4 GeV by extending the accelerator length and power and adds another pulsemore » stretcher ring and three new experimental areas for the higher energy work. This paper discusses each of these stages in detail and recommends their funding and scheduling.« less

A cryogenic tritium ( 3 H 2 ) gas target system was constructed and used for a program of electron scattering studies. The 3 H 2 was supplied and safely stored as solid U 3 H 3 . For the experiments, it was transferred to a thin walled cylindrical cell, where it was exposed to 25 μA electron beams with energies up to 800 MeV. During operation, the target cell contained 115000 Ci of tritium at 225 psia and 45 K. Multiple safety enclosures surrounded both target and gas transfer systems. A microprocessor-based control and monitoring system presented target parameters to the operators, identifying those out of range. The target system operated safely and effectively for about 2000 h, enabling completion of comprehensive elastic and elastic electron scattering study of the three nucleon system.

A beam of negative pi and mu mesons was moderated to very low energies and allowed to enter a hydrogen-filled 20-atmosphere continuously sensitive cloud chamber. The various phenomena were observed and classified. A detailed study was made of the internal pair formation of mesonic gamma rays produced in the pion-hydrogen reactions. The conversion coefficient for the reaction ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}+{e}^{+}+{e}^{\ensuremath{-}}$ was found to be 0.0053\ifmmode\pm\else\textpm\fi{}0.0009; for the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}n+{e}^{+}+{e}^{\ensuremath{-}}$ the coefficient is 0.0062\ifmmode\pm\else\textpm\fi{}0.0013. Distributions in angle and energy were obtained from thirty-five of the forty-seven observed cases.

Electron scattering form factors were measured for the low-lying levels of F19 and Ca40 for momentum transfers between 0.55 and 1.00 fm−1. Elastic scattering from F19 yields an rms charge radius of 2.885±0.015 fm. Transition strengths and transition radii are obtained for the lowest 52+, 52−, and 32+ states in F19. A deformed rotational model gives a very good fit to the form factors for the positive-parity levels with ground-state deformation parameters of β2=0.41 and β4=0.17. The form factors for excitation of the 3− and 2+ states in Ca40 are analyzed by phase-shift analysis, and transition strengths and transition radii are also obtained for these levels.

A general account is given of the methods of photoneutron spectrometry using nanosecond time of flight techniques and a pulsed electron source. Included are some details of the Massachusetts Institute of Technology electron linac facility with emphasis on the experimental geometry, the electron gun, the neutrons detectors and timing and logic circuitry. Problems associated with the gamma flash, the specific bremsstrahlung associated contributions to timing accuracy and resolution, optimum pulse width and neutron detection efficiency are discussed. By means of a specific example, C 13 ( γ ,n)C 12 , the reduction of data to differential cross section is elaborated. The sources and magnitudes of backgrounds are reviewed in this example.

Measurements have been carried out of the distribution in energy and angle of the high-energy protons emitted in the photodisintegration of 6 Li, with some limited studies also of 7 Li and 12 C. The experiments were performed at the University of Saskatchewan Accelerator Laboratory using a 100 MeV bremsstrahlung beam. Protons of energies between 40 MeV and 95 MeV were detected with about 4% resolution, at eight angles from 45° to 126° by an array of plastic scintillation counter telescopes. Proton spectra for “monochromatic” photons were obtained by forming a properly normalized difference between spectra measured with 102 and 95 MeV bremsstrahlung beams. The 6 Li(γ, p) data are compared with the prediction of a phenomenological quasi-deuteron model, and this model is found to reproduce satisfactorily the shape and scale of the data over the entire range of the measurement. The experimental results are also discussed in terms of a single-particle model. A Born approximation calculation using shell-model wave functions does not provide sufficient amplitudes at high momenta to account for the 6 Li(γ, p) data.

The ( gamma ,n) reaction is discussed as a method for obtaining data on the spin dependence of level spacings, the strength function for p and d-wave neutrons, and the distribution of partial radiation widths. The level parameters obtained for Pb/sup 208/ are presented. (C.E.S.)

The spectrum of electrons arising from the decay of the negative mu meson has been determined. The muons are arrested in the gas of a high pressure hydrogen filled diffusion cloud chamber. The momenta of the decay electrons are determined from their curvature in a magnetic field of 7750 gauss. The spectrum of 415 electrons has been analyzed according to the theory of Michel. The shape parameter, {rho}, is found to be 0.64 {plus_minus} .10. The significance of this result in terms of the beta interaction is discussed.