H.A. Enge

Split-pole magnetic spectrograph for precision nuclear spectroscopy

Abstract A split-pole, broad-range magnetic spectrograph has been designed that uses the fringing fields associated with four pole boundaries to obtain two-directional focusing over the full momentum range of p max / p min ≈2.8 (energy range E max / E min ≈8). The spectrograph is also approximately second-order focusing in the plane of dispersion (median plane) over this entire range. Different magnetic configurations (pole shapes) were simulated by computer and used in a program designed to trace rays of different initial conditions through the spectrograph. These computer experiments were then used to optimize the design and resulted in an instrument for which the median-plane aberration of second order was zero or very small over the entire energy range. Measured peak shapes and resolving power are in good agreement with calculations. A resolving power better than p / Δp = 5000 has been demonstrated in the 106 Pd(d,p) 107 Pd reaction with a 50 μg/cm 2 target and a solid angle of 0.8 msterad.

QMG/2, A MAGNETIC SPECTROGRAPH FOR NUCLEAR-RESEARCH

Abstract A new magnetic spectrograph, the QMG/2, has been designed for the Kernfysisch Versneller Instituut, Groningen. It is similar to the Q3D spectrographs in use at several nuclear physics laboratories but includes some new features. Among these are a second multipole, a straight focal plane, constant dispersion, constant angle of incidence (45°) on the detector, and a device called a “snake” used to adjust mechanically the effective shape of the field boundaries after manufacture.

Magnetic spectrographs and beam analyzers

Abstract A brief discussion is given of some of the magnetic spectrographs and spectrometers in use today for studies of charged-particle nuclear reactions. The need for new instruments with improved resolving power, higher accuracy, larger solid angle, and better signal-to-background ratio is acknowledged. Possible improvements in the design of time-tested spectrographs and beam analyzers, as well as entirely new approaches, are discussed.

Multiple‐Gap Magnetic Spectrograph for Charged‐Particle Studies

A spectrograph has been designed that simultaneously records broad‐range, charged‐particle spectra at twenty‐four different reaction angles, 7.5° apart, from 0 to 172.5°. At each angle, the spectrograph records a spectrum with a total energy range of about 2.3:1 and with a resolving power exceeding R=E/ΔE=1000, where ΔE is the full width at half‐maximum of a peak. The recorders are seventy‐two 2×10 in. nuclear‐track plates, which are developed and scanned under a microscope after the exposures. When half‐millimeter strips across the nuclear‐track plates are scanned, the information contained on the nuclear‐track plates after one exposure corresponds to about 36 000 data points. A typical exposure time with about a 0.5‐μA beam is of the order of 2 to 3 h.

Achromatic Magnetic Mirror for Ion Beams

A new type achromatic or nearly achromatic deflecting magnet for ion beams is discussed in this paper. The magnetic field in the x‐y (median) plane is given by B=0 for x 0. The particles enter the field through the origin at an angle α with the x axis, go through a loop of 180°+2α, and leave the field by again crossing the y axis at the origin or close to the origin. Several cases are studied with the field exponent n=1 or close to unity and with deflection angle 270°(90°) or nearly so.

Combined Magnetic Spectrograph and Spectrometer

A combination instrument is proposed in which a broad‐range magnetic spectrograph can be operated as such or in connection with a magnetic quadrupole lens to form a high‐intensity spectrometer. A solid angle of approximately 10−2 steradian can be attained with this spectrometer without use of very large magnet gaps.

PERFORMANCE OF A QDDD SPECTROGRAPH.

Abstract A new type magnetic spectrograph for charged-particle nuclear-reaction studies has been put into operation in conjuction with the Heidelberg MP-Tandem Van de Graaff accelerator. The main elements of the spectrograph are a quadrupole magnet and three dipoles (deflecting magnets). It is therefore called the QDDD or Q3D spectrograph. The instrument has an acceptance solid angle of 13 msr, a range E max / E min = 1.21 and a resolving power of the order of p / Δp = 10 4 . Other features of the instrument include a multipole used for magnetic correction of kinematic broadening and other aberrations and an electrostatic deflector for separation of particles according to their specific mass m / q .

A Single arm spectrometer detector system for high-energy heavy ion experiments

The recent availability of 14.6 GeV/c per nucleon 16O and 28Si ions from the Brookhaven National Laboratory Tandem-AGS accelerator facility has prompted the design, construction and operation of a large-solid-angle (25 msr) magnetic spectrometer with particle identification from ∼0.5 to ∼4.7 GeV/c. A small-solid-angle Cherenkov counter complex views the target through the magnet and extends the particle identification up to ∼15 GeV/c. This experiment (E-802) employs event characterization detectors, a charged-particle multiplicity array, a highly segmented lead-glass detector, and a zero degree calorimeter. The facility measures momentum spectra of identified heavy-ion-produced hadrons with high resolution (Δp/p≤0.005) as a function of collision centrality given by triggers from the event characterization detectors. Construction and performance details of the spectrometer components and auxiliary detectors are described.

Optical design of the TOFI (time-of-flight isochronous)spectrometer for mass measurements of exotic nuclei

Abstract The design of a novel recoil time-of-flight isochronous spectrometer for systematic mass measurements of nuclei which lie far from the valley of β-stability is described. Using a four identical cell approach, optical aberrations of the spectrometer are minimized resulting in a calculated flight-time mass resolving power of m Δm = 2000 . With the spectrometer designed for a solid angle acceptance of μ = 2.8 msr and a momentum over charge acceptance of ( Δp ze )/( p ze ) = ± 2% , use of the high intensity proton beam at LAMPF will facilitate good statistics experiments yielding new direct mass measurements with uncertainties of 30 keV to 1 MeV (depending on production rates) for nuclei with A

Magnetic spectrographs for nuclear reaction studies

Abstract A brief introduction is given to the terminology of ion optics as applied to magnetic spectrographs. First-order resolving power and aberration-limited resolving power are defined. Several examples of magnetic spectrographs are described and the main characteristics tabulated. Kinematic broadening and means of correcting it are discussed. Limitations to the final resolution imposed by target rather than spectrograph effects are treated next with special emphasis on heavy-ion reactions. Finally, one example of a multigap spectrograph is described.