D. A. Bromley

The energy calibration of tandem accelerators

Abstract The beam energy homogeneity, stability and reproducibility of a model MP tandem Van de Graaff accelerator has been investigated. The 90° analyzing magnet system was calibrated using a number of (p,n) thresholds whose proton energies are known absolutely in the range from 4 to 10 MeV. The linearity of the beam momentum analysis system was then checked for higher magnetic rigidities by observing the 2 H( 16 O, n) 17 F neutron threshold for several different 16 O ionic charge states. The magnet calibration constant, obtained from a least-squares different reactions, was reapplied to the data to obtain a new set of self-consistent energies for the calibration reactions themselves. This procedure, which relies on the assumption that the data are all measures of the same calibration constant, results in smaller statistical errors for the calibration energies than those previously cited. Measurements were then extended using the linearity of the analysis system as established by the 2 H( 16 O,n) 17 F measurements to include the 12 C(p,n) 12 N, 24 Mg(p,n) 24 Al, 28 Si(p,n) 28 P, 32 S(p,n) 32 Cl and 40 Ca(p,n) 40 Sc neutron thresholds at energies of 19.658 ± 0.005 MeV, 15.286 ± 0.003 MeV, 15.669 ± 0.004 MeV, 13.899 ± 0.014 MeV, and 15.491 ± 0.003 MeV, respectively. With the exception of the 32 S(p,n) 32 Cl reaction, for which there are target difficulties, these thresholds provide the first series of calibration points in the energy range from 10 to 20 MeV.

An advanced computer-based nuclear physics data acquisition system*

Abstract A collaborating group of Yale and IBM physicists have begun a sequence of particle-gamma correlation experiments at the Yale Emperor tandem Van de Graaff accelerator, where all data acquisition, analysis, display, and experimental control functions are to be performed within the framework of a general integrated hardware-software nuclear physics data acquisition system designed for the IBM System/360 Model 44 scientific computer. The system, developed jointly by IBM Research and the Yale Nuclear Structure Laboratory, is intended to enable physicists to assemble the required hardware and software for any of a wide variety of experimental configurations with a minimum of attention to detail, and to change configuration with ease upon completion of a given experiment. The core of the system is a versatile control interface, which makes it possible to connect any of a modular and compatible series of digital output nuclear instrumentation directly to the computer by merely plugging the component directly into the control unit. Through the device of a diode plugboard, up to twenty-eight components, for which space is provided in the interface, may be designated as belonging to a given event (i.e., a particular interaction which is singled out by the experimenters event detection logic), and when that event has been detected, the data generated in the components associated with that event, headed by a word identifying the event, are transmitted to the computer completely under channel-interface control in the cycle-steal mode without interrupting the activity of the central processing unit. As many as sixteen such events may be defined and provision is made for sharing a single component among any number of events. The initial system will be provided with 1024-channel 25 MHz ramp-type analog to digital converters, 25 MHz scaler/timers, and “monitor registers”. The latter are provided to allow the system to read standard logic levels, and may be used to connect other parallel output components to the system. Design approaches for a second generation of components with performance specifications significantly superior to those of the initial system have been considered. A set of programs to perform the tasks of data acquisition, data transformation and analysis, experiment control, and CRT display is in preparation. These subroutines, compiled by a FORTRAN-like language, provide light pen as well as conventional means of communication between physicist and computer, and are intended to make the computer-based system as easy to use as a fixed wire multiparameter analyzer, with significant improvement in flexibility. The on-line processing routines will be embedded in a multiprogramming supervisor, so that compiling and debugging of process and non-process programs and general scientific computing may proceed simultaneously with on-line experiment processing when excess computing power is available.

Heavy ion reaction product identification by measurement of dE/dx and E☆☆☆

Abstract A complete system for the identification and energy measurement of heavy ion reaction products is described. The system, based on sequential measurement of specific ionization, d E /d x and energy, E , is capable of resolving the isotopes of all elements at least as heavy as oxygen. The electronic system is based on an analogue pulse multiplier which is described in detail. The effect of ionic charge state distributions on these measurements is considered.

Enhanced E1 deexcitations in 218Ra and the evolution of reflection asymmetry at moderate spins

Abstract The kinematically reversed reaction 13 C( 208 Pb, 3n) 218 Ra was used at 5.31 MeV/u to measure lifetimes of states with spins up to 15 − in 218 Ra, employing the Doppler shift recoil distance method. The higher spin states in 218 Ra exhibit enhanced E1 decays with B (E1)≈6×10 −3 W.u.. These enhanced B (E1)s suggest a new form of collective dipole deexcitation arising from a reflection asymmetric intrinsic state. The measured B (E1)s increase with spin between the I π =6 + , 7 − and 8 + states. It is suggested that, at higher spins, reflection asymmetry is enhanced as a consequence of octupole deformations stabilized by rotations or equivalently because of larger wavefunction admixture from cluster states.

Simultaneous nuclide indentification and energy measurement of nuclear reaction products

Abstract A system of particle detectors has been developed which measures the kinetic energy of nuclear reaction products and identifies their charge and mass. The method of identification is based on the Bethe-Bloch equation for the rate of energy loss of a fast heavy particle. These detectors extend this method to the identification of the isotopes of heavy reaction products such as lithium, beryllium, boron, carbon, nitrogen, and oxygen.

The identification of mirror state structure in 21Na and 21Ne

Abstract Angular correlation studies with the 24 Mg ( p ,α) 21 Na (P O ) 20 Ne reaction establish J = 5 2 and 1 2 spin assignments for the respective 3540 and 2804 keV 21Na states. Mirror pair identification between the 21Ne 2790 keV and 21Na 2804 keV states indicates a J π = 1 2 − assignment thereto.

Two methods for the fabrication of self-supporting osmium targets☆

Abstract Two methods are described for the fabrication of self-supporting isotopically enriched targets of osmium suitable for use in nuclear reaction and scattering experiments. One method leads to thin targets of 2 , the other to targets of many mg/cm 2 . A description is provided both of the apparatus and of the procedures developed.

The north american MP tandem accelerators

Abstract The main features of the six North American MP tandem Van de Graaff accelerators are summarized as well as some of their main performance characteristics. The latest accelerator-related studies, developments and improvements are described for each facility. Ongoing and proposed future developments at some of these laboratories are briefly discussed.

Performance and operational characteristics of the Yale tandem accelerator

Abstract The MP-1 tandem Van de Graaff accelerator which was initially commissioned at Yale in 1966 is presently being converted to higher gradient operation. In April 1973 the charging belt was replaced by six Pelletron chains; the installation of a newly designed set of stainless-steel electrode acceleration tubes is currently in progress. This paper summarizes performance data and operational experience gained with the original MP-1 facility and the Pelletron charging system; it also discusses the characteristics and design of the more recent conversion modifications.

A versatile data acquisition system for general gamma ray spectroscopy

Abstract A description is given of the associated hardware and instrumentation which have been designed and adapted for use in general gamma-ray spectroscopy studies involving nuclear reactions where high bombarding energies, typically available from tandem electrostatic accelerators, are employed. The function of the system is illustrated by experimental data taken from recent particle-gamma-ray angular correlation and Doppler shift lifetime measurements involving utilization of the laboratory on-line IBM 360/44 data acquisition system.