A. M. Vander Molen

Particle identification via pulse-shape discrimination with a charge-integrating ADC

Abstract A charge-integrating ADC has been used to sample the intensity in two different time regions of a pulse and thus to sense the shape of the pulse. This idea has been applied to produce neutron/γ-ray discrimination from pulses in a liquid scintillation detector. Optimization of available parameters yields good pulse-shape discrimination for pulses greater than those produced by 100 keV electrons. The method uses only general purpose electronics.

The use of radioactive nuclear beams to study the equilibration of the N Z degree of freedom in intermediate-energy heavy-ion reactions

Abstract The effect of the neutron to proton ratio of the colliding system on the isotope ratio of the emitted fragments (1 ⩽ Z ⩽ 5) was studied for for a variety of constant mass beam-target combinations. To extend the N Z ratio as far as possible, one of the projectiles employed, 40Cl, was a radioactive secondary beam. The isotopic ratios depend on the N Z of the target and beam in a way which is not consistent with N Z > equilibration on the timescale of the emission of intermediate-mass fragments.

The STAR endcap electromagnetic calorimeter

The STAR endcap electromagnetic calorimeter will provide full azimuthal coverage for high-pT photons, electrons and electromagnetically decaying mesons over the pseudorapidity range 1.086⩽η⩽2.00. It includes a scintillating-strip shower-maximum detector to provide π0/γ discrimination and preshower and postshower layers to aid in distinguishing between electrons and charged hadrons. The triggering capabilities and coverage it offers are crucial for much of the spin physics program to be carried out in polarized proton–proton collisions.

Fragment production in noncentral collisions of intermediate-energy heavy ions

The defining characteristics of fragment emission resulting from the non-central collision of 114Cd ions with 92Mo target nuclei at E/A = 50 MeV are presented. Charge correlations and average relative velocities for mid-velocity fragment emission exhibit significant differences when compared to standard statistical decay. These differences associated with similar velocity dissipation are indicative of the influence of the entrance channel dynamics on the fragment production process.

The light response of plastic scintillator and the calibration of large arrays

Abstract The light response function for both fast and slow plastic scintillator (BC-412 and BC-444) has been studied in a series of experiments with phoswich (fast/slow plastic scintillator) detectors. The light response of the slow plastic element was determined as a function of the charge (Z), the mass number (A) and the energy(E) deposited by incident particles that were stopped within the scintillator material. The light response of the fast scintillation element was determined as a function of Z, A and E for both stopping and for transmitted particles. The response function was found to be independent of particle species for fragments that were transmitted through the scintillator. The response functions are independent of experimental configuration and are not specific to individual detectors. A method for the analysis of phoswich spectra which employs these calibration functions is developed. This method is suitable for calibrating large numbers of detectors.

Bragg curve spectroscopy in a 4π geometry

Abstract Ionization counters employing Bragg curve spectroscopy have been constructed for use in a 4π geometry. These detectors compare very favorably in terms of both energy and charge resolution with small solid angle devices. These detectors have a large dynamic range because they are backed by scintillation detectors, and are thus capable of detecting and identifying particles with energies from 1 MeV/nucleon up to 200 MeV/nucleon.

Impact parameter dependence of high energy gamma ray production in heavy-ion collisions☆

Abstract High energy photons ( E γ ⩾30 MeV) have been measured in coincidence with light particles observed in a multidetector array for the 40 Ar+ 51 V system at a bombarding energy of E A =65 MeV . Double differential cross sections were obtained as a function of the midrapidity charge representation of the centrality of the collision. The inverse slope parameter increases with centrality more strongly than predicted by a BUU model.

Excitation and decay of projectilelike fragments formed in dissipative peripheral collisions at intermediate energies

Projectile-like fragments (PLF:15<=Z<=46) formed in peripheral and mid-peripheral collisions of 114Cd projectiles with 92Mo nuclei at E/A=50 MeV have been detected at very forward angles, 2.1 deg.<=theta_lab<=4.2 deg. Calorimetric analysis of the charged particles observed in coincidence with the PLF reveals that the excitation of the primary PLF is strongly related to its velocity damping. Furthermore, for a given V_PLF*, its excitation is not related to its size, Z_PLF*. For the largest velocity damping, the excitation energy attained is large, approximately commensurate with a system at the limiting temperature

Fragment isospin as a probe of heavy-ion collisions

Isotope ratios of fragments produced at mid-rapidity in peripheral and central collisions of 114Cd ions with 92Mo and 98Mo target nuclei at E/A = 50 MeV are compared. Neutron-rich isotopes are preferentially produced in central collisions as compared to peripheral collisions. The influence of the size (A), density, N/Z, E*/A, and Eflow/A of the emitting source on the measured isotope ratios was explored by comparison with a statistical model (SMM). The mid-rapidity region associated with peripheral collisions does not appear to be neutron-enriched relative to central collisions.

A multitasking, multisinked, multiprocessor data acquisition front end

A description is given of a generalized data-acquisition front-end system that is based on MC68020 processors running a commercial real-time kernel (pSOS) and is implemented primarily in a high-level language (C). This system has been attached to the back-end online computing system at NSCL by means of a high-performance Ethernet protocol. Data may be simultaneously sent to any number of back-end systems. Fixed fraction sampling along links to back-end computing is also supported. A nonprocedural program generator simplifies the development of experiment-specific code. >