J. J. Kruse

Coulomb dissociation of 11Li.

Kinematically complete measurements for Coulomb dissociation of [sup 11]Li into [sup 9]Li+2[ital n] were made at 28 MeV/nucleon. The [ital n]-[ital n] correlation function suggests a large source size for the two-neutron emission. The electromagnetic excitation spectrum of [sup 11]Li has a peak, as anticipated in low-energy dipole resonance models, but a large post-breakup Coulomb acceleration of the [sup 9]Li fragment is observed, indicating a very short lifetime of the excited state and favoring direct breakup as the dissociation mechanism.

A large-area, position-sensitive neutron detector with neutron/γ-ray discrimination capabilities

Abstract To further study neutron-rich halo nuclei, we have constructed a neutron detector array. The array consists of two separate banks of detectors, each of area 2 × 2m 2 and containing 250l of liquid scintillator. Each bank is position-sensitive to better than 10 cm. For neutron time-of-flight measurements, the time resolution of the detector has been demonstrated to be about 1 ns. By using the scintillator NE-213, we are able to distinguish between neutron and γ-ray signals above 1 MeV electron equivalent energy. Although the detector array was constructed for a particular experiment it has also been used in a number of other experiments.

Neutron cross-talk in a multi-detector system

Abstract Two 2 m × 2 m “walls” were built for experiments with two neutrons in the final state. Each wall consists of 25 rectangular cells filled with NE-213 liquid scintillator. The close-packed design of the array makes cross-talk an inevitable contributor to distortion of measurements with this system. For E n ≤ 25 MeV almost all the detection efficiency comes from n-p scattering, and the simple two-body kinematics can be used as the basis for identifying cross-talk events. A Monte-Carlo code was developed to simulate the detection process. We found that most cross-talk events could be distinguished from real two-neutron events. A test experiment for comparison with the code was performed with neutrons from the 7 Li(p, n) 7 Be reaction at E p = 30 MeV. With this reaction all two-detector coincidences are cross-talk events. Consistency between the experimental data and the simulation results was obtained.

Neutron yields from 155 MeV/nucleon carbon and helium stopping in aluminum

Neutron fluences have been measured from 155 MeV/nucleon 4He and 12C ions stopping in an Al target at laboratory angles between 10 and 160 deg. The resultant spectra were integrated over angle and energy above 10 MeV to produce total neutron yields. Comparison of the two systems shows that approximately two times as many neutrons are produced from 155 MeV/nucleon 4He stopping in Al and 155 MeV/nucleon 12C stopping in Al. Using an energy-dependent geometric cross-section formula to calculate the expected number of primary nuclear interactions shows that the 12C + Al system has, within uncertainties, the same number of neutrons per interaction (0.99 +/- 0.03) as does the 4He + Al system (1.02 +/- 0.04), despite the fact that 12C has three times as many neutrons as does 4He. Energy and angular distributions for both systems are also reported. No major differences can be seen between the two systems in those distributions, except for the overall magnitude. Where possible, the 4He + Al spectra are compared with previously measured spectra from 160 and 177.5 MeV/nucleon 4He interactions in a variety of stopping targets. The reported spectra are consistent with previously measured spectra. The data were acquired to provide data applicable to problems dealing with the determination of the radiation risk to humans engaged in long-term missions in space; however, the data are also of interest for issues related to the determination of the radiation environment in high-altitude flight, with shielding at high-energy heavy-ion accelerators and with doses delivered outside tumor sites treated with high-energy hadronic beams.

REACTION CROSS SECTIONS IN SI OF LIGHT PROTON-HALO CANDIDATES 12N AND 17NE

Abstract Total reaction cross sections, σ R , on Si were measured near 40 A MeV for the proton-halo candidate 12 N and the two-proton-halo candidate 17 Ne, and were compared with σ R for other light proton-rich nuclei. The A -dependence shows enhanced σ R s for 12 N and 17 Ne, relative to their neighbors, but the effect is smaller than for 8 B which has been argued to have a proton halo. In general, nuclei with loosely bound last protons ( S p ⩽ 1.5 MeV) have significantly larger σ R s than their neighbors. Cross sections for charge-removal from 12 N and 17 Ne also were obtained.

Comparison of two liquid scintillators used for neutron detection

The pulse-shape discrimination capability and the scintillation e

Fragment detection system for studies of exotic neutron-rich nuclei

ciency of two liquid scintillators, BC519 and NE213 (BC501A) have been compared. Pulse-shape discrimination is not as good with BC519, but for large light pulses it should be adequate in many applications and may be a useful alternative to NE213 because it has a higher ratio of H-to-C atoms. Within 5% the scintillation e

Optical transmission of Mylar and Teflon films

ciencies are the same when the scintillators are excited by protons with energies up to 11 MeV. ( 2000 Elsevier Science B.V. All rights reserved.

Coulomb dissociation of Li11

We have developed a fragment detection system for use in studies of exotic, neutron-rich nuclei. Using a C-shaped dipole magnet, the system sweeps charged fragments and un-reacted beam particles through an angle before stopping them in an array of plastic scintillator detectors, recording time-of-flight and total energy. The system also includes a pair of silicon strip detectors to measure fragment angle of emergence from the target and energy loss for particle identification.

Erratum to: “Comparison of two liquid scintillators used for neutron detection” [Nucl. Instr. and Meth. A 440 (2000) 241–244]

In an application involving light transmission via total internal reflection, the light is attenuated at each reflection by passage through a thin film. To choose a film that would minimize the attenuation we had to measure the optical properties of Mylar and Teflon. Our results showed that type-D Mylar was preferable.