J. W. McConnell

Performance of the Recoil Mass Spectrometer and its Detector Systems at the Holifield Radioactive Ion Beam Facility

The recently commissioned Recoil Mass Spectrometer (RMS) at the Holifield Radioactive Ion Beam Facility (HRIBF) is described. Consisting of a momentum separator followed by an E-D-E Rochester-type mass spectrometer, the RMS is the centerpiece of the nuclear structure endstation at the HRIBF. Designed to transport ions with rigidities near K = 100, the RMS has acceptances of +/- 10% in energy and +/- 4.9% in mass-to-charge ratio. Recent experimental results are used to illustrate the detection capabilities of the RMS, which is compatible with many detectors and devices

The emittances and brightnesses of high-intensity negative ion sources

Abstract The emittances of high-intensity ion beams extracted from cesium sputter negative ion sources equipped with cylindrical and ellipsoidal solid tungsten and spiral-wound tantalum (General Ionex Corporation, Model 860) cesium surface ionizers have been measured for several ion species, including 12 C − , 28 Si − , 58 Ni − , and 197 Au − . While certain sets of data from the ellipsoidal and cylindrical geometry ionizer sources suggest a moderate growth in emittance with increasing negative ion beam intensity I over the range of intensities investigated (5 ⩽ I ⩽ 60 μ A) of perhaps 20%, not all data exhibit this dependence, especially those from the Model 860 source. As well, no evidence of a monotonic dependence of emittance on ion mass was found. The emittances of ion beams at the 80% intensity levels from the Model 860 source are found to be higher on the average by factors of 1.8 and 1.7, respectively, than those from sources equipped with ellipsoidal and cylindrical geometry cesium surface ionizers. Brief descriptions of the emittance-measuring device and the sources investigated are given. Emittance and brightness data for dc operation of each of the sources considered are presented and comparisons made of the results.

The HILI - a multidetector system for light ions and heavy ions

Abstract A detector system with a large acceptance, high granularity and a logarithmic response, has been built. It is well suited to detect simultaneously, heavy and light fragments from nucleus-nucleus collisions at energies higher than 10 MeV/nucleon. The angular range spanned by this detector system is ± 20° in-plane and ± 16° out-of-plane with the exclusion of a 2.5° cone around the beam axis. Coverage with a large dynamic range is provided with four large gas filled ionization chambers and behind them a 192-element hodoscope made of individual fast + slow plastic scintillation telescopes in a “phoswich” arrangement.

NE110 scintillator response to 10–100 MeV carbon ions☆

Abstract Measurements of the response of NE110 organic scintillator to 13, 34, 44, 70 and 95 MeV incident carbon ions are reported.

The use of a velocity filter in α-decay studies of microsecond radioactivities

Abstract A new method of studying microsecond radioactivities of evaporation residues produced by heavy-ion reactions is described. Forward recoiling products were separated from the beam particles by using a velocity filter and implanted into a Si(Au) detector. Their subsequent α decays were then studied with the same detector.

Fine structure in proton emission

Deformations and wave functions of proton‐radioactive nuclei are studied using measured fine structure properties of proton emission and microscopic theoretical models. The experimental data are available for 131Eu and 145Tm decays, as well as for 141gsHo, where an observation of fine structure in proton emission is reported for the first time.

Towards new proton radioactivities with radioactive beams and digital signal processing

Abstract Particle radioactivity studies using the XIA DGF-4C digital signal processing units at the Recoil Mass Separator of Oak Ridge National Laboratory are presented. Proton emission signals were observed starting from 500 ns after recoil implantation. An energy threshold below 100 keV for particle detection was achieved. For the 145 Tm and 146 Tm decay, evidence for the fine structure in proton emission was obtained. An experiment to search for a new proton emitter 149 Lu is described as an example where the combination of a 56 Ni radioactive beam and digital signal processing is a major advantage.

Prospects for future proton studies at HRIBF

Great progress has been made in the last 20 years in the study of proton emission from unstable nuclei, but the prospects for additional strides in the next several years are bright. The present main limitations on the study of proton radioactivity are related to the inability to produce copious quantities of nuclides beyond the proton drip line, and the difficulty of measuring proton radioactivity of a mass-separated nucleus in the first few microseconds of its existence. At the Holifield Facility we will attack the second of these limitations by using new signal processing CAMAC modules DGF-4C. Digitizing of the preamplifier signals should enable the analysis of a proton decay occurring at times even less than 1 microsecond after an implant in a strip detector. In the same process, the threshold energy at which we can make measurements will be lowered. These two things will hopefully enable the measurement of lower-energy, but faster decays of isotopes in the 100Sn region and below. For the latter regio...

Short-lived proton radioactivity studies at HRIBF

An accurate determination of the experimental spectroscopic factor of proton emitting nuclei precisely defines the main component of the proton wave function for the unbound state. However, this has proven difficult for nuclei with Z⩽71 due to the unknown beta-branching ratios involved. One way to solve this problem is to study proton-emitters with half-lives far too short for beta-emission to compete. Recent work at the Holifield Radioactive Ion Beam Facility has produced information on 141mHo, 145Tm, 150mLu and 151mLu, all of which have half-lives in the μs region. A comparison between calculated and experimental spectroscopic factors for these nuclei is given.

Proton decay studies of the light Lu, Tm and Ho isotopes

A double-sided Si-strip detector system has been installed and commissioned at the focal plane of the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. The system can be used for heavy charged particle emission studies with half-lives as low as a few μsec. In this paper we present identification and study of the decay properties of the five new proton emitters: 140Ho, 141mHo, 145Tm, 150mLu and 151mLu.