S. Rakers

Measuring the (d,He-2) reaction with the focal-plane detection system of the BBS magnetic spectrometer at AGOR

At intermediate energies, the (d, He-2) charge-exchange reaction can be used to observe Gamow-Teller strength in the direction. He-2 denotes the two-proton system being in the singlet S-1(0) state. In the present experiment the two protons, which in the laboratory frame are emitted into the forward direction, have been momentum analyzed and detected in coincidence by the same spectrometer and detector. Protons from deuteron breakup processes can induce a large accidental coincidence background because of the much larger breakup cross-section as compared to the (d, He-2) cross-section. Nevertheless, background-free He-2 spectra with a resolution of 145 keV at an incident energy of 170 MeV are obtained, allowing the identification of many levels with high precision in the residual nuclei. The essential features of the detection system and the data-acquisition and analysis techniques which make our (d 2 He) experiments possible are described. Two nuclei, C-12 and Mg-24, have been used as a test case

A DSP-BASED READOUT AND ONLINE PROCESSING SYSTEM FOR A NEW FOCAL-PLANE POLARIMETER AT AGOR

Abstract A Focal-Plane Polarimeter (FPP) for the large acceptance Big-Bite Spectrometer (BBS) at AGOR using a novel readout architecture has been commissioned at the KVI Groningen. The instrument is optimized for medium-energy polarized proton scattering near or at 0°. For the handling of the high counting rates at extreme forward angles and for the suppression of small-angle scattering in the graphite analyzer, a high-performance data processing DSP system connecting to the LeCroy FERA and PCOS ECL bus architecture has been made operational and tested successfully. Details of the system and the functions of the various electronic components are described.

Studies on the double-β decay nucleus Zn64 using the (d,He2) reaction

The (d, 2 He) charge-exchange reaction on the double-β decay (ββ) nucleus 64 Zn has been studied at an incident energy of 183 MeV. The two protons in the 1 S 0 state (indicated as 2 He) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. 2 He spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus 64 Cu with high precision. 64 Zn is one of the rare cases undergoing a ββ decay in β + direction. In the experiment presented here, Gamow-Teller (GT + ) transition strengths have been extracted. Together with the GT - transition strengths from 64 Ni( 3 He,t) data to the same intermediate nucleus 64 Cu, the nuclear matrix elements of the ββ decay of 64 Zn have been evaluated. Finally, the GT + distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell.

Testing quantum correlations with nuclear probes

We investigated the feasibility of quantum-correlation measurements in nuclear physics experiments. In the first approach, we measured spin correlations of singlet-spin (S-1(0)) proton pairs, which were generated in H-1(d,He-2) and C-12(d, He-2) nuclear charge-exchange reactions. The experiment was optimized for a clean preparation of the He-2 singlet state and offered a 2pi detection geometry for both protons in the exit channel. Our results confirm the effectiveness of the setup for these studies, despite limitations of a small data sample recorded during the feasibility studies.

On the determination of polarization observables in proton-induced reactions using large-acceptance magnetic spectrometers

Abstract For proton-induced reactions, a formalism is presented to determine polarization observables using a focal-plane polarimeter in combination with a large-acceptance spectrometer, where also the effect of the scattering in the non-dispersive plane of the spectrometer is taken into account. The inclusive proton-carbon analyzing power needed for the determination of spin observables was studied over a wide angular range and a new parameterization for this quantity was deduced.

A new wire chamber front-end system, based on the ASD-8 B chip.

Abstract The Focal-Plane Polarimeter (FPP) for the Big-Bite Spectrometer van den Berg (Nucl. Instr. and Meth. B 99 (1995) 637ff) at the KVI requires the read-out of four large-area MWPCs and two VDCs with 3872 wires in total. The EUROSUPERNOVA collaboration (SNOVA) developed a digital 16 channel preamplifier front-end board, housing two amplifier-shaper-discriminatorchips ASD-8 B. The main features of this board are a fast single-wire readout, a high integration density, a low power consumption and compatibility to common instrumentation standards. The board represents the first successfully running application of the ASD-8 for wire chamber readout.

Polarization correlations of 1S0 proton pairs as tests of hidden-variable theories

We are investigating the feasibility of nuclear physics experiments designed to overcome the loopholes of observer-dependent reality and satisfying the counterfactuality condition. In a first approach, we have measured polarization correlations of S-1(0) proton pairs produced in C-12(d, He-2) and H-1(d, He-2) reactions in one setting. The results of these measurements are used to test the Bell and Wigner-Belinfante inequalities against the predictions of quantum mechanics

High resolution study of the Gamow–Teller strength distribution starting from the ground state of 14N in the β− and β+ directions

The two charge exchange reactions 14N(d, 2He)14C and 14N(3He, t)14O were studied with high resolution in order to identify the Gamow–Teller (GT) strength distribution starting from the ground state (g.s.) of 14N in the β− and β+ directions. The isospin symmetry in the A = 14 mass system is investigated. An overview of the main features of the experimental investigation is summarized here.

Performance of an ASD-8 based wire chamber readout system

For the medium-energy proton polarimeter mounted at the focal-plane of the Big-Bite Spectrometer at Kernfysisch Versneller Instituut Groningen, a new wire-chamber readout has been developed. The charge-sensitive preamplifier is based on the ASD-8 B chip which has an input impedance of 115 /spl Omega/. This low impedance and the short integration time of 6 ns at a usable sensitivity of 5 fC allow high readout rates and low gas amplifications. This front-end circuit is mounted on all four multi-wire proportional chambers and on two vertical-drift chambers with 3872 wires in total. Measurements have been made using sources and intermediate energy protons. Special attention was given to determine the time-over-threshold properties of the circuit. The time-over-threshold capabilities of the readout system extend future applications to particle discrimination, or, in connection with other detector types, to energy-resolving readout. The operational performance of the readout system is presented.

The (d,{sup 2}He) reaction on {sup 76}Se and the double-{beta}-decay matrix elements for A=76

The (d,{sup 2}He) charge-exchange reaction on {sup 76}Se was studied at an incident energy of 183 MeV. The outgoing two protons in the {sup 1}S{sub 0} state, referred to as {sup 2}He, were both momentum analyzed and detected by the same spectrometer and detector. The experiment was performed at KVI, Groningen, using the magnetic spectrometer BBS at three angular positions: 0 deg., 2.5 deg., and 5 deg. Excitation-energy spectra of the residual nucleus {sup 76}As were obtained with an energy resolution of about 120 keV (FWHM). Gamow-Teller (GT{sup +}) transition strengths were extracted up to 5 MeV and compared with those from an (n,p) experiment at low resolution. Together with the GT{sup -} transition strengths from the {sup 76}Ge(p,n) experiment leading to the same intermediate nucleus, the nuclear matrix element of the two-neutrino double-{beta} decay of {sup 76}Ge was evaluated.