L. Weissman

A new measurement of the 7Li(d,p)8Li cross section and consequences for 7Be(p,γ)8B

Abstract A novel scheme for measuring the cross section of the 7Be(p,γ)8B reaction, the major source of high energy neutrinos from the sun, is presented. The scheme involves a strictly uniform particle beam and overcomes some of the recognized experimental uncertainties of previous measurements. A new measurement of σ[7Li(d,p)8Li] has been carried out using this setup, and the present value of σ [ 7 Li(d,p) 8 Li] = 155(8) mb at the top of the Ed(lab.) = 776 keV resonance is compared with previous measurements. A new issue regarding both the (d,p) and (p,γ) reactions has been examined: reaction-product nuclei which are backscattered out of the target. Measurements and simulations carried out in the course of this investigation are presented and discussed in the context of possible effects on the measured cross sections of these reactions.

Single particle signatures in high-spin, quasicontinuum states in 193,194Hg from g-factor measurements

The average g factors of high spin, high-excitation energy, quasicontinuum structures in {sup 194,193}Hg were measured by observing the precessions of the angular distributions of {gamma}-ray transitions in several normal-deformation bands that coalesce in the decay of the entry distribution of states. The average g factors of the states leading to the three main bands in the {sup 193,194}Hg isotopes were: {l_angle}g({sup 193}Hg){r_angle}=+0.19(1) and {l_angle}g({sup 194}Hg){r_angle}=+0.26(1), respectively. These average g factors are smaller than the average of the g factors of the high energy states in the three superdeformed bands of {sup 194}Hg, {l_angle}g(SD; {sup 194}Hg){r_angle}=+0.41(8). While the nucleus in the superdeformed well behaves like a rigid rotor, the present results demonstrate the important role played by multiple, quasiparticle neutron configurations in the structure of normal-deformation, highly-excited nuclear states.

Beam profile measurements with a phosphor imaging plate

Abstract Phosphor imaging plates, which are broadly used in biological research, may have applications in nuclear physics as imaging devices. We describe here a method for beam profile measurements of light-particle beams using these imaging plates.

Tilted foil polarization of radioactive ions

The tilted foil polarization technique has been applied to a beam of radioactive 23Mg (I = 32, T12 = 11.35 s) ions from ISOLDE. To achieve sufficient energy for penetration of the foils a high voltage platform has been constructed and used for acceleration of the initial 120 keV beam of 2+ 23Mg ions to 480 keV. The resulting asymmetry ϵ of the emitted β-radiation from the 23Mg implanted into a cold Pt stopper has been measured as a function of a holding magnetic field. At B = 0.09 T a value of ϵ = −7.4(1) × 10−3 was found. The asymmetry was reduced to ϵ = −3.3(4) × 10−3 at a field below 0.005 T. It is argued that this hard core asymmetry occurs as a result of the internal interaction between the polarized nuclei and the defects created in the implantation process.

A ‘global fit’ method for analysis of angular precession measurements at large Ge γ arrays

The recent availability of large γ-ray arrays has opened new domains in experiments for measurements of magnetic moments. The study of oblate structures in heavy nuclei as well as of superdeformed bands are good examples of the new nuclear regions that have become amenable to the transient field magnetic moment measurements. These measurements are very difficult to perform even with the modern ‘4π’ Ge arrays due to the weak transitions of interest and severe background conditions. Thus, it is very important to utilize the entire power of the 4π detector in the analysis of precession measurements. We propose here a new method for analyzing such measurements in the form of a ‘global fit’ procedure. Results are presented for three high-spin transitions of interest in 193Hg.

Measurement of the magnetic moment of 23Mg using the tilted foil polarization technique

Abstract We report here on the first measurement in an experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic moments of short-lived radionuclides. The nuclei are polarized by the tilted foil technique and the resulting 0°–180° β asymmetry is monitored as a function of the frequency of the rf applied in an NMR setup. In order to achieve sufficiently high energy for transmission through the foils the experiment was mounted on a high voltage platform. In this experiment, earlier asymmetry measurements were confirmed and an NMR resonance was observed, corresponding to a preliminary value of the magnetic moment of −0.533(6) n.m., in agreement with a previous measurement. During the experiment, problems were encountered with the buildup of contamination on the stopper surface. Improvements to the experimental setup are presently being designed, aiming at improved vacuum and possibly lower temperature. This will help pave the way for measurements of magnetic moments of T = 3 2 nuclei in the s-d shell and T = 1 2 f-shell nuclei. The study of relaxation times and other solid-state phenomena in semi-conductors and other materials of interest using this technique is also contemplated.

Magnetic moments of mirror nuclei with tilted-foil polarization

We report here on an ongoing experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic moments of short-lived radionuclides, with the emphasis on magnetic moments of mirror nuclei in far-from-stability regions. The nuclei are polarized by the tilted foil technique and the resulting 0–180○ βasymmetry is monitored as a function of rf frequency applied in an NMR setup. In order to achieve sufficiently high energy for transmission through the foils, the experimental setup is mounted on a high voltage platform. The first experiment in this program was the measurement of the βasymmetry and the NMR resonance for the ground state of 23Mg (I=3/2, T1/2=11.3 s), yielding μ=−0.533(6) nm. Improvements to the experimental setup are presently being designed, to be used in conjunction with the new developments at ISOLDE for obtaining high charge-state ions from the EBIS (REX-ISOLDE) ion source. This will help pave the way for measurements of magnetic moments of T=3/2 nuclei in the s–d shell and of T=1/2 f-shell nuclei. The study of relaxation times and other solid-state phenomena in semiconductors and other materials of interest using this technique is also contemplated.

Measurement of the 7Be(p,γ)8B cross-section with an implanted 7Be target

The 7 Be(p, γ) 8 B reaction plays a central role in the evaluation of solar neutrino fluxes. We report on a new precision measurement of the cross section of this reaction, following our previous experiment with an implanted 7 Be target, a raster-scanned beam, and the elimination of the backscattering loss. The new measurement incorporates a more abundant 7 Be target and a number of improvements in design and procedure. The point at E l a b = 991 keV was measured several times under varying experimental conditions, yielding a value of S 1 7 (E c . m . = 850 keV) = 24.0 ′ 0.5 eVb. Measurements were carried out at lower energies as well. Because of the precise knowledge of the implanted 7 Be density profile, it was possible to reconstitute both the off- and on-resonance parts of the cross section and to obtain from the entire set of measurements an extrapolated value of S 1 7 (0) = 21.2 ′ 0.7 eVb.

Measurement of the

The 7 Be(p, γ) 8 B reaction plays a central role in the evaluation of solar neutrino fluxes. We report on a new precision measurement of the cross section of this reaction, following our previous experiment with an implanted 7 Be target, a raster-scanned beam, and the elimination of the backscattering loss. The new measurement incorporates a more abundant 7 Be target and a number of improvements in design and procedure. The point at E l a b = 991 keV was measured several times under varying experimental conditions, yielding a value of S 1 7 (E c . m . = 850 keV) = 24.0 ′ 0.5 eVb. Measurements were carried out at lower energies as well. Because of the precise knowledge of the implanted 7 Be density profile, it was possible to reconstitute both the off- and on-resonance parts of the cross section and to obtain from the entire set of measurements an extrapolated value of S 1 7 (0) = 21.2 ′ 0.7 eVb.