88-Inch Cyclotron Research Articles

Production of an accelerated oxygen-14 beam

BEARS is an ongoing project to provide a light-ion radioactive-beam capability at the 88-Inch Cyclotron at LBNL. Light radioactive isotopes are produced at a 10 MeV proton medical cyclotron, transported 350 m via a high-speed gas transport capillary, cryogenically separated, and injected into the 88-Inch Cyclotron’s ion source. The first radioactive beam successfully accelerated was carbon-11 and beams of intensity more than 10 8 ions/s have been utilized for experiments. Development of oxygen-14 as the second BEARS beam presented considerable technical challenges, both due to its short half-life of 71 s and the radiation chemistry of oxygen in the target. The usual techniques developed for medical uses of oxygen-15 involve the addition of significant amounts of carrier oxygen, something that would overload the ion source. As a solution, oxygen-14 is produced as water in a carrier-free form, and is chemically converted in two steps to carbon dioxide, a form readily usable by the BEARS. This system has been built and is operational, and initial tests of accelerating an oxygen-14 beam have been performed.

Oliver Cecil Simpson

Oliver Cecil Simpson

Search for the Jacobi shape transition in rapidly rotating nuclei

We have studied quasicontinuous gamma radiation from reactions of ${}^{48}\mathrm{Ca}$ beams on targets of ${}^{50}\mathrm{Ti},$ ${}^{64}\mathrm{Ni},$ ${}^{96}\mathrm{Zr},$ and ${}^{124}\mathrm{Sn}.$ The bombarding energies were in the range 195--215 MeV, and were chosen so as to bring in a high angular momentum without severe fragmentation of the cross sections for fusion residues. Experiments were performed both with the 8PI spectrometer at the LBNL 88-Inch Cyclotron, and with Gammasphere at the ANL ATLAS accelerator. The results have been analyzed in a variety of ways, with the consistent result that in all but the heaviest target, the nuclear moments of inertia tend to increase with increasing angular momentum up to the highest values observed. This could come from a transition towards a highly deformed Jacobi-like shape, or possibly be due to the appearance of high-$j$ intruder orbitals at the Fermi surface. We will argue that these effects can be equivalent.

Prospects for exotic beam facilities in North America

There are several nuclear physics laboratories in North America that have on-going research using energetic and stopped radioactive beams. These include the large ISOL-type programs ISAC at TRIUMF and HRIBF at Oak Ridge and the in-flight fragmentation program at the NSCL of Michigan State University. There are also smaller, more specialized, programs using a variety of techniques at the 88-inch cyclotron of Berkeley, ATLAS at Argonne, the Cyclotron Institute of Texas A&M University, the Nuclear Structure Laboratory at Notre Dame University, and the Nuclear Structure Laboratory at SUNY/Stony Brook. There are also three projects on the horizon in North America for new capabilities in both the near term and more distant future. The intensities of the in-flight fragment beams at the NSCL will be increased dramatically very soon as the Coupled Cyclotron Project will be completed and commissioned for research by mid-2001. A new project, ISAC-II, has been approved in Canada. For the longer term, the United States is considering construction of a major new facility, the Rare Isotope Accelerator (RIA), which would have a very high-intensity heavy-ion driver linac. The RIA facility is proposed to utilize both ISOL and in-flight production mechanisms.

Marcus Laurence Elwin ‘Mark’ Oliphant

Marcus Laurence Elwin ‘Mark’ Oliphant

APS Honors Physics Contributions

APS Honors Physics Contributions

Electron-capture delayed fission probabilities of248Esand246Es

Electron-capture delayed fission was observed in 26-min {sup 248}Es and 7.7-min {sup 246}Es, which were produced at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron via {sup 249}Cf(p,2n) and {sup 249}Cf(p,4n) reactions at proton energies of 18 and 37 MeV on target, respectively. The delayed fission probabilities were determined to be (3.5{+-}1.8)x10{sup -6} for {sup 248}Es and (3.7{sub -3.0}{sup +8.5})x10{sup -5} for {sup 246}Es. These values were determined in separate experiments using our automated rotating wheel online collection and measurement system. Collection and measurement times were optimized for the isotope being measured. The measured delayed fission probabilities are consistent with the experimentally observed trend of increasing delayed fission probability with increasing Q value for electron capture.

Emittance Measurements for High Charge State Ion Beams Extracted from the AECR-U Ion Source

In order to investigate the ion-optical parameters of the AECR-U injection line into the 88-Inch Cyclotron, an electrostatic-deflection-type emittance scanner has been designed and constructed. It allows fast on-line measurements, while tuning the ion beam through the cyclotron. Emittance measurements have been performed for various high charge state ions. First results indicate a strong mass dependence of the normalized beam emittance. For example the normalized rms emittance for protons (0.24 π · mm · mrad) is four times higher than for O6+ (0.06 π · mm · mrad) and about 8 times higher than Kr19+ (0.03 π · mm · mrad). Furthermore it was found, that the emittance values are approximately independent of the current at the medium ion beam intensities. The predominant factor on the beam emittance is shown to be the plasma stability. The emittance measurements and the results are discussed in the paper.

Construction of the Superconducting ECR Ion Source Venus

A new, very high magnetic field superconducting ECR ion source, VENUS, is under development at the LBNL 88-Inch Cyclotron. It will boost the maximum energies and intensities for heavy ions from the cyclotron particularly for ions with mass greater than 60. It will also serve as R&D ion source for the proposed Rare Isotope Accelerator (RIA) project in the US, which requires up to 10 pµA of U30+. The superconducting magnet structure consists of three solenoids and six racetrack coils with iron poles forming the sextupole. The coils are designed to generate a 4 T axial mirror field at injection and 3 T at extraction and a radial sextupole field of 2.4 T at the plasma chamber wall. Test results of the magnet coils, which exceeded design requirements with minimum training, are presented. The magnet assembly with its cryostat will be enclosed by an iron shield and therefore must be designed to withstand any possible forces between coils and iron, which can be as high as 3.4 · 105 N (35,000 kgf). The low energy beam transport line (LEBT) and mass analyzing system of the ion source is designed to transport a proton- equivalent current of 25 mA at 20 kV extraction voltage. The design of the ion source and LEBT will be discussed.

Evidence for new isotopes of element 107: 266Bh and 267Bh

New neutron rich isotopes 267107Bh and 266107Bh were produced in bombardments of a 249Bk target with 117-MeV and 123-MeV 22Ne ions at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. Identification was made by observation of correlated alpha-particle decays between the Bh isotopes and their Db and Lr daughters using a rotating wheel system. 267Bh was produced with a cross section of approximately 70 pb and decays with a 17(+14)(-6) s half life by emission of alpha particles with an average energy of 8.83+/-0.03 MeV. One atom of 266Bh was observed, decaying within 1 s by emission of a 9.29-MeV alpha particle.

A rapid sample changer system for studying fission shape isomers through the electron-capture-delayed fission process

A new sample changer system has been designed to rapidly transport activity from a heavy element production target chamber at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron to a fission, α-particle, X-ray, and γ-ray detection site. This changer was specifically designed to help study the nuclear structure of isotopes involved in electron-capture-delayed fission decay with half-lives greater than 30 s. The system integrates a rotating wheel and a cycling piston to transport samples from the end of a gas transport capillary line to the detection site. The overall efficiency of the sample changer system was determined by running off-line experiments to determine the activity collection site efficiency and the detector efficiencies. Under the most favorable conditions, we calculated a relative He–KCl gas transport and collection efficiency of around 70%. Efficiencies were calculated by comparing the yield of 221Fr (half-life=4.8 min) at the sample changer collection site to the activity collected directly on a piece of glass filter paper.

Measurement of excitation functions in the reactions 197Au(11C, xn)208-xAt using a radioactive 11C beam

A light-element radioactive ion-beam capability has been developed at the LBNL 88-Inch Cyclotron. The system is based on the coupled-cyclotrons method and utilizes short-lived species, e.g., 11C, 14O, 13N produced by (p,n) and (p,alpha) reactions at the LBNL Biomedical Isotope Facility Cyclotron. In a first experiment, 197Au(11C,xn)208-xAt excitation functions have been measured for energies ranging from the Coulomb barrier up to 110 MeV using a beam of 11C with intensities up to (1-2)x10(8) ions/sec on target. The results of this experiment are compared to measurements of 197Au(12C, xn)209-xAt excitation functions.

Structure of normally deformed states in80Sr

High-spin states were populated in Sr-80 With the reaction Ni-58(Si-28,alpha 2p), using a 130 MeV Si-28 beam from the 88-Inch Cyclotron at LBNL. Gamma rays were detected with Gammasphere. and evaporated alphas and protons were detected with the Microball. The level scheme has been extended, and angular distributions of many of the transitions have been measured. A portion of the data was taken using a backed target, allowing lifetime measurements. No evidence for band termination was found in the spin range studied, but a cranking model analysis indicates possible shape evolution at higher spin.

Magnet system for an ECR ion source

A superconducting magnet assembly has been built for an ECR (Electron Cyclotron Resonance) ion source at the 88-inch cyclotron at LBL. Three 34-cm ID solenoids provide axial plasma confinement and a sextupole assembly in the solenoid bore provides radial stability. Two large solenoids are spaced 50 cm. Apart with a smaller opposing solenoid between. The sextupole assembly is 92 cm long with winding inner diameter of 20 cm. And outer diameter of 27.2 cm. The design goal is to achieve a field on axis of 4 T and 3 T at the mirrors with 0.4 T between and a sextupole field of 2.0 T at 15-cm diameter in the confinement volume. Each solenoid uses rectangular conductor wish copper/SC ratio of 4; the three coils are wet-wound on a one-piece aluminum bobbin with aluminum banding for radial support. The sextupole uses rectangular conductor with copper/SC ratio of 3. Each of the 6 coils is wet-wound with filled epoxy on a metal pole; the ends of the pole are aluminum and the central 34-cm is iron to augment the sextupole field. The six coils are assembled on a 20-cm-OD stainless steel tube with a 1.4-cm thick 30.0-cm OD aluminum tube over the assembly for structural support. Thin metal bladders are expanded azimuthally between each coil and axially at tire ends to pre-load the assembly. The sextupole assembly fits inside the solenoid bobbin, which provides support for the magnetic forces. The magnet exceeds design requirements with minimum training.

A new measurement of the strength of the superallowed Fermi branch in the beta decay of 10C with GAMMASPHERE

We report a new measurement of the strength of the superallowed 0 +→0 + transition in the β-decay of 10C. The experiment was done at the LBNL 88-inch cyclotron using forty-seven GAMMASPHERE germanium detectors. The technique used in this measurement was similar to that of an earlier experiment, but the systematic corrections were significantly different. The measured branching ratio: 1.4665±0.0038×10 −2 is used to compute the superallowed Fermi ft, which gives the weak vector coupling constant and the u to d element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix.

Decay and properties of the yrast superdeformed band in192Pb

The {sup 173}Yb({sup 24}Mg,5n) reaction at E({sup 24}Mg) = 134.5 MeV with a gold-backed target was used to populate high-angular momentum states in {sup 192}Pb. Resulting {gamma} rays were detected with Gammasphere located at the 88-Inch Cyclotron. A discrete transition of energy E{sub {gamma}} = 2057.7(6) keV has been identified in the depopulation the yrast superdeformed (SD) band in {sup 192}Pb. This transition has been tentatively placed in the level scheme based on coincidence relationships. Thus, the excitation energy of the SD level populated by the 262-keV in-band transition is tentatively assigned E{sub x} = 4.572(1) MeV. Confidence limits are discussed. Other transitions in coincidence with the SD band and general features of the band and its decay are also presented. In particular, we confirm that the J{sup (2)} of the SD band decreases by {approx}13{percent} at the lowest frequency. Also, by comparing the masses of the SD ground states in {sup 192,194}Pb to liquid drop model expectations and to each other we have been able to confirm enhanced stability for N=112 at superdeformation. {copyright} {ital 1997} {ital The American Physical Society}

Improved half-life measurement of224Paand its209Bi(18O,3n)224Paproduction cross section

${}^{224}\mathrm{Pa}$ was produced via the ${}^{209}{\mathrm{B}\mathrm{i}(}^{18}\mathrm{O},3n)$ reaction at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron and the half-life was determined to be 850\ifmmode\pm\else\textpm\fi{}20 ms by measuring its alpha decay using our rotating wheel system. Our value is consistent with a previously reported half-life of 950\ifmmode\pm\else\textpm\fi{}150 ms for ${}^{224}\mathrm{Pa}$ produced via the ${}^{205}{\mathrm{T}\mathrm{l}(}^{22}\mathrm{N}\mathrm{e},3n)$ reaction, but its much more precise. The cross section for the ${}^{209}{\mathrm{B}\mathrm{i}(}^{18}\mathrm{O},{3n)}^{224}\mathrm{Pa}$ reaction was measured to be 0.5\ifmmode\pm\else\textpm\fi{}0.1 mb for 87--89 MeV ${}^{18}{\mathrm{O}}^{5+}$ projectiles incident on the target.

Competing single-particle and collective structures in86Nb

The high-spin structure of odd-odd ${}^{86}$Nb was studied with the early implementation of GAMMASPHERE using 36 Compton-suppressed Ge detectors and the MICROBALL, a 95-element full-sphere charged-particle detector array. High-spin states were populated using the ${}^{58}$Ni${(}^{32}$S,$3pn)$ reaction at 135 MeV with beams from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. A number of bands were observed up to spins as high as ${(31}^{\ensuremath{-}})$. The yrast positive-parity band shares many characteristics with the $\ensuremath{\pi}{g}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$ bands in other odd-odd $f$-$p$-$g$ shell nuclei. These similarities include the behavior of the moments of inertia, the magnitude and phase of the signature splitting and its phase reversal near the ${10}^{+}$ state, and the strong alternations in the $B(M1)/B(E2)$ strengths. The moments of inertia in the lowest pair of negative-parity bands start out with a sharp upbend and then gradually fall back to the rigid-body value. New positive- and negative-parity bands appear in the quasiparticle alignment region and eventually become yrast. Some additional positive-parity states around spin $17\ensuremath{\Elzxh}$ are candidates for fully or nearly fully aligned shell-model-like configurations.

Yrast superdeformed band in194Pb:JπandEx

The yrast superdeformed band in ${}^{194}$Pb has been populated using the ${}^{174}$Yb${(}^{25}$Mg,5n)${}^{194}$Pb reaction at ${E}_{\mathrm{beam}}=130$ MeV. Decay $\ensuremath{\gamma}$ rays were detected using the GAMMASPHERE array at the 88-Inch Cyclotron. Twelve $\ensuremath{\gamma}$-ray transitions have been observed directly linking three members of the ${}^{194}$Pb yrast superdeformed band to low-lying normal deformed levels. Anisotropy measurements indicate that these linking decays include $E$1, $M$1, and mixed $M1/E2$ multipolarities. The radiative widths deduced are very inhibited, typically $B(E1)\ensuremath{\sim}{10}^{\ensuremath{-}8}$ Weisskopf units (W.u.) and $B(M1)\ensuremath{\sim}{10}^{\ensuremath{-}5}$ W.u. Without recourse to a priori assumptions ${J}^{\ensuremath{\pi}}{=6}^{+}$ and ${E}_{x}=4878.4(3)$ keV have been unambiguously assigned to the lowest-lying observed superdeformed state (the state populated by the 170-keV intraband transition). The intensity of the observed primaries accounts for 21(2)% of the superdeformed band population.

Two-frequency plasma heating in a high charge state electron cyclotron resonance ion source

The performance of the Lawrence Berkeley Laboratory (LBL) advanced electron cyclotron resonance ion source, which is a single stage source designed to operate at 14 GHz alone (single-frequency heating), is enhanced by heating the plasma simultaneously with microwaves of 10 and 14 GHz (two-frequency heating). Production of high charge state ions was increased a factor of 2–5 or higher for the very heavy ions such as bismuth and uranium, as compared to single- frequency heating. Plasma stability was improved and the ion charge state distribution shifted to higher charge state. With two-frequency heating, the source can produce more than 1×109 pps of fully stripped argon. High charge state ion beams of bismuth and uranium produced by the source were injected into the 88-Inch Cyclotron at LBL. After acceleration to energies greater than 6 MeV/nucleon, the extracted beam intensities were 1×106 pps or higher for Bi50+,51+ and 238U52+,53+.