A high-precision measurement of the 14O half-life has been performed using a mass-separated radioactive beam in combination with a germanium detector set-up. This is the first 14O half-life measurement with a contamination-free source. The final result of 70.560 ± 0.049 seconds is in agreement with the generally adopted mean value.

A technique for producing a high-quality radioactive Ni-56 (T-1/2 = 6.1 d) beam via the two-accelerator method has been developed. Beam intensities of 2 x 10(-7) Ni-56/s were extracted from the ion source and 2 x 10(4) Ni-56/s were delivered to the target. For a study of neutron transfer reactions in inverse kinematics, a high-efficiency detection system was built consisting of a large solid angle (2.8 sr) high-granularity Si detector array for measuring the outgoing protons in coincidence with the heavy reaction products identified with respect to mass A and nuclear charge Z in the focal plane of a recoil mass separator. (C) 2000 Elsevier Science B.V. All rights reserved.

By using complete fusion reactions S-32+ Er-164 and Ti-48+ Sm-144, leading to Po-196 and Po-192 compound nuclei, improved alpha-decay characteristics for neutron-deficient Po-190,Po-192 isotopes have been obtained. The experiments have been performed at the fragment mass analyzer (Argonne) and at the RITU gas-filled separator (Jyvaskyla). In Po-192 the l = 0 decay to the excited 0(+) state in Pb-188 is two times faster than the decay to the ground state. For Po-190 more precise values of the alpha-decay energy E-alpha = 7545(15) keV and half-life T-1/2 = 2.53(33) ms were measured. By using correlated alpha-decay chains alpha-branching ratios of 38(9)% and 9.3(8)% were experimentally deduced for the first time for Pb-186 and Pb-188, respectively. The reduced alpha-width systematics is extended for even Po isotopes, confirming a persistence of the saturation towards the lighter isotopes. Absence of any anomalies in the reduced alpha-widths for the neutron-deficient Pb isotopes is confirmed.

An efficient method for the production and post-acceleration of a pure F-18(T-1/2 = 109.8 min) radioactive beam has been developed. Large amounts of F-18 are produced via the O-18(p,n)F-18 reaction using a 15.5 MeV proton beam on an O-18-enriched water target. After the chemical purification of the target content, the F-18 activity is transferred into [F-18]-fluoromethane. It is then transported to an ECR ion source, where after dissociation of the molecules, the fluorine atoms are ionized. Finally, the F-18(2+) ions are accelerated to 14 MeV in a second cyclotron. The different steps in the production cycle and the characteristics of the final F-18 beam are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

The single-particle character of states outside the doubly magic (radioactive) nucleus ${}^{56}\mathrm{Ni}$ has been determined through a measurement of the $(d,p)$ neutron transfer reaction using inverse kinematics. From the spectroscopic factors of the low-lying states in ${}^{57}\mathrm{Ni}$, the astrophysically interesting yield for the ${}^{56}\mathrm{Ni}(p,\ensuremath{\gamma})$ reaction to the mirror nucleus ${}^{57}\mathrm{Cu}$ has been calculated, utilizing charge symmetry. The rate for this reaction in the temperature range typical of novae, supernovae, and x-ray bursts is found to be more than 10 times higher than previously assumed.

The gamma-ray spectroscopy of even- and odd-mass isotopes of polonium have been studied using arrays of Ge detectors coupled to recoil-mass analyzers, including recoil-decay tagging techniques. The level energies and B(E2) branching ratios can be reproduced by theoretical frameworks which do not explicitly include proton particle-hole excitations across the Z=82 shell, conclusions in contrast to those deduced from alpha-decay measurements.

The single-particle character of states outside the doubly magic (radioactive) nucleus 56Ni has been determined through a measurement of the sd, pd neutron transfer reaction using inverse kinematics. From the spectroscopic factors of the low-lying states in 57Ni, the astrophysically interesting yield for the 56Nisp, gd reaction to the mirror nucleus 57Cu has been calculated, utilizing charge symmetry. The rate for this reaction in the temperature range typical of novae, supernovae, and x-ray bursts is found to be more than 10 times higher than previously assumed. [S0031-9007(97)05085-0]

Levels in Po-202,Po-202 were studied via the pf and electron-capture decay of mass-separated At isotopes. Multiscaled singles gamma,x, and conversion-electron spectra as well as gamma-gamma-t, gamma-e(-)-t, and x-e(-)-t coincidences were measured. These isotopes contain key information for the presence of pi(4p-2h) intruder configurations in the light Po isotopes.

A test stand for development of ion sources for radioactive beams is currently being commissioned at Argonne. It is located at the Physics Division’s Dynamitron accelerator which will be used as a neutron generator with a flux of up to 1011 neutrons per second created by reactions of 4 MeV deuterons on various targets with beam currents of up to 100 μA. The primary targets will be located adjacent to heated secondary targets inside an on-line ion source. With this neutron-generator facility it will be possible to produce radioactive beams of various isotopes, such as He6, Na24, and neutron-rich fission fragments. For example, with a secondary target of uranium carbide containing 25 g of natural or depleted uranium the yields of individual isotopes in the target will be about 107/s for isotopes such as Sn132, Xe140, and Cs142, near the peak of the fission distribution. The ion sources to be evaluated will be located within a shielded cave with walls consisting of 30 cm of steel plus 60 cm of concrete to attenuate the prompt neutron radiation by a factor of about 104. Secondary beams of radioactive fission fragments with intensities on the order of 106/s per isotope will be extracted in the 1+ charge state at energies of 20 keV and mass separated with a Danfysik mass separator. Light isotopes, such as He6 and Na24, can be produced via (n,α) and (n,p) reactions on appropriate target materials. Commissioning began with measurements of fission yields from primary targets of C, Be, BeO, and BN. A surface ionization source which is a variation of the one used in the TRISTAN on-line mass seperator facility at Brookhaven National Laboratory has been installed and tested with stable Rb and Cs beams. The isotope separator was also commissioned with these beams. The development program will include emittance measurements and source optimization, initially with stable beams, and target-delay-time and release-efficiency measurements for various target/secondary-beam systems.

A neon gas target has been developed to produce radioactive fluorine. Small CF4 impurities were added to the neon gas and the recovery efficiency of 18F-labeled CF4 has been measured as a function of the impurity level. Extraction efficiencies up to 90% have been obtained, which makes this technique to produce and extract radioactive fluorine from a production target a powerful method to generate intense radioactive 17F and 18F beams, using the 20Ne(p,α)17F and 20Ne(d,α)18F reactions, respectively.

The population of the Na-20 resonances at 448, 661, 797, and 887 keV above the proton threshold has been studied in measurements of the Ne-19(p,gamma)Na-20 reaction with radioactive Ne-19 beams. The data have been analyzed fully in terms of resonance strengths, enabling a comparison with theoretical estimates and the extraction of upper and lower limits on the resonant part of the Ne-19(p, gamma)Na-20 astrophysical reaction rate. The total cross section of the Ne-19(d,n)Na-20 reaction has been measured from 0.6 to 1.8 MeV (c.m.). On the basis of the results of a subsequent distorted-wave Born approximation analysis the direct component of the Ne-19(p,gamma)Na-20 astrophysical reaction rate has been calculated in a potential model. The astrophysical implications of the resulting total reaction rate have been investigated: the conditions for the breakout from the hot CNO cycle into the rapid-proton capture process are determined by the preceding O-15(alpha, gamma)Ne-19 reaction and the photodisintegration of the produced Na-20 nuclei will not impede the breakout. [S0556-2813(98)05305-9].

The population of the ${}^{20}\mathrm{Na}$ resonances at 448, 661, 797, and 887 keV above the proton threshold has been studied in measurements of the ${}^{19}\mathrm{Ne}(p,\ensuremath{\gamma}{)}^{20}\mathrm{Na}$ reaction with radioactive ${}^{19}\mathrm{Ne}$ beams. The data have been analyzed fully in terms of resonance strengths, enabling a comparison with theoretical estimates and the extraction of upper and lower limits on the resonant part of the ${}^{19}\mathrm{Ne}(p,\ensuremath{\gamma}{)}^{20}\mathrm{Na}$ astrophysical reaction rate. The total cross section of the ${}^{19}\mathrm{Ne}{(d,n)}^{20}\mathrm{Na}$ reaction has been measured from 0.6 to 1.8 MeV (c.m.). On the basis of the results of a subsequent distorted-wave Born approximation analysis the direct component of the ${}^{19}\mathrm{Ne}(p,\ensuremath{\gamma}{)}^{20}\mathrm{Na}$ astrophysical reaction rate has been calculated in a potential model. The astrophysical implications of the resulting total reaction rate have been investigated: the conditions for the breakout from the hot CNO cycle into the rapid-proton capture process are determined by the preceding ${}^{15}\mathrm{O}(\ensuremath{\alpha},\ensuremath{\gamma}{)}^{19}\mathrm{Ne}$ reaction and the photodisintegration of the produced ${}^{20}\mathrm{Na}$ nuclei will not impede the breakout.

excited states has now been established with, in some c deformed rotational-like bands built on top of them. The d formed configurations can be interpreted in terms of proton-pair excitation across the closed Z582 shell gap. These structures ‘‘intrude’’ into the low-energy structure d to a gain in total pairing energy and an increase in to proton-neutron interaction energy, which gives rise to t coexisting structures. Also in the odd-mass Tl ( Z581) and Bi (Z583) isotopes intruder states have been observe low energy and have been interpreted as p~1p@1h9/2#-2h! and p~2p-1h@3s1/2]) configurations, respectively @2–4#. A stringent test for the description of intruder states would be identification of shape coexistence based on p~4p-2h! configurations above theZ582 closed shell in the Po isotope corresponding to the excitation of two extra protons to next major shell. Low-lying 0 states have been observed Po and Po fed by thea decay of Rn and Rn, respectively@5–7#, and in Po populated by the b decay of At @7#. Extra 2 and 4 states have been observe in Po by Alberet al. @8# and have been interpreted a belonging to a band built upon the 0 1 excited states. This assignment has been questioned by Younes and Cizewsk @9# who described the Po energy levels including the rece observed levels of Po@10–13# within the particle-core model~PCM! where the two protons are coupled to a vibr ing core. To explain the microscopic evolution of collecti

The single-particle character of states outside the doubly magic (radioactive) nucleus Ni-56 has been determined through a measurement of the (d,p) neutron transfer reaction using inverse kinematics. From the spectroscopic factors of the low-lying states in Ni-57, the astrophysically interesting yield for the Ni-56(p,gamma) reaction to thr mirror nucleus Cu-57 has been calculated, utilizing charge symmetry. The rate for this reaction in the temperature range typical of novae, supernovae, and x-ray bursts is found to be more than 10 times higher than previously assumed. [S0031-9007(97)05085-0].

A technique for separating and identifying reaction products from radiative capture reactions induced by radioactive ion beams has been developed. The F-18(p,gamma)Ne-19 and O-18(p,gamma)F-19 reactions have been measured in inverse kinematics by identifying the F-19 and Ne-19 reaction products with respect to mass and charge at forward angles in the Fragment Mass Analyzer. A total detection efficiency of 30% and a suppression factor for the incident beam relative to the (p,gamma) reaction products of better than 10(12):1 was achieved. Details of the detection technique, the beam monitoring procedure as well as experience in the use of polypropylene targets in experiments with radioactive beams are discussed. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Stripping efficiencies for Kr+, Xe+, and Pb+ beams in helium and nitrogen gas targets have been measured at energies varying between 0.8 and 2.0 MeV. The stripping yields were determined for different target densities, ranging from single-collision conditions to equilibrium. Based on these results, approximate predictions of the equilibrium charge state distributions for low velocity (v/c=0.0040-0.0060) heavy ions with 28<Z<92 in collisions with helium atoms are made. Furthermore, measurements of the small-angle scattering of these heavy ion beams in collisions with dilute helium and nitrogen gases are reported. The presented results are important in view of a proposed postacceleration scheme for low-energy radioactive ion beams using a linac. These data show that helium generally produces higher yields of 2(+) and 3(+) ions and that the optimal choice of gas thickness for the proposed application is somewhat less than that required for equilibrium. (C) 1997 American Institute of Physics.