Recoil Mass Separator Research Articles

Facilities for direct measurement of 4He( 12C, 16O)γ reaction cross section at KUTL

A recoil mass separator designed to achieve a highest possible capability of the background rejection in the condition of inverse kinematics has been developed at Kyushu University tandem accelerator laboratory. Developments at accelerator have also been carried out to obtain a pulsed beam of high current and good emittance. With the mass separator and the pulsed heavy-ion beam, we are about to start the investigation of the 4He( 12C, 16O)γ reaction of astrophysical interest.

Ternary particle yields in249Cf(nth,f)

An experiment measuring ternary particle yields in ${}^{249}\mathrm{Cf}{(n}_{\mathrm{th}},f)$ was carried out at the high flux reactor of the Institut Laue-Langevin using the Lohengrin recoil mass separator. Parameters of energy distributions were determined for 27 ternary particles up to ${}^{30}\mathrm{Mg}$ and their yields were calculated. The yields of 17 further ternary particles were estimated on the basis of the systematics developed. The heaviest particles observed in the experiment are ${}^{37}\mathrm{Si}$ and ${}^{37}\mathrm{S};$ their possible origin is discussed.

Results from the development of ionization detection systems for the DRAGON facility

We discuss the implementation of an ionization detection system for the focal plane of the DRAGON recoil mass separator. We report recent tests performed with stable beams to test the feasibility of such a system for use in measurements of radiative capture reactions in inverse kinematics with radioactive beams.

The DRAGON facility for nuclear astrophysics at TRIUMF-ISAC: design, construction and operation

A facility for measuring cross-sections (resonance strengths) for reactions of astrophysical importance involving short-lived, radioactive reactants has been designed, built and installed at the new TRIUMF-ISAC Radioactive Beams Laboratory in Canada. Named DRAGON (Detector of Recoils And Gamma-rays of Nuclear reactions), it has been successfully commissioned with stable and radioactive heavy ion beams from ISAC. This report presents the main components of the facility, namely, the windowless gas target, the surrounding g detector array, the subsequent electromagnetic recoil mass separator, the focal plane detectors for recoils, the detection system for elastics, and the modular electronics and computer software used for the data acquisition. Examples of the operation of the facility for both stable beam reactions and the first radioactive beam reaction study, 21 Naðp;gÞ 22 Mg are also presented, along with future plans for the program. r 2003 Elsevier Science B.V. All rights reserved. PACS: 29.0

The Present and the Future of JAERI Recoil Mass Separator

A recoil mass separator has been in operation at the JAERI tandem-booster facility since 1995, for in-flight separation of low-yield reaction products recoiling out in the beam direction. The current status and future plan together with a brief description of the design performance are presented.

A recoil mass separator for nuclear astrophysics experiments

A recoil mass separator was constructed for experiments of nuclear astrophysics using radioactive nuclear beams, and its performance was tested. The observed beam suppression factor around M∼20 was 10 −4 when the system was tuned for ΔM=1 heavier ions than beam ions. With a charge state breeding technique, it became 10 −8 when the system was tuned for Δq=+1 larger ions than beam ions.

Towards new proton radioactivities with radioactive beams and digital signal processing

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 145Tm and 146Tm decay, evidence for the fine structure in proton emission was obtained. An experiment to search for a new proton emitter 149Lu is described as an example where the combination of a 56Ni radioactive beam and digital signal processing is a major advantage.

From NABONA to ERNA

The recoil mass separator NABONA has been used at the TTT-3 tandem accelerator in Naples to perform a new direct measurement of the cross section of the p( 7 Be,γ) 8 B reaction at 1 MeV center of mass energy. The extracted astrophysical S factor at zero energy is S(0) = 15.3±4.6 eV b. The experiment shows the feasibility of small cross section measurements by the RMS method. An upgraded separator (ERNA) has been designed and is presently being installed in Bochum with the aim of measuring the cross section of the α( 12 C,γ) 16 O reaction in the c.m energy range 0.7–5 MeV. The peculiarities of this reaction which require a different lay-out of the separator with respect to that used for the p( 7 Be,γ) 8 B will be discussed together with the present status of the ERNA project.

Sub-barrier fusion of deformed nuclei in60Ni+154Smand32S+182Wreactions

We have investigated the sub-barrier fusion between spherical projectiles and well-deformed targets in ${}^{60}\mathrm{Ni}{+}^{154}\mathrm{Sm}$ and ${}^{32}\mathrm{S}{+}^{182}\mathrm{W}$ reactions, and both lead to the same compound nucleus ${}^{214}\mathrm{Th}.$ In order to get direct evidence that the projectile really fuses with the deformed target, the fusion evaporation residues emitted to the beam direction were measured by using the JAERI recoil mass separator and identified on the basis of time- and position-correlated $\ensuremath{\alpha}$ decays. The angular distributions of fission fragments were also measured to obtain the total fusion cross section. The measured cross sections of the fusion fission and the fusion evaporation were compared with the results of the coupled channel calculation and the statistical model calculation, respectively. In the ${}^{32}\mathrm{S}{+}^{182}\mathrm{W}$ system, a good agreement between them was obtained for $xn,$ $pxn,$ and $\ensuremath{\alpha}\mathrm{xn}$ channels. In the heavy projectile system of ${}^{60}\mathrm{Ni}{+}^{154}\mathrm{Sm},$ on the other hand, the observed evaporation residue cross sections below the Bass barrier were much less than the calculated results whereas they were well reproduced above the barrier. It was found that this large hindrance could be reproduced by assuming an extra-extra push energy of around 20 MeV in the tip collision of the deformed target and nearly zero in the side collision.

Experiments with a radioactive 56Ni beam

A technique for producing a high-quality radioactive 56 Ni (T 1/2=6.1 d) beam via the two-accelerator method has been developed. Beam intensities of 2×10 7 56Ni/s were extracted from the ion source and 2×10 4 56Ni/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.

Transport efficiency of JAERI recoil mass separator

Abstract Solid angles and transport efficiencies of the JAERI recoil mass separator were measured by using three procedures, that is, by using (1) α-particles from an 241 Am source, (2) elastic recoils of 197 Au produced in the bombardments of 28 Si beams on 197 Au targets and (3) evaporation residues produced in the fusion reaction of 30 Si+ 141 Pr. The solid angles of 11 and 21 msr were obtained for the focus conditions of the mass dispersion (x | δ m )=−1.1 and 0 cm /% respectively. The measured transport efficiency was compared with the ion-optical calculation of GIOS and a good agreement between the calculation and the present data was obtained. The charge state distributions of low-energy heavy recoils 167 Ta and 197 Au were also measured and compared with the various calculations. It was found that the empirical formula by Shima et al. well reproduced the present data.

Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the 28Si+68Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.

Recent results from the JAERI recoil mass separator

In order to separate rare fusion evaporation residues from the primary beam in flight, a recoil mass separator has been constructed at the JAERI tandem-booster facility. By using the recoil mass separator, new neutron-deficient isotopes209Th and212Pa have been produced. After a brief facility description, some recent experimental results are presented.

In-beam spectroscopy study of the proton emitter151Lu

Gamma rays decaying from the excited states of the proton-unbound ${}^{151}\mathrm{Lu}$ were observed for the first time in an experiment using the ${}^{96}\mathrm{Ru}{(}^{58}\mathrm{Ni},{p2n)}^{151}\mathrm{Lu}$ reaction. These \ensuremath{\gamma} rays were identified by correlating prompt \ensuremath{\gamma} radiations at the target position with ${}^{151}\mathrm{Lu}$ proton radioactivities at the focal plane of a recoil mass separator. Systematic data on $N=80$ isotones suggest a possible isomeric level at high spin in ${}^{151}\mathrm{Lu}.$ Our measurement was unable to observe such an isomer, but provided an upper limit on its half-life. The observed \ensuremath{\gamma} rays in ${}^{151}\mathrm{Lu}$ can be interpreted in terms of two possible level structures.

Alignments and new band structures in the doubly odd nucleus 80Rb

The high spin structure of 80Rb has been investigated using the reaction 51V( 32S,2pn) at a beam energy 105 MeV. The level scheme was established from γ-γ and recoil-γ-γ coincidence measurements obtained using the Gamma Detector Array consisting of eight Compton suppressed Ge detectors coupled to the recoil mass separator HIRA. Rotational states upto an excitation energy 13 MeV and a spin 25ħ were studied. Band crossings at ħω = 0.63 and 0.73 MeV in the negative parity band, due to successive g 9 2 proton and neutron alignment, were observed for the first time. Evidence has also been found for a hitherto unknown sideband. The yrast positive parity bands in 78Kr and 80Rb have similar transition energies beyond a rotational frequency ħω ≈ 0.55 MeV. This is the only known example of identical bands in nuclei differing by two quasiparticles, in this mass region.

One- and two-nucleon transfer in the28Si+68Zn system at energies below the Coulomb barrier

Excitation functions for one- and two-nucleon transfer in {sup 28}Si + {sup 68}Zn system have been measured at energies below the Coulomb barrier. The experiment was carried out by detecting the forward recoiling targetlike nuclei using the recoil mass separator, HIRA. With a pulsed beam, the time-of-flight of the recoils was measured and used to resolve the M/q ambiguity. This enabled the determination of the two-nucleon transfer yields. The role of one- and two-nucleon transfer in the sub-barrier fusion cross-section enhancement has been investigated. It turns out that the coupling of the positive Q-value two-neutron transfer channel results in a significant contribution to the enhancement. Coupling to both the transfer and the inelastic channels is able to explain the observed enhancement. {copyright} {ital 1997} {ital The American Physical Society}

Transfer and higher-order phonon coupling effects in the sub-barrier fusion of28Siand93Nb

Measurements have been carried out for the fusion excitation function and one and two nucleon transfer probabilities at energies near and below the Coulomb barrier for the system 28 Si 93 Nb. The recoil mass separator HIRA at the Nuclear Science Center, New Delhi, has been used for these measurements. A coupledchannels formalism has been employed for explaining the observed enhancement in the sub-barrier fusion cross section. Present results support the significance of positive Q-value transfer channel in the sub-barrier enhancement. The possible role of higher-order multiphonon coupling effects in the reaction mechanism have also been investigated. S0556-28139703910-1

The feature of the JAERI recoil mass separator

A recoil mass separator has been constructed at the JAERI tandem-booster facility. It has a symmetric configuration of Q1Q2-ED1-MD-ED2-Q3Q4-O, where two electric dipoles ED1 and ED2, and a magnetic dipole MD are used to disperse reaction products by their mass/charge ratio ( m q ) and focus their energies. Two quadrupole doublets (Q1Q2 and Q3Q4) are used for focusing reaction products spread spatially. The octupole magnet O is used to correct a non-linearity of the m q dispersion. The m q and energy acceptances are designed to be ±4% and ±12%, respectively. In order to reduce a beam background scattered from the ED1 anode, the anode is split into two parts, so that the primary beam can pass through without hitting the anode. The performance of the recoil mass separator has been tested by using the 127I and 28Si beams from the JAERI tandem accelerator. The capability of the background suppression at the beam direction is excellent and the obtained mass resolution is A ΔA ≅ 300 . By using the recoil mass separator, a new neutron-deficient isotope 209Th has been produced in the reaction of 32S on 182W at beam energy of 171 MeV. An α-decay energy and a half-life of 209Th have been determined to be 8.080(50) MeV and 3.8 −1.5 +6.9 ms, respectively.

Monte Carlo simulation of ion transport through the RMS spectrometer of Laboratori Nazionali di Legnaro

Simulation of beam (recoil) interaction with the target has been carried out to produce a realistic input for the Recoil Mass Separator (RMS) of Laboratori Nazionali di Legnaro. Subsequent transport of the recoils through RMS is calculated using transport matrices. Good agreement with experimental spectra is obtained and RMS transmission evaluation fairly compares with measured values.

Rotational bands in77Rb: Spectroscopy near theZ=38deformed shell gap

The $\ensuremath{\gamma}$ decays of high spin states in ${}^{77}$Rb populated in the reaction ${}^{40}$Ca${(}^{40}$Ca,$3p)$${}^{77}$Rb were studied with the EUROGAM I $\ensuremath{\gamma}$-ray spectrometer at Daresbury Laboratory, in conjunction with the recoil mass separator. The data were used to extend or establish three positive parity and five negative parity bands in ${}^{77}$Rb. Level lifetimes and sidefeeding times were then measured with the NORDBALL $\ensuremath{\gamma}$-ray spectrometer, using the Doppler shift attenuation method. A very detailed level scheme including many weakly populated states was established and the bands were observed over large spin ranges. The deduced lifetimes demonstrate the high collectivity of the excited states and are consistent with their having large prolate deformations. The structures of the bands and their crossings are discussed in relation to the large shell gap at prolate deformation ${\ensuremath{\beta}}_{2}\ensuremath{\approx}0.4$.