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A new setup for transfer reactions at REX-ISOLDE
Progress in Particle and Nuclear Physics 59 (2007) 386–388 www.elsevier.com/locate/ppnp
Review
A new setup for transfer reactions at REX-ISOLDEI V. Bildstein a,∗ , R. Gernh¨auser a , Th. Kr¨oll a , R. Kr¨ucken a , R. Raabe b , P. Van Duppen b , REX-ISOLDE and MINIBALL Collaborations a Physik-Department E12, Technische Universit¨at M¨unchen, Garching, Germany b Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, Belgium
Abstract A new setup is proposed aimed at the study of single particle structures of nuclei far from stability by nucleon transfer reactions in inverse kinematics using radioactive ion beams obtained from REX-ISOLDE. The setup combines particle and γ -ray detection using the MINIBALL array and was designed to achieve a high particle efficiency by covering a large angular range while retaining the high γ -ray efficiency of the MINIBALL setup. All particle detectors are segmented and/or position-sensitive silicon detectors, for forward angles built as 1E − Erest telescopes for light particle identification. As a first experiment with this new setup, the d(30 Mg, 31 Mg)p reaction at 3 MeV/u will be performed in 2007. c 2007 Elsevier B.V. All rights reserved.
1. Introduction The ‘island of inversion’ is a region on the neutron-rich side of the nuclear chart around 32 Mg, where intruder states from the fp-shell favour deformed ground states instead of spherical ones + 30 Mg and formed by the normal sd-states. Recent studies of the B(E2; 0+ gs → 21 )-values of 32 Mg at ‘safe’ and intermediate beam energies have shown that, indeed, 30 Mg has a spherical ground state and is thus outside the ‘island of inversion’, while 32 Mg has a deformed intruder ground state and lies inside the ‘island of inversion’ [1, and references therein]. Measurement of the magnetic moment of the ground state of 31 Mg, which may be directly on the shore of I Supported by BMBF 06MT190 and 06MT238. ∗ Corresponding author.
E-mail address: [email protected] (V. Bildstein). c 2007 Elsevier B.V. All rights reserved. 0146-6410/$ - see front matter doi:10.1016/j.ppnp.2007.01.010
V. Bildstein et al. / Progress in Particle and Nuclear Physics 59 (2007) 386–388
387
Fig. 1. Schematical drawing of the setup (left) and simulated angular distributions using GEANT4 for the ground state and the first three states of 31 Mg in the laboratory system (right).
the ‘island of inversion’, has established the spin-parity assignment of 1/2+ [2]. This was not predicted by theory and could only recently be reproduced by adjusting the monopole part of the interaction for the fp-shell [3]. We aim to extend the study of single particle configurations around the ‘island of inversion’ also to excited states populated by neutron transfer reactions in inverse kinematics [4]. Nucleon transfer reactions are a well-established tool for investigation of the single particle structure of nuclei. Relative spectroscopic factors extracted from transfer cross sections are a measure of the occupation numbers of single particle configurations (particles or holes). These can be compared directly to results from shell-model calculations. The transferred orbital momentum leading to the spin assignment of a state is determined from the angular distribution of the particles. Additionally, the neutron-pair transfer will allow the study of pairing correlations. 2. Setup & simulation Fig. 1 shows on the left a picture of the setup as it was implemented in a GEANT4 simulation. The silicon array consists of two annular DSSSD detectors (CD detectors) for forward and backward angles and a quadratic barrel of position-sensitive strip detectors (16 strips perpendicular to the beam with ≈0.5 mm position resolution) around 90◦ . In a previous experiment performed with a simplified setup at REX-ISOLDE with MINIBALL, only an angular range from 15◦ –55◦ was covered [5]. Here it was not possible to determine the transferred orbital momentum unambiguously. The new setup will cover an extended angular range of ϑlab. ≈ 8◦ –75◦ and 105◦ –172◦ and, as can be seen in Fig. 1 (right), the ambiguities can be resolved. Particle identification for different masses and Q-values requires the use of thin 1E detectors and thick Erest detectors. This allows protons for a large range of energies to pass through the 1E detector and to be stopped in the Erest detector. The inverse kinematics combined with small Qvalues translates for backward angles an excitation energy difference of 1 MeV into a difference in kinematic energy of the protons of a few hundred keV. This compression effect, combined with the energy spread due to the target thickness (≈0.5 mg/cm2 ), limits the achievable energy resolution and makes it necessary to detect the γ -rays in coincidence for the identification of the populated levels. With this new setup, an angular resolution of 3◦ –5◦ and an energy resolution of 60 keV (backward CD) to 2 MeV (forward CD) for protons emitted in the transfer reaction d(30 Mg, 31 Mg)p at 3 MeV/u can be achieved. The energy resolution for both CD detectors is mainly
388
V. Bildstein et al. / Progress in Particle and Nuclear Physics 59 (2007) 386–388
limited by the energy losses in the target, whereas for the barrel it is dominated by the beam spot size (≈5 mm). The efficiency of the setup to detect a particle is ≈62%. References [1] [2] [3] [4] [5]
O. Niedermaier, et al., Phys. Rev. Lett. 94 (2005) 172501. G. Neyens, et al., Phys. Rev. Lett. 94 (2005) 022501. F. Mar´echal, et al., Phys Rev. C 72 (2005) 044314. Th. Kr¨oll, et al. CERN-INTC-2006-036, INTC-P-219, 2006. M. Pantea, Ph.D. Thesis, TU Darmstadt, Germany, 2005.
Review
A new setup for transfer reactions at REX-ISOLDEI V. Bildstein a,∗ , R. Gernh¨auser a , Th. Kr¨oll a , R. Kr¨ucken a , R. Raabe b , P. Van Duppen b , REX-ISOLDE and MINIBALL Collaborations a Physik-Department E12, Technische Universit¨at M¨unchen, Garching, Germany b Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, Belgium
Abstract A new setup is proposed aimed at the study of single particle structures of nuclei far from stability by nucleon transfer reactions in inverse kinematics using radioactive ion beams obtained from REX-ISOLDE. The setup combines particle and γ -ray detection using the MINIBALL array and was designed to achieve a high particle efficiency by covering a large angular range while retaining the high γ -ray efficiency of the MINIBALL setup. All particle detectors are segmented and/or position-sensitive silicon detectors, for forward angles built as 1E − Erest telescopes for light particle identification. As a first experiment with this new setup, the d(30 Mg, 31 Mg)p reaction at 3 MeV/u will be performed in 2007. c 2007 Elsevier B.V. All rights reserved.
1. Introduction The ‘island of inversion’ is a region on the neutron-rich side of the nuclear chart around 32 Mg, where intruder states from the fp-shell favour deformed ground states instead of spherical ones + 30 Mg and formed by the normal sd-states. Recent studies of the B(E2; 0+ gs → 21 )-values of 32 Mg at ‘safe’ and intermediate beam energies have shown that, indeed, 30 Mg has a spherical ground state and is thus outside the ‘island of inversion’, while 32 Mg has a deformed intruder ground state and lies inside the ‘island of inversion’ [1, and references therein]. Measurement of the magnetic moment of the ground state of 31 Mg, which may be directly on the shore of I Supported by BMBF 06MT190 and 06MT238. ∗ Corresponding author.
E-mail address: [email protected] (V. Bildstein). c 2007 Elsevier B.V. All rights reserved. 0146-6410/$ - see front matter doi:10.1016/j.ppnp.2007.01.010
V. Bildstein et al. / Progress in Particle and Nuclear Physics 59 (2007) 386–388
387
Fig. 1. Schematical drawing of the setup (left) and simulated angular distributions using GEANT4 for the ground state and the first three states of 31 Mg in the laboratory system (right).
the ‘island of inversion’, has established the spin-parity assignment of 1/2+ [2]. This was not predicted by theory and could only recently be reproduced by adjusting the monopole part of the interaction for the fp-shell [3]. We aim to extend the study of single particle configurations around the ‘island of inversion’ also to excited states populated by neutron transfer reactions in inverse kinematics [4]. Nucleon transfer reactions are a well-established tool for investigation of the single particle structure of nuclei. Relative spectroscopic factors extracted from transfer cross sections are a measure of the occupation numbers of single particle configurations (particles or holes). These can be compared directly to results from shell-model calculations. The transferred orbital momentum leading to the spin assignment of a state is determined from the angular distribution of the particles. Additionally, the neutron-pair transfer will allow the study of pairing correlations. 2. Setup & simulation Fig. 1 shows on the left a picture of the setup as it was implemented in a GEANT4 simulation. The silicon array consists of two annular DSSSD detectors (CD detectors) for forward and backward angles and a quadratic barrel of position-sensitive strip detectors (16 strips perpendicular to the beam with ≈0.5 mm position resolution) around 90◦ . In a previous experiment performed with a simplified setup at REX-ISOLDE with MINIBALL, only an angular range from 15◦ –55◦ was covered [5]. Here it was not possible to determine the transferred orbital momentum unambiguously. The new setup will cover an extended angular range of ϑlab. ≈ 8◦ –75◦ and 105◦ –172◦ and, as can be seen in Fig. 1 (right), the ambiguities can be resolved. Particle identification for different masses and Q-values requires the use of thin 1E detectors and thick Erest detectors. This allows protons for a large range of energies to pass through the 1E detector and to be stopped in the Erest detector. The inverse kinematics combined with small Qvalues translates for backward angles an excitation energy difference of 1 MeV into a difference in kinematic energy of the protons of a few hundred keV. This compression effect, combined with the energy spread due to the target thickness (≈0.5 mg/cm2 ), limits the achievable energy resolution and makes it necessary to detect the γ -rays in coincidence for the identification of the populated levels. With this new setup, an angular resolution of 3◦ –5◦ and an energy resolution of 60 keV (backward CD) to 2 MeV (forward CD) for protons emitted in the transfer reaction d(30 Mg, 31 Mg)p at 3 MeV/u can be achieved. The energy resolution for both CD detectors is mainly
388
V. Bildstein et al. / Progress in Particle and Nuclear Physics 59 (2007) 386–388
limited by the energy losses in the target, whereas for the barrel it is dominated by the beam spot size (≈5 mm). The efficiency of the setup to detect a particle is ≈62%. References [1] [2] [3] [4] [5]
O. Niedermaier, et al., Phys. Rev. Lett. 94 (2005) 172501. G. Neyens, et al., Phys. Rev. Lett. 94 (2005) 022501. F. Mar´echal, et al., Phys Rev. C 72 (2005) 044314. Th. Kr¨oll, et al. CERN-INTC-2006-036, INTC-P-219, 2006. M. Pantea, Ph.D. Thesis, TU Darmstadt, Germany, 2005.