[RIBF-ULIC-miniWS-023] SUNFLOWER - In-beam gamma and MINOS

20 Feb 2013, 09:00 → 21 Feb 2013, 18:40 Asia/Tokyo

Nishina Hall (Nishina bldg., RIKEN Nishina Center)

Alexandre Obertelli (CEA Saclay), Pieter Doornenbal (RIKEN)

After first experiments with secondary beams produced from 48Ca and 238U primary beams in 2008 and 2009, a first longer in-beam gamma-ray spectroscopy experimental campaign using 48Ca primary beam was performed in November/December 2010. In 2011 and 2012, experimental campaigns using 238U, 124Xe, and 70Zn primary beams followed. Independently, the MINOS (MagIc Numbers Off Stability) project, led by the CEA Saclay, started in 2010 with the aim to develop an active liquid hydrogen target capable of vertex position reconstruction. The MINOS target cell will have a length of up to 150 mm and its performance will first be tested with fast beams in 2013. From 2014, it is planned to couple MINOS to the DALI2 gamma-ray spectrometer and BigRIPS/ZeroDegree. Also experiments with the SAMURAI spectrometer are envisaged. With MINOS, yield enhancements of up to one order of magnitude are expected compared to solid plastic, beryllium, or carbon targets. In addition, great efforts by the RIKEN Nishina Center's accelerator division have led to maximum achieved primary beam intensities of 415 pnA 48Ca, 100 pnA 70Zn, 27 pnA 124Xe, and about 10 pnA 238U at 345 MeV/u. For 2013, the development of a 78Kr primary is foreseen. The main objective for this SUNFLOWER - in-beam gamma and MINOS workshop is therefore the elaboration of in-beam experimental proposals/LOI taking advantage of these primary beam intensities and/or MINOS. Ideally, the proposals will be presented at the 12th NP-PAC meeting, held on June 28-29th, 2013 at the RIKEN Nishina Center. In addition to new experimental ideas and new developments (Clover Array, SHOGUN, MINOS), the status of performed experiments and the experimental conditions (DALI2 resolution and efficiency, atomic and other background, tracking detectors, etc.) will be discussed. Approved experiments seeking for a revision are encouraged to present their physics case.

Application to ULIC app_miniWS023_revised.pdf

Details on MINOS MINOS_IRFUInstrumentation_2012.pdf

Report report_miniWS023.pdf

Wednesday, 20 February

09:30 → 11:00 Introduction

09:30 Welcome

Speaker: Alexandre Obertelli (CEA Saclay)

09:35 Overview of in-beam gamma-ray spectroscopy at the RIBF

An overview of in-beam gamma-ray spectroscopy at the RIBF will be given.

Speaker: Pieter Doornenbal (RIKEN)

10:05 MINOS: description and capabilities

Speaker: Anna Corsi (CEA Saclay)

10:35 Introduction to SAMURAI

Speaker: Ken-Ichiro Yoneda (RIKEN)

11:00 → 11:20 Break

11:20 → 12:30 SAMURAI Experiments and Status of Performed Experiments I

11:20 Overview of the SAMURAI Dayone experiments

The first experimental campaign using the new spectrometer SAMURAI was carried out in May, 2012. I will introduce SAMURAI and report the campaign in the workshop. Future SAMURAI experiment together with MINOS will also be discussed.

Speaker: Yosuke KONDO (Tokyo Institute of Technology)

11:50 Probing neutron correlations in two-neutron halos

Speaker: Tomohiro Uesaka (CNS, University of Tokyo)

12:10 Structure study of the neutron-rich nuclei beyond 132Sn via in-beam γ-ray spetroscopy at RIBF

The structure of the nuclei around doubly magic nucleus 132Sn (Z=50, N=82) is of great importance from the nuclear structure point of view as well as the nuclear astrophysics point of view. The newly commissioned rare isotope facilities in the RIBF provide great opportunities to explore this region. We have invesigated the structure of the nuclei beyond 132Sn via an in-beam γ-ray spectroscopy technique by using high energy RI beams produced by in-flight fission of a 238U primary beam at the BigRIPS fragment separator. We will report the new results from our experiment.

Speaker: He Wang (RIKEN Nishina Center)

12:30 → 13:40 Lunch

13:40 → 15:40 Status of Performed Experiments II and New Experiments I

13:40 Exploring the Island of Inversion

Speaker: Pieter Doornenbal (RIKEN)

14:00 In-beam gamma-ray spectroscopy of 40Mg

The two-proton knockout reaction from 42Si was used to produce 40Mg at the RI Beam Factory, RIKEN Nishina Center. The status and results of this experiment will be presented in connection with the goal to measure gamma-ray decays from excited states and using the direct reaction cross-section to derive information on the structure of 42Si and 40Mg. Possible steps towards future experiments aimed at the spectroscopy of 40Mg will be discussed.

Speaker: Paul Fallon (Lawrence Berkeley Laboratory)

14:20 Status Report of Experiment NP0702-RIBF28

Excited states in the nuclei 38,40,42Si have been studied using in-beam gamma-ray spectroscopy following multi-nucleon removal reactions to investigate the systematics of excitation energies along the $Z=14$ isotopic chain. Experiment have been performed at RIBF with high intensity 48Ca beam emplyed to produce the secondary beams of 40S and 44S. The DALI2 gamma-ray spectrometer have been employed to measure the de-excitaion gamma-rays from excited nuclear states via C(40S,38Si+gamma), C(44S,40Si+gamma) and C(44S,42Si+gamma) reactions. Here, we will report on the status of analysis: the observed excited states, tentative spin-parity assignment and future plan.

Speaker: Masafumi Matsushita (Center for Nuclear Study, University of Tokyo)

14:40 Investigating the structures of neutron-rich Ca isotopes: Outcome of the first Zn-70 campaign at the RIBF

The structures of neutron-rich nuclei around Ca-54 were investigated using in-beam gamma-ray spectroscopy via nucleon knockout reactions with Sc-55 and Ti-56 radioactive beams at the RIBF. This was the first experimental campaign at the facility to use a Zn-70 primary beam at 345 MeV/u. In this presentation a summary of the results and experiment details will be given, and future prospects for studies in this mass region with a Zn-70 beam will be discussed.

Speaker: David Steppenbeck (University of Tokyo)

15:00 Neutron intruder structures in heavy Ti isotopes

Isotopes below Nickel about N=40 are known to exhibit enhanced collectivity, instead of signatures of an N=40 sub-shell closure which is evident in 68Ni. The enhancement of collectivity has been seen in Fe and Cr isotopes in the region through the lowering of 2+1 energies as well as rise in B(E2) excitation strengths, mainly due to an early population of the neutron g9/2 orbital. We intend to test the persistence of this onset of collectivity to lower-Z isotopes, namely Ti, just above the Ca Z=20 magic shell closure. Shell model calculations from different groups predict a siginificant lowering of the neutron d5/2 orbit and a presence of a new "island of inversion" in the region, or rather significant populations of the g9/2 orbital. In either case this would lead to a softening of the N=50 shell closure, and thus an enhanced collectivity in heavy Ti isotopes. To study the single particle structure of heavy Ti isotopes up to A=62, energies of the lowest excited states in even-even nuclei are important, as well as their B(E2) excitation strength, and effective single-particle energies of the relevant orbitals may be deduced from the odd-A Ti isotopes. While in the lighter Ti's up to about A=60 Coulomb excitation to the first excited states should be possible with RIBF intensities and using DALI2. Excited states in the heavier isotopes, especially those higher than the first excited state, can only be reached via knockout reactions. The availability of MINOS in conjunction with DALI2 would offer a steep rise in cross-section for this type of experiments.

Speaker: Volker Werner (Yale University)

15:20 Spectroscopy of 52Ar and 56Ca with DALI2 and MINOS

In the context of nuclear structure evolution with isospin towards the drip-line and local magic numbers phenomena, gamma-spectroscopy of nuclei located in the neutron-rich region around 54Ca is intensively investigated. Indeed, shell-model calculations using the GXPF1 interaction have indicated a new sub-shell closure at N=34. However, this is not confirmed experimentally by the 2+ excitation energy of 58Cr and 56Ti, and other shell-model interactions and mean-field calculations do not predict this sub-shell closure. The important role of 3-body force in explaining shell-closures is suggested by recent ab-initio calculations. Recently, the gamma-spectroscopy of 54Ca was measured at RIKEN to obtain evidence for the N=34 new sub-shell closure. The preliminary results do not indicate high 2+ excitation energy. To further investigate this region, we propose to measure the gamma-spectroscopy of 52Ar and 56Ca. Since these nuclei are very neutron-rich, they are produced at few particles per second only, making their spectroscopy measurement challenging. The measurements in a reasonable time could be possible by using MINOS coupled to the high-efficiency gamma-spectrometer DALI2. In this talk we will discuss the feasibility of measuring 52Ar and 56Ca spectroscopy with the DALI2-MINOS setup.

Speaker: Simon Boissinot (CEA Saclay)

15:40 → 16:00 Break

16:00 → 17:30 Other Projects

16:00 The PRESPEC-AGATA in-beam spectroscopy campaign at GSI

The goal of the PRESPEC-AGATA project is to investigate the structure of exotic nuclei by performing in-beam gamma-spectroscopy experiments employing the SIS-FRS accelerator complex at GSI. The experimental set-up currently includes 19 AGATA high-resolution tracking gamma detectors providing about 10% full energy efficiency at 1 MeV. A set of advanced heavy ion detectors is used for identification and tracking of exotic nuclei selected and transported through the fragment separator FRS. An active target and the heavy ion calorimeter and ToF detector LYCCA-1 complete the arrangement. The set-up constitutes the first full implementation of the HISPEC experiment for NUSTAR at the future FAIR facility. After successful commissioning, a first series of relativistic Coulomb excitation and secondary fragmentation experiments were performed in Autumn 2012. They dealt with the determination of B(E2) values in neutron-rich unstable Pb, Hg and Pt isotopes, fine structure of the pygmy resonance in 64Fe, Coulomb excitation of yrast-trap states in 52Fe and life times in neutron-rich Zr and Mo nuclei. First results show an unrivaled sensitivity of the set-up, surpassing the predecessor experiment RISING by at least one order of magnitude, offering unique access to the structure of exotic nuclei.

Speaker: Juergen Gerl (GSI)

16:30 Status and recent results of the EURICA project

Speaker: Shunji Nishimura (Researcher)

17:00 Clover Array at RCNP and RIBF

A project to construct a Compton-suppressed Ge Clover array by combining the Clover Ge detectors in Japan and the U.S. is proposed to study in detail excited states in exotic nuclei produced at the RIBF facility in RIKEN. This array will be suited for studies utilizing energy-degraded RI beams and also stopped RI beams. Before starting experiments using the Clover array at RIBF, commissioning runs and physics runs are planned at RCNP, Osaka University to check entire system and also output physics results. At RCNP, there is a world unique high-resolution spectrometer, Grand Raiden and also low-energy RI beam line, EN course. Combination of the array with these facilities will also provide unique physics opportunities. Overview and prospects of the Clover Array project will be presented.

Speaker: Eiji Ideguchi (RCNP, Osaka University)

Thursday, 21 February

09:30 → 11:00 Status of Performed Experiments III

09:30 High resolution missing mass spectroscopy using gamma-ray tagging at SHARAQ

Speaker: Susumu Shimoura (CNS, University of Tokyo)

10:00 Structures of neutron drip line nuclei studied by inclusive breakup reactions at ZDS

The breakup reactions of neutron rich nuclei near N=20 and N=28 have been measured with C and Pb targets at about 240 MeV/nucleon at the ZDS spectrometer at RIBF. The breakup with a light target is induced primarily by the nuclear interaction, which is sensitive to the single-particle state of the removed neutron. The gamma ray detected by the DALI2 detector in coincidence with the outgoing charged fragment distinguishes whether the initial state is in excited states. The breakup with Pb target is induced mainly by the Coulomb interaction (Coulomb breakup), where the soft E1 excitation for halo nuclei can be identified. We have found that the combination of these breakup reactions can clarify the configuration (spectroscopic factor and separation energy) of the loosely bound nuclei. We discuss also the halo states in 29Ne,31Ne,and 37Mg, revealed in the experiment.

Speaker: Takashi Nakamura (Tokyo Institute of Technology)

10:20 Status report of experiment NP0811RIBF70R and NP1112-RIBF94

The coulomb excitation of 104Sn was measured in July 2012 at RIBF. At the same time, nuclear inelastic scattering from 12C and hydrogen has been undertaken, as well as neutron-removal cross section measurements. These new data sets provide valuable information on open question of collectivity in light Tin isotopes. The cross section measurement should (i) give a better understanding on the role of undirect processes in the nucleon removal process, (ii) have a better control of cross section estimates, in particular to evaluate the feasibility of the first spectroscopy of 100Sn from in-beam gamma technique coupled to two-neutron removal. In the presentation, preliminary results for both coulomb excitation and knockout measurements will be shown and discussed.

Speaker: Alexandre Obertelli (CEA Saclay)

10:40 Status report of experiment NP0702-RIBF30

Speaker: Ken-ichiro YONEDA (RIKEN Nishina Center)

11:00 → 11:20 Break

11:20 → 12:20 New Experiments II

11:20 Spectroscopy of 78Ni with DALI2 and MINOS

Expected to be doubly magic, 78Ni is a key nucleus to further understand the nuclear shell structure. Its spectroscopy will allow to probe the Z=28 and N=50 shell closures for neutron-rich nuclei. Several experiments on neighbouring nuclei have been performed to this end. The study of N=50 isotones reveals that copper (Z=29), zinc (Z=30), germanium (Z=32) and selenium (Z=34) isotopic chains all exhibit a persistence of the N=50 shell closure. On the other hand, the comparison of experimental data to shell model calculations with a 48Ca core suggests a reduction of the Z=28 shell gap, interpreted as possibly due to the tensor term of the in-medium nucleon-nucleon interaction. Being a very neutron-rich nucleus, 78Ni is a challenge to be produced at sufficient intensity for its spectroscopy in reasonable time, thus rendering the use of the MINOS device with the high efficiency gamma ray DALI2 a clear advantage. In this talk, the feasibility of the spectroscopy of 78Ni with the MINOS-DALI2 setup will be addressed.

Speaker: Clementine Santamaria (CEA Saclay, SPhN)

11:40 Study of shell evolution towards to 78Ni by in-beam gamma-ray spectroscopy

We will propose an experiment for coming MINOS campaign at RIBF to investigate proton shell evolution towards to 78Ni by means of in-beam gamma-ray spectroscopy. The goal of the experiment is to characterize a proton f7/2 hole states in the Cu isotopes populated by one-proton knockout reaction: (p,2p). This will allow us to understand a migration of shell structure induced by the tensor part of the nucleon-nucleon interaction. In the workshop, a physics motivation and feasibility for MINOS@RIBF campaign will be discussed.

Speaker: Megumi NIIKURA (Department of Physics, University of Tokyo)

12:00 Further upgrade of methodology of in-RIbeam spectroscopy

In-beam gamma-ray spectroscopy with RI beams has been cultivated and intensively used in the last two decades to make a major contribution to the progress of the spectroscopy on nuclei far from stability. The main reaction processes so far used with in-flight RI beams are the intermediate-energy Coulex, proton inelastic scattering, and one-nucleon removal reactions. These processes have been so useful to locate collective states as well as to determine the transition strengths. Yet the accessible range of the method is rather limited to low-lying low-spin excited states, and firm spin-parity assignments are often missing. Thus employment of new reaction channels and relevant methods to make unambiguous spin-parity assignments are demanded. In this talk I would like to propose a couple of methodological possibilities to cope with such demands. In particular I emphasize importance of the measurement of gamma-ray angular distributions possibly to afford a useful method for spin-parity assignment.

Speaker: Masayasu Ishihara (RIKEN Nishina Center)

12:20 → 13:30 Lunch

13:30 → 15:30 Approved and Upgrade Experiments

13:30 Study of Collectivities in Neutron-rich N~40 Cr isotopes

A life-time measurement of excited states in neutron-rich deformed nuclei in the mass A≈60 region is planned (NP0906-RIBF07). The recoil distance method (RDM) using the intermediate energy RI beams will be used to measure the lifetimes of 2+ and 4+ states in 60-64Cr and their neighbors. The Big RIPS fragment separator at RIBF will be used to produce the neutron-rich isotope beams in N~40 region by impinging 345AMeV 70Zn beams on a 9Be target. Gamma rays from the excited states at the secondary target will be measured by CNS GRAPE and DALI-2, and the scattered ions will be identified with the Zero Degree spectrometer. The main purpose of the experiment is to study collectivities of the neutron-rich Cr isotopes in a new island of inversion by extracting B(E2) values precisely through lifetime measurements.

Speaker: Eiji Ideguchi (RCNP, Osaka University)

13:50 The pygmy resonance in medium-mass nuclei

Medium-heavy neutron rich isotopes are cheacterized by a layer of excess neutrons on the nuclear surface. The question whether the excess neutrons in the skin can be excited to perform collective oscillations against the N=Z core has attracted considerable interest in recent years. Results and proposed experiments at RIKEN and GSI will be discussed. Additionally possible experimental approaches to study this subject with DALI2 at RIKEN will be shown.

Speaker: Oliver Wieland (INFN sezione di Milano)

14:10 Search for mixed-symmetry states in 136Te and 138Xe

We propose to study the excitation and decay of a second excited 2+ state in the nucleus 136Te at an excitation energy around 1.5-1.6 MeV which is predicted by theoretical calculations to be of mixed-symmetry character. This study will allow to explore for the first time the potential of the Coulomb excitation technique at intermediate energies for the study of mixed-symmetry states (MSS) in radioactive nuclei. We plan to use the known electromagnetic transition strength between the ground and the first excited 2+ state in 132Te, B(E2;01+→21+)= 0.216(22) e2b2, for the normalization of the experimental yields to be obtained in 136Te. In this way, our experiment will provide at the same time a verification of the B(E2) anomaly observed in previous studies in 132Te and 136Te, two protons and either two neutron-holes or two neutrons outside doubly magic 132Sn. It is planned to extend these studies to the heavier N=84 isotone 138Xe. The nuclei of interest will be produced in the projectile fission of a 238U beam on a lead target and Coulomb excited at intermediate energies on a lead target positioned at the F8 focus of the BigRIPS fragment separator. De-excitation γ-rays will be detected by the DALI2 spectrometer in coincidence with the reaction products identified in the Zero Degree Spectrometer. The results of these measurements will shed new light on the irregularities observed in the development of quadrupole collectivity in nuclei around 132Sn and will allow to discriminate between the different theoretical approaches employed in the description of this region of the chart of nuclei far-off stability.

Speaker: Andrea Jungclaus (Instituto de Estructura de la Materia - CSIC)

14:30 Proton induced reactions for exploring structure of neutron rich nuclei

For the previous PAC meetings we submitted proposals to study the structure of neutron rich nuclei via proton inelastic scattering and nucleon removal reactions. Availability of a new hydrogen target and the MINOS setup may trigger the resubmission of the proposals. At one of the first PAC meetings we proposed the study of odd nuclei below the N=50 shell closure to get information on the systematic behavior of the single particle states approaching 78Ni, The energies to be measured determine the strength of the shell closures at N=50 and Z=28. For this purpose we intended to use mainly proton removal reactions the sensitivity of which will be enhanced by use of the MINOS setup. Depending on the success of the previous 78Ni experiment, we are going to resubmit this proposal with highest priority. Based on our results obtained on the enhanced cross section of excitation of states in 27F we proposed to study the F and Ne isotopes next to the N=20 shell closure trough combined use of proton inelastic scattering and Coulomb excitation in order to show that there is an extended neutron distribution – similarly to the carbon case – which is caused by the weakly bound p3/2 neutrons intruding from the next major shell. The extended neutron distribution of the p3/2 neutrons has been shown in 31Ne during the previous 48Ca campaign. A similar proposal has also been submitted for exploration of the region beyond 132Sn, where some times ago anomalously low B(E2) values have been measured. This experiment was intended as a follow up of the Coulomb excitation studies in the region, which will provide information on the charge distribution. The physics problem addressed in the proposal is still actual.

Speaker: Zsolt Dombradi (MTA ATOMKI)

14:50 Isoscalar and isovector dipole excitations in tin isotopes

An experimental campaign has been initiated in order to investigate the dipole response of tin isotopes, in particular, the low-energy part of the spectrum including the Pygmy Dipole Resonance. Stable and unstable isotopes will be investigated utilizing different probes. The program includes experiments at the photon tagger NEPTUN, the HiGS facility, R3B-LAND, and at RIBF. At the RIBF at RIKEN, an experiment on alpha scattering off neutron-rich tin isotopes in inverse kinematics is being planned to study the isoscalar part of the dipole response. The status of the experimental program will be discussed.

Speaker: Thomas Aumann (Technische Universitaet Darmstadt)

15:10 Upgrading of structure study of the exotic nuclei beyond 132Sn

We propose to upgrade NP-0702-RIBF-31 experiment. The proposal is aiming for a systematic study of the nuclear structure beyond 132Sn using high energy RI beams produced by in-flight fission of 238U at BigRIPS. 238U primary beam with higher intensity is available at RIBF. It provides great opportunities to explorer more in this region.

Speaker: He Wang (RIKEN Nishina Center)

15:30 → 15:50 Break

15:50 → 16:50 Discussion and Closing