ISOLDE Solenoidal Spectrometer Workshop 2020

20 Jul 2020, 12:40 → 21 Jul 2020, 17:40 Europe/London

The third ISOLDE Solenoidal Spectrometer Workshop will be held virtually across two afternoons on 20th and 21st July. This workshop will aim to update the community on the status of the ISOLDE Solenoidal Spectrometer project and future developments that will expand the capabilities of the device. The primary objective of the workshop is for the collaboration to discuss proposals to the upcoming INTC for experiments to run in 2021.

If you are planning to submit a proposal to the November meeting of the INTC (submission deadline 22nd September 2020) using the ISS, then we ask that you present your plans to the collaboration during this workshop.. The collaboration will provide advice/feedback on the technical feasibility of all proposals.

The workshop will take place over two afternoons sessions via Zoom (connection details below). We ask you to register to receive updates about the schedule and connection details in due course.

 

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Meeting ID: 945 5801 5954
Password: 635247

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Monday, 20 July

13:00 → 13:55 Introduction and status updates

13:00 Introduction and purpose of workshop

Speaker: Liam Gaffney (University of Liverpool (GB))

Introduction-ISS-Workshop2020.pdf

Introduction-ISS-Workshop2020.pptx

13:10 Project update and overview

Speaker: Robert Page (University of Liverpool (GB))

Page_ISS_project_status+overview.pdf

13:25 Status of SpecMAT: first recorded events and characterisation of the detector

Speaker: Oleksii Poleshchuk (KU Leuven, Institute for Nuclear and Radiation Physics)

2020-07-20_Oleksii_ISS.pdf

13:40 Ideas and Considerations for a Cryogenic Gas Target for the ISS

A cryogenic gas target would be a key device for maximising the range of studies that are possible with the ISS at HIE-ISOLDE. Such a target would open up a number of opportunities relevant to nuclear astrophysics (capitalising on the unique suite of HIE-ISOLDE beams), including ($\alpha$,$p$) reactions as well as being a key tool for structure research [through e.g. ($^{3}$He,$d$)].

The preliminary design of this target is based on the device previously employed with HELIOS at Argonne National Laboratory. In this talk, we will discuss some of the physics opportunities of the device as well as discussing some of the technical challenges.

Speaker: Dr Daniel Doherty (University of Surrey)

ISS2020_DTD.pdf

13:55 → 14:15 Coffee break

Everyone welcome to stay on the call, but this is a chance to stretch your legs and get a fresh coffee

14:15 → 15:15 New proposals: I

14:15 Probing single-particle structure in the Island of Inversion via the 30Mg(d,p) reaction

Speaker: Dr David Sharp (University of Manchester (GB))

14:27 The ($d$,$p$) reaction on $^{132}$Sn: First complete determination of single-neutron excitations outside of doubly magic $^{132}$Sn

Over the decades, there have been many attempt to identify the single-neutron excitations outside of $^{132}$Sn, with beta decay being a common approach. ISOLDE played a key role in identifying a subset of these states in the 90s [1]. A measurement of the $^{132}$Sn($d$,$p$) reaction, the ideal tool to probe these single-particle excitations, has been considered a flagship measurement, often used to motivate the development of the current and next generation radioactive ion beam facilities and equipment. To date, the (presumed) unbound $i_{13/2}$ excitation has not been observed, only estimated [2].
In 2010, a pioneering measurement of this reaction was carried out at Oak Ridge National Laboratory [3] at a beam energy of 4.77 MeV/u using a barrel-like array of silicon detectors. The measurement revealed for the first time the single-particle strength of the levels corresponding to the $f_{7/2}$, $p_{3/2}$, $p_{1/2}$ and $f_{5/2}$ orbitals. These states appear to carry all the single-particle strength, confirming the doubly magic nature of $^{132}$Sn. However, due to the low beam energy, below barrier in the outgoing channel for all bar the ground state, the high-$j$ states were not populated or, in the case of the $h_{9/2}$ excitation, could not be observed due to low resolution. Higher beam energy and the high resolution made possible by the solenoidal-spectrometer technique are is essential for such a measurement. Indeed, the development of the solenoidal spectrometer concept was motivated largely by an eventual measurement of the $^{132}$Sn($d$,$p$)$^{133}$Sn reaction [4]. Thus, ISOLDE and ISS offer a unique opportunity to completely map out the single-neutron excitations outside of $^{132}$Sn, with a beam energy that makes it just possible.
For heavy systems, the performance of the ISS has been emphatically demonstrated in its inaugural year, with a study of the $^{206}$Hg($d$,$p$) reaction at 7.4 MeV/u, revealing for the first time the single-neutron structure outside of $N=126$ [5]. Other facilities (Argonne, FRIB), may have slightly higher beam energy, but in the next 2-5 years, are unlikely to have comparable intensity and purity Sn beams.
For this measurement, we have assumed a beam energy of 8.5 MeV/u with an intensity of $1\times10^5$ particles per second or greater. The purity, if better than 90% is tolerable from past experience. At 2 T, the outgoing protons are dispersed across the whole array, taking advantage of the new ISS Si array. Recoil detection will be necessary, limiting the statistics slightly.
Furthermore, we can also consider the prospect of pushing for a measurement of the $^{134}$Te($d$,$p$) reaction, which would complete our knowledge the evolution of these single-neutron excitations from Sn to Sm, as the $g_{7/2}$ and $d_{5/2}$ protons fill the core up to the $Z=64$ sub-shell at Gd.

[1] P. Hoff et al., Phys. Rev. Lett. 77, 1020 (1996)
[2] Talwar et al. Phys. Rev. C 96, 024310 (2016)
[3] K. L. Jones et al., Nature 465, 454 (2010)
[4] J. P. Schiffer, in Workshop on the Experimental Equipment for an Advanced ISOL Facility, edited by C. Baktash, I. Y. Lee, and K. E. Rehm, Lawrence Berkeley National Laboratory Report No. LBNL-43460, 1999. 
[5] T. L. Tang et al., Phys. Rev. Lett. 124, 062502 (2020)

Speaker: Benjamin Peter Kay (Argonne National Laboratory (US))

sn.pdf

14:39 Probing single-particle states in the 100Sn region through (d,p) transfer reactions

Speaker: Joochun (Jason) Park (Institute for Basic Science )

14:51 Investigation of core-breaking for $Z$ = 50 shell in Sn isotopic chain: Study of proton-hole states in $^{108,110,112}$Sn via single proton transfer reaction

The Sn isotopic chain is a formidable testing ground for the study of shell evolution in various kinds of nuclear models. Even though the first 2$^{+}$ energies in even-even isotopes between $^{102}$Sn and $^{130}$Sn are quite similar, in agreement with the seniority scheme for this valence neutron space, the significant increment of the B(E2: 0$^{+} \rightarrow 2^{+}$) approaching $^{100}$Sn has remained a major puzzle over decades. Recently, the results of state-of-the-art calculations with the Monte Carlo shell model (MCSM) on Sn isotopes, performed in a large model space including single-particle orbits below and above the magic numbers 50 and 82, has explained the anomalous trend of B(E2: 0$^{+} \rightarrow 2^{+}$) by considering a core breaking contribution, namely from $g_{9/2}$ proton orbits. The MCSM calculations also suggest that the numbers of proton holes for the first 0$^{+}$, 2$^{+}$ and 4$^{+}$ states in even-even Sn isotopes will increase when approaching $N$ = 60, e.g., being around 1.2 for the 4$^+_1$ state in $^{110}$Sn. Thus, we want to measure the spectroscopic factor for the protons in the first 0$^{+}$, 2$^{+}$ and 4$^{+}$ states of $^{108,110,112}$Sn which can be produced via single-proton-transfer reactions.

The following projectile + target combinations can be candidates for the current LOI:

$^{107,109,111}$In + $^3$He $\rightarrow$ $^{108,110,112}$Sn + $^2$H;

$^{107,109,111}$In + $^4$He $\rightarrow$ $^{108,110,112}$Sn + $^3$H;

$^{109,111,113}$Sb + $^2$H $\rightarrow$ $^{108,110,112}$Sn + $^3$He;

$^{109,111,113}$Sb + $^3$H $\rightarrow$ $^{108,110,112}$Sn + $^4$He;

The secondary beams which are optimized for In or Sb isotopes can be produced by HIE-ISOLDE at the energy of 5.5~MeV/u, and the light ejectiles will be measured by Solenoidal Spectrometer.

Speaker: Dr Guangxin Zhang (Padova-infn)

15:03 Recoil-particle spectroscopy with the ISOLDE Solenoidal Spectrometer for investigations of mirror nuclei and isobaric analogue states

Speaker: Dr Michael Bowry (University of the West of Scotland)

15:15 → 15:35 Coffee break

Everyone welcome to stay on the call, but this is a chance to stretch your legs and get a fresh coffee

15:35 → 16:47 New proposals: II

15:35 Digging out protons to unearth their impact on the structure of neutron-rich nuclei by (t,α) reactions in inverse kinematics

Speaker: Simone Bottoni (Università degli Studi e INFN Milano (IT))

ISS_Bottoni.pdf

15:47 Probing short range interactions in neutron rich system at ISS

G. de Angelis1, K. Kaneko2, A. Gottardo1, F. Recchia3, J. Valiente Dobon1, C. Domingo Pardo4, R.D. Page4, A. Gottardo1, , D. Mengoni3, B. Rubio4, A. Gargano6, S.J. Freeman7, D.K. Sharp7, I.H. Lazarus7, P. Morrall7, A. Grant7, J. Thornhill4, D.R. Wells4, L.P. Gaffney4, C. Everett4, K. Green5, C. Unsworth8, M. Kogimtzis8, I. Burrows8, M. Cordwell8, ISS collaboration

1 INFN-LNL, Legnaro, Italy
2 Kyushu Sangyo University, Kyushu, Japan
3 Physics and Astromony department, University of Padova, Italy
4 IFIC-Valencia, Spain
5 University of Liverpool, UK
6 INFN- Sezione di Napoli, Napoli, Italy
7 University of Manchester, UK
8 STFC Daresbury Laboratory, UK

Pairing correlations are basic elements of superconductivity and superfluidity in strongly interacting quantum many-body systems. These phenomena span very different size scales, from color-superconducting quark matter to neutron stars, and very different energies, from below meV in superconductors to MeV in nuclei and 100 MeV at the quark scale. Of particular interest are superfluid fermionic states in multicomponent systems with cross-species pairing. Nuclei in this respect represent a very interesting case and indeed the existence of a coherent pn pairing state has been longly investigated with different experimental probes along the line of stability. Open question is if pairing is modified in systems with neutron excess. A recent electron and proton scattering experiment [1] has shown that nucleon in nuclei form close proximity pairs, but, that the fraction of high-momentum protons increases markedly with the neutron excess in the nucleus, whereas the fraction of high momentum neutrons decreases slightly. This effect is somewhat unexpected in the classical shell model, where protons and neutrons fill independent orbits, indicating the presence of a strong pn interaction. For more neutron rich systems, since the neutrons are occupying higher momentum orbitals a strong pn interaction will shift the protons toward more excited states across the Fermi energy surface making the proton distribution more diffuse. As an example we have calculated the proton occupancies for the gs of 68Ni comparing them with those of 56Ni. Using a Shell Model space of f7/2, p3/2, f5/2, p1/2 and g9/2 for both protons and neutrons we obtain spectroscopic factors of 7.754, 0.218, 0,021, 0.004, 0.004 for protons and 7.993, 3.933, 5.769, 0.099, 2.206 for neutrons in the case of 68Ni and 7.310, 0.595, 0.076, 0.015, 0.004 for protons and 7.313, 0.587, 0.079, 0.016, 0.005 for neutrons in the case of 56Ni. Clearly if such effect should be confirmed a revision of the role of the pn interaction would be required.
Proton stripping reactions for nuclei close to shell closures (Z=28 or 50) are suited to probe such effect. Examples are 68Ni(t,4He)67Co or 132Sn(t,4He)131In using the ISS solenoid. For a 68Ni beam (8 10^5 pps at Isolde) at 9 MeV/n, cross sections of the order of several tents mb/sr are expected.

[1] Probing high-momentum protons and neutrons in neutron-rich nuclei Nature 2018 Aug, 560(7720):617-621. Doi: 10.1038/s41586-018-0400-z.

Speakers: Giacomo de Angelis (INFN LNL), Andres Gottardo (INFN LNL)

15:59 206Hg beam on triton target at ISS

Information gained on neutron-rich N~126 nuclei is essential for the understanding of nuclear structure in heavy nuclei. Studies around doubly magic systems allow direct tests of the purity of shell model wave functions. From a longer-term perspective, experiments in this region pave the way toward the understanding of the nuclear-astrophysical r-process waiting point nuclei along the N = 126 shell closure.

The recent pioneering experiment with the Isolde Solenoidal Spectrometer (ISS) used a radioactive $^{206}$Hg beam impinging on a deuterium target. Excited states in $^{207}$Hg were populated via the (d,p) reaction and the properties (energies and spectroscopic factors) of the single-neutron states $g_{9/2}$, $_{d5/2}$, $s_{1/2}$, $d_{3/2}$ and $g_{7/2}$ have been determined [1]. We suggest a continuation of the study of the heavy neutron-rich region using $^{206}$Hg mercury beams, this time on a triton target.

Single-proton states will be studied in the semi-magic $^{205}$Au nucleus populated in (t,alpha) reaction. One excited state above the $d_{3/2}$ proton-hole ground-state is known in $^{205}$Au, which is the $h_{11/2}$ proton-hole isomer at 907(5) keV [2]. At ISS we aim to identify the $d_{5/2}$ and $g_{7/2}$ and proton-hole dominated states.

Two neutron states will be populated in $^{208}$Hg following (t,p) reactions. In addition to the neutron $g^2_{9/2}$ states known from an isomeric decay experiment [3], we expect to populate $i^2_{11/2}$ states in the 2-3.5 MeV region (but no $l$=0 transfer), and the yrast 3-. The latter is due the mixing between the collective octupole phonon and the neutron $g_{9/2} j_{15/2}$ 3- states. The observation of the 3- state will provide information on the evolution of octupole collectivity south-east of $^{208}$Pb.

The above predictions are based on equivalent (t,p) [4] and (t,alpha) [5] reactions performed on a $^{208}$Pb target at triton beam energies of 20 MeV and 17 MeV, respectively. The two reactions can be studied at ISS simultaneously, assuming the availability of Si detectors both downstream and upstream of the triton target. $^{205}$Au is expected to be populated with higher cross-section than $^{208}$Hg, and its associated particle spectrum will be cleaner. Presently, theoretical calculations are being performed by N. Timofeyuk, which will be used for detailed yield calculations.

[1] T.L. Tang et al., Phys.Rev.Lett. 124, 062502 (2020).
[2] Zs. Podolyak et al., Phys.Lett. B 672, 116 (2009).
[3] N. Al-Dahan et al., Phys. Rev. C 80, 061302 (2009).
[4] E.R. Flynn et al, Nucl. Phys. A 195, 97 (1972).
[5] E.R. Flynn et al, Nucl. Phys. A279, 394 (1977).

Speaker: Zsolt Podolyak (University of Surrey)

zsolt_ISS_july2020.pdf

16:11 Probing the 11Li low-lying dipole strength via 9Li(t,p) with the ISS

The exotic, two-neutron halo nucleus $^{11}$Li has proven to be an extraordinarily fruitful laboratory for the study of the nuclear many-body system under very low density conditions. The halo, consisting of the two valence neutrons outside the $^{9}$Li core, form a thin mist of nuclear matter, held together by a subtle mix of the bare NN-interaction and the induced interaction arising from the exchange of collective dipole and quadrupole vibrations. The resulting intertwining of pairing (gauge space) and surface (3D-space) correlations manifests itself not only in the structure of the ground state of $^{11}$Li, but also in the low-lying resonant dipole strength observed at an excitation energy of ~1 MeV.
Recent studies suggest that this symbiotic collaboration between pairing and dipole surface modes would result in an enhanced two-neutron transfer cross section for the population of the dipole mode in the reaction $^{9}$Li(t,p)$^{11}$Li*. Such an experiment constitutes a novel probe of the low-lying dipole strength (pygmy dipole resonance, PDR), and would highlight the role of multipole (in this case, dipole) pairing vibrations in their structure. Such a probe would complement the much-studied characterization of the PDR in terms of its isovector decomposition. It would also confirm the predicted vorticoid character of such a mode, by populating its most elementary manifestation: a single quantum vortex.
The new ISOLDE Solenoidal Spectrometer is one of the most promising tools to perform this challenging experiment, beyond past, conventional approaches. The spectrometer will enable the exclusive measurement of this reaction with unprecedented resolution and sensitivity, which are mandatory to disentangle the $^{11}$Li structure and shed light on the character of the low-lying dipole strength. The expected $^{9}$Li beam yield of around 10$^{6}$ pps makes ISOLDE together with the ISS unique for this type of low-energy measurements not possible in other facilities.

Speakers: Yassid Ayyad (Facility for Rare Isotope Beams), Gregory Potel Aguilar (Lawrence Livermore National Laboratory)

16:23 Anomalous Neutron Pairing Vibrations in Xe Nuclei beyond N=82

Pairing correlations play a crucial role in defining the properties of atomic nuclei. The evolution of these correlations in exotic nuclei is a subject which has received much attention in recent years, as new accelerator facilities are providing unique radioactive beams for study. Of particular interest is the role of pairing in neutron-rich isotopes. In particular in the proton-magic Sn isotopes, theoretical calculations based on Skyrme-Hartree-Fock mean field and continuum RPA predict a significant increase in the neutron pair-transfer strength to low-lying excited 0+ states (pairing vibrations) for N = 82 – 90 nuclei [1].

The first excited 0+2 state can be regarded as a pairing vibrational mode built on the weakly bound p3/2 and p1/2 orbits, which shows a rather long tail in the transition density extending beyond the nuclear surface (>10 fm) resulting in a large strength, comparable to that populating the ground state. The large increase in the pair-transfer probability for N > 82 is almost independent of the volume/surface pairing parametrization used in the mean field calculations. Theoretical calculations for 138Xe (N=84) have been performed [2] and show that a similar phenomenon is also expected in the Xe isotopes. The enhanced tail in the pair transition density depends on the neutron Fermi energy and thus in 138Xe, with more strongly bound neutrons compared to 134Sn, the effect is less pronounced in the Xe isotopes but still noticeable cross N = 82.

Motivated by these predictions and the unique beam and instrumentation capabilities available at CERN, we propose to study (t,p) reactions in reverse kinematics using Xe beams from HIE ISOLDE impinging on a radioactive tritium target and the Solenoidal Spectrometer ISS to identify the outgoing protons, with improved resolving power over conventional setups. According to the anticipated yields [3] we could systematically compare the 2n-transfer cross sections as a function of the projectile mass using beams of 134,136,138,140Xe. Absolute and relative measurements of the L=0 pair transfer strength to the ground and excited 0+ states along the Xe isotopic chain will give us insights into the nature of this novel aspect of pairing collectivity.

References.

1. H. Shimoyama and M. Matsuo. Phys. Rev. C, 84:044317, 2011.
2. S. Tamaki. Master thesis, Niigata University, 2016.
3. https://test-isoyields2-dev1.web.cern.ch/Yield_Home.aspx

Speaker: Augusto Macchiavelli (Lawrence Berkeley National Laboratory)

ISS2020_final.pdf

16:35 Probing the p-n interaction near $^{133}$Sb

The strength of p-n interaction between various orbitals gives an important information to understand the nuclear system [1]. With an intense 133Sb beam of ~5×10^5 pps produced by the HIE-ISOLDE, the p-n interaction near 133Sb can be probed via the (d,p) and (d,t) reactions. We will discuss the feasibility of these reactions such as the yield, the Q-value resolutions, and experimental requirement.

References

[1] J.P. Schiffer and W.W. True, "The effective interaction between nucleons deduced from nuclear spectra," Reviews of Modern Physics, vol. 48, p. 191, 1976.

Speaker: Tsz Leung Tang (Argonne National Laboratory (US))

Tuesday, 21 July

13:00 → 14:00 New proposals: III

13:00 Evolution of single-particle structure outside N=126

Speaker: David Sharp (University of Manchester (GB))

13:12 The nuclear structure of $^{79,80}$Zn

We wish to exploit the superior resolution allowed by the ISS to study the structure of the isotopes $^{79}$Zn and $^{80}$Zn correlating excitation energy and gamma decay in (d,p) and inelastic scattering reactions on CD$_2$ and C target.

Speaker: Riccardo Raabe (Instituut voor Kern- en Stralingsfysica, K.U.Leuven)

13:24 Spectroscopy of proton rich Ar and Ne isotopes with the ISS spectrometer

The ideal nuclear picture derived from the shell model considers the nucleus as composed of defined nuclear states fully occupied by nucleons. However in a real nucleus correlation effects [1] lead to the mixing of configurations, reducing the occupancies as the Fermi energy is reached. For stable nuclei the (e,e’p) data reveals a quenching factor a round ~ 0.7 with respect to the independent-particle shell model [2], but the situation in the regions of beta-instability is still greatly unknown. Neutron quenching factors for exotic 31S, 32Cl, and 33Ar determined with knockout reactions decrease to around ~ 0.5 [3]. For the case of 32Ar a small value of ~ 0.25 was reported, showing the effect of correlations on neutron subshells N=15,16 far from stability. For Ne isotopes, spectroscopic factors for 23Ne and stable isotopes are given in [4], and the case of 25Ne was investigated in [5]. On the other hand, there is very few spectroscopic information available for the proton orbitals. Detailed knowledge of proton rich Ar and Ne isotopes is relevant for understanding the formation of proton haloes and skins in the vicinity of the drip lines [6, 7]. The present proposal aims to exploring the evolution of single-particle occupancies on sd-shell nuclei close to the drip lines. The novel Isolde Solenoidal Spectrometer recently commissioned at ISOLDE [8] can be used to study the spectroscopic factors to the ground and low excited states in inverse kinematics.
References
[1] W. Dickhoff, C. Barbieri, Prog. Nucl. Part. Sci. 52 (2004) 377.
[2] V.R. Pandharipande et al., Rev. Mod. Phys. 69 (1997) 981.
[3] A. Gade et al., Eur. Phys. J. A 25, s01, (2005) 251–253; Phys. Rev. C 69 (2004) 034311. [4] M. B. Tsang et al., Phys. Rev. Lett. 95 (2005) 222501.
[5] W N Catford et al 2005 J. Phys. G: Nucl. Part. Phys. 31 S1655.
[6] A. Ozawa et al., Nuclear Physics A 709 (2002) 60–72.
[7] R. Kanugo et al, Eur. Phys. J. A 25, 327–330 (2005).
[8] T. L. Tang et al. Phys. Rev. Lett. 124 (2020) 062502.

Speaker: Ismael Martel Bravo (University of Huelva (ES))

13:36 Exploring the use of ($d$,$d$') in inverse kinematics to measure nuclear deformations

Speaker: Liam Gaffney (University of Liverpool (GB))

13:48 Study of the $^{61}$Zn($d,p$)$^{62}$Zn reaction with the ISS

We propose to study the $^{61}$Zn($d,p$)$^{62}$Zn reaction in inverse kinematics for the first time, using the ISOL Solenoidal Spectrometer currently being installed at ISOLDE. This measurement represents the mirror analog of the astrophysically important $^{61}$Ga($p$,$\gamma$)$^{62}$Ge process (a reaction that cannot be presently studied with conventional means) and will allow for the first ever constraints to be placed on the stellar reaction rate. In particular, the energies and spectroscopic factors obtained for excited states in $^{62}$Zn will be used to determine the resonant properties of proton-unbound levels in the nucleus $^{62}$Ge, which are expected to dominate the $^{61}$Ga($p$,$\gamma$)$^{62}$Ge reaction in X-ray bursts. This study is very timely as the $^{61}$Ga($p$,$\gamma$)$^{62}$Ge reaction directly affects astronomical observables that are currently being obtained by the latest generation of space-based telescopes with unprecedented precision. Moreover, it complements previous work with the ISOL Solenoidal Spectrometer by extending the programme to studies relevant for nuclear astrophysics.

Speaker: Dr Gavin Lotay (University of Surrey)

61Zn(d,p).pdf

61Zn(d,p).pptx

14:00 → 14:20 Coffee break

Everyone welcome to stay on the call, but this is a chance to stretch your legs and get a fresh coffee

14:20 → 15:20 New proposals: IV

14:20 Direct reactions at ISS with Kr and Se beams in batch mode

G. de Angelis1, C. Domingo Pardo2, F. Recchia3, R.D. Page4, A. Gottardo1, J. Valiente Dobon1, D. Mengoni3, B. Rubio2, A. Gargano5, S.J. Freeman6, D.K. Sharp6, I.H. Lazarus7, P. Morrall7, A. Grant7, J. Thornhill4, D.R. Wells4, L.P. Gaffney4, C. Everett4, K. Green4, C. Unsworth7, M. Kogimtzis7, I. Burrows7, M. Cordwell7, ISS collaboration

1 INFN-LNL, Legnaro, Italy
2 IFIC-Valencia, Spain
3 Physics and Astromony department, University of Padova, Italy
4 University of Liverpool, UK
5 INFN- Sezione di Napoli, Napoli, Italy
6 University of Manchester, UK
7 STFC Daresbury Laboratory, UK

Neutron capture reactions on unstable targets are of considerable interest for astrophysical models since a knowledge of their cross sections, combined with an experimental knowledge of the beta decay rates and the isotopic abundances, allows one to determine the neutron flux and, therefore, the environmental conditions for s-process or r-process nucleosynthesis. Unfortunately, since such nuclei are unstable and a neutron target cannot be realized, most of them are out of reach for direct measurements using present RIB facilities. An alternative possibility is to use indirect methods. In this letter of intent we want to propose neutron capture cross sections of astrophysical interest for the s-process using the so-called surrogate method. The surrogate method has largely been used in the past for the study of neutron-induced fission reactions. More recently the method has been extended to the case of neutron capture reactions of astrophysical interest and the conditions for the validity of its use have been determined. The method is based on the use of transfer reactions ((d,p) with conditions on the phase space) as a surrogate for the relevant neutron capture reaction.
85Kr and 79Se beams are two interesting examples. They have both a long half-life allowing a batch mode operation, inserting the gas directly into the ion-source of the ISOLDE Linac. They are both an s-process branching point, located in a region where two scenarios may contribute, the one from massive stars (weak s-process component) and that of AGB stars (main s-process component). Knowledge of the n-capture cross section of 85Kr and 79Se provides therefore a crucial test of our understanding of s-process nucleosynthesis in massive stars and can be achieved through (d,p) reactions using ISS and gamma detections.
85Kr(d,p) is also a very interesting reaction from the nuclear structure point of view. Since 86Kr is located on the N=50 shell closure for neutrons, spectroscopic factors would directly probe the hole states into the shell gap providing a direct test of the stability of the shell closure. If gamma detection will be implemented to ISS, lifetime measurements with the plunger method could also be an additional and very promising possibility.
Being the two radioactive beams realized in batch, those reactions are perfectly suited for operation in shut-down periods or running in parallel with low-energy ISOLDE experiment

Speaker: Giacomo de Angelis (INFN LNL)

14:32 Production of $^{60}$Fe.

The isotope $^{60}$Fe contributes substantially to the Galactic $\gamma$-radioactivity measured with satellite-based instruments and it is characterized by a diffuse distribution along the galactic plane.
Numerous studies focused on the nucleosynthesis $^{60}$Fe/$^{26}$Al ratio.
A significant contribution to the interstellar $^{60}$Fe abundance is provided by the s-process during convective shell C-burning in massive stars, where high neutron densities are produced by the $^{22}$Ne($\alpha$, n)$^{25}$Mg reaction.
A number of new missions have been proposed as next generation $\gamma$-ray satellites that are well-suited to measuring $^{26}$Al and $^{60}$Fe in supernova remnants (AMEGO e-ASTROGAM, COSI, ETCC and Lunar Occultation Explorer). It is expected that the sensitivity limit will allow the detection of old core-collapse supernova remnants (SNRs) in the Milky Way from their gamma-ray emission from the decay of $^{60}$Fe shows that the next generation of gamma-ray missions could be able to discover up to ∼100 such old SNRs as well as measure the $^{60}$Fe yields of a handful of known Galactic SNRs [2].
The cross section of the astrophysical production reaction, $^{59}$Fe(n, $\gamma$)$^{60}$Fe has been measured only once using a relativistic Coulomb dissociation experiment [1]. We propose to measure the $^{59}$Fe(n, $\gamma$)$^{60}$Fe cross section at astrophysical energies indirectly via the reaction $^{59}$Fe(d,p) with the much improved resolution offered by the ISS spectrometer.

[1] E. Uberseder, et al. PRL 112, 211101 (2014)

[2] S.W. Jones. et al. MNRAS 485, 3, 4287–4310 (2019)

Speaker: Antonio Caciolli (Univeristy and INFN Padova)

14:44 Spectroscopy of 8Be: Search for Rotational Band Above 16 MeV

Speaker: Prof. Moshe Gai (University of Connecticut (US))

14:56 Studies of np pairing in N=Z nuclei at ISOLDE with the ISS: the 48Cr(3He,p)50Mn reaction

The question of np pairing in N=Z nuclei remains a subject of much interest in the nuclear structure community [1]. While clearly T=1 np pairing exists on an equal footing with T=1 nn and pp pairing, it is still an open question if the T=0 part of the force gives rise to collective pairing effects.

Two-nucleon transfer reactions such as (t,p) and (p,t) reactions provided a unique tool to understand pairing correlations in nuclei [2], and suggest that the transfer of an np pair from even-even to odd-odd self conjugate nuclei may stand out as the best tool to study these correlations. The (p,3He) and (3He,p) reactions appear as the best choice since the np pair can be transferred in both isospin states. Beyond 40Ca, these studies require radioactive beams and
the use of reverse kinematics techniques.

Cross-section measurements for np transfers from an even-even projectile to the lowest Jπ=0+,1+ states in the odd-odd neighbor, and specifically the ratio σ(0+)/σ(1+) itself (which minimizes systematic effects) are sensitive to the pairing collectivity in the respective channels. Recent systematic studies in N=Z sd-shell nuclei [3] showed that these are indeed key observables to quantify the interplay between T=0 and T=1 pairing [3].

First measurements with radioactive beams have been carried out at ATLAS [4] and GANIL [5], where the reactions 44Ti(3He,p)46V and 56Ni, 52Fe(3He,p)54Co,50Mn were respectively studied. The combined results provide strong evidence for an isospin-triplet superfluid phase but the anticipated collective nature in the isospin-singlet pairing remains elusive.

These reactions are well suited to be studied at HIE-ISOLDE with the Solenoidal Spectrometer ISS setup, which offers a large acceptance and excellent resolving power in terms of particle identification and effective energy resolution.
Since we are interested in L=0 (S=0, S=1) transfers, the cross-sections are forward peaked in the CM frame. Due to the reverse kinematics and typical Q-values, the forward CM protons go backwards in the Lab with energies of about 5MeV. Here we propose to complete the study of f-shell nuclei with the 48Cr(3He,p)50Mn reaction. With 48Cr located at mid-shell, simple arguments suggest that pairing collective effects are maximized and are confirmed by realistic GXPF1+DWBA calculations [5]. The anticipated yield of 48Cr, ~106 pps on target [6], is very adequate for a successful 7 days measurement.

References:

[1] S. Frauendorf and A.O. Macchiavelli, Prog. in Part. and Nucl. Phys. 78, 24 (2014) and references therein.
[2] R.A.Broglia, O.Hansen and C.Riedel, Adv. Nucl. Phys. Vol 6 (1973)
[3] Y. Ayyad et al., Phys. Rev. C 96, 021303(R) (2017).
[4] A.O.Macchiavelli, Report on the second EURISOL User Group Topical Meeting 1, Pag. 94 (2011) .
[5] B. Le Crom, M. Assie´, Y. Blumenfeld, et al., Submitted to Phys. Rev. Lett. (2020).
[6] https://test-isoyields2-dev1.web.cern.ch/Yield_Home.aspx

Speaker: Yassid Ayyad (NSCL)

15:08 The ($d$,$p$) reaction on $^{11}$Be: Bringing clarity to our understanding of the structure of $^{12}$Be

A quantitative description of the interplay between the $p$-, $s$- and $d$-shell configurations in $^{12}$Be still alludes us despite numerous attempts via direct and indirect reactions. To resolve this situation we would like to explore the possibility of a study of the $^{11}$Be($d$,$p$)$^{12}$Be reaction at a beam energy of around 10 MeV/u, using the ISS to achieve the necessary 100-keV FWHM resolution.
The available data on 12Be are ambiguous and limited [1,2]. It has been difficult to probe via transfer reactions at ideal energies, around 10 MeV/u. Measurements of the ($d$,$p$) reaction have been made before at low (5 MeV/u) [3] and high (27 MeV/u) [4] incident beam energies, both yielding new insights. However, each measurement had limiting factors which hampered the interpretation of the data. The low-energy measurement was done at large center-of-mass angles, over a narrow range, and the Q-value resolution was >100 keV resulting in an ambiguous interpretation of the excited 0+ state. Similarly, the high-energy measurements suffered from low resolution. The low-lying states are expected to be either two 1$s_{1/2}$0$d_{5/2}$ neutrons coupled to a $^{10}$Be ground state, 0$p_{1/2}$-shell configurations, or a mixture of these. Clearly, the ($d$,$p$) reaction is the ideal probe, if a suitable beam energy and spectrometer are available. As such, we would like to propose a measurement of the $^{11}$Be($d$,$p$) reaction at ISOLDE with the new ISOLDE Solenoidal Spectrometer to help resolve the long-standing uncertainties in the low-lying structure of $^{12}$Be and to better determine the $s_{1/2}$ and $d_{5/2}$ single-particle energies, which are of interest in the exploration of weak binding effects in light neutron-rich nuclei.
Such a measurement has been considered at Argonne using an in-flight produced beam, but the emittance prohibits a high-resolution measurement and furthermore a $^{11}$Be beam will not be available for several years at suitable intensities at FRIB. ISOLDE and ISS represent the ideal combination for this measurement and an opportunity to clarify our understanding of this fascinating nucleus, $^{12}$Be, removing many of the existing ambiguities. The measurement will complement a new background free measurement of the $^{10}$Be($t$,$p$)$^{12}$Be reaction at ReA using SOLARIS.

[1] H. T. Fortune, Phys. Rev. C 99, 064314 (2019)
[2] H. T. Fortune, Phys. Rev. C 99, 064314 (2019)
[3] R. Kanungo et al., Phys. Lett. B 682, 391 (2010)
[4] J. Chen et al., Phys. Lett. B 781, 412 (2018)
[5] J. Chen et al., Phys. Rev. C 98, 014616 (2018)
[6] C. R. Hoffman et al., Phys. Rev. C 89, 061305(R) (2014)

Speaker: Jie Chen (FRIB)

15:20 → 15:40 Coffee break

Everyone welcome to stay on the call, but this is a chance to stretch your legs and get a fresh coffee

15:40 → 16:40 Collaboration and planning

Discussion of the collaboration structure, memorandum of understanding and commissioning in 2020/21.

Summary-ISS-Workshop2020.pdf

Summary-ISS-Workshop2020.pptx