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COLLAPS experiment and spectroscopy beam lines in the ISOLDE facility at CERN

The COLinear LAser SPectroscopy (COLLAPS) experiment is located in the ISOLDE facility at CERN. The purpose of the experiment is to investigate ground and isomeric state properties of exotic, short lived nuclei, including spins, electro-magnetic moments and charge radii.[1] The experiment has been operating since the late 1970s, and is the oldest active experiment at ISOLDE.[2][3]

Isotope Separator On Line Device
(ISOLDE)
List of ISOLDE experimental setups
COLLAPS, CRIS, EC-SLI, IDS, ISS, ISOLTRAP, LUCRECIA, Miniball, MIRACLS, SEC, VITO, WISArD
Other facilities
MEDICISMedical Isotopes Collected from ISOLDE
508Solid State Physics Laboratory

Background

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The technique of collinear spectroscopy was developed in the mid-1970s by S.L. Kaufman.[4] This describes a method of obtaining narrow absorption lines, specifically providing a sensitivity ideal for experiments on short-lived isotopes.

Two beams are used in the technique: a laser beam sent through the sample, and a probe beam. The alignment of both beams collinearly (along the same path) allow for control of the time and spatial overlap.[5] This enables investigation into the nuclear properties of the sample simultaneously.[6]

Experiment setup

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Optical detection region at COLLAPS in the ISOLDE facility

COLLAPS is located within the ISOLDE facility at CERN, giving it access to the radioactive ions produced by ISOLDE's resonance ionisation laser ion source (RILIS).[7] The ions are delivered to the COLLAPS beamline and are excited using tunable continuous-wave lasers through the technique of collinear spectroscopy.[8][9] The laser systems produce laser light in the 210 nm to 1000 nm range with a narrow linewidth. The systems allow access to the atomic transitions necessary for the short-lived nuclei produced by ISOLDE.[3]

Laser spectroscopy is better performed on a neutral atom, and therefore a charge exchange cell (CEC) is needed to neutralise the ionic beam from ISOLDE.[7] A CEC neutralises the ions by causing the ionic beam to collide with the alkali vapours in the cell and transfer charge. Prior to entering the CEC, the ions are reaccelerated (retarded) and a scan of the atomic transition is taken using Doppler-tuning electrodes.[10] Laser spectroscopy is then performed on the neutral atom, however can also be performed directly on the ion. The detection system, located at the end of the beamline, consists of eight large-diameter aspheric lenses.[3] The atoms de-excite and release fluorescent light, which is transferred to the four photomultiplier tubes (PMTs) by the lenses.

Results

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The following are some notable results from the COLLAPS experiment.[11][3]

  • Charge radii, spins and electro-magnetic moments for various isotopes, including magic isotopes
  • Developing the laser spectroscopy setup to examine very exotic isotopes[12]
  • Found first direct evidence for the importance of proton and neutron excitations across shell gaps in ground state wave functions of neutron-rich Mn isotopes[13]
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References

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  1. ^ "COLLAPS | ISOLDE". isolde.cern. Archived from the original on 2023-07-11. Retrieved 2023-07-11.
  2. ^ "Exploring nuclei at the limits". CERN Courier. 2020-09-18. Retrieved 2023-07-11.
  3. ^ a b c d "COLLAPS @ ISOLDE-CERN". collaps.web.cern.ch. Retrieved 2023-07-11.
  4. ^ Kaufman, S. L. (1976-06-01). "High-resolution laser spectroscopy in fast beams". Optics Communications. 17 (3): 309–312. Bibcode:1976OptCo..17..309K. doi:10.1016/0030-4018(76)90267-4. ISSN 0030-4018.
  5. ^ Neugart, R; Billowes, J; Bissell, M L; Blaum, K; Cheal, B; Flanagan, K T; Neyens, G; Nörtershäuser, W; Yordanov, D T (2017-06-01). "Collinear laser spectroscopy at ISOLDE: new methods and highlights". Journal of Physics G: Nuclear and Particle Physics. 44 (6): 064002. Bibcode:2017JPhG...44f4002N. doi:10.1088/1361-6471/aa6642. ISSN 0954-3899.
  6. ^ Wang, S. J.; Yang, X. F.; Bai, S. W.; Liu, Y. C.; Zhang, P.; Liu, Y. S.; Hu, H. R.; Li, H. W.; Tang, B.; Cui, B. Q.; He, C. Y.; Ma, X.; Li, Q. T.; Chen, J. H.; Ma, K. (2022-06-01). "Construction and commissioning of the collinear laser spectroscopy system at BRIF". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1032: 166622. arXiv:2203.07859. Bibcode:2022NIMPA103266622W. doi:10.1016/j.nima.2022.166622. ISSN 0168-9002.
  7. ^ a b Heylen, H.; Devlin, C. S.; Gins, W.; Bissell, M. L.; Blaum, K.; Cheal, B.; Filippin, L.; Ruiz, R. F. Garcia; Godefroid, M.; Gorges, C.; Holt, J. D.; Kanellakopoulos, A.; Kaufmann, S.; Koszorús, Á.; König, K. (2021-01-25). "High-resolution laser spectroscopy of $^{27--32}\mathrm{Al}$". Physical Review C. 103 (1): 014318. arXiv:2010.06918. doi:10.1103/PhysRevC.103.014318.
  8. ^ "The COLLAPS experiment at ISOLDE (CERN)". fys.kuleuven.be. Retrieved 2023-07-12.
  9. ^ "Exploring nuclei at the limits". CERN Courier. 2020-09-18. Retrieved 2023-07-13.
  10. ^ Wraith, C.; Yang, X. F.; Xie, L.; Babcock, C.; Bieroń, J.; Billowes, J.; Bissell, M. L.; Blaum, K.; Cheal, B.; Filippin, L.; Garcia Ruiz, R. F.; Gins, W.; Grob, L. K.; Gaigalas, G.; Godefroid, M. (2017-08-10). "Evolution of nuclear structure in neutron-rich odd-Zn isotopes and isomers". Physics Letters B. 771: 385–391. Bibcode:2017PhLB..771..385W. doi:10.1016/j.physletb.2017.05.085. hdl:2043/23715. ISSN 0370-2693.
  11. ^ COLLAPS. "COLlinear LAser SPectroscopy @ ISOLDE-CERN". Archived from the original on 18 November 2013. Retrieved 12 July 2023.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  12. ^ Ruiz, R F Garcia; Gorges, C; Bissell, M; Blaum, K; Gins, W; Heylen, H; Koenig, K; Kaufmann, S; Kowalska, M; Krämer, J; Lievens, P; Malbrunot-Ettenauer, S; Neugart, R; Neyens, G; Nörtershäuser, W (2017-04-01). "Development of a sensitive setup for laser spectroscopy studies of very exotic calcium isotopes". Journal of Physics G: Nuclear and Particle Physics. 44 (4): 044003. Bibcode:2017JPhG...44d4003G. doi:10.1088/1361-6471/aa5a24. ISSN 0954-3899.
  13. ^ Babcock, C.; Heylen, H.; Billowes, J.; Bissell, M. L.; Blaum, K.; Campbell, P.; Cheal, B.; Garcia Ruiz, R. F.; Geppert, C.; Gins, W.; Kowalska, M.; Kreim, K.; Lenzi, S. M.; Moore, I. D.; Neugart, R. (2015-11-12). "Evidence for Increased neutron and proton excitations between 51−63Mn". Physics Letters B. 750: 176–180. doi:10.1016/j.physletb.2015.09.012. hdl:11577/3185428. ISSN 0370-2693.
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