Journal of Physics: Conference Series PAPER • OPEN ACCESS Related content - The status of the micro-calorimeter at the Cryogenic micro-calorimeters for mass Shanghai EBIT - The Variability of the Recombination of spectrometry of keV neutral atoms and molecules Hydrogen Atoms on Metal Surfaces - SQUID gradiometer for ultra-low To cite this article: O Novotný et al 2015 J. Phys.: Conf. Ser. 635 032023 temperature magnetic micro-calorimeter View the article online for updates and enhancements. This content was downloaded from IP address 129.13.72.197 on 04/11/2020 at 09:19 XXIX International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC2015) IOP Publishing Journal of Physics: Conference Series 635 (2015) 032023 doi:10.1088/1742-6596/635/3/032023 Cryogenic micro-calorimeters for mass spectrometry of keV neutral atoms and molecules O Novotn´y∗;y 1, S Allgeierz, C Enssz, A Fleischmannz, L Gamerz, D Hengstlerz, S Kempfz, C Krantz∗, A Pabingerz, C Piesz, D W Saviny, D Schwalm∗;⋄, A Wolf∗ 2 ∗ Max Planck Institute for Nuclear Physics, D-69117 Heidelberg, Germany y Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA z Kirchhoff Institute for Physics, Heidelberg University, D-69120 Heidelberg, Germany ⋄ Faculty of Physics, Weizmann Institute of Science, Rehovot 76100, Israel Synopsis We demonstrate the capability of micro-calorimeters to detect and mass-resolve neutral atoms and molecules at ∼ keV energies, reaching single H-atom resolution. Mass spectrometric identification of fragmen- also studied in detail the MMC response function tation products is one of the most important for molecular projectiles of masses up to 56 amu. tools for molecular collision physics. Most molec- We have demonstrated the capability of iden- ular mass-spectrometry methods employ electro- tifying neutral fragmentation products of these magnetic fields to determine the mass-to-charge molecules by calorimetric mass spectrometry (see ratio of ionized particles. Two major limitations Figure 1) with single H-atom resolution. We have arise from this approach. First, the ratios may modeled the MMC response function for molecu- be ambiguous, e.g., singly charged monomers are lar projectiles and concluded that backscattering indistinguishable from doubly charged dimers. is the dominant source of the observed energy Second, neutral fragments cannot be directly an- spread at the impact energies studied. Further- alyzed and either a \neutral loss" must be ac- more, we have successfully demonstrated the use cepted or an additional ionization stage must be of a detector absorber coating to minimize such used, which results in additional ambiguities. spreads. As an alternative method, the mass of a neu- Our findings [3] are of general interest for tral particle can be deduced from its kinetic en- mass spectrometric techniques with special ad- ergy if the particle velocity is known. This calori- vantage for neutral-particle mass measurements. metric approach has been successfully used in high-energy physics experiments by employing, 120 120 for example, surface barrier detectors [1]. These CH0-3 100 100 C CH3 CO detectors, however, are very restricted in their 80 O ∼ 80 O 60 use at the keV energies relevant for low-energy CH CH 40 2 collision experiments, as their energy resolution 60 20 becomes poor and they often are insensitive to 0 40 30 35 40 the low-energy incident particles. C H 2 0-2 C H O C H 3 5-6 Intensity (arbitrary) 20 3 A promising approach to solve the needs for 0-2 CH3CO low kinetic energy measurements is the use of 0 cryo-detectors, such as micro-calorimeters. With these detectors the particle kinetic energy is 0 20 40 60 80 100 120 140 160 Fragment energy (keV) transformed into heat and sensitive tempera- ture monitoring then provides the measure of Figure 1. MMC energy spectrum of neutral prod- the kinetic energy deposited. The operation at ucts arising from collisions of 150 keV acetone rad- + ∼ 10 mK limits the thermal noise and thus en- icals (C3H6O , 56 amu) with residual gas. ables resolving low measured energies. References We have systematically investigated the en- ergy resolution of magnetic micro-calorimeters [1] H. Buhr at al 2010 Phys. Rev. A. 81 062702 (MMC) [2] for atomic and molecular projectiles [2] A. Fleischmann, C. Ens, and G.M. Seidel 2005 in at impact energies ranging from E ≈ 13 keV to Cryogenic Particle Detection pp. 151-216 150 keV. For atoms we obtained relative energy [3] O. Novotn´y et al, in preparation resolutions down to ∆E=E ≈ 10−3 and absolute 1 energy resolutions down to ∆E ≈ 120 eV. We E-mail: [email protected] 2E-mail: [email protected] Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1.