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A mobile Raman spectrometer to determine the spin population of deuterium gas

English title A mobile Raman spectrometer to determine the spin population of deuterium gas
Applicant Kirch Klaus
Number 150651
Funding scheme R'EQUIP
Research institution Institut für Teilchen- und Astrophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Particle Physics
Start/End 01.12.2013 - 30.11.2014
Approved amount 81'000.00
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Keywords (3)

Ultracold neutrons; Deuterium; Raman spectroscopy

Lay Summary (German)

Lead
Am Paul Scherrer Institut ist eine hochintensive Quelle für sehr langsame, sogenannte ultrakalte Neutronen (UCN) in Betrieb. Diese werden mit dem weltweit leistungsstärksten Protonenstrahl durch Spallation auf einem Bleitarget freigesetzt und in schwerem Wasser abgebremst und danach in festem Deuterium (schwerem Wasserstoff) weiter gekühlt bis einige von ihnen als UCN für Experimente zur Verfügung stehen. Unsere Gruppe ist führend an Experimenten mit UCN beteiligt sowie an Untersuchungen zum Verständnis der UCN-Produktion und weiterer Produktionsverbesserungen. Für die UCN-Produktion sind die Eigenschaften des festen Deuteriums von grösster Wichtigkeit. Das mobile Ramanspektrometer erlaubt Untersuchungen der molekularen Eigenschaften des Deuteriums.
Lay summary
Deuteriummoleküle (D2) sind aus zwei Deuteriumatomen mit Deuteronkernen gebildet. Deuteronen sind schwere Wasserstoffkerne mit einem Neutron zusätzlich zu dem Proton. Der Kernspin des Deuterons ist 1, so dass sich für D2 mögliche Gesamt-Kernspins von 0, 1 und 2 ergeben. Die geraden Kernspins bilden aus Symmetriegründen Rotationszustände des Moleküls zu geradem Gesamtdrehimpuls J=0, 2, 4, … und werden als Ortho-D2 bezeichnet. Die D2-Moleküle mit Kernspin 1 haben ungeraden Gesamtdrehimpuls J=1, 3, 5, … und heissen Para-D2. Der Grundzustand des D2-Moleküls ist J=0 Ortho-D2. Para-D2 mit J=1 hat mit einer um 7meV höheren Energie bereits viel mehr Energie als der kinetischen Energie von UCN entspricht (etwa 100neV). Daher können UCN in Stössen mit Para-D2 kinetische Energie aufnehmen, während das Molekül sich zum Orthozustand abregt. Die Neutronen sind danach als UCN verloren. Daher ist für die UCN-Produktion eine möglichst hohe Ortho-Konzentration unbedingt nötig. Ramanspektroskopie der Rotationszustände erlaubt eine quantitative Messung der Ortho- bzw. Para-Konzentration. Das mobile Ramanspektrometer kann zu Untersuchungen am PSI und in unserem ETH-Labor eingesetzt werden. Die Ortho-Konzentration kann in gasförmigem D2 selbst bei Drücken unter einer Atmosphäre gemessen werden. Methoden zur Erzeugung von Ortho-D2 können ebenso studiert werden wie die zeitliche Entwicklung der Konzentration unter verschiedenen Bedingungen wie Temperatur, Bestrahlung oder mit Katalysatoren.
Direct link to Lay Summary Last update: 28.04.2014

Responsible applicant and co-applicants

Publications

Publication
A prestorage method to measure neutron transmission of ultracold neutron guides
Blau B., Daum M., Fertl M., Geltenbort P., Goeltl L., Henneck R., Kirch K., Knecht A., Lauss B., Schmidt-Wellenburg P., Zsigmond G. (2016), A prestorage method to measure neutron transmission of ultracold neutron guides, in NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND, 807, 30-40.
An ultracold neutron storage bottle for UCN density measurements
Bison G., Burri F., Daum M., Kirch K., Krempel J., Lauss B., Meier M., Ries D., Schmidt-Wellenburg P., Zsigmond G. (2016), An ultracold neutron storage bottle for UCN density measurements, in NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND, 830, 449-453.
Neutron production and thermal moderation at the PSI UCN source
Becker H., Bison G., Blau B., Chowdhuri Z., Eikenberg J., Fertl M., Kirch K., Lauss B., Perret G., Reggiani D., Ries D., Schmidt-Wellenburg P., Talanov V., Wohlmuther M., Zsigmond G. (2015), Neutron production and thermal moderation at the PSI UCN source, in NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND, 777, 20-27.
Transmission of ultra-cold neutrons through guides coated with materials of high optical potential
Daum M., Franke B., Geltenbort P., Gutsmiedl E., Ivanov S., Karch J., Kasprzak M., Kirch K., Kraft A., Lauer T., Lauss B., Mueller A. R., Paul S., Schmidt-Wellenburg P., Zechlau T., Zsigmond G. (2014), Transmission of ultra-cold neutrons through guides coated with materials of high optical potential, in NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND, 741, 71-77.

Collaboration

Group / person Country
Types of collaboration
UCN Physics Group of PSI Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Abteilung Spallationsquelle ASQ at PSI Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Associated projects

Number Title Start Funding scheme
137664 Pushing the high intensity frontier for ultracold neutrons 01.11.2011 Project funding
163413 Improving ultracold neutron intensities for frontier precision experiments in fundamental physics 01.11.2015 Project funding
126562 Search for the neutron EDM at the high intensity ultracold neutron source at PSI with an upgraded high sensitivity spectrometer 01.10.2009 Project funding
144473 Search for the neutron EDM at the high intensity ultracold neutron source at PSI with an upgraded high sensitivity spectrometer - Follow-up application 01.10.2012 Project funding
149211 Measurement of the neutron electric dipole moment 01.11.2013 Project funding
149813 Pushing the high intensity frontier with ultracold neutrons 01.11.2013 Project funding
105172 Experiments on critical properties of solid deuterium for a source of ultra-cold neutrons 01.10.2004 Project funding
138211 Measurement of the neutron electric dipole moment 01.11.2011 Project funding

Abstract

We ask for R'EQUIP support to acquire a mobile Raman spectrometer, at a price of about CHF 182’000,-- , allowing to accurately determine and monitor the para-deuterium content of the deuterium (D2) which we use for the production of ultracold neutrons at the Paul Scherrer Institute (PSI). We have successfully tested such an instrument. Maintaining a minimal para-D2 content in the UCN production moderator is of paramount importance in order to achieve high ultracold neutron (UCN) intensities. Any improvement in UCN intensity will directly contribute to a higher sensitivity of experiments performed at the source, e.g. the search for the neutron electric dipole moment (nEDM). Also, any improvement in efficiency for producing and maintaining high ortho-D2 concentrations will gain running time for experiments using UCN. At times, when monitoring of the source is not needed, the Raman spectrometer will allow studying relevant para-to-ortho conversion processes offline in the laboratory of the group at ETH Zurich.The new high-intensity UCN source at PSI has started regular operation in August 2011 and has delivered UCN already for several months in 2011 and 2012. The production of high UCN densities is important for several experiments to test the Standard Model (SM) of particle physics and its possible extensions. A major driving force comes from the search for the electric dipole moment of the neutron in which we are playing a leading role.UCN production at PSI is based on the down-scattering of neutrons in solid deuterium at a temperature of ~5K. Several UCN loss mechanisms in solid D2 must be considered, most prominently phonon up-scattering, spin-flip up-scattering and nuclear capture. Deuterium molecules exist either as para-deuterium (J-odd states) or as ortho-deuterium (J-even states). Loss cross sections strongly depend on the D2 spin state. Around 5K UCN thermal up-scattering on para-D2 has a factor 10 larger cross-section than on ortho-D2. UCN up-scattering via spin-flip on para-D2 is a factor of ~200 larger than any other loss mechanism in D2. Consequently, para-D2 in the converter strongly reduces the UCN intensity and one aims at para-D2 contents below 1%. Then, the up-scattering losses are on the same level as nuclear capture, the latter being a deuterium property which cannot be modified.Part of the D2 system of the UCN source is a para-to-ortho converter applying a paramagnetic catalyst material at low temperatures. D2 gas samples can be extracted from the system in order to measure the para-ortho fraction. Determination of the para-content in this D2 is necessary to optimize the conversion and UCN output. Raman spectroscopy - mostly of rotational states - has been established as the method of choice for the determination of the para-D2 content. We have in the recent past contributed considerably to establishing the methods for para-to-ortho conversion and Raman spectroscopy for D2 based UCN sources.The mobile Raman spectrometer, subject of this proposal, will allow us to directly determine the para-D2 content in D2 gas samples taken at the UCN source’s sample port. It will allow optimizing the D2 para-ortho conversion and monitoring the temporal behavior and stability. It will also allow studying radiation induced conversion in solid D2, an important topic at PSI and reactor and spallation UCN sources worldwide. This can be done in-situ at the PSI UCN source but also offline in our laboratory at ETH Zurich. There we can also study other catalysts that may allow for more efficient conversion in the long term. This mobile, easy-to-use Raman system will replace a stationary and complex system, requiring considerable attention, and will thus be a major step forward.We ask for R'EQUIP support for a Raman spectrometer for D2 gas samples. It will directly contribute to an improved understanding of UCN source physics and possibly an improved UCN intensity at the ultracold neutron source at PSI. It will allow important offline studies aiming at understanding, e.g., radiation induced conversion and better conversion mechanisms.
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