Natural ortho-para conversion rate in liquid and gaseous hydrogen

Milenko, Yu. Ya.; Sibileva, R. M.; Strzhemechny, M. A.

doi:10.1007/bf02396837

Cited by 68 publications

(40 citation statements)

References 9 publications

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“…Energy differences between spin states of unpaired electrons exposed to magnetic fields are much greater, for example, from those of protons. The magnetic fields associated with protons are small by comparison and unlikely to result in changes in chemical reactivity but can be modulated by the ortho/para conversion in a process known to be modulated by paramagnetic impurities such as metallic cations including copper [9] nor are the oscillations we observe with water due to the net final equilibrium position determining ortho/para conversions which are temperature dependent [10] and reduced in ice [11]. The period length of the oscillatory phenomena reported here by contrast is temperature-independent at physiological temperatures [3] and only reduced from 24 min at room temperature to 22.8 min at liquid nitrogen temperatures as observed from ESR measurements.…”

Section: Discussionmentioning

confidence: 80%

Response of the regulatory oscillatory behavior of copperII-containing ECTO-NOX proteins and of CuIICl2 in solution to electromagnetic fields

Morré¹,

Jiang²,

Marjanovic³

et al. 2008

Journal of Inorganic Biochemistry

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Section: Discussionmentioning

confidence: 80%

Response of the regulatory oscillatory behavior of copperII-containing ECTO-NOX proteins and of CuIICl2 in solution to electromagnetic fields

Morré¹,

Jiang²,

Marjanovic³

et al. 2008

Journal of Inorganic Biochemistry

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“…However, the oscillations we observe with water are apparently not due to the net final equilibrium position determining ortho/para conversions. Net ortho/para conversions are temperature dependent [14] and reduced in ice [8]. While amplitudes of the oscillatory phenomena reported here are temperature dependents, the period length by contrast is temperature-independent [3] and unchanged even at liquid nitrogen temperatures [Results unpublished].…”

Section: Discussionmentioning

confidence: 93%

Regular oscillatory behavior of aqueous solutions of CuII salts related to effects on equilibrium dynamics of ortho/para hydrogen spin isomers of water

Morré

Orczyk

Hignite

et al. 2008

Journal of Inorganic Biochemistry

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“…On the other hands, the experimental data shows that the intensity increases monotonically over time in this energy range although the intensity at 132hours seems to be approaching maximum since the difference between the intensities at 88hours and 132hours is small, which is very similar to the trend of the calculations at the para-hydrogen concentration up to 60%. The ortho/para ratio expected by natural conversion [12] appears in Figure 5, which indicates about 65% para-hydgrogen after 132 hours, so we concluded that the effect of the radiation on the ortho-to-para conversion is not very large at the Lujan center. If we assume the natural conversion, the para ratios at each time are about 26% at 2.5h, 47% at 48h, 57% at 88h and 65% at 132h.…”

Section: Observed Change In Energy Spectrummentioning

confidence: 65%

Measurements of the change of neutronic performance of a hydrogen moderator at Manuel Lujan Neutron Scattering Center due to conversion from ortho- to para-hydrogen state

Ooi

Ichihara

Muhrer

et al. 2006

Nuclear Instruments and Methods in Physics Research Section A:

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The ortho/para hydrogen ratio is a key parameter for the neutronic performance of a liquid hydrogen moderator. In order to get a better understanding of the influence that the ortho/para-hydrogen ratio has on the performance of such a moderator, we measured the neutronic performance of the partially coupled liquid-hydrogen moderator at the LANSCE Manuel Lujan Jr. Neutron Scattering Center, Los Alamos, USA, as a function of time after condensation. This was done by measuring the energy spectra and pulse shapes (neutron emission time distributions) of this moderator. It was found that the neutronic characteristic of the moderator changes with the elapsed time after condensation, and that the changes were so significant that for any scattering experiment made on such a moderator, the effect should be carefully evaluated.Keyword: Pulsed neutron source, Hydrogen moderator, ortho-para conversion, energy spectrum, emission time distribution IntroductionAt 1 MW class high power spallation neutron sources, liquid hydrogen is at present a unique realistic candidate for a cold moderator material. Therefore, liquid hydrogen moderators have been adopted in the new high-power spallation neutron sources, JSNS (Japan Spallation Neutron Source) in Japan and SNS (Spallation Neutron Source) in the USA. Simulation calculations indicate that the neutronic performance of a liquid hydrogen moderator depends on the para-hydrogen concentration.[1-3] Also, it is shown in the experimental result that the neutron pulse peak intensities increase with the higher para hydrogen concentrations.[4] However, there is no experimental data of time dependent neutronic performance from a hydrogen moderator in the high radiation field. Such data would be of great benefit not only to new spallation neutron sources but also to existing neutron facilities.The Manuel Lujan Jr. Neutron Scattering Center has four water moderators and two liquid hydrogen moderators but there is no ortho-para conversion catalyst in the hydrogen loop. Therefore, it is expected that the para-hydrogen concentration in the loop will increase over time after liquefaction. The para hydrogen concentration in the state of equilibrium for hydrogen at T=20 K is 99.8%, whereas at T=300 K the equilibrium is 25% para hydrogen. Since the liquefaction process is significantly faster than the ortho-to-para conversion time without a catalyst at T=20K, the hydrogen loop at the Lujan Center always contains 25% para and 75% ortho-hydrogen right after a fresh filling. However, due to the different points of equilibrium for hydrogen at T=20K and at room temperature, a conversion from ortho to para hydrogen will start immediately. Even though the time constant for this process is fairly long, the ortho/para concentration and with it the neutronic performance will change during a typical period of operation (~10 days) at the Lujan Center. We have therefore measured the neutronic performance of the lower tier partially coupled liquid hydrogen moderator at the Lujan Center continuously for 132...

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Natural ortho-para conversion rate in liquid and gaseous hydrogen

Cited by 68 publications

References 9 publications

Response of the regulatory oscillatory behavior of copperII-containing ECTO-NOX proteins and of CuIICl2 in solution to electromagnetic fields

Response of the regulatory oscillatory behavior of copperII-containing ECTO-NOX proteins and of CuIICl2 in solution to electromagnetic fields

Regular oscillatory behavior of aqueous solutions of CuII salts related to effects on equilibrium dynamics of ortho/para hydrogen spin isomers of water

Measurements of the change of neutronic performance of a hydrogen moderator at Manuel Lujan Neutron Scattering Center due to conversion from ortho- to para-hydrogen state

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