All posts by tmertzi

(Σκληρο)πυρηνική φυσική

Για τους πρωτοετείς φοιτητές που παρακολούθησαν το σεμιναριακό μάθημα της προηγούμενης Πέμπτης καιι εξέφρασαν το ενδιαφέρον τους να μάθουν περισσότερα για την πυρηνική φυσική και τις εφαρμογές της, μπορούν να με συναντήσουν την ερχόμενη Πέμπτη 1.11.2018 μετά τις 13’15 (δηλ. μετά το τέλος και του δεύτερου σεμιναριακού μαθήματος). Ελάτε με καλή διάθεση να μιλήσουμε για ό,τι σας απασχολεί. -ΘΜ

Radioactive molecules in space – a first detection!

After a long search, a cosmic mystery has an answer. Astronomers have made the very first unambiguous detection of a radioactive molecule in space – an isotope of aluminium, found in the heart of a rare nova.

Scientists have long been searching for 26AlF – or Aluminium monofluoride – containing 26Al, but a direct observation has been exceptionally illusive.

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EIC: a new billion-$$ electron accelerator to look inside protons and neutrons

The next dream machine for U.S. nuclear physicists got an important boost today in a report from the National Academies of Sciences, Engineering, and Medicine. The report committee glowingly approved of the science that could be done with the proposed Electron-Ion Collider (EIC), a billion-dollar accelerator that would probe the innards of protons and neutrons. The endorsement should help the Department of Energy (DOE) justify building the EIC at one of two national laboratories competing to host it, although the project probably won’t get the go-ahead for several years.

“We’re basically saying, ‘You’ve really got to do this,’” says Ani Aprahamian, a nuclear physicist at the University of Notre Dame in South Bend, Indiana, and co-chair of the report committee.

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Nuclear-Spin Comagnetometer Based on a Liquid of Identical Molecules

Atomic comagnetometers are used in searches for anomalous spin-dependent interactions. Magnetic field gradients are one of the major sources of systematic errors in such experiments. Here we describe a comagnetometer based on the nuclear spins within an ensemble of identical molecules. The dependence of the measured spin-precession frequency ratio on the first-order magnetic field gradient is suppressed by over an order of magnitude compared to a comagnetometer based on overlapping ensembles of different molecules. Our single-species comagnetometer is capable of measuring the hypothetical spin-dependent gravitational energy of nuclei at the 10−17 eV level, comparable to the most stringent existing constraints. Combined with techniques for enhancing the signal such as parahydrogen-induced polarization, this method of comagnetometry offers the potential to improve constraints on spin-gravity coupling of nucleons by several orders of magnitude.

Figure 2

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How deadly is your kilowatt?

Everyone’s heard of the carbon footprint of different energy sources, the largest footprint belonging to coal because every kWhr of energy produced emits about 900 grams of CO2. Wind and nuclear have the smallest carbon footprint with only 15 g emitted per kWhr, and that mainly from concrete production, construction, and mining of steel and uranium. Biomass is supposedly carbon neutral as it sucks CO2 out of the atmosphere before it liberates it again later, although production losses are significant depending upon the biomass.

 

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Improved evaluation of nuclear charge radii for superheavy nuclei

Although significant progress has been made in the synthesis of superheavy nuclei, the experimental knowledge of them is still very limited while the alpha decay chain is the main tool used to identify newly produced superheavy nuclei. Previously, we have extracted nuclear charge radii of superheavy nuclei via the experimental alpha decay data. As a further step, the density dependent cluster model is improved by introducing the difference between the density distributions of protons and neutrons. Besides, the important quantity, i.e., the alpha preformation factor, is connected with the microscopic correction of nuclear mass during this procedure, to perform a more reasonable description of the alpha decay process. It is found that the present deduced nuclear charge radii of heavy nuclei are in a better agreement with the measured values as compared to those in our previous evaluations. Subsequently, the nuclear radii of heavier even–even isotopes with Z = 98–116 are probed, accompanied by the consistency with the empirical evaluations. Moreover, the effect of the depressed density at the center of superheavy nucleus on the final extracted nuclear radius plus the decay lifetime is discussed, which appears to be different from the case of lighter nuclide.

 

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Isoscalar and isovector spin response in sd-shell nuclei

The spin magnetic-dipole transitions and the neutron-proton spin-spin correlations in sd-shell even-even nuclei with N=Z are investigated by using shell-model wave functions taking into account enhanced isoscalar (IS) spin-triplet pairing as well as the effective spin operators. It was shown that the IS pairing and the effective spin operators gives a large quenching effect on the isovector (IV) spin transitions to be consistent with data observed by (p,p’) experiments. On the other hand, the observed IS spin strengths show much smaller quenching effect than expected by the calculated results. The IS pairing gives a substantial quenching effect on the spin magnetic-dipole transitions, especially on the IV transitions. Consequently, an enhanced IS spin-triplet pairing interaction enlarges the proton-neutron spin-spin correlation deduced from the difference between the IS and the IV sum-rule strengths. The β-decay rates and the IS magnetic moments of the sd shell are also studied in terms of the IS pairing as well as the effective spin operators.

Figure 7

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Generic features of the neutron-proton interaction

We show that fully aligned neutron-proton pairs play a crucial role in the low-energy spectroscopy of nuclei with valence nucleons in a high-j orbital. Their dominance is valid in nuclei with valence neutrons and protons in different high-j orbitals as well as in N=Z nuclei, where all nucleons occupy the same orbital. We demonstrate analytically this generic feature of the neutron-proton interaction for a variety of systems with four valence nucleons interacting through realistic, effective forces. The dominance of fully aligned neutron-proton pairs results from the combined effect of (i) angular momentum coupling and (ii) basic properties of the neutron-proton interaction.

Figure 6

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