Background: Mainly because of its long half-life and despite its scientific relevance, spectroscopic measurements of Lu176 forbidden β decays are very limited and lack formulation of shape factors. A direct precise measurement of its Q value is also presently unreported. In addition, the description of forbidden decays provides interesting challenges for nuclear theory. The comparison of precise experimental results with theoretical calculations for these decays can help to test underlying models and can aid the interpretation of data from other experiments. Purpose: Perform the first precision measurements of Lu176β-decay spectra and attempt the observation of its electron capture decays, as well as perform the first precision direct measurement of the Lu176β-decay Q value. Compare the shape of the precisely determined experimental β spectra to theoretical calculations, and compare the end point energy to that obtained from an independent Q value measurement. Method: The Lu176β-decay spectra measurements and the search for electron capture decays were performed with an experimental setup that employed lutetium-containing scintillator crystals and a NaI(Tl) spectrometer for coincidence counting. The β decay Q value was determined via high-precision Penning trap mass spectrometry (PTMS) with the LEBIT facility at the National Superconducting Cyclotron Laboratory. The β-spectrum calculations were performed within the Fermi theory formalism with nuclear structure effects calculated using a shell model approach. Results: Both β transitions of Lu176 were experimentally observed and corresponding shape factors formulated in their entire energy ranges. The search for electron capture decay branches led to an experimental upper limit of 6.3×10-6 relative to its β decays. The Lu176β-decay and electron capture Q values were measured using PTMS to be 1193.0(6) and 108.9(8) keV, respectively. This enabled precise β end point energies of 596.2(6) and 195.3(6) keV to be determined for the primary and secondary β decays, respectively. The conserved vector current hypothesis was applied to calculate the relativistic vector matrix elements. The β-spectrum shape was shown to significantly depend on the Coulomb displacement energy and on the value of the axial vector coupling constant gA, which was extracted according to different assumptions. Conclusion: The implemented self-scintillation method has provided unmatched observations of Lu176, independently validated by the first direct measurements of its β-decay Q value by Penning trap mass spectrometry. Theoretical study of the main β transition led to the extraction of very different effective gA and log10f values, showing that a high-precision description of this transition would require a realistic nuclear structure with nucleus deformation.

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This paper describes the methods and results for the localization by triangulation of cosmic gamma-ray bursts (GRBs) independently observed by two space experiments: the Mercury Gamma-ray and Neutron Spectrometer (MGNS) and the High Energy Neutron Detector (HEND). MGNS is onboard the MPO/BepiColombo mission and on a stage of cruise to Mercury whereas HEND is onboard Mars Odyssey mission and in orbit around Mars. An analysis is performed of the accuracy of localization of the GRBs jointly observed by the two instruments at interplanetary distances by comparing their light curves. Notable achievements and scientific opportunities are described also in light of the recent inclusion of MGNS within the program of interplanetary network for gamma-ray burst localization (IPN).

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An updated set of goals and objectives for the Mercury Gamma and Neutron Spectrometer (MGNS) are presented based on the most recent findings of the MESSENGER mission. The updated design of MGNS with the new CeBr₃ crystal for detection of gamma-ray along with its benefits for the detection of ⁴⁰K and K/Th ratio are discussed. MGNS will then be capable of measuring the elemental composition of shallow subsurface in order to empirically evaluate the fittest model on the origin of Mercury, as well as the presence of possible water ice deposits on the permanently shadowed polar craters on the planet. We present the results of the first measurements in space performed during the instrument commissioning phase and during the first Earth flyby which occurred in April 2020.

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The dual spacecraft mission BepiColombo is the first joint mission between the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) to explore the planet Mercury. BepiColombo was launched from Kourou (French Guiana) on October 20th, 2018, in its packed configuration including two spacecraft, a transfer module, and a sunshield. BepiColombo cruise trajectory is a long journey into the inner heliosphere, and it includes one flyby of the Earth (in April 2020), two of Venus (in October 2020 and August 2021), and six of Mercury (starting from 2021), before orbit insertion in December 2025. A big part of the mission instruments will be fully operational during the mission cruise phase, allowing unprecedented investigation of the different environments that will encounter during the 7-years long cruise. The present paper reviews all the planetary flybys and some interesting cruise configurations. Additional scientific research that will emerge in the coming years is also discussed, including the instruments that can contribute.

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BepiColombo has a larger and in many ways more capable suite of instrumentsrelevant for determination of the topographic, physical, chemical and mineralogical proper-ties of Mercury’s surface than the suite carried by NASA’s MESSENGER spacecraft. More-over, BepiColombo’s data rate is substantially higher. This equips it to confirm, elaborateupon, and go beyond many of MESSENGER’s remarkable achievements. Furthermore, thegeometry of BepiColombo’s orbital science campaign, beginning in 2026, will enable itto make uniformly resolved observations of both northern and southern hemispheres. Thiswill offer more detailed and complete imaging and topographic mapping, element mappingwith better sensitivity and improved spatial resolution, and totally new mineralogical map-ping.We discuss MESSENGER data in the context of preparing for BepiColombo, and de-scribe the contributions that we expect BepiColombo to make towards increased knowledgeand understanding of Mercury’s surface and its composition. Much current work, includinganalysis of analogue materials, is directed towards better preparing ourselves to understandwhat BepiColombo might reveal. Some of MESSENGER’s more remarkable observationswere obtained under unique or extreme conditions. BepiColombo should be able to confirmthe validity of these observations and reveal the extent to which they are representative ofthe planet as a whole. It will also make new observations to clarify geological processesgoverning and reflecting crustal origin and evolution.We anticipate that the insights gained into Mercury’s geological history and its currentspace weathering environment will enable us to better understand the relationships of surfacechemistry, morphologies and structures with the composition of crustal types, including thenature and mobility of volatile species. This will enable estimation of the composition of the mantle from which the crust was derived, and lead to tighter constraints on models forMercury’s origin including the nature and original heliocentric distance of the material fromwhich it formed.@en

Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data. Purpose: Compare a direct measurement of the La138β-decay Q value with the β-decay spectrum end-point energy measured by Quarati et al. using LaBr3 detectors [Appl. Radiat. Isot. 108, 30 (2016)ARISEF0969-804310.1016/j.apradiso.2015.11.080]. Use new precise measurements of the La138β-decay and electron capture (EC) Q values to improve theoretical calculations of the β-decay spectrum and EC probabilities. Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of La138, Ce138, and Ba138 ions from which β-decay and EC Q values for La138 were obtained. Results: The La138β-decay and EC Q values were measured to be Qβ=1052.42(41) keV and QEC=1748.41(34) keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang, Chin. Phys. C 41, 030003 (2017)1674-113710.1088/1674-1137/41/3/030003] by an order of magnitude. These results are used for improved calculations of the La138β-decay shape factor and EC probabilities. New determinations for the Ce138 2EC Q value and the atomic masses of La138, Ce138, and Ba138 are also reported. Conclusion: The La138β-decay Q value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for La138β decay using our new Q value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data.@en

The results obtained by experimentally studying gamma rays emitted by samples prepared as analogs of planetary matter and irradiated with thermal neutrons are presented. The intensities of spectral lines of gamma rays emitted by such samples differing in chemical composition are compared. These results will be used in processing data on gamma-ray spectra of the Moon and Mercury from measurements performed onboard spacecrafts with the aim of studying the composition of the surface of these celestial bodies.

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