IMT Institutional Repository: No conditions. Results ordered -Date Deposited. 2024-03-28T18:02:16ZEPrintshttp://eprints.imtlucca.it/images/logowhite.pnghttp://eprints.imtlucca.it/2014-11-10T13:34:02Z2015-03-25T09:16:39Zhttp://eprints.imtlucca.it/id/eprint/2361This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/23612014-11-10T13:34:02ZAlmahata Sitta meteorite: gamma-activity measurements at Monte dei Cappuccini Laboratory in Torino The asteroid 2008 TC3 was telescopically seen prior to entering Earth’s atmosphere
and was predicted to fall in Sudan on October 7, 2008, as it actually happened.
Subsequently, many fragments were collected from the Nubian desert. At Monte
dei Cappuccini Laboratory (IFSI, INAF) in Torino, using a selective gamma spectrometer
we measured gamma rays from fragment #15, one of the largest retrieved, a ureilite of mass
75 g. Six cosmogenic radionuclides have been measured (46Sc, 57Co, 54Mn, 22Na, 60Co and
26Al). 60Co and 26Al activities allowed us to deduce that the fragment was located at a depth
of 41�14 cm inside the 1.5–2m radius asteroid. Moreover, 22Na activity is slightly greater
than expected on the basis of the average cosmic ray flux and this could be ascribed to the
prolonged solar minimum preceding the meteorite fall.Carla TariccoNarendra BhandariPaolo ColombettiAlberto RomeroGianna Vivaldogianna.vivaldo@imtlucca.itNeeharika SinhaPeter JenniskensMuawia H. Shaddad2014-11-10T13:11:37Z2015-03-25T09:16:39Zhttp://eprints.imtlucca.it/id/eprint/2360This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/23602014-11-10T13:11:37ZCosmogenic radioisotopes in the Almahata Sitta ureiliteAsteroid 2008 TC3 was predicted to fall in Sudan on October 7, 2008, and 2 months later, 15 meteorite fragments were recovered from the Nubian Desert. Most of these fragments were classified as polymict ureilites. In the largest ureilitic fragment #15, weighing 75 g, we have measured six gamma emitting radionuclides (46Sc, 57Co, 54Mn, 22Na, 60Co, and 26Al) by nondestructive whole rock counting using a sensitive gamma-ray spectrometer. The activities of 60Co, produced mainly by neutron capture in cobalt, and 26Al indicate that fragment #15 was located at a depth of 41 ± 14 cm inside the 1.5–2 m radius asteroid. The activity of other radionuclides is also consistent with this shielding depth within the asteroid. The 22Na/26Al activity ratio is higher than expected for the average cosmic ray flux, probably due to the unusually prolonged solar minimum before the fall.Carla TariccoNarendra BhandariPaolo ColombettiAlberto RomeroGianna Vivaldogianna.vivaldo@imtlucca.itNeeharika SinhaPeter JenniskensMuawia H. ShaddadG. M. Ballabh2014-11-10T11:20:52Z2015-03-25T09:16:39Zhttp://eprints.imtlucca.it/id/eprint/2355This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/23552014-11-10T11:20:52ZReconstruction of solar activity variations in the past by measurement of cosmogenic radioisotopes in meteoritesMany reconstructions of solar activity variations in the past are based on the measurement of cosmogenic isotopes (such as 14C and 10Be) stored in terrestrial archives. The concentration of these isotopes is however influenced by terrestrial phenomena. In order to avoid this problem our group is studying cosmogenic radioisotopes in meteorites at the underground laboratory of Monte dei Cappuccini in Torino (Italy). Measurement of 44Ti decay activity in 21 meteorites has revealed a centennial oscillation superimposed on a decreasing trend of the cosmic ray flux in the last 235 years. The decreasing trend is consistent with some models based on solar open magnetic field variations. We show some preliminary results obtained using a new acquisition system we have recently developed and set up in order to enhance selectivity of 44Ti detection.Carla TariccoNarendra BhandariPaolo ColombettiAlberto RomeroNeeharika VermaGianna Vivaldogianna.vivaldo@imtlucca.it2014-11-07T13:04:39Z2015-03-25T09:16:39Zhttp://eprints.imtlucca.it/id/eprint/2347This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/23472014-11-07T13:04:39ZExperimental set-up for gamma-activity measurements of astromaterialsThe most important proxies of past solar activity are radionuclides produced by nuclear interactions of cosmic rays in the Earth’s atmosphere, in meteorites and in planetary surfaces. In fact, the production of these radioisotopes depends on the cosmic ray flux and energy spectrum and vary in the heliosphere because of solar modulation. Therefore the study of cosmogenic isotopes in terrestrial archives and in meteorites, which fell at different times, gives information on solar activity in the past. Because of its half life, 44Ti (T½ = 59.2 years) in meteorites has been proposed as an ideal index for the study of centennial scale solar activity variations. The main experimental difficulties are related to the very low (∼1 dpm/kg) 44Ti γ activity in meteorites and to the strong interference by 214Bi γ’s from the decay chain of the naturally occurring 238U. On the basis of the decay scheme of 44Ti, we have set up a low background spectrometer, whose high specificity derives from a selective coincidence between the principal HPGe detector and the active shield of NaI(Tl). Using this spectrometer we have reconstructed the solar activity over the past 235 years by measuring 44Ti and 26Al in meteorite falls; in particular we have shown that the intensity of cosmic rays has linearly decreased during this period, in agreement with some models proposed for the past solar activity. In order to improve the Ge-NaI coincidence spectrometer, we have recently developed a multiparametric acquisition system, allowing better selectivity in the choice of the coincidence windows, crucial for the 44Ti detection. A background measurement of the apparatus, taken for about a month, shows efficient elimination of the 214Bi γ signal in coincidence mode. Moreover the coincidence spectrum of Dhajala meteorite (fall, 1976) shows a - - good 44Ti γ peak.Paolo ColombettiCarla TariccoNarendra BhandariAlberto RomeroNeeharika VermaGianna Vivaldogianna.vivaldo@imtlucca.it