Radiogenic Isotopes and Late Pleistocene Climate Changes in the Central Equatorial Pacific

This work focuses on reconstructing changes in atmospheric and bottom water circulation in the Central Equatorial Pacific (CEP) through the last 150 000 years, to examine how atmospheric and oceanic system respond to changes in global temperature in glacial-interglacial timescales. This work is part of a larger conversation in paleoclimate and paleoceanography that investigates the link between changes in northern hemisphere insolation and ocean-atmosphere interactions in the Southern Ocean. These focus in these relationship from two different perspectives. Section 2 and 3 examine dust provenance to reconstruct changes in tropical hydroclimate, in particular the changes in the position of the Intertropical Convergence Zone (ITCZ) the zone of maximum precipitation. I study a 7° north-south transect in the CEP at 160° W, across the annual latitudinal range of the modern ITCZ. This dust provenance work relies on measuring the changes in lead (Pb) and neodymium (Nd) isotopes in the chemically isolated dust fraction of marine sediments. First, I look at ITCZ changes from the last 30 kyr to the mid-Holocene, in order to examine the difference between glacial and interglacial conditions. I suggest that the ITCZ reached its southernmost position during glacial times. I identify this shift in the ITCZ by noting an increase in dust of Asian provenance in the more southern cores. During warmer global climate periods, the ITCZ migrates farther north. I also examine the changes in the ITCZ across the penultimate deglaciations by examining samples from 110 to 150 kyr. I found that the southernmost position of the ITCZ occurred during the peak deglaciation (between 136 and 131 kyr), with a subsequent interglacial movement of more than 7° north. I also investigate the changes in deep-water circulation in the CEP over the last two glacial cycles (from the mid-Holocene to 150 kyr ago) using the Nd isotopic composition of fossil fish debris as a water mass tracer. I discovered an interesting response of Nd in fish debris to low oxygen conditions, a critical contribution to the field, as it complicates the paleoceanographic reconstructions that have been published using Nd isotopes as a conservative tracer. By taking a holistic multi-proxy approach, I was able to constrain the sources that affect Nd in fish debris and improve our current understanding of the respired carbon pool that is argued to be ventilated by the Southern Ocean during deglaciations

Correction to: Sant'Imbenia (Alghero): further archaeometric evidence for an Iron Age market square

n/

Sant'Imbenia (Alghero): further archaeometric evidence for an Iron Age market square

AbstractLead isotope compositions were determined for 18 metal objects from the archaeological site of Sant'Imbenia, NW Sardinia, dating to the end of the ninth century BCE onwards. The provenance of some objects is unambiguously traced to SW Sardinia; other objects could derive either from central Sardinia or the Iberian coastal ranges. The variety of the provenances attests to a wide trade network that spanned the entire island of Sardinia and extended to the Iberian sites

Dose ratio proton radiography using the proximal side of the Bragg peak

Purpose: In recent years there has been a movement towards single-detector proton radiography, due to its potential ease of implementation within the clinical environment. One such single-detector technique is the dose ratio method, in which the dose maps from two pristine Bragg peaks are recorded beyond the patient. To date, this has only been investigated on the distal side of the lower energy Bragg peak, due to the sharp fall-off. We investigate the limits and applicability of the dose ratio method on the proximal side of the lower energy Bragg peak, which has the potential to allow a much wider range of water-equivalent thicknesses (WET) to be imaged. Comparisons are made with the use of the distal side of the Bragg peak. Methods: Using the analytical approximation for the Bragg peak we generated theoretical dose ratio curves for a range of energy pairs, and then determined how an uncertainty in the dose ratio would translate to a spread in the WET estimate. By defining this spread as the accuracy one could achieve in the WET estimate, we were able to generate look-up graphs of the range on the proximal side of the Bragg peak that one could reliably use. These were dependent on the energy pair, noise level in the dose ratio image and the required accuracy in the WET. Using these look-up graphs we investigated the applicability of the technique for a range of patient treatment sites. We validated the theoretical approach with experimental measurements using a complementary metal oxide semiconductor active pixel sensor (CMOS APS), by imaging a small sapphire sphere in a high energy proton beam. Results: Provided the noise level in the dose ratio image was 1% or less, a larger spread of WETs could be imaged using the proximal side of the Bragg peak (max 5.31 cm) compared to the distal side (max 2.42 cm). In simulation it was found that, for a pediatric brain, it is possible to use the technique to image a region with a square field equivalent size of 7.6 cm2, for a required accuracy in the WET of 3 mm and a 1% noise level in the dose ratio image. The technique showed limited applicability for other patient sites. The CMOS APS demonstrated a good accuracy, with a root-mean-square-error of 1.6 mm WET. The noise in the measured images was found to be σ =1.2% (standard deviation) and theoretical predictions with a 1.96σ noise level showed good agreement with the measured errors. Conclusions: After validating the theoretical approach with measurements, we have shown that the use of the proximal side of the Bragg peak when performing dose ratio imaging is feasible, and allows for a wider dynamic range than when using the distal side. The dynamic range available increases as the demand on the accuracy of the WET decreases. The technique can only be applied to clinical sites with small maximum WETs such as for pediatric brains

The HPS electromagnetic calorimeter

The Heavy Photon Search experiment (HPS) is searching for a new gauge boson, the so-called “heavy photon.” Through its kinetic mixing with the Standard Model photon, this particle could decay into an electron-positron pair. It would then be detectable as a narrow peak in the invariant mass spectrum of such pairs, or, depending on its lifetime, by a decay downstream of the production target. The HPS experiment is installed in Hall-B of Jefferson Lab. This article presents the design and performance of one of the two detectors of the experiment, the electromagnetic calorimeter, during the runs performed in 2015–2016. The calorimeter's main purpose is to provide a fast trigger and reduce the copious background from electromagnetic processes through matching with a tracking detector. The detector is a homogeneous calorimeter, made of 442 lead-tungstate (PbWO4) scintillating crystals, each read out by an avalanche photodiode coupled to a custom trans-impedance amplifier

Proton imaging apparatus for protontherapy application

Radiotherapy with protons, due to the physical properties of these particles, offers several advantages for cancer therapy as compared to the traditional radiotherapy with photons. In the clinical use of proton beams, a pCT (proton Computed Tomography) apparatus can contribute to improve the accuracy of the patient positioning and dose distribution calculation. In this paper a pCT apparatus built by the PRIMA (PRoton IMAging) Italian Collaboration will be presented and the preliminary results will be discussed

Data acquisition system for a proton imaging apparatus

New developments in the proton-therapy field for cancer treatments, leaded Italian physics researchers to realize a proton imaging apparatus consisting of a silicon microstrip tracker to reconstruct the proton trajectories and a calorimeter to measure their residual energy. For clinical requirements, the detectors used and the data acquisition system should be able to sustain about 1 MHz proton rate. The tracker read-out, using an ASICs developed by the collaboration, acquires the signals detector and sends data in parallel to an FPGA. The YAG:Ce calorimeter generates also the global trigger. The data acquisition system and the results obtained in the calibration phase are presented and discussed

PRIMA+: A proton Computed Tomography apparatus

The proton Computed Tomography (pCT) is a medical imaging method, based on the use of proton beams with kinetic energy of the order of 250 MeV, aimed to directly measure the stopping power distribution of tissues thus improving the present accuracy of treatment planning in hadron therapy. A pCT system should be capable to measure tissue electron density with an accuracy better than 1% and a spatial resolution better than 1 mm. The blurring effect due to multiple Coulomb scattering can be mitigated by single proton tracking technique. As a first step towards pCT the PRIMA+ Collaboration built a prototype capable to carry out a single radiography and a tomographic image of a rotating object. This apparatus includes a silicon microstrip tracker to identify the proton trajectory and a YAG:Ce calorimeter to measure the particle residual energy