We investigate the angular momentum removal from fission fragments (FFs) through neutron and γ-ray emission, finding that about half the neutrons are emitted with angular momenta ≥1.5ℏ and that the ...change in angular momentum after the emission of neutrons and statistical γ rays is significant, contradicting usual assumptions. Per fission event, in our simulations, the neutron and statistical γ-ray emissions change the spin of the fragment by 3.5-5ℏ, with a large standard deviation comparable to the average value. Such wide angular momentum removal distributions can hide any underlying correlations in the fission fragment initial spin values. Within our model, we reproduce data on spin measurements from discrete transitions after neutron emissions, especially in the case of light FFs. The agreement further improves for the heavy fragments if one removes from the analysis the events that would produce isomeric states. Finally, we show that while in our model the initial FF spins do not follow a sawtoothlike behavior observed in recent measurements, the average FF spin computed after neutron and statistical γ emissions exhibits a shape that resembles a sawtooth. This suggests that the average FF spin measured after statistical emissions is not necessarily connected with the scission mechanism as previously implied.
In the last decades, it has been a fast-growing concept in the neuroscience field. The passive brain-computer interface (p-BCI) systems allow to improve the human-machine interaction (HMI) in ...operational environments, by using the covert brain activity (eg, mental workload) of the operator. However, p-BCI technology could suffer from some practical issues when used outside the laboratories. In particular, one of the most important limitations is the necessity to recalibrate the p-BCI system each time before its use, to avoid a significant reduction of its reliability in the detection of the considered mental states. The objective of the proposed study was to provide an example of p-BCIs used to evaluate the users' mental workload in a real operational environment. For this purpose, through the facilities provided by the École Nationale de l'Aviation Civile of Toulouse (France), the cerebral activity of 12 professional air traffic control officers (ATCOs) has been recorded while performing high realistic air traffic management scenarios. By the analysis of the ATCOs' brain activity (electroencephalographic signal-EEG) and the subjective workload perception (instantaneous self-assessment) provided by both the examined ATCOs and external air traffic control experts, it has been possible to estimate and evaluate the variation of the mental workload under which the controllers were operating. The results showed (i) a high significant correlation between the neurophysiological and the subjective workload assessment, and (ii) a high reliability over time (up to a month) of the proposed algorithm that was also able to maintain high discrimination accuracies by using a low number of EEG electrodes (~3 EEG channels). In conclusion, the proposed methodology demonstrated the suitability of p-BCI systems in operational environments and the advantages of the neurophysiological measures with respect to the subjective ones.
There is an urgent need for new, better instrumentation and techniques for detecting and characterizing special nuclear material (SNM), i.e., highly enriched uranium and plutonium. The development of ...improved instruments and techniques requires experiments performed with the SNM itself, which is of limited availability. This paper describes the findings of experiments performed at the National Criticality Experiments Research Center conducted using new instruments and techniques on unclassified, kg-quantity SNM objects. These experiments, performed in the framework of the Department of Energy, National Nuclear Security Administration Consortium for Monitoring, Technology, and Verification, focused on detecting, characterizing, and localizing SNM samples with masses ranging from 3.3 to 13.8 kg, including plutonium and highly enriched uranium using prototype detectors and techniques. The work demonstrates SNM detection and characterization using recently-developed prototype detection systems. Specifically, we present new results in passive detection and imaging of plutonium and uranium objects using gamma-ray and dual particle (fast neutron and gamma-ray) imaging. We also present a new analysis of the delayed neutron emissions during active interrogation of uranium using a neutron generator.
Background model of the CUPID-0 experiment Azzolini, O.; Beeman, J. W.; Bellini, F. ...
The European physical journal. C, Particles and fields,
07/2019, Letnik:
79, Številka:
7
Journal Article
Recenzirano
Odprti dostop
CUPID-0 is the first large mass array of enriched Zn
82
Se scintillating low temperature calorimeters, operated at LNGS since 2017. During its first scientific runs, CUPID-0 collected an exposure of ...9.95 kg year. Thanks to the excellent rejection of
α
particles, we attained the lowest background ever measured with thermal detectors in the energy region where we search for the signature of
82
Se
neutrinoless double beta decay. In this work we develop a model to reconstruct the CUPID-0 background over the whole energy range of experimental data. We identify the background sources exploiting their distinctive signatures and we assess their extremely low contribution down to
∼
10
-
4
counts/(keV kg year) in the region of interest for
82
Se
neutrinoless double beta decay search. This result represents a crucial step towards the comprehension of the background in experiments based on scintillating calorimeters and in next generation projects such as CUPID.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report the generation of MeV x rays using an undulator and accelerator that are both driven by the same 100-terawatt laser system. The laser pulse driving the accelerator and the scattering laser ...pulse are independently optimized to generate a high energy electron beam (>200 MeV) and maximize the output x-ray brightness. The total x-ray photon number was measured to be ∼1×10(7), the source size was 5 μm, and the beam divergence angle was ∼10 mrad. The x-ray photon energy, peaked at 1 MeV (reaching up to 4 MeV), exceeds the thresholds of fundamental nuclear processes (e.g., pair production and photodisintegration).
This is a report of 148 patients with hematologic malignancies who received an unmanipulated haploidentical bone marrow transplant (BMT), followed by post-transplant high-dose cyclophosphamide ...(PT-CY). All patients received a myeloablative conditioning consisting of thiotepa, busulfan, fludarabine (n=92) or TBI, fludarabine (n=56). The median age was 47 years (17-74); 47 patients were in first remission (CR1), 37 in second remission (CR2) and 64 had an active disease; all patients were first grafts. The diagnosis was acute leukemia (n=75), myelodisplastic syndrome (n=24), myelofibrosis (n=16), high-grade lymphoma (n=15) and others (n=18). GVHD prophylaxis consisted in PT-CY on days +3 and +5, cyclosporine (from day 0), and mycophenolate (from day +1). The median day for neutrophil engraftment was day +18 (13-32). The cumulative incidence of grades II-IV acute GVHD was 24%, and of grades III-IV GVHD 10%. The incidence of moderate-severe chronic GVHD was 12%. With a median follow-up for the surviving patients of 313 days (100-1162), the cumulative incidence of transplant-related mortality (TRM) is 13%, and the relapse-related death is 23%. The actuarial 22 months overall survival is 77% for CR1 patients, 49% for CR2 patients and 38% for patients grafted in relapse (P<0.001). Major causes of death were relapse (22%), GVHD (2%) and infections (6%). We confirm our initial results, suggesting that a myeloablative conditioning regimen followed by unmanipulated haploidentical BMT with PT-CY, results in a low risk of acute and chronic GVHD and encouraging rates of TRM and overall survival, also for patients with active disease at the time of transplant.
The suppression of spurious events in the region of interest for neutrinoless double beta decay will play a major role in next generation experiments. The background of detectors based on the ...technology of cryogenic calorimeters is expected to be dominated by
α
particles, that could be disentangled from double beta decay signals by exploiting the difference in the emission of the scintillation light. CUPID-0, an array of enriched Zn
82
Se scintillating calorimeters, is the first large mass demonstrator of this technology. The detector started data-taking in 2017 at the Laboratori Nazionali del Gran Sasso with the aim of proving that dual read-out of light and heat allows for an efficient suppression of the
α
background. In this paper we describe the software tools we developed for the analysis of scintillating calorimeters and we demonstrate that this technology allows to reach an unprecedented background for cryogenic calorimeters.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
.
Detailed information on the fission process can be inferred from the observation, modeling and theoretical understanding of prompt fission neutron and
γ
-ray observables. Beyond simple average ...quantities, the study of distributions and correlations in prompt data,
e.g.
, multiplicity-dependent neutron and
γ
-ray spectra, angular distributions of the emitted particles,
n
-
n
,
n
-
γ
, and
γ
-
γ
correlations, can place stringent constraints on fission models and parameters that would otherwise be free to be tuned separately to represent individual fission observables. The FREYA and CGMF codes have been developed to follow the sequential emissions of prompt neutrons and
γ
rays from the initial excited fission fragments produced right after scission. Both codes implement Monte Carlo techniques to sample initial fission fragment configurations in mass, charge and kinetic energy and sample probabilities of neutron and
γ
emission at each stage of the decay. This approach naturally leads to using simple but powerful statistical techniques to infer distributions and correlations among many observables and model parameters. The comparison of model calculations with experimental data provides a rich arena for testing various nuclear physics models such as those related to the nuclear structure and level densities of neutron-rich nuclei, the
γ
-ray strength functions of dipole and quadrupole transitions, the mechanism for dividing the excitation energy between the two nascent fragments near scission, and the mechanisms behind the production of angular momentum in the fragments, etc. Beyond the obvious interest from a fundamental physics point of view, such studies are also important for addressing data needs in various nuclear applications. The inclusion of the FREYA and CGMF codes into the MCNP6.2 and MCNPX - PoliMi transport codes, for instance, provides a new and powerful tool to simulate correlated fission events in neutron transport calculations important in nonproliferation, safeguards, nuclear energy, and defense programs. This review provides an overview of the topic, starting from theoretical considerations of the fission process, with a focus on correlated signatures. It then explores the status of experimental correlated fission data and current efforts to address some of the known shortcomings. Numerical simulations employing the FREYA and CGMF codes are compared to experimental data for a wide range of correlated fission quantities. The inclusion of those codes into the MCNP6.2 and MCNPX - PoliMi transport codes is described and discussed in the context of relevant applications. The accuracy of the model predictions and their sensitivity to model assumptions and input parameters are discussed. Finally, a series of important experimental and theoretical questions that remain unanswered are presented, suggesting a renewed effort to address these shortcomings.
MCNPX-PoliMi for nuclear nonproliferation applications Pozzi, S.A.; Clarke, S.D.; Walsh, W.J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2012, Letnik:
694
Journal Article
Recenzirano
This paper describes the use of the Monte Carlo code MCNPX-PoliMi for nuclear-nonproliferation applications, with particular emphasis on the simulation of spontaneous and neutron-induced nuclear ...fission. New models for the outgoing neutrons and gamma rays emitted in spontaneous and induced fission are described. For spontaneous fission, the models include prompt neutron energy distributions that depend on the number of neutrons emitted in the individual fission events. For neutron-induced fission, due to lack of data, the prompt neutron energy distributions are independent of the number of neutrons emitted in the individual fission events. Gamma rays are sampled independently of the neutrons. Code validation is performed on well-characterized mixed-oxide fuel and plutonium-oxide samples.
Central venous access is extensively used in oncology, though practical information from randomized trials on the most convenient insertion modality and site is unavailable.
Four hundred and three ...patients eligible for receiving i.v. chemotherapy for solid tumors were randomly assigned to implantation of a single type of port (Bard Port™, Bard Inc., Salt Lake City, UT), through a percutaneous landmark access to the internal jugular, a ultrasound (US)-guided access to the subclavian or a surgical cut-down access through the cephalic vein at the deltoid–pectoralis groove. Early and late complications were prospectively recorded until removal of the device, patient's death or ending of the study.
Four hundred and one patients (99.9%) were assessable: 132 with the internal jugular, 136 with the subclavian and 133 with the cephalic vein access. The median follow-up was 356.5 days (range 0–1087). No differences were found for early complication rate in the three groups {internal jugular: 0% 95% confidence interval (CI) 0.0% to 2.7%, subclavian: 0% (95% CI 0.0% to 2.7%), cephalic: 1.5% (95% CI 0.1% to 5.3%)}. US-guided subclavian insertion site had significantly lower failures (e.g. failed attempts to place the catheter in agreement with the original arm of randomization, P=0.001). Infections occurred in one, three and one patients (internal jugular, subclavian and cephalic access, respectively, P=0.464), whereas venous thrombosis was observed in 15, 8 and 11 patients (P=0.272).
Central venous insertion modality and sites had no impact on either early or late complication rates, but US-guided subclavian insertion showed the lowest proportion of failures.
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