The energy-dependent cross section of the Be7(n,alpha)He4 reaction, of interest for the so-called cosmological lithium problem in big bang nucleosynthesis, has been measured for the first time from ...10 meV to 10 keV neutron energy. The challenges posed by the short half-life of Be7 and by the low reaction cross section have been overcome at n_TOF thanks to an unprecedented combination of the extremely high luminosity and good resolution of the neutron beam in the new experimental area (EAR2) of the n_TOF facility at CERN, the availability of a sufficient amount of chemically pure Be7, and a specifically designed experimental setup. Coincidences between the two alpha particles have been recorded in two Si-Be7-Si arrays placed directly in the neutron beam. The present results are consistent, at thermal neutron energy, with the only previous measurement performed in the 1960s at a nuclear reactor. The energy dependence reported here clearly indicates the inadequacy of the cross section estimates currently used in BBN calculations. Although new measurements at higher neutron energy may still be needed, the n_TOF results hint at a minor role of this reaction in BBN, leaving the long-standing cosmological lithium problem unsolved.
OBJECTIVES:
First, to investigate whether the severity of acute respiratory distress syndrome (ARDS) influences ventilator-induced lung injury (VILI) risk in ventilated patients with similar ...mechanical power of respiratory system (MP
RS
). Second, to determine whether, under these circumstances, there is a relationship between transpulmonary mechanical power (MP
Tp
) normalized to the aerated lung (specific lung mechanical power or SLMP) and VILI risk, and third, to determine whether normalizing MP
RS
to compliance of respiratory system (CRS) can replace SLMP to bedside.
DESIGN:
Prospective cohort study.
SETTING:
The study was conducted in a tertiary academic ICU.
PATIENTS:
The study included 18 patients with ARDS.
INTERVENTIONS:
Ventilatory settings were adjusted to achieve a similar MP
RS
.
MEASUREMENTS AND MAIN RESULTS:
Mechanical power was normalized to CRS (specific mechanical power or SMP = MP
RS
/CRS), and SLMP was calculated as the ratio between MP
Tp
and end-expiratory lung volume (SLMP = MP
Tp
/EELV). The strain was defined as the ratio between tidal volume and EELV (strain = V
t
/EELV), stress as transpulmonary pressure at the end of inspiration, and atelectrauma as the difference between expiration and inspiration in the nonaerated lung. Although patients had been ventilated with similar MP
RS
= 23.75 (23–24) J/min and MP
Tp
= 11.6 (10.8–12.8) J/min, SLMP increased linearly with the fall in Pa
o
2
/F
io
2
(
R
= –0.83,
p
= 0.0001). MP
RS
only correlated positively with VILI-associated mechanisms when normalized to aerated lung size: correlations between SLMP and stress (
R
= 0.9,
R
2
= 0.84,
p
= 0.00004), strain (
R
= 0.97,
R
2
= 0.94,
p
< 0.00001) and atelectrauma (
R
= 0.82,
R
2
= 0.70,
p
= 0.00002), and correlations between SMP and stress (
R
= 0.86,
R
2
= 0.75,
p
= 0.00001), strain (
R
= 0.68, R
2
= 0.47,
p
= 0.001) and atelectrauma (
R
= 0.67,
R
2
= 0.46,
p
= 0.002).
CONCLUSIONS:
The results suggest that normalizing mechanical power to lung-aerated size or CRS may correlate positively with stress, strain, and atelectrauma.
With the aim of measuring the 235U(n,f) cross section at the n_TOF facility at CERNover a wide neutron energy range, a detection system consisting of two fission detectors and threedetectors for ...neutron flux determination was realized. The neutron flux detectors are RecoilProton Telescopes (RPTs), based on scintillators and solid state detectors, conceived to detectrecoil protons from the neutron-proton elastic scattering reaction. This system, along with afission chamber and an array of parallel plate avalanche counters for fission event detection, wasinstalled for the measurement at the n_TOF facility in 2018, at CERN. An overview of the performances of two RPTs — especially developed for this measurement — and of theparallel plate avalanche counters are described in this article. In particular, the characterizationin terms of detection efficiency by Monte Carlo simulations and response to neutron beam, the studyof the background, dead time correction and characterization of the samples, are reported. Theresults of the present investigation show that the performances of these detectors are suitable foraccurate measurements of fission reaction cross sections in the range from 10 to 450 MeV.
•Erbium can be directly mixed in nuclear fuel with an improving of the nuclear safety.•Current erbium cross-sections uncertainties are too high for nuclear technology.•The erbium-associated ...uncertainties present in the ENDF/B-VIII.0 seems to be too low.•S&U analysis on an Er-SHB system shows that erbium Xs (n,γ) evaluations appear inadequate to provide accurate criticality calculations for a full erbium-doped system.•U.S. Nuclear Energy Agency added the revaluation of Er-167(n, γ) in its High Priority Request List based on the outcomes reported in this work.
Research conducted in the last twenty years in the field of burnable absorbers showed that erbium isotopes can be considered as an excellent alternative absorber to gadolinium isotopes for their neutronic and nuclear safety improving features. The development of the Erbium Super High Burnup (Er-SHB) concept demonstrated that erbium could be directly mixed in all fuel pins of a fuel assembly (FA) at the Beginning of Life (BOL). This innovative design allows an improvement of nuclear safety, a better control of the operational and accidental transient phase and an extension of the fuel life with respect to the most used burnable absorber (i.e., gadolinium). Furthermore, the extensive use of an Er-SHB fuel design would allow the production of higher enriched nuclear fuel (i.e., >5 wt%) within the existing manufacturing facilities without any modification of the facility itself and with a general improvement of the nuclear safety of the front-end phase of the nuclear fuel cycle. Nevertheless, reported erbium cross-sections are dated and poorly investigated in the high sensitivity thermal energy region for nuclear technology. In addition, some of them (i.e., Er-166) are reported with an uncertainty that is too high for their use in the future design of the erbia-doped LWR assembly by the industry. On the other hand, evaluated uncertainties by the ENDF/B-VIII.0 library in the thermal/epithermal region for the most sensitive isotopes (i.e., Er-167) seem to be too low with respect to both the experimental data and the analysis of the results provided by some erbia-doped critical systems of the International Critical Safety Benchmark Evaluation Project (ICSBEP). Based on the reanalysis of the ICSBEP outcomes, and a sensitivity-uncertainty analysis (S&U) on an Er-SHB LWR assembly, this article shows that recent evaluations appear inadequate to provide accurate criticality calculations for a system all equipped with erbium fuel pins for neutronic design purpose. Moreover, the S&U results have shown the importance of erbium isotopes to correctly evaluate the uncertainty associated with a Light Water Reactor (LWR) critical system. They confirmed the need for a re-evaluation of their neutron capture cross section by means of a new experimental campaign. A proposal aiming at performing a new capture measurement of erbium isotope cross sections has already been submitted to GELINA facility at Geel (Belgium), which is particularly suitable for neutron capture and transmission measurements in the thermal and epithermal energy regions. On August 2021, U.S. Nuclear Energy Agency (NEA) added the revaluation of Er-167(n, γ) in its High Priority Request List (HPRL) based on the outcomes reported in this work. On January 2022, GELINA Scientific Committee accepted the proposal within the 2021 calls for open access to JRC Research Infrastructures in the research filed of European Research for nuclear reaction, radioactivity, radiation and technology studies in science and application (EUFRAT).
The electron beam emitted backward by plasma focus devices is being considered as a radiation source for Intra-Operative Radiation Therapy (IORT) applications. Radiobiological investigations have ...been conducted to assess the potential of this new prototype of IORT device. A standard x-ray beam, ISO-H60, was used for comparison, irradiating cell cultures in a holder filled with an aqueous solution. The influence of scattering by the culture water and by the walls of the holder was investigated to determine their influence on the dose delivered to the cell culture. MCNPX simulations were run and experimental measurements conducted. The effect of scattering by the holder was found to be negligible; scattering by the culture water was determined to give an increase in dose of the order of 10%.
With the aim of measuring the $^{235}$U(n,f) cross section at the n_TOF facility at CERN over a wide neutron energy range, a detection system consisting of two fission detectors and three detectors ...for neutron flux determination was realized. The neutron flux detectors are Recoil Proton Telescopes (RPT), based on scintillators and solid state detectors, conceived to detect recoil protons from the neutron-proton elastic scattering reaction. This system, along with a fission chamber and an array of parallel plate avalanche counters for fission event detection, was installed for the measurement at the n_TOF facility in 2018, at CERN. An overview of the performances of two RPTs - especially developed for this measurement - and of the parallel plate avalanche counters are described in this article. In particular, the characterization in terms of detection efficiency by Monte Carlo simulations and response to neutron beam, the study of the background, dead time correction and characterization of the samples, are reported. The results of the present investigation show that the performances of these detectors are suitable for accurate measurements of fission reaction cross sections in the range from 10 to 450~MeV.
.
Neutron capture cross section measurements on
155
Gd and
157
Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements ...were carried out in the n_TOF experimental area EAR1, at 185 m from the neutron source, with an array of 4 C
6
D
6
liquid scintillation detectors. At a neutron kinetic energy of 0.0253 eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for
155
Gd and
157
Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181 eV and 307 eV, respectively for
155
Gd and
157
Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1 keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of
2
.
01
(
28
)
×
10
-
4
and
2
.
17
(
41
)
×
10
-
4
; average total radiative width of 106.8(14) meV and 101.1(20) meV and
s
-wave resonance spacing 1.6(2) eV and 4.8(5) eV for n +
155
Gd and n +
157
Gd systems, respectively.
The TOP-IMPLART project Ronsivalle, C.; Carpanese, M.; Marino, C. ...
European physical journal plus,
07/2011, Letnik:
126, Številka:
7
Journal Article
Recenzirano
A new proton therapy center is planned to be built in Rome, Italy. The project, named TOP-IMPLART, is developed by three institutions, ENEA (Agenzia Nazionale per le Nuove tecnologie, l’Energia e lo ...Sviluppo Economico Sostenibile - Italian national agency for new technologies, energy and sustainable economic development), ISS (Istituto Superiore di Sanità, Italian National Institute of Health) and IFO-IRE (Istituto Fisioterapico Ospedaliero - Istituto Regina Elena, Regina Elena, National Cancer Institute in Rome). The project is centered on a medium-energy proton accelerator designed as a sequence of linear accelerators. Two phases of construction are foreseen: the first (funded by the Italian Regione Lazio for 11 M€ spread over four years) with a maximum energy of 150 MeV and the second one up to 230 MeV. The segment up to 150 MeV is under construction and will be tested at the ENEA Research Center in Frascati before the transfer to IFO that is the clinical user. The basic concepts of the design are described here.
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