Direct evaluation of high neutron density environment using (n,2n) reaction induced by laser-driven neutron source

2021 ◽  
Vol 104 (1) ◽  
Author(s):  
Takato Mori ◽  
Akifumi Yogo ◽  
Takehito Hayakawa ◽  
Seyed R. Mirfayzi ◽  
Zechen Lan ◽  
...  
Keyword(s):  
Neutron Source ◽  
Neutron Density ◽  
Direct Evaluation ◽  
High Neutron

Rubidium in Barium Stars

2020 ◽  
Author(s):  
M P Roriz ◽  
M Lugaro ◽  
C B Pereira ◽  
N A Drake ◽  
S Junqueira ◽  
...  
Keyword(s):  
Neutron Source ◽  
Slow Neutron ◽  
Asymptotic Giant Branch ◽  
Neutron Density ◽  
Data Sets ◽  
Agb Stars ◽  
Branching Points ◽  
Theoretical Predictions ◽  
Low Mass ◽  
Chemically Peculiar Stars

Abstract Barium (Ba) stars are chemically peculiar stars that display in their atmospheres the signature of the slow neutron-capture (the s-process) mechanism that occurs in asymptotic giant branch (AGB) stars, a main contributor to the cosmic abundances. The observed chemical peculiarity in these objects is not due to self-enrichment, but to mass transfer between the components of a binary system. The atmospheres of Ba stars are therefore excellent astrophysical laboratories providing strong constraints for the nucleosynthesis of the s-process in AGB stars. In particular, rubidium (Rb) is a key element for the s-process diagnostic because it is sensitive to the neutron density and therefore its abundance can reveal the main neutron source for the s-process in AGB stars. We present Rb abundances for a large sample of 180 Ba stars from high resolution spectra (R = 48000), and we compare the observed [Rb/Zr] ratios with theoretical predictions from AGB s-process nucleosynthesis models. The target Ba stars in this study display [Rb/Zr] <0, showing that Rb was not efficiently produced by the activation of branching points. Model predictions from the Monash and FRUITY data sets of low-mass (≲ 4 M⊙) AGB stars are able to cover the Rb abundances observed in the target Ba stars. These observations indicate that the 13C(α,n)16O reaction is the main neutron source of the s-process in the low-mass AGB companions of the observed Ba stars. We have not found in the present study candidate companion for IR/OH massive AGB stars.

A neutron source with 1014 DT neutron yield

2019 ◽  
Vol 28 (11) ◽  
pp. 1950097 ◽  
Author(s):  
Yasar Ay
Keyword(s):  
Neutron Source ◽  
Plasma Focus ◽  
Neutron Yield ◽  
Pressure Range ◽  
Gas Pressure ◽  
Plasma Focus Device ◽  
Operational Conditions ◽  
Rate Of Increase ◽  
Spherical Plasma ◽  
High Neutron

The developed spherical plasma focus model is used in this study to investigate the optimum neutron yield in terms of the gas pressure, cathode radius and external inductance. The optimum values for these parameters are found separately. Then, the charging voltage is varied from 25[Formula: see text]kV to 35[Formula: see text]kV with 1[Formula: see text]kV increment by using these separately found optimum values to see the rate of increase in neutron yield. While the used gas pressure range is 1–40[Formula: see text]Torr with 1[Formula: see text]Torr increment, cathode radius range is 11.5–17[Formula: see text]cm with 0.5[Formula: see text]cm increment. External inductance is varied from 10[Formula: see text]nH to 150[Formula: see text]nH with 5[Formula: see text]nH increment. The optimum values for gas pressure, cathode radius and external inductance are found to be 26[Formula: see text]Torr, 15[Formula: see text]cm and 75[Formula: see text]nH, respectively. Even though combining these separately found optimum values of pressure, cathode radius and external inductance does not necessarily form an optimized set of operational conditions for the SPF, they lead to a higher neutron yield in that while neutron yield with these separately found optimum values at 25[Formula: see text]kV charging voltage is [Formula: see text] (higher than the measured neutron yield of [Formula: see text] at 25[Formula: see text]kV), it increases to [Formula: see text], when charging voltage is increased to 35[Formula: see text]kV. Using these values shows that spherical plasma focus device can be used as a neutron source with high neutron yield (on the order of [Formula: see text]).

scholarly journals Asymptotic-Giant-Branch Models at Very Low Metallicity

2009 ◽  
Vol 26 (3) ◽  
pp. 139-144 ◽  
Author(s):  
S. Cristallo ◽  
L. Piersanti ◽  
O. Straniero ◽  
R. Gallino ◽  
I. Domínguez ◽  
...  
Keyword(s):  
Metal Content ◽  
Asymptotic Giant Branch ◽  
Neutron Density ◽  
Surface Chemical ◽  
Mass Model ◽  
Surface Chemical Composition ◽  
Low Metallicity ◽  
Low Mass ◽  
Very High ◽  
High Neutron

AbstractIn this paper we present the evolution of a low-mass model (initial mass M = 1.5 M⊙) with a very low metal content (Z = 5 × 10−5, equivalent to [Fe/H] = –2.44). We find that, at the beginning of the Asymptotic Giant Branch (AGB) phase, protons are ingested from the envelope in the underlying convective shell generated by the first fully developed thermal pulse. This peculiar phase is followed by a deep third dredge-up episode, which carries to the surface the freshly synthesized 13C, 14N and 7Li. A standard thermally pulsing AGB (TP-AGB) evolution then follows. During the proton-ingestion phase, a very high neutron density is attained and the s process is efficiently activated. We therefore adopt a nuclear network of about 700 isotopes, linked by more than 1200 reactions, and we couple it with the physical evolution of the model. We discuss in detail the evolution of the surface chemical composition, starting from the proton ingestion up to the end of the TP-AGB phase.

scholarly journals Heavy elements nucleosynthesis on accreting white dwarfs: building seeds for the p-process

2020 ◽  
Vol 497 (4) ◽  
pp. 4981-4998
Author(s):  
U Battino ◽  
M Pignatari ◽  
C Travaglio ◽  
C Lederer-Woods ◽  
P Denissenkov ◽  
...  
Keyword(s):  
White Dwarf ◽  
Stellar Structure ◽  
Neutron Density ◽  
Surface Layers ◽  
Near Surface ◽  
Main Site ◽  
Intermediate Neutron ◽  
Thermonuclear Supernovae ◽  
Long Time ◽  
High Neutron

ABSTRACT The origin of the proton-rich trans-iron isotopes in the Solar system is still uncertain. Single-degenerate thermonuclear supernovae (SNIa) with n-capture nucleosynthesis seeds assembled in the external layers of the progenitor’s rapidly accreting white dwarf (RAWD) phase may produce these isotopes. We calculate the stellar structure of the accretion phase of five white dwarf (WD) models with initial masses ≥ 0.85 $\, \mathrm{M}_\odot$ using the stellar code mesa The near-surface layers of the 1, 1.26, 1.32 and 1.38 $\, \mathrm{M}_\odot$ models are most representative of the regions in which the bulk of the p nuclei are produced during SNIa explosions, and for these models we also calculate the neutron-capture nucleosynthesis in the external layers. Contrary to previous RAWD models at lower mass, we find that the H-shell flashes are the main site of n-capture nucleosynthesis. We find high neutron densities up to several 1015 cm−3 in the most massive WDs. Through the recurrence of the H-shell flashes these intermediate neutron densities can be sustained effectively for a long time leading to high-neutron exposures with a strong production up to Pb. Both the neutron density and the neutron exposure increase with increasing the mass of the accreting WD. Finally, the SNIa nucleosynthesis is calculated using the obtained abundances as seeds. We obtain solar to supersolar abundances for p-nuclei with A > 96. Our models show that SNIa are a viable p-process production site.

Design of a Neutron Source for Calibration

2002 ◽  
Author(s):  
Aureliano Carrillo-Nuñez
Keyword(s):  
Neutron Source

Current uses of intracranial vessel wall imaging for clinical practice: a high-resolution MR technique recently available

2020 ◽  
Vol 78 (10) ◽  
pp. 642-650
Author(s):  
Felipe Torres PACHECO ◽  
Luiz Celso Hygino da CRUZ JUNIOR ◽  
Igor Gomes PADILHA ◽  
Renato Hoffmann NUNES ◽  
Antônio Carlos Martins MAIA JUNIOR ◽  
...  
Keyword(s):  
Clinical Practice ◽  
Vessel Wall ◽  
Vascular Diseases ◽  
Vascular Wall ◽  
Vessel Wall Imaging ◽  
Clinical Settings ◽  
Direct Evaluation ◽  
Intracranial Vessel ◽  
Indirect Evaluation ◽  
Wall Imaging

ABSTRACT Intracranial vessel wall imaging plays an increasing role in diagnosing intracranial vascular diseases. With the growing demand and subsequent increased use of this technique in clinical practice, radiologists and neurologists should be aware of the choices in imaging parameters and how they affect image quality, clinical indications, methods of assessment, and limitations in the interpretation of these images. Due to the improvement of the MRI techniques, the possibility of accurate and direct evaluation of the abnormalities in the arterial vascular wall (vessel wall imaging) has evolved, adding substantial data to diagnosis when compared to the indirect evaluation based on conventional flow analyses. Herein, the authors proposed a comprehensive approach of this technique reinforcing appropriated clinical settings to better use intracranial vessel wall imaging.

Closed loop auto control system software for Miniature Neutron Source Reactors (MNSRs)

Kerntechnik ◽  
2009 ◽  
Vol 74 (5-6) ◽  
pp. 280-285
Author(s):  
M. Iqbal ◽  
J. Qadir ◽  
T. K. Bhatti ◽  
Q. Abbas ◽  
S. M. Mirza
Keyword(s):  
Control System ◽  
Neutron Source ◽  
Closed Loop ◽  
System Software
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