Please use this identifier to cite or link to this item: https://ah.nccu.edu.tw/handle/140.119/137207


Title: 紊流混合對快中子捕獲過程(r-process)核合成的影響
Effect of turbulence mixing on R-process nucleosynthesis
Authors: 陳樂仁
Chen, Le-Ren
Contributors: 吳孟儒
楊志開
李尚凡

Meng-Ru Wu
Jhih-Kai Yang
Shang-Fan Lee

陳樂仁
Chen, Le-Ren
Keywords: 快過程核合成
紊流
中子星合併
短Gamma射線爆(sGRB)
r-process nucleosynthesis
turbulence
neutron stars mergers(NSM)
short gamma-ray burst(sGRB)
Date: 2021
Issue Date: 2021-09-03
Abstract: 2017 年 8 月雙中子星合併 (BNSM) 事件 GW170817 的重力波和電磁輻射的觀測,不僅標誌著重力波多信使天文學的開始,也提供了不少的證據——證實雙中子星合併是由快中子補獲過程 (r-process 或 快過程) 的不穩定核衰變,來為短γ射線暴 (sGRB) 和千新星提供能量。

最近的研究顯示,諸如短γ射線暴噴流穿透雙中子星合併之噴出物的機制,可能會導致噴出物內部大規模的紊流。這種紊流可能會導致噴出物中不同成分,且可能具有不同的核合成條件的流體混合。如果紊流引起的混合發生在快過程期間,與沒有混合的情況相比,它可能會影響快過程的最終產物。

在本論文中,我們使用一個簡單的雙流體簡單模型來探討成分混合對雙中子星合併事件中,快過程核合成結果的潛在影響。而我們發現不僅混合本身會改變最終結果,而且混合發生的時間點也會使結果具有不同的狀況。

特別是我們發現,如果當其中一流體處在快過程中,而另一種流體已完成其快過程時發生混合,混合效應會導致後者的自由中子的突然增加。因此,它可以幫助在快過程已停止的流體重新啟動快過程;與兩種未混合流體的直接平均值相比,這使得整個系統整體得以生成更重的核素。
另一方面,如果當兩種流體仍在快過程中時發生混合,則混合讓兩流體交換其剩餘的自由中子,使高Ye流體獲得更多自由中子進行快過程,而低Ye流體獲得較少的自由中子進行快過程。這將導致兩種流體的最終元素分布彼此接近,並且與在混合系統剛開始時取部分初始Ye平均值非常相似。
The detection of the gravitational wave and electromagnetic emissions from the binary neutron star merger (BNSM) event GW170817 in August 2017 not only marked the beginning of the gravitational-wave multi-messenger astronomy, but also provided evidence that BNSMs are the sources of the short gamma-ray bursts (sGRB) and kilonovae -- transients powered by the decay of unstable nuclei synthesis by the rapid neutron-capture process (r-process).

Recent studies suggested that mechanisms such as the sGRB jet penetrating the BNSM ejecta may result in large-scale turbulence inside the ejecta. Such turbulence can possibly cause composition mixing of different fluid components inside the ejecta, which might have different nucleosynthesis conditions. If the mixing caused by the turbulence happens during r-process, it may affect the resulting r-process yield predictions when compared to cases without mixing.

In this thesis, we use a simple two-fluid toy-model to study the impact of a potential composition mixing on the r-process nucleosynthesis outcome in BNSM events. We find that not only mixing itself will alter the final result, but also the time that mixing happen will make the result have different shape.

In particular, we find that if mixings happen when one of fluids is within the r-process while the other one has finished its r-process, mixing effect leads to sudden increase of free neutrons in the latter. Thus, it can help re-start the r-process in the fluid wherein the r-process had ceased. This allows the whole system to produce overall heavier nuclei when compared to the direct average of two unmixed fluids.
On the other hand, if mixings occur when both fluids are still within the r-process, then mixing let both fluids exchange their remaining free neutrons, make high $Y_e$ fluid get more free neutron to r-process, and low $Y_e$ fluid get lesser free neutron to r-process, where $Y_e\equiv n_e/n_b$, and $n_e$ ($n_b$) is the electron (baryon) number density. This will cause both fluids' final abundance distribution getting close toward each other, and it pretty similar to take a partial initial $Y_e$ averaging at begin of mixing system.
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Description: 碩士
國立政治大學
應用物理研究所
108755006
Source URI: http://thesis.lib.nccu.edu.tw/record/#G0108755006
Data Type: thesis
Appears in Collections:[應用物理研究所 ] 學位論文

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