Introducing the fission-fusion reaction process: using a laser-accelerated Th beam to produce neutron-rich nuclei towards the N = 126 waiting point of the r-process
Introducing the fission-fusion reaction process: using a laser-accelerated Th beam to produce neutron-rich nuclei towards the N = 126 waiting point of the r-process
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DOI：
10.1007/s00340-010-4261-x
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发表时间：
2011-05-01
影响因子：
2.1
通讯作者：
Schreiber, J.
中科院分区：
文献类型：
--
作者：
Habs, D.;Thirolf, P. G.;Schreiber, J.
我们建议在等待点N=126附近的天体物理r过程（快速中子捕获过程）范围内产生富中子核（Kratz et al. in Prog.部分Nucl.Phys.59：147，2007; Arnould等人在Phys.Rep.450：97，2007; Panov和Janka在Astron. Astrophys。494：829，2009），其中光束的光裂变碎片与靶的光裂变碎片融合。使用激光辐射压力加速（RPA）的“钻孔”（HB）模式（罗宾逊等人，Plasma Phys. Control. Fusion 51：024004，2009; Henig等人，Phys.Rev.Lett. 103：245003，2009; Tajima等人，Rev. Accel. Sci. 2：221，2009），可以非常有效地从Th层（约200 μ m）产生具有固态密度的Th-232的聚束。560 nm厚），放置在氘代聚乙烯箱（CD 2，具有约520 nm），两者形成生产目标。激光加速到约7 MeV/u的Th离子将穿过置于紧靠生产靶后面的较厚的第二Th箔（两者形成反应靶）前面的薄CH 2层，并分裂成轻裂变碎片和重裂变碎片。此外，来自CD 2产生靶的轻离子（d，C）也将被加速到约7 MeV/u，也在第二Th层中诱导Th-232的裂变过程。具有固态密度的激光加速离子束的密度比传统加速离子束的密度高约10（14）倍，这使得当来自钍束的碎片撞击反应靶的Th层时，所产生的裂变产物能够再次熔合的可能性很高。其中，一种离子种类的强烈但低密度的放射性束与稳定的靶合并，新颖的裂变-聚变过程利用来自束和靶的富含中子的、短寿命的轻裂变碎片之间的聚变。此外，高离子束密度可以通过“雪犁式”去除靶电子而导致靶中阻止本领的强烈集体修改，从而导致显著的射程增强，从而允许我们使用相当厚的靶。例如，对于布加勒斯特的ELI-Nuclear Physics项目（ELI-NP）（http：www.eli-np.ro，2010）所设想的，数量级估计承诺在A=180-190的质量范围内每个激光脉冲约10（3）个离子的聚变产率，从而使我们能够接近N=126处的r-过程等待点。关于离子加速，停止行为的集体修改和富中子核的产生的第一项研究也可以在即将到来的新激光设施CALA（先进激光应用中心）进行。
We propose to produce neutron-rich nuclei in the range of the astrophysical r-process (the rapid neutron-capture process) around the waiting point N=126 (Kratz et al. in Prog. Part. Nucl. Phys. 59:147, 2007; Arnould et al. in Phys. Rep. 450:97, 2007; Panov and Janka in Astron. Astrophys. 494:829, 2009) by fissioning a dense laser-accelerated thorium ion bunch in a thorium target (covered by a polyethylene layer, CH2), where the light fission fragments of the beam fuse with the light fission fragments of the target. Using the 'hole-boring' (HB) mode of laser radiation pressure acceleration (RPA) (Robinson et al. in Plasma Phys. Control. Fusion 51:024004, 2009; Henig et al. in Phys. Rev. Lett. 103:245003, 2009; Tajima et al. in Rev. Accel. Sci. Technol. 2:221, 2009) using a high-intensity, short pulse laser, bunches of Th-232 with solid-state density can be generated very efficiently from a Th layer (ca. 560 nm thick), placed beneath a deuterated polyethylene foil (CD2 with ca. 520 nm), both forming the production target. Th ions laser-accelerated to about 7 MeV/u will pass through a thin CH2 layer placed in front of a thicker second Th foil (both forming the reaction target) closely behind the production target and disintegrate into light and heavy fission fragments. In addition, light ions (d,C) from the CD2 production target will be accelerated as well to about 7 MeV/u, also inducing the fission process of Th-232 in the second Th layer. The laser-accelerated ion bunches with solid-state density, which are about 10(14) times more dense than classically accelerated ion bunches, allow for a high probability that generated fission products can fuse again when the fragments from the thorium beam strike the Th layer of the reaction target.In contrast to classical radioactive beam facilities, where intense but low-density radioactive beams of one ion species are merged with stable targets, the novel fission-fusion process draws on the fusion between neutron-rich, short-lived, light fission fragments from both beam and target. Moreover, the high ion beam density may lead to a strong collective modification of the stopping power in the target by 'snowplough-like' removal of target electrons, leading to significant range enhancement, thus allowing us to use rather thick targets.Using a high-intensity laser with two beams with a total energy of 300 J, 32 fs pulse length and 3 mu m focal diameter, as, e.g. envisaged for the ELI-Nuclear Physics project in Bucharest (ELI-NP) (http://www.eli-np.ro, 2010), order-of-magnitude estimates promise a fusion yield of about 10(3) ions per laser pulse in the mass range of A=180-190, thus enabling us to approach the r-process waiting point at N=126. First studies on ion acceleration, collective modifications of the stopping behaviour and the production of neutron-rich nuclei can also be performed at the upcoming new laser facility CALA (Center for Advanced Laser Applications) in Garching.