Photofission of Heavy Nuclei from 0.2 to 3.8 GeV
Photofission of Heavy Nuclei from 0.2 to 3.8 GeV
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0.2 至 3.8 GeV 重核光裂变
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
G. Kezerashvili
中科院分区：
文献类型：
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作者：
C. Cetina;P. Heimberg;B. Berman;W. Briscoe;G. Feldman;L. Murphy;H. Crannell;A. Longhi;D. Sober;J. Sanabria;G. Kezerashvili
在Jefferson实验室B厅，利用能量范围为E{Sub{Gamma}}=0.17-3.84GeV的标记光子，同时测量了{sup 237}Np，{sup 233}U，{sup 235}U，{sup 238}U，{sup 232}Th和{sup nat}Pb的光裂变总截面。裂变碎片是用平行板雪崩探测器探测的。我们的结果表明，在这些核子中，{sup 237}Np具有最大的每核子光裂变截面，在整个能量范围内，{sup 238}U相对于{sup 237}Np的光裂变截面约为80%。每个核子的相对光裂变截面随着裂隙参数Z{sup 2}/A的增大而增大，在{sup 2 37}np的Z{sup 2}/A处接近一明显的渐近线，并且在整个能量范围内它们不强烈地依赖于入射光子的能量。这些结果，再加上每个核子的{sup 237}Np的光裂变截面与总的光吸收数据的比较，表明{sup 237}Np的光裂变几率几乎是1。如果我们做这个假设，我们观察到从1.5GeV以下开始的内部核子有显著的阴影，因此在4GeV附近光吸收截面减少了20%。
Total photofission cross sections for {sup 237}Np, {sup 233}U, {sup 235}U, {sup 238}U, {sup 232}Th, and {sup nat}Pb have been measured simultaneously, using tagged photons in the energy range E{sub {gamma}} = 0.17-3.84 GeV in Hall B at Jefferson Lab. The fission fragments were detected using parallel-plate avalanche detectors. Our results show that, of these nuclei, {sup 237}Np has the largest photofission cross section per nucleon, and that the photofission cross section for {sup 238}U relative to that for {sup 237}Np is about 80% over the entire energy range. The relative photofission cross sections per nucleon increase with the fissility parameter Z{sup 2}/A, approaching an apparent asymptote at the Z{sup 2}/A value for {sup 237}Np, and they do not depend strongly on the incident photon energy over this entire energy range. These results, together with a comparison of the {sup 237}Np photofission cross section per nucleon with total photoabsorption data, indicate that the photofission probability for {sup 237}Np is almost unity. If we make this assumption, we observe a significant shadowing of the interior nucleons starting below 1.5 GeV, so that the photoabsorption cross section decreases by 20% near 4 GeV.