Neutron Kinetics and Reactor Control

A nuclear reactor is designed to achieve the very delicate balance between neutron “production” (release) in fission reactions and neutron loss by absorption and leakage. A given neutron will be “born” in a fission event and will then usually scatter about the reactor until it meets its eventual “death” either by being absorbed in some material or by leaking out of the reactor. A certain number of these neutrons will be absorbed by fissionable nuclei and induce further fissions, thereby leading to the birth of new fission neutrons, that is, to a new generation of neutrons. The ratio of the number of neutrons born in a fission-neutron generation to the number born in the previous generation is called the effective reactor multiplication factor, keff. The keff characterizes the balance or imbalance in the chain reaction. Alternatively, keff can be defined by the ratio of production rate to loss rate of neutrons in the reactor. These definitions are given below:

Reaksi Fisi dan Reaksi Fusi dalam Mekanisme Bom Atom dan Senjata Termonuklir

Tujuan penelitian ini membahas mengenai reaksi fisi dan fusi pada bom atom dan senjata termonuklir. Penelitian ini adalah penelitian kualitatif, jenis penelitiannya menggunakan studi analitik komprehensif. Bagian paling vital dari ledakan fisi yang terjadi dalam bom atom tak lain adalah material yang berfisi itu sendiri. Ada dua unsur radioaktif yang biasa dipakai, yakni uranium dan plutonium, masing-masing dengan aneka isotopnya. Mulai dari U-232, U-234, U-235, dan U-238 untuk uranium, hingga Pu-238, Pu-239, dan Pu240 untuk plutonium. Elemen pemicu ledak yang dipakai dalam ledakan termonuklir ialah deuterium (D) alias hydrogen berat atau yang juga popular dengan sebutan ‘air berat’ (heavy water). Dari setiap 5000 atom hydrogen, bisa dipastikan satu isotop di antaranya dalam bentuk deuterium. Inti deuterium (deutron) terdiri dari satu proton (p) dan satu neutron (n). saat berpasangan, dua deutron membentuk inti atom helium (He-4) yang relatif stabil. Dalam semua jenis reaksi ini, inti atom berat terbentuk melalui proses fusi. Kata Kunci: bom atom, reaksi fisi, reaksi fusi, senjata termonuklir The purpose of this research is to discuss fission and fusion reactions in atomic bombs and thermonuclear weapons. This research is a qualitative research. This type of research uses a comprehensive analytical study. The most vital part of the fission explosion that occurs in an atomic bomb is none other than the fission material itself. There are two radioactive elements in common use, uranium and plutonium, each with its different isotopes. They range from U-232, U-234, U-235, and U-238 for uranium, to Pu-238, Pu-239, and Pu240 for plutonium. The explosive trigger element used in thermonuclear explosions is deuterium (D) heavy hydrogen or also popularly known as "heavy water" (heavy water). For every 5000 hydrogen atoms, one can be sure of one of them in the form of deuterium. The nucleus of heuterium (deutron) consists of one proton (p) and one neutron (n). When paired, the two deutrons form a relatively stable nucleus of helium (He-4). In all of these types of reactions, heavy atomic nuclei are formed by fusion. Keywords: atomic bombs, fission reactions, fusion reactions, thermonuclear weapons

Investigation of level density parameter dependence for some 233U, 235U, 237U, 239U, 249Cf, 251Cf, 237Pu and 247Cm nuclei in neutron fission cross sections with the incident energy up to 20 MeV

Level density models have increasing importance to gain more in-depth into the nature of nuclear reactions. Many novel and advanced medical application use radioisotopes, which are produced with nuclear reactions. In this study, the effect of the level density parameters of the nucleus on the cross sections of neutron-fission reactions for 233U, 235U, 237U, 239U, 249Cf, 251Cf, 237Pu and 247Cm nuclei were investigated for up to 20 MeV neutrons. TALYS 1.8 software was used to calculate the cross-sections of neutron-fission reactions for different level density parameters. The calculations were compared with the EXFOR nuclear data library and the level density parameters, and the closest fit were searched. As outputs of the study, the effect of selection of level density parameter on cross section calculations was observed. The theoretically obtained data were compared with the experimental data taken from the literature. The results are presented graphically for better interpretation.

Systematic study of the de-excitation of neutron-rich nuclei produced in different fission reactions

In this paper we present results from two recent studies, both related to the emission of prompt fission γ rays. Firstly, we have analyzed data from the reaction 235U(n, f) induced by fast neutrons of average energy E̅n = 1.7 MeV. The deduced spectral characteristics are an average multiplicity M̅γ = 7.11 ± 0.44 γ rays per fission and an average total γ-ray energy release in fission E̅γ,tot = 5.51 ± 0.46 MeV, corresponding to an average γ-ray energy ɛ̅γ = 0.77 ± 0.08 MeV. Secondly, we have addressed – and answered – the question how those characteristics in general depend on the width of the chosen prompt time window and the timing resolution, determined by the employed detectors and electronics. The conclusion is that once this is known, it is possible to compare results from different experiments in a more meaningful way.

Temperature- and pressure-dependent kinetics of the competing C–O bond fission reactions of dimethoxymethane

Under typical shock tube conditions, dimethoxymethane decomposes mainly to give CH3 + OCH2OCH3.

Mass-split dependence of pre-scission neutron multiplicity by four-dimensional Langevin dynamics in 16,18O, 40Ar and 64Ni-induced fusion–fission reactions

By using the multidimensional Langevin model, including elongation, neck thickness, asymmetry parameter and orientation degree of freedom, the fission dynamics of some [Formula: see text]O-, [Formula: see text]Ar- and [Formula: see text]Ni-induced fusion–fission reactions were investigated. We calculated mean pre-scission neutron kinetic energy, pre-scission neutron multiplicity and fission time. Mass-split dependence of pre-scission neutron multiplicity and sensitivity of multiplicity on different value of the level density parameter for fission and neutron emission of highly excited compound nuclei were studied. One can conclude reasonable agreement between theory and tentative results for different reactions.