Thermal Neutron Induced Fission Of 239Pu Research Articles

Monte Carlo simulation of the measurement by the 2E technique of the average prompt neutron multiplicity as a function of the mass of fragments from thermal neutron-induced fission of 239Pu

Using a Monte Carlo method, we simulate the measurement, by the 2E technique, of the average prompt neutron multiplicity as a function of the mass of fragments from the thermal neutron-induced fission of 239Pu. The input data for the simulation, associated with the primary fragment mass (A), consist of the yield (Y), the distribution of the total kinetic energy characterized by its average ((TKE) ̅) and its standard deviation (σ_TKE), the average prompt neutron multiplicity (ν ̅_s, a sawtooth approach of experimental data), and the slope of neutron multiplicity against total kinetic energy (dν_s/d<TKE>). The output data, associated with the simulated as the fragment mass measured by the 2E technique (µ), consist of the yield (y), the distribution of the total kinetic energy characterized by its average ((tke) ̅) and its standard deviation (σ_tke), and the average prompt neutron multiplicity (ν ̅_µ). In the mass regions A≈115 and A>150, ν ̅_µ is higher than ν ̅_s. This result suggests that, in those mass regions, the 2E experimental values associated with the average neutron multiplicity are overestimated, referred to the corresponding to the primary fragments.

Oversize of the average prompt neutron multiplicity measured by the 1V1E method in the symmetric region of thermal neutron-induced fission of 239Pu

Using a Monte Carlo method, the measurement by the 1V1E technique of the average prompt neutron multiplicity as a function of the mass of fragments from the thermal neutron-induced fission of 239Pu is simulated. The input data, associated with the masses of complementary primary fragments (A1, A2), consist of the yield (Y), the average total kinetic energy (TKE-) and its standard deviation (σTKE), the average prompt neutron multiplicity (ν-s, a sawtooth approach of an experimental curve ν-), and the slope of neutron multiplicity against total kinetic energy, -dν/d<TKE>, plotted as a function of fragment mass. The output data, associated with the provisional masses of complementary fragments (m1∗, m2∗) calculated with the 1V1E method, consist of the simulated quantities Y, TKE-, σTKE, N-, comparable to the measured ones. In comparison with ν-s, N- and ν-are oversized in the region of light fragment masses near the symmetric fission. To interpret the results, the neighboring masses ratio RA =YA+1/Y(A) and the term FA=A-m∗, where m∗ is the average of provisional mass as a function of A, are defined. It is shown that N--ν-s and ν--ν-s are correlated with -F(R-1). It is concluded that the oversize of ν- relative to ν-s is due to the interplay of the prompt neutron emission and the slope of the mass yield curve.

Estimation of the Yield of “Scission” Neutrons from Thermal Neutron-Induced Fission of 239Pu

Results of investigations of the angular and energy distributions of prompt neutrons from 239Pu fission observed on WWR-M type research reactor (Gatchina) are presented. Peculiarities observed in both angular and energy distributions of prompt neutrons can be explained by assuming the existence of neutrons emitted near the instant of fissioning nucleus rupture. Anisotropy of the angular distribution of prompt neutrons in the frame of the center of mass of fission fragments (ψ(0°)/ψ(90°) ≈ 1.07–1.09) should also be taken into consideration.

Probing energy dissipation, $\gamma$ -ray and neutron multiplicity in the thermal neutron-induced fission of 239Pu

The incorporation of the four-dimensional Langevin equations led to an integrative description of fission cross-section, fragment mass distribution and the multiplicity and energy distribution of prompt neutrons and \( \gamma\)-rays in the thermal neutron-induced fission of 239Pu. The dynamical approach presented in this paper thoroughly reproduces several experimental observables of the fission process at low excitation energy.

Distribution and behavior of some radionuclides associated with the Trinity nuclear test

The activities of 133Ba, 137Cs, 152Eu, 154Eu, 155Eu, 239Pu, and 241Am were determined by gamma spectroscopy on the largest sample set (n = 49) of bulk trinitite to date. The range in activity for all isotopes is large. For example, the activity of 241Am (normalized to the time of detonation) ranges between 1 and 42 Bq/g. Comparison of activities for isotopes derived from the device, 241Am versus 137Cs, 155Eu, and 239Pu, indicate positive trends. Correlations were not observed between the activities of the soil-derived activation products 152Eu and 154Eu and the radioisotopes from the device. The calculated ratio of fission products (155Eu/137Cs) is 0.012 ± .006 (1σ, n = 3), which is lower than predicted for the thermal neutron-induced fission of 239Pu (~0.03). This discrepancy may be attributed to the spontaneous fission of the natural U tamper resulting in mixing between fission products from 239Pu and 235U. The spatial distribution of the trinitite samples relative to ground zero has been modeled based on the activity of 152Eu. The calculated distances do not correlate with any of the activities for the radioisotopes investigated here, and suggest a relatively homogeneous distribution. However, trinitite samples with the highest activities for 137Cs, 239Pu, and 241Am yield the shortest calculated distances of 50–60 m away from ground zero.

Measurement and evaluation of some low-energy fission yield

Methods of independent fission yield measurement are briefly reviewed and compared one to another, experimental yield data are compiled for some low-energy fissioning systems. Example of predicting fission yields in thermal-neutron induced fission of239Pu is evaluated with even-odd effect presented. Future directions of experiments and evaluations are discussed.

Levels in 107Rh

The levels in 107Rh have been investigated via the γ-rays following the β − decay of 3.75 min 107Ru. The ruthenium activity was produced in the thermal neutron-induced fission of 239Pu and separated chemically from the fission product mixture with the on-line centrifuge system SISAK. The emitted γ-rays were studied by γ singles and γγ( t) coincidence measurements. In addition, the 108Pd(d, 3He) reaction was investigated at E d = 50 MeV to study the proton-hole states in 107Rh. From the comparison of the measured angular distributions with DWBA calculations l-transfers and spectroscopic factors were deduced. The obtained level scheme of 107Rh is discussed and compared with neighbouring nuclei and with recent calculations in the framework of the interacting boson-fermion (IBFM-1) model.

The collective structure of106,108Ru

Levels in106,108Ru have been studied by measuringγγ coincidences andγγ directional correlations of theγ-rays following theβ−-decay of 36 s106Tc and 5 s108Tc. Tc activities were separated chemically from the fission products of thermal neutron induced fission of239Pu by the continuously running system “SISAK 2” and theγ-radiation was measured on-line. An extended level scheme for108Ru, spin assignments,E2/M1 multipole mixing ratios andB(E2) ratios for106Ru and108Ru have been obtained. The collective structure of the two nuclei is discussed in the framework of different nuclear models.

Properties of3H-particles emitted during the thermal neutron-induced fission of239Pu

The study of the physical characteristics of light particles emitted from nuclei at the moment of fission is useful in the evaluation of the nuclear state in the configuration of scission. The importance of this evaluation, especially with respect to the velocity of the fragments at the instant of their separation, has prompted much experimental work in the past ten years to determine the energetic and angular properties of these light particles (1). In a preceding article (2) we reported for the first time the angular distribution of the particle 6He. This distribution is taken with respect to the line of flight of the light fragment in the thermal fission of 239pu. This distribution, together with the energy-angle correlations obtained, has shown that the emission of the isotope 6He has properties analogous to those measured for long-range alpha-particles and thus provides a proof that the emission of these isotopes of helium is due to the same physical mechanism. In this Letter we report briefly on the experimental results concerning the angular distribution of the particle aH emitted in the thermal neutron-induced fission of ~39pu. The experimental apparatus described earlier (2) pcrmits for each event thc simultaneous measurement of the energy of one of the fragments and of the light particle, which is also identified by a selniconductor telescope. Four separate runs were made, for which the angle between the directions of the light particle and the observed flagment was 68 ~ 88 ~ 108 ~ and 129 ~ respectively. During each run the fission fragments were detected by five surface barrier detectors in parallel, all placed at the same angle with respect to the direction of flight of the light particle. The angular acceptance of both the AE detector of the telescope and of the fragment detectors with respect to the centre of the target was • 5 ~ Unfortunately, due to the thickness (19 izm) of the AE detector available, it was not possible to observe completely the spectrum of the 3H-particles. The analysis was limited to the energy interval of 3.5 to 7 McV.