Mass Yield Distribution Research Articles

Measurement of fission product yields in the quasi-mono-energetic neutron-induced fission of 238U

The cumulative yield of the fission products within the mass range of 83–117 and 123–153 have been measured in the 6.61and 10.92 MeV quasi-mono-energetic neutron-induced fission of 238U by using an off-line γ-ray spectrometric technique. The neutron beams were obtained from the 7Li(p,n) reactions with the proton energies of 11 and 18.8 MeV. The mass chain yields were obtained from the cumulative yields by using charge distribution correction. The peak-to-valley (P/V) ratio, the average value of light mass (⟨AL⟩), heavy mass (⟨AH⟩) and the average number of neutrons (<ν>) were obtained from the mass yield data. The data in the 238U(n, f) reaction from the present work and literature at various energies were compared with the similar data in the 238U(γ, f) reaction and following observations were obtained. (i) In both the reactions, the mass yield distributions are double humped. (ii) The yield of fission products for A = 133–134, A = 138–139, and A = 143–144 and their complementary products are higher than those of other fission products due to the nuclear structure effect. (iii) The yield of symmetric product increases and thus the peak-to-valley (P/V) ratio decreases with excitation energy. (iv) With the increase of excitation energy, the <ν> vale increases in a similar way in both the reactions. (v) The changing trend of ⟨AL⟩ and ⟨AH⟩ values with the increase of excitation energy are entirely different in between the two reactions.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 235U

Cumulative and independent yields of various fission products within the mass ranges of 78 to 117 and 123 to 155 have been measured in the epi-cadmium reactor neutron-induced fission of 235U by using an off-line gamma-ray spectrometric technique. The average neutron energy <En> of the epi-cadmium reactor spectrum is 1.9 MeV. From the cumulative yields, post-neutron mass chain yields were obtained by applying the charge distribution correction. In the mass yield distribution, values of the full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, and average number of neutrons <ν> were obtained. The peak-to-valley ratio in the epi-cadmium neutron-induced fission of 235U was obtained for the first time. The present data in the 235U(n,f) reaction were compared with the literature data in the 235U(nth,f) reaction to examine the role of excitation energy on the mass yield distribution parameters and nuclear structure effect. The role of the standard I and standard II asymmetric modes of fission was also discussed.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 239Pu

In the epi-cadmium neutron-induced fission of 239Pu, cumulative and independent yields of various fission products within the mass ranges of 83 to 117 and 123 to 156 have been measured by using an off-line gamma-ray spectrometric technique. The spectrum average neutron energy is 1.9 MeV. Charge distribution correction on the cumulative yields was applied to obtain their post-neutron mass yields. Mass yield distribution parameters such as the peak-to-valley (P/V) ratio, the full-width at tenth-maximum of light and heavy mass wings, the average light mass <AL> and heavy mass <AH>, and the average neutron number <ν> were obtained. The mass yields in the epi-cadmium and thermal neutron–induced fission of 239Pu were compared to examine the role of excitation energy on the P/V ratio and the nuclear structure effect.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 233U

Post-neutron mass yield distribution in the epi-cadmium neutron-induced fission of 233U has been carried out by measuring the cumulative yields of various fission products within the mass ranges of 77 to 117 and 123 to 153 using an off-line gamma-ray spectrometric technique. Independent yields of a few fission products were also measured by using the same technique. Charge distribution correction has been applied on cumulative yields to obtain the post-neutron mass yields. The mass yield distribution parameters such as full-width at tenth-maximum of light and heavy mass wings, the average light mass <AL> and heavy mass <AH>, and the average number of neutrons <ν> were obtained. The spectrum average neutron energy is 1.9 MeV. Thus, the role of excitation energy on the nuclear structure effect was examined by comparing the mass yield data in between the epi-cadmium and thermal neutron–induced fission of 233U.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron–Induced Fission of 238Pu

The cumulative and independent yields of various fission products within the mass range of 78 to 157 have been measured in the epi-cadmium neutron–induced fission of 238Pu by using an off-line γ-ray spectrometric technique. The lower yield of 136I than the usual trend indicates the formation of delayed neutron emitter 137I. From the cumulative yields, post-neutron mass chain yields were obtained by using the charge distribution correction. From the mass yield data, the peak-to-valley (P/V) ratio, the full-width at tenth-maximum of light and heavy mass wings, the average light mass <AL> and heavy mass <AH> as well as the average number of neutrons <ν> emitted were obtained. The mass chain yield data in the 238Pu(n,f) reaction were compared with similar data of the 238Pu(nth,f) reaction to examine the role of excitation energy on the nuclear structure effect and P/V ratio.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 241Pu

The cumulative and independent yields of various fission products within the mass range of 83 to 117 and 123 to 157 have been measured in the epi-cadmium neutron–induced fission of 241Pu using an off-line γ-ray spectrometric technique. From the cumulative yields, post-neutron mass yields were obtained using the charge distribution correction. The full-width at tenth maximum of the light and heavy mass wings and the average light mass <AL> and heavy mass <AH>, as well as the average number of neutrons <ν>, were obtained. The mass yields in the epi-cadmium– and thermal neutron–induced fission of 241Pu were compared to examine the role of excitation energy on the nuclear structure effect.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 245Cm

The cumulative and independent yields of various fission products within the mass ranges of 83 to 117 and 123 to 161 have been measured in the epi-cadmium neutron-induced fission of 245Cm by using an off-line gamma-ray spectrometric technique. Charge distribution correction was applied on the cumulative yields to obtain the post-neutron mass yield distribution. From the mass yield distribution data, the full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, average neutron number <ν>, and peak-to-valley ratio were obtained for the first time. Comparison of mass yield distributions was made between the epi-cadmium and thermal neutron–induced fission of 245Cm to examine the role of excitation energy on the nuclear structure effect and P/V ratio.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 229Th

In the epi-cadmium neutron-induced fission of 229Th, cumulative yields of relatively long-lived fission products within the mass range of 77 to 151 were measured by using an off-line gamma-ray spectrometric technique. The mass yields were obtained from the cumulative fission product yields by using charge distribution correction. The peak-to-valley (P/V) ratio, full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, and average neutron number <ν> were obtained. The P/V ratio was obtained for the first time and was found to be about three times lower in the epi-cadmium neutron fission than in the thermal neutron fission of 229Th, which shows the role of excitation energy. The fine structure of the mass yield distribution in the 229Th(nf,f) reaction was explained from the viewpoint of nuclear structure effect and the Standard I and Standard II asymmetric modes of fission.

Post-Neutron Mass Yield Distribution in the Thermal Neutron Induced Fission of 233U

In the thermal neutron–induced fission of 233U, the cumulative and independent yields of various fission products within the mass ranges of 77 to 109 and 123 to 155 have been measured by using an off-line gamma-ray spectrometric technique. The lower yields of 86Br and 136I than usual trend indicate the formation of delayed neutron emitters 87Br and 137I. From the cumulative yields, the post-neutron mass yield distribution was obtained after applying the charge distribution correction. The data from the present and earlier work of our laboratory in the 233U(nth,f) reaction were compared with similar data of 232,235U(nth,f) and 238U(n,f) reactions to examine the effect of mass difference of the fissioning systems on the fine structure of the mass yield distribution. The mass yield distribution in the 233U(nth,f) reaction was also compared with those of 229Th(nth,f), 241Pu(nth,f), and 245Cm(nth,f) reactions to examine the effect of charge and mass difference of the fissioning systems and also to examine the different behaviors of standard I and standard II asymmetric modes of fission.

Post-Neutron Mass Yield Distribution in the Thermal Neutron Induced Fission of 235U

The cumulative and independent yields of various fission products within the mass ranges of 78 to 108 and 123 to 155 have been measured in the thermal neutron–induced fission of 235U by using an off-line gamma-ray spectrometric technique. The post-neutron mass yield distribution was obtained from the cumulative yields after applying the charge distribution correction. The data from present and earlier work of our laboratory in the 235U(nth,f) reaction were compared with similar data of 229Th(nth,f), 245Cm(nth,f), and 252Cf(SF) reactions to examine the fine structure in the mass yield distribution for four different even-even fissioning systems with charge of 90 to 98. The comparison shows that the fine structure in the mass yield distribution depends on spherical and deformed neutron shell combinations. The shell combination favors the standard I asymmetric mode of fission in the 235U(nth,f) and 245Cm(nth,f) reactions, whereas it favors the standard II asymmetric mode of fission in the 229Th(nth,f) and 252Cf(SF) reactions.

Post-Neutron Fission Product Yield Distribution in the Spontaneous Fission of 244Cm

The cumulative yield of fission products within the mass range of 85 to 115 and 127 to 156, as well as the independent yield of some of the fission products, have been measured in the spontaneous fission of 244Cm by using an off-line γ-ray spectrometric technique. From the cumulative yield of the fission products, their mass chain yields were obtained by applying the charge distribution correction. Mass yield distribution parameters like full width at tenth maximum of light and heavy mass wing and the average light mass <AL> and heavy mass <AH>, as well as the total average neutron multiplicity <ν>expt were obtained. The fission yield data in the 244Cm(SF) reaction were compared with similar data in the neutron-induced fission and spontaneous fission of other actinides to examine the role of excitation energy. The effect of nuclear structure on the excitation energy deficit spontaneous systems has been clearly observed.

The FFIS spectrometer for determination of fission fragment mass distribution with the energy–velocity method

The FFIS spectrometer (Fission Fragment Identification Spectrometer) for determining independent fission yields has been developed based on the E–v method. By directly measuring the time-of-flight (TOF) and kinetic energy of fission fragments on their flight path, the post-neutron-emission mass yield distributions can be obtained. With the aim of getting the highest possible mass resolution, an axial grid ionization chamber and a TOF measurement system based on microchannel plate (MCP) detectors were designed. The ionization chamber with a silicon nitride entrance window of 100 nm thickness was tested and calibrated with a 252Cf spontaneous fission source. The intrinsic energy resolution for 1.27 MeV/u 63Cu particles is measured to be 450 keV (FWHM). The time resolution was determined with two MCP timing detectors to be 157 ps (FWHM) for 241Am radiation source, implying that the intrinsic time resolution is about 110 ps (FWHM) for a single timing detector. Thermal-neutron-induced fission of 235U was studied at the In-hospital Neutron Irradiator (IHNI). An event-by-event energy loss addback technique was developed based on Geant4 calculation to minimize the correction error. The first results of mass yield distributions from 235U(nth,f) are reported.

A general framework for describing photofission observables of actinides at an average excitation energy below 30 MeV * *Supported by the National Natural Science Foundation of China (11675075), Independent research project of key laboratory of plasma physics, CAEP (JCKYS2021212009) and Hengyang Municipal Science and Technology Project (202150054076)

A reasonable prediction of photofission observables plays a paramount role in understanding the photofission process and guiding various photofission-induced applications, such as short-lived isotope production, nuclear waste disposal, and nuclear safeguards. However, the available experimental data for photofission observables are limited, and the existing models and programs have mainly been developed for neutron-induced fission processes. In this study, a general framework is proposed for characterizing the photofission observables of actinides, including the mass yield distributions (MYD) and isobaric charge distributions (ICD) of fission fragments and the multiplicity and energy distributions of prompt neutrons (np ) and prompt γ rays (γ p ). The framework encompasses various systematic neutron models and empirical models considering the Bohr hypothesis and does not rely on the experimental data as input. These models are then validated individually against experimental data at an average excitation energy below 30 MeV, which shows the reliability and robustness of the general framework. Finally, we employ this framework to predict the characteristics of photofission fragments and the emissions of prompt particles for typical actinides including 232Th, 235, 238U and 240Pu. It is found that the 238U(γ, f) reaction is more suitable for producing neutron-rich nuclei compared to the 232Th(γ, f) reaction. In addition, the average multiplicity number of both np and γ p increases with the average excitation energy.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 241Am

Mass yield distribution has been carried out in the epi-cadmium neutron-induced fission of 241Am by measuring the cumulative yields of fission products within the mass ranges of 80 to 119 and 123 to 161. An off-line gamma-ray spectrometric technique was used for the measurement. From the cumulative yields of the fission products, mass chain yields were obtained by applying the charge distribution correction. From the mass yield distribution, the full-width at tenth-maximum of the light and heavy mass wings, the peak-to-valley (P/V) ratio, the average light mass <AL> and heavy mass <AH>, and the average number of neutrons <ν> were obtained. The mass yield data in the epi-cadmium neutron fission of 241Am were compared with similar data of thermal and 14.8-MeV neutron-induced fission to examine the role of excitation energy on the nuclear structure effect and P/V ratio.

Post-Neutron Mass Yield Distribution in the Thermal Neutron Induced–Fission of 239Pu

Mass chain yield distribution has been done in the thermal neutron–induced fission of 239Pu by measuring the cumulative yields of various fission products within the mass range of 78 to 159 and the independent yields of a few products. An off-line gamma-ray spectrometric technique was used to measure the gamma-ray activities of the fission products. From the measured values of the cumulative yields, the post-neutron mass chain yield distribution was obtained after applying the charge distribution correction. Data from the present and earlier work of our laboratory in the 239Pu(nth,f) reaction were compared with similar data of 238,241Pu(nth,f) and 240Pu(n,f) reactions, and it was found that the fine structures of the mass yield distributions are similar. The mass yield distribution in the 239Pu(nth,f) reaction was also compared with those of 229Th(nth,f) and 252Cf(SF) reactions to examine the effect of charge and mass difference of the fissioning systems on the mass yield distribution. It was found that the asymmetric standard I mode of fission is favorable in the 238,239,241Pu(nth,f) and 240Pu(n,f) reactions whereas the standard II mode is favorable in the 229Th(nth,f) and 252Cf(SF) reactions.

Post-neutron mass yield distribution in the epi-cadmium neutron induced fission of 243Am

The cumulative yields of fission products within the mass range of 83 to 119 and 123 to 158 have been measured in the epi-cadmium neutron-induced fission of 243Am by using an off-line gamma-ray spectrometric technique. Mass chain yields were obtained from the cumulative yields of the fission products by applying the charge distribution correction. From the mass yield data, the full-width at tenth-maximum of the light and heavy mass wing, the peak-to-valley (P/V) ratio, the average light mass <AL> and heavy mass <AH>, and the average number of neutrons <ν> were obtained. The mass yield data in the 243Am(n,f) reaction were compared with similar data in the 243Am(nth,f) and 243Am(n16.5 MeV,f) reactions to examine the role of excitation energy on the nuclear structure effect and P/V ratio.

Evidence for competing bi-faceted compound nucleus fission modes in 232Th(α,f) reaction

Relative isotopic yield distributions have been extracted for nine correlated fission fragment pairs following a detailed analysis of prompt γ−γ coincidence events from 232Th(α,f) reaction at Elab = 30 MeV. Simultaneously, the charge and mass yield distributions of the even-even fission fragments have been obtained from the measured relative isotopic yields. The onset of a triple-hump structure is seen in the extracted charge as well as mass yield distributions of the fragments. The results are consistent with the two-mode fission hypothesis of compound nucleus and in good agreement with the theoretical predictions, based on relevant fission models. The detailed results provide experimental evidence for the presence of two distinct compound nucleus fission modes, where the asymmetric and symmetric fission components are 83% and 17%, respectively. An average neutron multiplicity value of 4.60 ± 0.09 has been obtained, and the extracted neutron multiplicity distribution pattern corroborates the observed features of the multifaceted fission modes. Comparing the measured yield distributions following the 232Th(α,f) surrogate reaction, which produces 236U⁎ at an excitation energy of 21.5 MeV, with that of the direct reaction of 14 MeV neutron induced fission of 235U, an increase of about 11% in the yield of the symmetric component has been observed.

Post-Neutron Mass Yield Distribution in the Thermal Neutron Induced Fission of 232U

In the thermal neutron–induced fission of 232U, cumulative and independent yields of various fission products within the mass ranges of 72 to 107 and 123 to 158 have been measured using an off-line gamma-ray spectrometric technique. The fission yields were determined relative to the yield of a monitor product 92Sr. Charge distribution correction was applied on the cumulative yields to obtain the post-neutron mass yield distribution. Mass yield distribution parameters such as full-width at tenth-maximum of light and heavy mass wings, average light mass number <AL> and heavy mass number <AH>, and average number of emitted neutrons <ν> were obtained. Data from the present and earlier work on the 232U(nth,f) reaction were compared with similar data of the 235U(nth,f) reaction. It was found that the mass chain yield distribution in the 232U(nth,f) reaction is asymmetric with two major humps as in the case of the 235U(nth,f) reaction. Besides this, in the 232U(nth,f) reaction, the mass yield distribution shows a small third hump for the symmetric fission products. It was also found that the standard II asymmetric mode of fission is favorable in the 232U(nth,f) reaction whereas the standard I asymmetric mode of fission is favorable in the 235U(nth,f) reaction.

Post-neutron mass yield distribution in the epi-cadmium neutron induced fission of 99.9997 atom % 238U

The cumulative yields of various short and relative long-lived fission products within the mass range of 80–115 and 123–157 have been measured in the epi-cadmium neutron induced fission of 99.9997 atom % 238U, by using an off-line γ-ray spectrometric technique. The mass chain yields were obtained from the cumulative yields by applying the charge distribution correction. The present and earlier data in the 238U(n, f) reaction was compared with the similar data of 232Th(n, f) reaction. In the 38U(n, f) reaction, the yields around the mass range 134–138 and their complementary are higher than the other fission products, which indicate the favorable standard I asymmetric mode of fission. On the other hand, in the 232Th(n, f) reaction, the yields around 139–144 and their complementary are higher than the other fission products, which indicate the favorable standard II asymmetric mode of fission.

Mass yield distribution in the 3 GeV bremsstrahlung induced fission of 232Th

The cumulative yields of various fission products within the mass region of 77–153 in the 3-GeV bremsstrahlung induced fission of 232Th have been measured by using the method of recoil catcher and an off-line γ–ray spectrometry at the Pohang accelerator laboratory, Korea. The mass yields were obtained from the cumulative yields of fission products after charge-distribution corrections in the high energy fission. We obtained the mass distribution parameters such as peak-to-valley (P/V) ratio, average light mass (AL), and heavy mass (AH), as well as the average post-fission number of neutrons (vexpt) in the 232Th(γ,f) reactions. We compared the fission yield data in the 232Th(γ,f) and 238U(γ,f) reactions at various bremsstrahlung energies and the following facts were observed. (i) At the bremsstrahlung end-point energy of 2.0–3.5 GeV, the mass yield distribution in the 232Th(γ,f) reaction is triple humps, whereas in the238U(γ,f) reaction, it is double humps. This is due to the different type of potential energy surface between the two fissioning systems. (ii) In both the 232Th(γ,f) and 238U(γ,f) reactions, the yields of asymmetric products decrease marginally, whereas for those of symmetric products increase significantly with bremsstrahlung energy and thus the value of P/V ratio decrease accordingly. (iii) At all the bremsstrahlung energy, the P/V ratio of the 232Th(γ,f) reaction is lower than that of the 238U(γ,f) reaction due to the presence of the third peak in the mass yield distribution of former.