Mass and nuclear charge yields for 237Np(2nth,f) at different fission fragment kinetic energies

doi:10.1016/0375-9474(90)90593-B

Nuclear Physics A

Volume 515, Issue 3, 3 September 1990, Pages 433-465

https://doi.org/10.1016/0375-9474(90)90593-B Get rights and content

Abstract

The recoil mass separator LOHENGRIN of the Laue-Langevin Institute Grenoble has been used to measure for the first time, the yields of light fission fragments from the fissioning system: ²³⁹₉₃Np; this odd-Z nucleus is formed after double thermal neutron capture in a ²³⁹₉₃Np target. The mass distributions were measured for different kinetic energies between 92 and 115.5 MeV, but the nuclear charge distributions were determined only up to 112 MeV. These distributions are compared to the distributions obtained for the even-even system ²⁴⁰₉₄Pu. At high kinetic energy, the mass distribution shows a prominent peak around mass number A_L = 106. These cold fragmentations are discussed in terms of a calculation based on a scission point model extrapolated to the cold fission case. As expected for an odd-Z fissioning nucleus, the nuclear charge distributions do not reveal any odd-even effect. The global neutron odd-even effect is found to be (8.1 ± 1.5)%. A simple model has been used to show that most of the neutron odd-even effect results from prompt neutron evaporation from the fragments.

References (26)

W. Lang et al.
Nucl. Phys.
(1980)
U. Quade et al.
Nucl. Phys.
(1988)
C. Schmitt et al.
Nucl. Phys.
(1984)
J.P. Bocquet et al.
Nucl. Instrum. Meth.
(1988)
H.G. Clerc et al.
Nucl. Phys.
(1986)
S. Cohen et al.
Ann. of Phys.
(1962)
P. Möller et al.
At. Nucl. Data Tables
(1981)
M. Djebarra et al.
Nucl. Phys.
(1989)
N. Boucheneb et al.
J.P. Bocquet et al.

J.F. Ziegler

S. Liran et al.

At. Nucl. Data Tables

(1976)

C. Signarbieux et al.

J. de Phys.

(1981)

Cited by (21)

Charge distribution of light mass fission products in the fast neutron induced fission of 237Np, 241Am and 243Am
2022, Applied Radiation and Isotopes
Citation Excerpt :
In such a case, the most probable charge (ZP) can be obtained by using a known width parameter (σZ) without considering the even-odd effect. The σZ values for individual light mass chains in the 237Np(2nth,f) reaction based on physical measurement are given in Ref. (Martinez et al., 1990). As shown in our earlier work (Naik et al., 2007), in all the fissioning systems, the average width parameter (<σZ>) based on physical measurements is systematically higher than the value obtained from the radiochemical and off-line γ-ray spectrometry.
In the fast neutron induced fission of ²³⁷Np, ²⁴¹Am and ²⁴³Am, fractional cumulative yields (FCY) of various light mass fission products have been measured for the first time by using an off-line γ-ray spectrometric technique. The most probable charge (Z_P) and the experimental charge polarization (ΔΖ_EXPT) as a function of fragment mass were obtained. The ΔΖ_EXPT values for the light mass chains from the present work and for the heavy mass chains from earlier work show a decreasing trend towards symmetric split with fluctuations for some of the mass chains due to the effect of shell closure proximity. The ΔΖ_MPE values based on minimum potential energy surface were theoretically calculated, which also shows a systematic decrease trend with the approach of symmetric split without any fluctuation due to the liquid drop behaviour of the fissioning nucleus.
Extensive Study of the Quality of Fission Yields from Experiment, Evaluation and GEF for Antineutrino Studies and Applications
2021, Nuclear Data Sheets
The understanding of the antineutrino production in fission and the theoretical calculation of the antineutrino energy spectra in different, also future, types of fission reactors rely on the application of the summation method, where the individual contributions from the different radioactive nuclides that undergo a beta decay are estimated and summed up. The most accurate estimation of the independent fission-product yields is essential to this calculation. This is a complex task because the yields depend on the fissioning nucleus and on the energy spectrum of the incident neutrons.
In the present contribution, the quality of different sources of information on the fission yields is investigated, and the benefit of a combined analysis is demonstrated. The influence on antineutrino predictions is discussed.
In a systematic comparison, the quality of fission-product yields emerging from different experimental techniques is analyzed. The traditional radiochemical method, which is almost exclusively used for evaluations, provides an unambiguous identification in Z and A, but it is restricted to a limited number of suitable targets, is slow, and the accuracy suffers from uncertainties in the spectroscopic nuclear properties. Experiments with powerful spectrometers, for example at LOHENGRIN, provide very accurate mass yields and a Z resolution for light fission products from thermal-neutron-induced fission of a few suitable target nuclei.
On the theoretical side, the general fission model GEF has been developed. It combines a few general theorems, rules and ideas with empirical knowledge. GEF covers almost all fission observables and is able to reproduce measured data with high accuracy while having remarkable predictive power by establishing and exploiting unexpected systematics and hidden regularities in the fission observables. In this article, we have coupled for the first time the GEF predictions for the fission yields to fission-product beta-decay data in a summation calculation of reactor antineutrino energy spectra. The first comparisons performed between the spectra from GEF and those obtained with the evaluated nuclear databases exhibited large discrepancies that highlighted the exigency of the modelisation of the antineutrino spectra and showing their usefulness in the evaluation of nuclear data. Additional constraints for the GEF model were thus needed in order to reach the level of accuracy required by the antineutrino energy spectra. The combination of a careful study of the independent isotopic yields and the adjunction of the LOHENGRIN fission-yield data as additional constraints led to a substantially improved agreement between the antineutrino spectra computed with GEF and with the evaluated data. The comparison of inverse beta-decay yields computed with GEF with those measured by the Daya Bay experiment shows the excellent level of predictiveness of the GEF model for the fundamental or applied antineutrino physics.
The main results of this study are:
- –
  an improved agreement between the antineutrino energy spectra obtained with the newly tuned GEF model and the JEFF-3.1.1 and JEFF-3.3 fission yields for the four main contributors to fission in standard power reactors;
- –
  indications for shortcomings of mass yields for ²⁴¹Pu(n_th, f) and other systems in current evaluations;
- –
  a demonstration of the benefit from cross-checking the results of different experimental approaches and GEF for improving the quality of nuclear data;
- –
  an analysis of the sources of uncertainties and erroneous results from different experimental approaches;
- –
  the capacity of GEF for predicting the fission yields (and other observables) in cases (in terms of fissioning systems and excitation energies) which are presently not accessible to experiment;
- –
  predictions of antineutrino energy spectra that aim to assess the prospects for reactor monitoring, and based on the GEF fission yields associated with the beta-decay data of the most recent summation model.
Charge distribution studies in the odd-Z fissioning systems
2007, Nuclear Physics A
Charge distribution studies have been carried out in the odd-Z fissioning systems by determining the isobaric and isotopic yields for heavy mass fission products in the fast neutron induced fission of ²³⁷Np, ²⁴¹Am and ²⁴³Am using radiochemical and gamma ray spectrometric technique. From the yields data the width parameter ( $σ_{Z} / σ_{A}$ ), the most probable charge $(Z_{P}) / mass$ ( $A_{P}$ ) as well as the elemental yields ( $Y_{Z}$ ) of Sn, Sb, Te, I, Xe, Cs, Ba, La, Ce and Pr were deduced. From the elemental yields local even–odd effects for proton ( $D_{Z}$ ) were obtained in the odd-Z fissioning systems. The charge polarization (ΔZ) as a function of fragment mass ( $A^{'}$ ), the slope of charge polarization with mass asymmetry [ $δ (Δ Z) / δ A^{'}$ ] and average isobaric dispersion parameter ( $〈 σ_{Z} 〉$ ) were also obtained for these fissioning systems. The $δ (Δ Z) / δ A^{'}$ , $〈 σ_{Z} 〉$ , $D_{Z}$ and $Y_{Z}$ of various elements in the above three fissioning systems were determined for the first time. These data in the odd-Z fissioning systems (e.g. ^238,239Np^* and ^242,244Am^*) from present and earlier work are compared with the literature data for other odd-Z fissioning systems (e.g. ^212–226Ac^* and ^224–232Pa^*) and even-Z fissioning systems (e.g. ^217–233Th^*, ^230–239U^*, ^239–242Pu^*, ²⁴⁴Cm(SF), ^245,246Cm^*, ²⁵⁰Cf^* and ²⁵²Cf(SF)) to examine the role of nuclear structure effect (e.g. even–odd effect and shell effect). The dynamics of descent from saddle to point of neck formation and from the latter to the scission point are also discussed.
Super-asymmetric fission in the 245Cm(n<inf>th</inf>,f) reaction at the Lohengrin fission-fragment mass separator
2004, Nuclear Physics A
Mass, isotopic yields and single-fragment kinetic energy measurements for thermal-neutron induced fission of ²⁴⁵Cm at the Lohengrin fission-product mass separator are described. Using an ionization chamber coupled to the mass separator, we have measured the mass and isotopic yields from fragment mass A=67 up to A=77 over three yield decades. This considerably extends the data set previously known for the light peak. A full set of data is now available for this actinide in the super-asymmetric mass region. The results of mass and isotopic yields are compared with those of other compound nuclei to highlight the shell effect at mass 70 for the ²⁴⁶Cm^★ compound-nucleus system. Also, the present results are compared to the data from the European library JEF2 and the evaluation from Wahl's Z_p model.
Mass and charge distributions in the very asymmetric mass region of the neutron induced fission of 238Np
2001, Nuclear Physics A
The mass-separator Lohengrin was used to measure the yields of the light fission products with $A=74−85$ and their nuclear charge and kinetic energy distributions from the odd- $Z$ compound nucleus $^{239} Np^{∗}$ formed by double capture of thermal neutrons. The mass yield distribution reveals an influence of the fragment shell with $N=50$ affecting also the nuclear charge and kinetic energy distributions. An odd–even effect for protons is found in the very asymmetric mass division, increasing from 4% to 35% with increasing fission asymmetry. This is in contrast to findings in normal asymmetric fission (region of high fission yields) where no odd–even effect for protons was observed. An odd–even effect for neutrons is also found comparable in size with that for protons. The latter effect exists also in normal asymmetric fission and is at least partly attributed to prompt neutron emission from the fragments. Some information on the number of prompt neutrons emitted is also obtained. From this information and from the energy dependence of the odd–even effect for protons it is concluded that the very light fragments originate from a cold and nearly undeformed light sphere of a dumbbell scission configuration characterised by a double shell closure with 28 protons and about 50 neutrons. In contrast to the double shell closure at mass 132 ( $Z=50$ , $N≈82$ ) the two shell closures in the light sphere do not coincide at one mass but are realised at $A=70$ and 80, respectively. This leads to a layered structure of the light sphere of the dumbbell scission configuration.
Mass and charge distributions in the very asymmetric thermal neutron induced fission of the odd-Z nucleus 242mAm
1999, Nuclear Physics A
Yields of light fission products (A = 68, 70–84, 87, 88, 94, 96, 98, 102 and 106–108), their kinetic energies and nuclear charge distributions (A = 71–84, 87 and 88) in the thermal neutron induced fission of the odd-Z nucleus ^242mAm(Z = 95) were measured using the mass-separator Lohengrin at the Institute Laue-Langevin in Grenoble (France). The mass yield curve shows a fine structure at A = 70, probably due to shell and/or odd-even effects affecting also the nuclear charge distribution. The analysis of isotopic chain yields gives evidence for a very low excitation energy of the lightest fission fragments observed. A preferential formation of fragments with even Z is found for this odd-Z compound nucleus. Calculated values for the local odd-even effect are comparable with those for the neighbouring even-Z fissile nuclides and increase from 13% to 30% with increasing asymmetry of the mass split (A_L = 84 to 68 and Z_L = 35 to 28). The neutron odd-even effect shows a similar but less pronounced behaviour.

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Nuclear Physics A

Abstract

References (26)

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Instrum. Meth.

Nucl. Phys.

Ann. of Phys.

At. Nucl. Data Tables

Nucl. Phys.

At. Nucl. Data Tables

J. de Phys.

Cited by (21)

Charge distribution of light mass fission products in the fast neutron induced fission of <sup>237</sup>Np, <sup>241</sup>Am and <sup>243</sup>Am

Extensive Study of the Quality of Fission Yields from Experiment, Evaluation and GEF for Antineutrino Studies and Applications

Charge distribution studies in the odd-Z fissioning systems

Super-asymmetric fission in the <sup>245</sup>Cm(n<inf>th</inf>,f) reaction at the Lohengrin fission-fragment mass separator

Mass and charge distributions in the very asymmetric mass region of the neutron induced fission of <sup>238</sup>Np

Mass and charge distributions in the very asymmetric thermal neutron induced fission of the odd-Z nucleus <sup>242m</sup>Am