S. M. Sahakundu

Absolute yields of 99Mo and 111Ag in the reactor neutron induced fission of 238U

Abstract The absolute fission yields of 99Mo and 111Ag have been measured in the reactor neutron induced fission of depleted uranium employing a fission track-cum-radiochemical technique. The absolute disintegrations were determined from beta decay and Ge(Li) gamma spectrometry. The total number of fissions were measured by fission track registration on lexan solid state track detector immersed in fissile material solution. The yields for99Mo and 111Ag were found to be (6.27 ± 0.30)% and (0.046 ± 0.002)% respectively. The results are compared with the published data and the merits of the present method have been discussed.

A new method for the radiochemical separation of copper from fission products

A new method for obtaining radiochemically pure67Cu from highly active fission product solutions is described. The method is based on the solvent extraction of the Cu(II)-diethyldithiocarbamate complex in n-butyl acetate in the presence of hold-back carriers for Ni, Co, Mn, Mo, rare earths, Cd, Te and Sb, and subsequent purification steps involving scavengings for Ag, Ba, Sr and Fe followed by an anion-exchange purification step for decontamination from Te. Copper is finally extracted as the α-benzoin oxime complex in which form it is mounted and counted. The method has several advantages over other methods in that decontamination is very high and it is sufficiently fast considering the stringent radiochemical purity achieved. The67Cu separated by this procedure from a one-day-old mixture of fission products arising from 1010 fissions was found to be completely free of any contamination.

Effect of entrance channel parameters on fission fragment angular momentum in medium energy fission

Independent isomeric yield ratios of132I were radiochemically determined in alpha particle induced fission of238U in the energy range 25–44 MeV. Fission fragment angular momenta were deduced from the measured isomeric yield ratios using spin dependent statistical model analysis. It was seen that angular momentum of132I increases with increase of excitation energy and angular momentum of the fissioning nucleus. Comparison of the present data on132I in238U(α,f) with the literature data for the same product in238U(p, f) and238U(γ, f) at various excitation energies show that fragment angular momentum strongly depends on the input angular momentum in the range of excitation energy considered. Experimental fragment angular momentum at all excitation energies were seen to be in agreement with the theoretical values calculated based on thermal equilibration of the various collective rotational degrees after considering the occurence of multichance fission. Thus, strong effect of input angular momentum as well as the statistical equilibration among the various collective rotational degrees of freedom in medium energy fission is corroborated.

Excitation Functions for Multi-Nucleon Emission in Helium Ion Reactions with 197Au

Excitation functions for the production of heavy residues through He reactions on Au targets have been measured in the incident energy range of 35 — 50 MeV which probes and extends the lower limits of the excitation functions for cluster and multi-nucleon emission. The older cross-section values that partially cover this energy region have been re-evaluated using more recent decay scheme data and compared with the present measurements. Interference from secondary neutrons in the cross-sections of interest were investigated.

Influence of collective rotational degrees of freedom in medium energy fission

In the present work rms angular momenta have been deduced for the fission fragments corresponding to131Tem,g and133Tem,g in232Th(α40 MeV,f) and238U(α40 MeV,f) systems from the radiochemically determined independent isomeric yield ratios and statistical model based analysis. For131Te and133Te the rms angular momenta deduced are 5.9±1.0 and 7.9±1.2 ħ respectively in232Th(α40 MeV,f) and 7.2±0.6 and 8.0±0.8 ħ respectively in238U(α40 MeV,f). Comparison of the present data with the literature data for these fragments in the same compound nuclei236U* and242Pu* at lower excitation energies shows increase in the fragment angular momentum with increasing excitation energy and angular momenta of the fissioning nuclei. Fragment angular momentum deduced theoretically for asymmetric and deformed fragments on the basis of thermal equilibration of the collective rotational degrees e.g., rigid rotation, wriggling, tilting, bending and twisting modes considering the effect of multichance fission, are in good agreement with the experimental observations.

Separation of heavier rare earths from neutron irradiated uranium targets

A radiochemical method is described for the separation of heavier rare earths from the fission of uranium. The method is particularly suitable for the separation of low yield (10−5%–10−7%), highly asymmetric rare earth fission products viz.179,177Lu,175Yb,173Tm,172,171Er,167Ho and161,160Tb in the neutron induced fission of natural and depleted uranium targets. Additional separation steps have been incorporated for decontamination from239Np (an activation product) and93-90Y (a high fission-yield product) which show similar chemical behaviour to rare earths. Separation of individual rare earths is achieved by a cation exchange method performed at 80°C by elution with α-hydroxyisobutyric acid (α-HIBA).

Charge distribution study in the alpha-particle induced fission of232Th+ effect of excitation energy

The fractional cumulative yields of135I,138Xe and140Ba in the α particle (30 MeV) induced fission of232Th have been determined following the growth and decay of135gXe,138gCs and140La, respectively, employing high resolution gamma ray spectroscopy. The fractional cumulative yield values are 0.766±0.02, 0.813±0.03 and 0.991±0.004, respectively. The analysis of the data indicates a broader width of charge distribution (σ) compared to the normally observed σ=0.56±0.06 for thermal neutron fission of235U.