J.E. Gindler

Alpha half-lives of 216Po, 217At and 218Rn☆

Abstract The α-half-lives of 216Po, 217At and 218Rn have been measured to be 0·145 ± 0·002 sec, 0·0323 ± 0·0004 sec and 0·035 ± 0·001 sec, respectively. The alpha hindrance factor of 217At has been calculated to be 1·2 on the basis of its measured half-life and an α-particle energy of 7·064 MeV.

The mass distribution for spontaneous fission of 252Cf

Abstract The distribution of mass in the spontaneous fission of 252Cf has been investigated by the radiochemical determination of the fission yields for 35 mass chains. Absolute fission yields were measured for four nuclides, 99Mo, 111Ag, 132Te and 140Ba. Ratios of the yields of fission product isomers to total chain yields were determined for 115gCd, 125gSn, 127mTe and 129mTe. A comparison of this work with that of previous investigators has resulted in “recommended” yields for 51 mass chains.

Formation of 111Pd isomers in neutron fission of several heavy nucleides

Abstract The cumulative yields of the 111Pd isomers have been measured in fission of 232Th, 233U, 235U, 238U and 239Pu by neutrons. The ratios of the 11 2 metastable state yield to the 5 2 ground state yield are 0·0043, 0·0209, 0·0096, 0·0048 and 0·0186 for the respective nucleides. The estimated error in each value is ±10%. Independent yield isomeric ratios have been calculated for various assumptions of charge distribution. The results of these calculations are discussed in terms of the parameters which describe the charge dispersion of mass-chain 111 and the angular momentum with which the fragments are formed. An upper limit of 0·43% has been placed on the β-decay branch of 111Rh111mPd.

Electron-capture/negatron-emission branching ratio of 236Np (22 hr)

Abstract A value of 1·05 ± 0·17 has been determined for the electron-capture/negatron-emission branching ratio of 22 hr 236Np using a combination of α-counting techniques and mass spectrometric measurements. The relative production of 22 hr 236Np to that of long-lived 236Np has been recalculated and found to be about seven for the interaction of 18 MeV deuterons with 235U.

Thermal neutron fission cross-section of 229Th

Abstract The fission cross-section of 229 Th for thermal neutrons has been determined by counting samples placed in the thermal column of the Argonne heterogeneous heavy-water reactor, CP-5 Comparison of the fission counting rates of 229 Th samples with those of 235 U and 239 Pu standards gave a cross-section value of 30·5 ± 3 barns.

Mass distributions for the spontaneous fission of 248Cm and 250Cf

Abstract The distribution of mass in spontaneous fission of 248Cm and 250Cf has been investigated radiochemically and with γ-ray spectrometry. Both distributions are asymmetric with peak-to-valley ratios of > 1000 for 248Cm and > 300 for 250Cf. The average light and heavy masses ( A L , A H ) are respectively 104.6, 139.9 and 105.2, 141.5. Values for the average number of neutrons emitted per fission obtained by subtracting A L + A H from the mass of the fissioning nucleus are respectively 3.5±0.5 and 3.3±0.5.

Mass distributions for the spontaneous fission of 253Es and the thermal-neutron-induced fission of 254Es☆

Abstract The distribution of mass in the spontaneous fission of 253Es and the thermal-neutron-induced fission of 254Es have been investigated radiochemically. Both mass distributions are asymmetric with peak-to-valley ratios of 326 and 6, respectively. The average light and heavy masses ( A L , A H ) for the respective systems are 105·9, 142·4 and 110·6, 140·2. The average numbers of neutrons emitted per fission determined by subtracting A L + A H from the mass of the fissioning nucleus are respectively 4·7 and 4·2.

The negatron half-life of the long-lived 236Np isomer

Abstract The partial negatron half-life of the long-lived 236Np isomer has been determined by observing the growth of its 236Pu daughter for a period of approximately 4 yr. The half-life obtained is 1·29± 0·07 0·05 x 10 6 yr.

The ratio of 111Pd isomers formed in charged-particle and photon-induced fission of several heavy nuclides☆

Abstract Cumulative yield isomeric ratios ( σ m / σ g ) c have been measured in the fission of 230 Th, 232 Th, and 236 U by helium ions of various energies. The data show the ratio to increase with energy. The angular distribution of the 111 Pd fission products indicates a maximum at 180° to the beam direction and a minimum at 90°. The isomeric ratio does not vary with angle within the accuracy of the experiment. Measurements of ( σ m / σ g ) c in the photofission of 232 Th, 238 U, 236 U, 235 U, 234 U and 233 U show a sharp increase with the fission parameter Z 2 /A. Independent yield isomeric ratios have been calculated from the measured ratios by applying the results of various charge distribution studies reported in the literature. These calculated ratios suggest that there is little correlation between the initial angular momentum of the compound nucleus and the isomeric ratio of the fission product.

Mass distribution in thermal-neutron-induced fission of long-lived 236Np

The yields of forty-fission products were determined for the fission of the long-lived 236Np isomer with thermal neutrons. Fission product activities were measured by Ge(Li) γ-ray spectrometry of catcher foils which had been placed in intimate contact with the 236Np target and by chemical separation of the fission product elements followed by β counting. The resulting mass distribution is asymmetric. Average masses of the light and heavy mass groups are 96.3 and 137.9, respectively. The ratio of the 140Ba-to-111Ag yields is 153. There is evidence for a fine structure peak at mass 134. The mass distribution is compared with that of its isotonic neighbour 235U. The fission cross section for 236Np is evaluated to be (2.54±0.46) × 103 barns.