J. Halperin

The alpha decay half lives of 242Pu and 244Pu

Abstract The partial alpha decay half lives of 242 Pu and 244 Pu have been determined by a relative specific activity technique using 239 Pu as the reference. The measured alpha decay half lives are (3·869±0·016) × 10 5 yr and (8·28±0·10) × 10 7 yr respectively. Alpha particle energies (and intensities) to the ground state and to the first excited state in 240 U from the decay of 244 Pu have been measured to be 4·587±0·001 MeV (80·6 per cent) and 4·544±0·001 MeV (19·4 per cent) respectively. The alpha decay Q-value for 244 Pu has been determined to be 4·701±0·001 MeV.

The thermal neutron absorption cross-section of 240Pu☆

Abstract A measurement of the thermal neutron absorption cross-section of 240Pu has been made using the Oak Ridge Pile Oscillator. Enriched 240Pu samples and almost isotopically pure 239Pu samples were compared with gold standards. All samples were sufficiently thin so as to offer negligible self protection. The 240Pu was found to give a response per atom 2·94 times that of gold. Upon correcting for the non-(1/ν) character of 240Pu absorption, a value of285 ± 15 barns is computed for the 2200 m/sec absorption cross-section. The value of 314 ± 30 barns calculated from the resonance parameters of 240Pu is in agreement with this measurement.

Neutron capture and fission in /sup 254g/ Es

Integral neutron capture and neutron fission cross sections have been measured for the 276-day /sup 254g/ Es. Thermal cross sections and resonance integrals were evaluated using a cadmium filter technique. Capture cross sections were determined from alpha-particle spectrum measurements following neutron irradiations with cobalt flux monitors. Fission cross sections were measured using fission track detection techniques with STTU monitors. The fission cross-section values compared favorably with an absorption cross-section determination from a burnout experiment of SVTEs-SVUEs. The integral neutron capture and fission cross sections determined for /sup 254g/ Es are: sigma /sub c/ /sup th/ = 28.3 + or - 2.5 and I /sub c/ = 18.2 + or - 1.5 b, and sigma /sub F/ /sup th/ = 1970 + or - 200 and I /sub F/ = 1200 + or - 250 b.

Search for spontaneous fission emitters in Atlantis II (Part I)

No evidence for spontaneous fission decay (and the implied presence of superheavy nuclides) has been found in a several kilogram precipitate gathered at the Atlantis-II site in the Red Sea. The sample was investigated with a neutron multiplicity counternon-destructively so that no chemical losses should have been sustained. Upper limits have been determined for possible superheavy element concentrations in the sample.

Thermal-Neutron Capture and Fission Cross Sections and Resonance Integrals for Curium-243

The thermal-neutron capture cross section and capture resonance integral for /sup 243/Cm have been measured in cobalt-monitored reactor irradiations of nearly isotopically pure /sup 243/Cm (99.94 percent) using cadmium filter techniques. The thermal-neutron absorption (capture plus fission) cross section and corresponding resonance integral for /sup 243/Cm have also been measured in a separate experiment relative to /sup 248/Cm. Values of sigma/sub 2200/(n,..gamma..) = 130.7 +- 9.6, sigma/sub 2200/(n,f) = 609.6 +- 25.9, I(n,..gamma..) = 214.7 +- 20.3, and I(n,f) = 1575 +- 136 b are reported.

Neutron Multiplicity Distributions in the Spontaneous Fission of 244 Cm, 248 Cm, and 252 Cf

The neutron multiplicities P(n) in the spontaneous fission of 246Cm, 248Cm, and 252Cf have been measured in a 3He neutron counter assembly. The efficiency ∊ for detection of a single neutron was me...

Search for superheavy elements in monazites

Abstract Samples of monazite from Australia; Malaysia; South Africa; Georgia, U.S.A.; and Madagascar were examined by using a multiplicity counter capable of detecting coincident neutrons from binary or ternary spontaneous fission decay of any element. Corrections were made for empty counter background, uranium spontaneous fission, muon reactions with rare earth and thorium, and neutron absorption by Sm and Gd. The corrected counts showed no evidence of spontaneous fission decay of superheavy elements. Derived limits indicate that if superheavy elements were present, their spontaneous fission half-lives must be extremely long or their concentrations extremely small.

Further search for superheavy elements in nature with neutron multiplicity scintillation counter

Abstract We have measured neutron multiplicities emitted by a large number of natural samples as an indication of the presence of superheavy elements. Such elements are expected to emit some 10 neutrons in their spontaneous fission compared to ≤4 for all known nuclides. We used a neutron multiplicity scintillation counter which had been placed in a tunnel under some 250 m of rock and dirt to minimize neutron multiplicities resulting from reactions of cosmic ray muons with heavy atomic nuclei. The samples included K, Cr, Fe, Ni, Cu, Zn, Sr, Ag, Ce, Pt, Au, Hg, Pb ores, ore concentrates, ore residues, as well as iron meteorites and some ultra basic rocks. We conclude that our results were negative within the accuracy of our measurements.

Half-life of 208Bi

A value for the half life of Bi/sup 208/ was determined to be 3.68 x 10/ sup 5/ years with a standard error of 1% from measurements of the specific activity of the 2.615 Mev gamma ray and isotopic composition of samples of neutron irradiated bismuth. (auth)