Neutron Activation Cross Sections Research Articles

A new isomer of bromine: 82 mBr

The decays of 82 m Br have been studied by γ-ray scintillation spectroscopy and a beta proportional counter. This new isomer was observed to decay with a half-life of 6·20 ± 0·05 min, exciting a highly converted γ-ray transition in 82Br of 46 ± 2 keV. α K is 268. A total combined beta branching of 2·4 per cent was also observed. The thermal neutron activation cross section and resonance integral for 82 m Br are 3·0 and 34 barns, respectively, and the corresponding values for the total production of 82Br are 3·23 ± 0·2 and 41·3 ± 1 barns.

The Ar 40 thermal activation cross-section and resonance integral

The Ar 40(n, γ)Ar 41 thermal neutron activation cross section has been determined to be 0.723±0.025 b, utilizing both Au ( σ 0=98.4±0.5) and Co ( σ 0=37.7±0.7 b) as reference standards. This value is 26% higher than the normally accepted activation cross section of 0.53 b and is 14% higher than the weighted mean elemental absorption cross section of 0.62 b. The resonance capture integral above 0.5 eV, which has not previously been measured, was found to be 0.41±0.03 b relative to 1534 b to Au 197. The Westcott temperature-independent resonance parameter s 0 was found to be 0.217±0.010.

Thermal Neutron Activation: Measurement of Cross Section for Manganese-53

The product of the thermal neutron activation cross section and half-life for manganese-53 is (350 +/- 100) x 10(6) barn-years. If a value of 2 x 10(6) years is assumed for the half-life of manganese-53, then the cross section is 170 barns. This large cross section affords much greater sensitivity for the determination of manganese-53.

IsomerRe188m

Two new transitions in ${\mathrm{Re}}^{188m}$ were found which are responsible for the 18.7-min half-life of this isomer. The energies and branching ratios of these transitions which originate from a 6-state at 171.9 keV, are 2.4 keV (57%) and 15.9 keV (43%). Their multipole orders are $M3$. Each transition is followed by an $M1$ transition, 105.9 and 92.4 keV, respectively, both terminating in the first excited (2-) state at 63.58 keV, which decays by an $M1$ transition to the ground state. The ground state and the first two excited states appear to be members of a rotational band with $K=1\ensuremath{-}$, whereas the 3rd and 4th excited states can be interpreted as composed of the same proton orbit as that of the ground state, but of different neutron orbits. The thermal neutron activation cross section of ${\mathrm{Re}}^{187}$ leading to the isomer was found to be 1.25\ifmmode\pm\else\textpm\fi{}0.25 b.

Effects of Nuclear Explosions on Oil Reservoir Stimulation

Abstract A general description of Project Plowshar's Gnome atomic explosion near Carlsbad, N. M. is given from the point of view of possible application to oil reservoir stimulation. Post-shot exploratory mining and drilling into the explosion environment and blast cavity are discussed. Petroleum reservoir core and crude oil samples placed near the explosion were subjected to shock energy, high pressures and radiation from the atomic blast. These samples were recovered, analyzed and compared with unexposed, duplicate samples. Additional investigations, which must be undertaken to resolve problems that will be encountered in the use of an atomic device in an oil reservoir, are discussed. Introduction With the advent of nuclear explosions a new, concentrated source of energy bas become available. One promising use for this compact power source is in increasing oil reserves and oil production. This could be accomplished by using the shock energy from the nuclear explosion to change or upgrade the properties of oil reservoir rock. Project Gnome was the first scientific experiment with nuclear explosives to yield information on what effects such a blast would have on reservoir rock and oil samples. The major purposes of the Gnome experiment were:to study the effects of an underground nuclear explosion in salt;to determine the feasibility of recovering radioisotopes produced by the nuclear explosion;to measure neutron activation cross sections and resonance fission characteristics of several isotopes as a function of the neutron energy spectrum produced by the explosion;to make measurements to determine if heat energy could be recovered from the molten salt; andto make seismic measurements to aid in understanding differences between natural disturbances and nuclear explosions. An additional experiment was to subject a variety of rock and organic samples to a range of shock pressures to study the effect of the explosion on the samples. Among the samples incorporated in the experiment were a number of reservoir rocks (limestones, dolomites and sandstones) and typical crude oils. These samples were submitted by the Bureau of Mines and several major oil companies. This phase of the experiment was coordinated by the Bureau of Mines. Gnome was detonated in the Salado rock formation of Permian age (Fig. 1). This 3.1-kiloton nuclear shot was fired in bedded salt 25 miles southeast of Carlsbad, N. M. The working point, or location of the device, was at a depth of 1,184. ft. The region affected by the detonation was composed of 89 per cent halite (rock salt), 7 per cent polyhalite, 1 per cent anhydrite and 3 per cent silt or clay. The Gnome nuclear device was placed at the end of a buttonhook- shaped drift 987 ft from the shaft (Fit 2).The small reservoir rock and oil samples discussed in this paper were located in Drill Holes 3 and 15 (Figs. 2 and 3). The cores were grouted into thin-walled metal containers using saltcrete cement with the same acoustical properties as the surrounding salt. Small oil samples were placed in brass machined containers. The cores and oil samples were attached to a 1 -in. pipe and the assembly placed in Hole 3. Additional saltcrete cement was pumped in through the pipe in an attempt to make contact between the main salt body and the samples. Larger oil samples were placed in accumulators with working pressures of 1,500 psi. These were placed in Hole 15, which was ungrouted. The shot was fired on Dec. 10, 1961. Environment Created by the Explosion Following the detonation, the environment created by the explosion was explored in considerable detail by five vertical drill holes from the surface, six exploratory holes drilled from underground, in addition to mining exploration near the working point. While mining, the shock-effects samples were recovered from Drill Hole 3 (Fig. 2) and irradiated samples recovered from Hole 15. In attempting to recover samples that were exposed to shock pressure greater than about 45 kb, mining advanced directly into the standing cavity produced by the explosion (Fig. 4). JPT P. 473^

Neutron Activation Cross Sections forBr79,Br81,Rh103,In115,I127, andTa181

Neutron activation cross sections for ${\mathrm{Br}}^{79}$, ${\mathrm{Br}}^{81}$, ${\mathrm{Rh}}^{103}$, ${\mathrm{In}}^{115}$, ${\mathrm{I}}^{127}$, and ${\mathrm{Ta}}^{181}$ have been measured in the incident neutron energy range from 130 to 1800 keV. The results agree rather well with other activation measurements. The activation cross sections are combined to form the total neutron-capture cross sections of the natural elements and compared with the capture gamma-ray data of Diven et al. and Gibbons et al. The elemental cross sections agree rather well with the results of Diven et al. but do not agree with the lower results of Gibbons et al.

Thermal Activation Cross Sections and Resonance Integrals of In115

New measurements of the thermal neutron activation cross sections and the resonance activation integrals (14 sec and 54 min activity) of In115 are described. The results are discussed and compared with those of other recent determinations.

Decay of 131Ba 131Cs

The absolute intensities of eight γ-rays emitted following electron capture in 131Ba have been determined: 0·130 MeV (0·28), 0·220 MeV (0·380 MeV (0·16), 0·496 MeV (0·60), 0·600 MeV (0·0.32), 0·820 MeV (0·0034), 0·910 MeV (0·0009), and 1·04 MeV (0·017). The method used was to prepare 131Ba free from its 131Cs daughter, allow the 131Cs activity to grow in, separate the 131Cs activity from the parent and measure its activity, measure the γ-activity of the 131Ba by γ-ray spectrometry, and calculate the absolute amount of 131Ba from parent daughter growth relationships. The half-life of 131Cs has been determined to be 9·83 ± 0·28 days. The ratio of the pile neutron activation cross-sections for the production of 131Ba and 133Ba has been found to be σ 130 σ 132 = 1·36 ± 0·08 .

The cross sections of (n, p) reactions producing isomeric and ground states of indium and antimony isotopes

The 14.2 MeV neutron-activation cross sections have been measured for (n, p) reactions producing the isomeric as well as the ground states of several indium and antimony isotopes. Separated tin and tellurium isotopes have been used as target material. The analysis of the reaction products has been performed by measurements of their disintegration periods and by successive measurements of the gamma spectrum of the observed reaction products. In some cases chemical separation was used. The experimental results are compared with values calculated from the statistical theory of nuclear reactions accounting for the nucleon pairing energy. The existence of Levkowskij's isotopic effect in the A-dependence of the (n, p) reaction was confirmed.

Thermal neutron activation cross-sections for isomer production (II)

Thermal neutron activation cross-sections have been measured for the following cases: Hg 196(n, γ)Hg 197m(130±12% b); Hg 196(n, γ)Hg 197(2936±15% b); Pt 194(n, γ)Pt 195m(< 200 mb); Pt 192(n, γ)Pt 193m(70±20% b); Os 190(n, γ)Os 191m(8.55±18% b); Os 190(n, γ)Os 191(3.9±20% b); Er 170(n, γ)Er 171(4.3±15% b); Pd 110(n, γ)Pd 111m(37±15% mb); Gd 158(n, γ)Gd 159(2780±18% mb); Gd 160(n, γ)Gd 161(768±15% mb); Ba 134(n, γ)Ba 135m(158±15% mb); Ba 132(n, γ)Ba 133m(< 150 mb); Sn 122(n, γ)Sn 123(206±15% mb); Sn 124(n, γ)Sn 125(125±15% mb) Using the spin distribution form due to Beths 1) and Block 2) theoretically calculated isomeric ratios have been compared with experimentally measured values.

14.8 MeV neutron activation cross-section measurements of a few tellurium isotopes

The activation cross-sections of the (n, 2n) and (n, α) products of different tellurium isotopes for 14.8 MeV neutrons have been measured. Enriched isotopes were used to determine the (n, 2n) cross-sections of the 9.36 h Te 127 and of the 67.5 min Te 129 and 33 d Te 129∗ activities relative to the known Al 27 (n, p)Mg 27 cross-section. By means of chemical separation, the 27 h Sn 121, 39.7 min Sn 123 and 2.45 h Sn 127 activities were compared amongst themselves in tellurium-free samples. The three tin cross-sections were finally obtained from the decay analyses of quickly separated Sn-products by comparing with the 67.5 min Te 129 residual activity as internal standard. The 9.7 min Sn 125 cross-section was also determined. A hitherto unreported activity ≈ 2 min was noticed. Analyses of the combined (n, α) data in the heavy element region suggest the presence of flat peaks in the observed cross-sections away from magic numbers. The simple evaporation theories do not predict such peaks.

Absolute activation cross sections for reactions of niobium with 14·5 MeV neutrons

Absolute neutron activation cross sections at 14·5 MeV have been measured for the mono-isotopic nuclide, 93Nb, by means of γ-scintillation spectroscopy and β-proportional counting as well as by the use of chemical separation techniques. The observed reactions, product half-lives, and cross-sections are as follows: 93Nb ( n, 2 n) 92 g Nb, 10·1 days, 499 ± 91 mbarns; 93Nb ( n, γ) 94 m Nb, 6·6 min, 0·44 ± 0·25 mbarns; 93Nb ( n, α) 90bY, 64 hr, 8·6 ± 2·5 mbarns; 93Nb ( n, α) 90 m Y, 3·0 hr, 5·9 ± 2·0 mbarns; 93Nb ( n, n′ α) 89 m Y, 16 sec, 2·5 ± 1·1 mbarns. No activity was observed in the zirconium fraction, the ( n, p) product, nor was the 13 hr 92 m Nb produced through an ( n, 2 n) reaction. Half-lives of 90 m Y and 89 m Y were determined by least squares analysis to be 3·02 ± 0·09 hr and 16·3 ± 1·3 sec, respectively.

Thermal neutron activation cross-sections for isomer production

Abstract Thermal neutron activation cross-sections for the following cases have been measured by making irradiation with the “Swimming pool” reactor at Trombay, Bombay with the following results: • Pt 196 (n, γ )Pt 197m (69±20% mb); • W 184 (n, γ )W 185 m(22±20% mb); • Te 130 (n, γ )Te 131 (161±15% mb); • Te 126 (n, γ )Te 127 (1034±15% mb); • Cd 108 (n, γ )Cd 109 (1410±25% mb); • Zn 70 (n, γ )(9±20% mb); • Zn 68 (n, γ )(83±15% mb); • Os 189 (n, γ )Os 190m (8±25% mb); • Dy 164 (n, γ )Dy 165 (951±25% b); • Te 128 (n, γ )Te 129 (178±15% mb); • Cd 16 (n, γ )Cd 117 ( • Cd 110 (n, γ )Cd 111m (132±15% mb); • Zn 70 (n, γ )Zn 71 (111±20% mb); • Zn 68 (n, γ )Zn 69 (116±15% mb); The activation method was employed for these measurements.

Neutron Activation Cross Sections of Pm147, Pm148, and Pm148m

The thermal cross sections and the resonance integrals have been measured for the activation of Pm147 to both Pm148 isomers. The thermal activation cross sections are: 124 ± 13 barns to 5.39-day Pm148 and 111 ± 11 barns to 40.6-day Pm148m. The resonance integrals are: 1700 ± 250 barns to 5.39-day Pm148 and 1520 ± 230 barns to 40.6-day Pm148m. Approximate cross sections have been obtained for neutron capture by both Pm148 isomers. The pile cross section of 40.6-day Pm148m is 29,000 ± 5000 barns and is due mainly to thermal neutron capture. The pile cross section of 5.39-day Pm148 is 3,000 ± 2,000 barns and is due mainly to resonance neutron capture.

Fast Neutron Activation Cross Section ofAu197

The neutron activation cross section of gold was measured in the neutron range from 30-1500 kev. The absolute value of the cross section was based on the ${\mathrm{U}}^{235}$ fast fission cross section which was used for absolute neutron flux measurements from 200-1500 kev. For measurements below 200 kev, the ${\mathrm{B}}^{10}(n, \ensuremath{\alpha})$ cross section was used for monitoring the neutron flux. The relative cross section from 30-200 kev was then normalized at 200 kev to the absolute measurement. The results agree well with recent measurements, except for some pulsed beam---liquid scintillator measurements and spherical shell transmission measurements which yield much lower cross section values.

Effective neutron activation cross-sections of some chlorine and sulphur reactions in NRX

Reaction rates have been measured in the lattice and reflector of NRX for those neutron activation reactions of chlorine and sulphur that lead to the production of38Cl,32P and35S. The effective cross-sections of these reactions for reactor neutrons have been calculated from cobalt monitors enclosed with the irradiated samples.

Cross Sections of Various Materials in the Godiva and Jezebel Critical Assemblies

Neutron activation (n, γ) cross sections of various isotopes have been determined in the Los Alamos Godiva and Jezebel assemblies by a comparison activation method. Where these values represent tot...

Reactor Neutron Activation Cross Sections for a Number of Elements

Experimentally determined reactor neutron activation cross sections found by use of the ORNL Graphite Reactor are listed. The general method of measurement is described. (auth)

The thermal neutron activation cross section of105Ru

In order to calculate the thermal neutron activation cross section of105Ru, the enriched104Ru was exposed to a thermal neutron flux of 1.2·1014 neutrons cm−2s−1. After the decay of the 40-day activity of103Ru, the silver impurity was removed and the contributions from Co and Eu impurities were subtracted. The γ-ray energies and the coincidence results were consistent with the previously established results for106Ru-106Rh. From γ-ray intensities consideration, the thermal neutron activation cross section of105Ru was calculated to be (0.20±.02) barn.

New isomers of scandium-50 and indium-120; γ-rays in lutecium-178 decay

In the course of a systematic study of fast neutron activation cross-sections utilizing the Arkansas 400 kV Cockcroft-Walton accelerator, several new radioactive species have been identified and γ-rays assigned in the decay of others. In addition, several unidentified new radioactivities have been observed, but not studied further. What follows below is a summary of all our available new information on these activities.