J.E. Thun

Spallation neutron production by 0.8, 1.2, and 1.6 GeV protons on various targets

Spallation neutron production in proton induced reactions on Al, Fe, Zr, W, Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at the SATURNE accelerator in Saclay is reported. The experimental double-differential cross-sections are compared with calculations performed with different intra-nuclear cascade models implemented in high energy transport codes. The broad angular coverage also allowed the determination of average neutron multiplicities above 2 MeV. Deficiencies in some of the models commonly used for applications are pointed out.

Experimental determination of the conversion coefficient of the 412 keV E2 transition in Hg198

Abstract The K-conversion coefficient of the 412 keV transition in Hg198 has been measured using a coincidence method. The result obtained αK = 0.0305±0.0010 is in agreement with the theoretical value for a pure E2 transition as calculated by Rose and by Sliv and Band. We disagree with recent results obtained by the internal-external conversion method.

Levels and transitions in 133Cs

Abstract The decay of 133 Ba to levels of 133 Cs has been studied. Energies of the transitions in 133 Cs have been determined from internal conversion spectra recorded in an iron-free, double-focussing spectrometer. From these data, precise level energies were obtained, 80.997±0.006 (ref. 1 )), 160±0.06, 384.09±0.20, and 437.26±0.16 keV. Intensities of conversion lines recorded in the double-focussing as well as in a lens spectrometer and of gamma transitions from Ge(Li) and NaI recordings are reported and used for ICC determinations. The following results were obtained: α K (384) = 0.017±0.004; α K (303) = 0.037±0.005 and α K (276) = 0.050±0.008. The following conversion coefficients were determined in separate coincidence experiments: α K (81) = 1.36±0.05, α K (80) = 1.36±0.10 and α K (161) = 0.39±0.13. Furthermore, the following directional correlation results are reported: A 2 (356 γ −81 γ ) = 0.037±0.005, A 4 (356 γ −81 γ ) =−0.002±0.006, A 2 (356K−81 γ ) = −0.064±0.064, A 2 (356 γ −81K) = −0.0081±0.0040, A 4 (356 γ −81K) = −0.0076±0.0080 and A 2 (53K−384 γ ) = 0.012±0.006. The EC decay energy to the 437 keV level is determined from the K/K+L+M… capture ratio to 49.0±0.7 keV. Using the experimental data and earlier results of lifetime measurements, we have calculated transition probabilities for most of the transitions. These are discussed and compared to predictions made by Kisslinger and Sorensen on the basis of their description of the levels in 133 Cs. The agreement is fairly good. Finally, the internal conversion process of the retarded l -forbidden Ml-transitions is discussed. No evidence for penetration effects is found.

Magnetic and quadrupole interactions in Hg197m. Angular correlations

A series of electron-gamma angular correlation studies of the 165-134 kev cascade in Hg/sup 1//sup 9//sup 7//sup m/ and the 130-279 kev cascade.in the decay-product Au/sup 1//sup 9//sup 7/ /sup m/ are reported. The experiments are undertaken primarily to settle the problem of the possible existence of a time dependent coupling between the nucleus and the electron core, excited by virtue of a preceding conversion or electron-capture process. For the Au/sup 1//sup 9// sup 7/ /sup m/ cascade no observable attenuations of the angular correlation pattern are found because of the short lifetime (2.3 x 10/sup -11/ s) of the intermediate level. In Hg/sup 107m/, where the corresponding lifetime is 1 x 10/ sup -//sup 8/ s, the correlation is found to be attenuated by a static quadrupole interaction for carrier-free sources deposited onto different metal and insulator backings. No measurable attenuation due to an interaction with the electron core is seen for metallic source backings. However, an additional attenuation attributed to the aftereffects of the conversion-process is found for sources embedded in insulating environments. The interplay between the two different types of interaction gives a complicated attenuation mechanism, which, however, can be disentangled by means of time-differential angular correlations.morexa0» A direct proof of the existence of an attenuation-effect due to the excitation of the electron core is furnished by a magnetic decoupling experiment, confirming the results obtained in the correlation experiments. (auth)«xa0less

Spallation study with proton beams around 1 GeV: neutron production

Experiments performed at Lab. Nat. SATURNE on neutron produced by spallation from proton beams in the range 0.8 - 1.6 GeV are presented. Experimental data compared with codes show a significant improvement of the recent intra-nuclear cascade (J. Cugnon). This is also true in the same way for the neutron production from thick targets. However the model underestimates the energetic neutrons produced in the backward direction and other quantities as residual nuclei cross sections are not accurately predicted.

Reorientation precession measurements on 108, 110Pd and the quadrupole moments of their first 2+ states

Abstract The reorientation precession technique, REPREC, for measurements of quadrupole moments is described. The application of REPREC to the measurement of the static electric quadropole moments of the first excited 2 + states in 108, 110 Pd is presented. The possibility to measure the sign of the matrix product P 4 = M 02 M 22′ M 02′ M 22 is also discussed. Such measurements are presented for 108, 110 Pd. The results of these measurements are P 4 108 Pd and 110 Pd. For 108 Pd the quadrupole moment of the first excited 2 + state was found to be −0.66±0.18 e ·b and for 110 Pd, −0.72±0.14 e ·b. Intrinsic nuclear properties for 106−110 Pd are derived using the sum rules suggested by Kumar.

A decoupling experiment on the α-γ correlation in Am243

The directional correlation betweenα particles from the decay of Am243 to the 75 keV level in Np239 and the deexciting 75 keVγ-rays has been studied. The recoiling atoms were allowed to escape into vacuum. This brings about a strong hfs interaction between the heavily ionized daughter atom and the nuclear magnetic moment, which has been shown earlier to result in an almost isotropic correlation pattern. By the application of a magnetic field along the direction of the emission of theα-particlesAsaro andSiegbahn showed that the correlation pattern could be restored to, or almost to, the theoretical value, depending on the theory chosen. This is interpreted as a decoupling of the Ms-interaction, where the degree of decoupling is dependent on the strength of the applied field. The highest field used in the earlier experiment was 12 kG.For this experiment a decoupling magnet giving 24 kG was constructed. Applying this magnetic field on three different sources gave a result (A2=−0.404±0.010) which confirms the so called quadrupole correction ofChasman andRasmussen to the theory ofBohr et al. of alpha decay of deformed nuclei.The decoupling magnet used in the experiment is described.

The Quadrupole Moments of the First Excited 2+ States in 96 100 104Ru

The quadrupole moments of the first excited 2+ states in 96,100,104Ru have been measured using the reorientation precession technique. In 104Ru the sign of the Coulomb interference term P4 = M0+12+1 M0+12+2 M2+22+1 × M2+12+1 was determined and found to be P4 < 0. The quadrupole moment in 104Ru was determined to be -0.76 ± 0.19 eb. In 96Ru and 100Ru the measurements revealed quadrupole moments of -0.15 ± 0.27 eb and -0.40 ± 0.12 eb, respectively, independent of the sign of P4. The experimentally determined values are compared with theoretical calculations.

An in-beam electron-gamma spectrometer

Abstract A sweeping-current less spectrometer with a high-resolution Si(Li) detector and 1.7% absolute efficiency has been installed on-line at an angle of 125° to the beam at the Uppsala EN tandem accelerator. The system includes background suppression and ADC-deadtime correction. It is equipped with a γ-correlation table for Ge(Li) detectors.

ALPHA--GAMMA ANGULAR CORRELATION AND HYPERFINE INTERACTION IN THE DECAY OF

The angular correlation between the main α-transition (5.81 MeV) and the following 388 KeV E1 gamma transition (and in one case also the 333 KeV E1 transition branching from the same level) in the decay of 24998Cf to 24596Cm has been studied. Thin sources were used. The recoiling daughter ions were allowed to escape into vacuum. The strong hyperfine interaction perturbing the correlation in this case was neutralized by a longitudinal decoupling field with a strength of some kilogauss. The unperturbed values of the A22-coefficients do not support the mixing ratios (L=0, L=2, L=4) from the Bohr-Froman-Mottelson theory. The correlation was also studied, in silver and nickel surroundings where it was found to be almost unperturbed. In an insulator a strong perturbation was found which was not influenced by the longitudinal field.