A method of spin assignment of neutron resonances based on capture gamma-ray detection

doi:10.1016/0375-9474(68)90833-6

Nuclear Physics A

Volume 117, Issue 3, 23 September 1968, Pages 586-614

https://doi.org/10.1016/0375-9474(68)90833-6 Get rights and content

Abstract

In a time-of-flight neutron spectrometer, capture gamma rays were detected by two NaI(Tl) crystals. Single and coincidence counts were registered separately. It is shown that, with a proper choice of the energy threshold for single counts, the ratio of singles to coincidences in an s-wave resonance of a given nucleus is characteristic of the spin of the level. The interpretation of the experiment is supported by a numerical simulation of the gamma decay process. Experimental results are presented for odd-neutron target nuclei with spin $I = 52 and I = 72$ . Spins were assigned to 50 resonances in ¹⁰⁵Pd, 36 resonances in ⁹⁹Ru and ¹⁰¹Ru, 24 resonances in ⁹⁵Mo and ⁹⁷Mo and 46 resonances in ¹⁷⁷Hf. Isotopic identification of resonances was performed in Pd and Ru. An indication of variation with spin of the s-wave neutron strength function in the direction $S(I + 12) > S(I − 12)$ is found for ¹⁷⁷Hf(n, γ). The comparison of the level densities of the two spin states gives a lower limit for the spin cut-off parameter σ_min = 3.3_−0.1^+0.5 for the compound nucleus ¹⁰⁶Pd and σ_min = 3.1_−0.1^+0.5 for ¹⁷⁸Hf.

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We have used the 4π BaF $_{2}$ gamma-ray detector array at the n_TOF neutron time-of-flight facility at CERN for an experiment in order to determine the spins of resonances of n +⁸⁷Sr by measuring the gamma-ray spectra and multiplicity distributions. The first results are presented here. We have assigned the orbital momentum ℓ to all evaluated resonances on the basis of their neutron widths. Further we have assigned the spin J to 16 s-wave resonances on based the population of low-lying levels.
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^†: Present address: CBNM, EURATOM, Geel, Belgium.

^††: Present address: Centro di Calcolo CNEN, Bologna, Italy.

^†††: Work performed at CBNM, EURATOM, Geel, Belgium within an Euratom-CNEN cooperation program for nuclear data measurements.

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A method of spin assignment of neutron resonances based on capture gamma-ray detection

Abstract

Nucl. Phys.

Nucl. Phys.

Sov. J. Nucl. Phys.

Phys. Rev.

Phys. Rev.

Nucl. Phys.

Nuovo Cim.

Phys. Rev.

Phys. Lett.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.