Das magnetische Moment des 2,083 MeV-Zwei-Protonen-Niveaus des gerade-gerade-Kerns Ce¹⁴⁰

Abstract

The nuclearg-factor of the 2·083 MeV-state of Ce¹⁴⁰ has been determined as:g=1·11±0·04

This value suggests the interpretation of the level as the (g7/2,d5/2)₄ two proton shell model configuration.

The investigation implies an integral measurement as well as a time dependent differential measurement (spin rotation method) of the rotation of the 329 keV-487 keVγγ-angular correlation in strong external magnetic fields. Liquid sources of lanthanum nitrate solved in 3n HNO₃ were used in these experiments. Some cerium (IV)nitrate was added to make sure that the 4f;-electronic shell remained empty after theβ ⁻-decay. This prevented paramagnetic effects.

Additional runs were performed without adding cerium (IV)nitrate and finally by using liquid sources of lanthanum chloride solved in 2n HCl with some iron (II)-chloride added. It was expected that the Fe⁺⁺ ions would reduce the primarily formed Ce⁺⁺⁺⁺ ions into the Ce⁺⁺⁺ state. The Ce⁺⁺⁺ shell is paramagnetic and enlarges the effective magnetic field at the position of the nucleus by about 36%. As no definitely faster rotation could be observed, one has to conclude that the ion reaction Ce⁺⁺⁺⁺+Fe⁺⁺⇒Ce⁺⁺⁺+Fe⁺⁺⁺ takes more than about 10⁻⁸s.

The half life of the 2·083 MeV state has been redeterminded asT _1/2=(3·41±0·04)·10⁻⁹s.

Differential measurements of the angular correlation of the 329 keV-487 keV cascade as a function of the time delay showed that perturbations by internal fields were very small. The coefficientsA ₂ andA ₄ of the angular correlation and the attenuation parameterλ ₂ were determined from measurements with sources of the first type as:A ₂=−0·105±0·003A ₄=−0·001±0·002 andλ ₂=(0·0065±0·0040)·10⁹S⁻¹=(0·032±0·020)·λ

A comparison with the theoretical coefficients of a (3-4-2)-cascade shows that the multipolarity of the 329 keV radiation is a mixture of 99·83%M1 and (0·17±0·03) %E2.