1287 one arrives at an upper limit for the width of the 665-kev excited state of Mo 97 , r<5XlO~4 ev, and at a lower limit for the lifetime of this state of 1.5X10~1 2 second. This lifetime is one order of magnitude longer than the one expected from the Weisskopf formula. Thus, the Ml transition in Mo 97 shows the same behavior as the low-energy MVs.It should be mentioned that the Mo 97 transition, as well as most of the low-energy transitions measured by the Canadian group, involve a change of two units of orbital angular momentum, whereas the Li 7 gamma ray presumably leads from a p\ to a p\ state.t Assisted by the joint program of the U. S. Fig. 1 is one of two obtained in a hydrogen-filled diffusion cloud chamber exposed to a beam of 1.5-Bev negative pions 0~) from the Cosmotron. The hydrogen was at a pressure of 18 atmospheres, and a field of 11 000 gauss was applied. The picture is believed to represent the production of a Vi° particle by a TT~ interaction with a proton. Track a is the incident w~, the end point of which is to be called A. Tracks b and c are the decay products of the Vi°. A single neutral heavy meson also may have been produced at A, which would travel in the direction indicated by d. 1 Since track a is short, its momentum can only be estimated to lie near the nominal TT" beam momentum of 1.63 Bev/c. This track is parallel to the other beam tracks and thus probably is not due to a secondary particle. The line connecting point A with the vertex of b and c, to be called G, forms an angle of 26° with a. The distance between A and G is 0.65 cm. Tracks a, b, and c are coplanar, while only coplanarity of A, b } and c is necessary for the tracks to be associated. In addition, the components of momentum of b and c perpendicular to line AG balance. Track b forms an angle of 16° with a; b is caused by a positive particle with a measured momentum of 480±80 Mev/c and an estimated ionization density of 3X minimum. Thus b is identified as a proton track. The angle between b and c is 37°. Track c is negative, with a momentum of 210±70 Mev/c and estimated ionization density of less than 1.5X minimum. An upper limit of 410 m e is inferred for its mass, indicating a IT. Assuming that b and c represent the decay of a Fi°(->/>-Hr~+()), one finds a Q-value of 51 Mev from these data. 2 Assuming the generally accepted Q of 37 Mev one would find that, for the given angles, the momenta should be 460 Mev/c for the proton and 180 Mev/c for the iT. These values fall within the errors given for the measured values and have been used for the further computations. The lifetime of this Fi° is 4X10" 11 sec. T HE photograph reproduced inThe total energy of the Fi° is 1.26 Bev, and its momentum is 610 Mev/c. To conserve energy and momentum at least one other neutral particle must start at A. Assuming a single particle, its total energy would have to be 1.31 Bev and its momentum 1.11 Bev/c, leading to a mass of 1350±70 m e for a kinetic energy of 1.5 Bev for the incident it~. For an energy of 1.2 Bev instead of 1.5 Bev one wo...

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These directional correlation coefficients, 7 -8 together with the conversion data and the cross-over intensity, suggest an angular momentum assignment of 3, 2, and 0 to the states of the Sr 88 nucleus (Fig. 3) and characterize the first (3-»-2) transition as an Sr 88 E3 2% 0+ FIG. 3. Spin and parity assignments to the levels of Sr 88 .electric dipole transition with 0.015 percent to 0.002 percent magnetic quadrupole admixture, the two radiations being in phase. The second (2->0) transition is by pure electric quadrupole radiation. These results are'in good agreement with the internal conversion data and also remove the last exception to the Goldhaber-Sunyar rule.From an accurate determination of the magnetic quadrupole admixture information can be obtained about the reduction of the electric dipole matrix element. In view of the importance of this particular mixing ratio, extensive studies are in progress to determine the Sr 88 gamma-gamma angular correlation with even higher precision.A CCORDING to Goertzel 1 and Alder 2 -3 the angular correlation of successive nuclear radiation can be disturbed by extranuclear fields. In the case of the Cd 111 7-7 cascade, ~uch a disturbing effect has been established by Aeppli et al}> h The dependence of the anisotropy A = [W(180°) -W(90°)3/W(90°) on an externally applied magnetic field allowed the determination of the magnetic moment of the first excited state of this nucleus. Furthermore the anisotropy was found to depend strongly on the source Crystal c Exp.l FIG. 1. Diagram of the c axis orientation of the In single crystal with respect to the detector directions. material, metallic sources showing values for A varying from -5 percent up to the maximum value of -20 percent whereas ionic crystal sources show nearly isotropic correlations.The question arose as to whether the source effects are due to the magnetic field of the electron shell (magnetic interaction) or to an inhomogeneous electric crystalline field (quadrupole interaction). Frauenf elder 6 has discussed the first possibility. The difference between metallic and ionic crystal sources would be explained on the assumption that after the K capture the electron shell remains excited during a time comparable with the lifetimes of the excited nuclear states in the case of the ionic crystals, whereas in the case of metallic sources the excited states would decay more rapidly. A series of experiments have been made to test this and further the possibility of the presence of an electric quadrupole interaction.If the interaction were magnetic in origin a "magnetic decoupling experiment" should be possible. If the attenuation of the anisotropy is the result of the coupling between the angular momenta / of the nucleus and / of the shell, then it is possible to obtain the "true" correlation by applying an external magnetic field H in the direction defined by the source and one of the two detectors. The coupling between / and / will be broken if the * A -.20 -.10 W(180)-WC90) WC90D 90° o° <* FIG. 2. Anisotropy vs angle a of ...

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