T HE ground state of K 41 is classified as a dzn level, 1 while the first excited state of the 19th proton would be expected to be an fj/2 level A gamma-ray transition between these levels would then be magnetic quadrupole (M2).About 99.3 percent of A 41 beta-disintegrations lead to a L3-Mev excited state in K 41 , and 0.7 perent lead to the ground state. 2 An assignment of fm to this excited state is consistent with these observed beta-transition probabilities. The theoretical half-life given by Weisskopf s formula 3 for such a 1.3-Mev Ml transition is 0.45X1O~9 second.The half-life of this 1.3-Mev excited state in K 41 has been measured by the following delayed coincidence experiment, A source of the 109-minute A 41 activity was prepared by thermal neutron irradiation of a sample of 99.6 percent tank argon sealed in a thin quartz bulb. After a 20-minute neutron irradiation, the source was placed between two trans-stilhene scintillation counters using IP21 photomultipliers. One counter was sensitive to betarays, while the other was covered with sufficient absorber to stop the beta-radiation and leave the counter sensitive to gammaradiation. The counter pulses were led to a coincidence apparatus consisting of four coincidence mixers arranged with beta-pulse delays of 4X 10"~9 second inserted between successive mixers. The individual mixers are similar in principle to that described by Bell and Petch 4 and were adjusted to have a resolving time of about 2TO=4X10~9 second. Coincidence counts were then recorded in the four mixing channels for a series of delays in either the betaor the gamma-counter lines leading to the coincidence apparatus. In this way four independent sets of data were obtained in each run. The set of data obtained in one of the mixing channels during one run and corrected for A 41 decay is shown in Fig. 1. Prompt | I L t L» I-t ] I -4 0 4 8 12 !6 20 24 DELAY INSERTED IN BETA-PULSES , 10" 9 SEC UNITS : FIG. 1. The delayed coincidence curve taken in one mixing channel and showing the half-life of the l^Mev gamma-transition in K 41 with a prompt coincidence curve for comparison. The measured background of random coincidences was small and has been subtracted at each point.coincidence curves were obtained by replacing the source of A 41 by a source of Au 198 . One such curve is also shown in Fig. 1 for comparison.The mean value of the half-life of the 1.3-Mev excited state in K 41 obtained from two runs using different sources is (6.7 ±0.5) X10~9 second. This is seen to be appreciably longer than the theoretical half-life given by Weisskopf's formula. I T is known that a system of two protons and two neutrons has an unusually high binding energy. If one considers that the filling of neutrons and protons in a nucleus is, in general, independent of each other, one might infer that a certain amount of binding energy may be obtained if two neutrons are substituted for the two protons in the above case; thus forming a tetraneutron.Assuming the tetraneutron is unstable with respect to a helium nucleus but...
The total yield and angular distribution of fast neutrons from bombardment of thick targets of pure Be, Al, Ti, Cr, Mn, Co, Cb, Mo, Ag, Cd, Ta, Au, Pb, and Bi by 15-Mev deuterons and 30-Mev alpha-particles was measured. These studies were made using the reaction S^i^p)? 32 as a threshold detector and also with fission ionization chambers. The total neutron yield per second per /.tamp of the cyclotron beam, N, was observed to decrease with increase in nuclear charge, Z, of the target according to the approximate empirical equations, logiV r =10.18-0.0234Z for deuteron bombardment and logiV=9.68-0.0234Z for alpha. In all cases studied, the angular distribution of fast neutrons from target bombarded by deuterons showed a pronounced peak in the yield in the forward direction.
EDITOR
459The initial condition on H is that it be uniform throughout all space. The boundary condition is that H have a value Ho independent of time on the surface of the cylinder (r-ro). The solution of Eq. (1) subject to these conditions isxfj exp(a n 2 u)fy(u)-l]rf«|. (2) Here, we have R~r/c\ 0 *, T**/
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