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The recoil-free emission and resonant absorption 1 of the 14.4-kev nuclear gamma ray of Fe 57 , has been used to determine the quadrupole coupling for the 3/2-excited state of Fe 57 bound in Fe 2 0 3 , and to measure an energy shift of this nuclear gamma ray which is attributed to effects of chemical binding. This effect is corollary to the effects of chemical environment on internal conversion coefficients 2 and on electron capture disintegration rates. 3 These measurements also yield the value of the internal magnetic field at the position of the Fe 57 nucleus when it is bound in antiferromagnetic Fe 2 0 3 .The Ml emission line of Fe 57 bound in ordinary metallic iron is split into six components by the magnetic hyperfine interaction. 4 The resonant absorption of this emission spectrum by Fe 57 bound in Fe 2 O s has been examined, as well as the much simpler absorption pattern which results when the "unsplit" emission line from Fe 57 bound in a stainless steel lattice 5 is used. Because the interpretation of the two sets of measurements agree, only the latter measurements are presented in this Letter. The former measurements, in which a Co 57 source co-plated with iron onto 1-mil copper was used, will only briefly be remarked upon.The ~2-mg/cm 2 Fe 2 0 3 absorber used in these measurements contained Fe 57 enriched to -30%. The source consisted of Co 57 plated onto 0.001-inch stainless steel (25% Cr, 20% Ni). After plating, this source was annealed for one hour at 900°C in a hydrogen atmosphere. All measurements were made with source and absorber at a temperature of 25°C.In order to obtain a Doppler shift of the emission line, a uniform motion was obtained by coupling a pneumatically driven cylinder to another cylinder filled with oil, the ports of which were connected via a needle valve. A wide range of uniform velocities could be selected by adjusting this valve. The direction of source travel was reversed automatically by means of microswitches. Additional microswitches, set to exclude the region of nonuniform motion near the travel limits, were used to provide gate signals for the counters. The distance of travel between the limits of the counting gates was 0.973 cm. Source velocity was determined by counting the cycles from a 1000 cps tuning fork oscillator during the time between the gate limits.The 14.4-kev gamma ray was detected with a Nal(Tl) scintillation counter. The phosphor was 2 mm thick and 1.5 inches in diameter. The counter face was located 5.4 cm above the upper limit of vertical travel of the source. The absorber was placed 4.7 cm from the counter face. A single-channel pulse-height analyzer selected the 14.4-kev gamma ray photopeak. The outputs of this analyzer and the 1000 cps clock were switched between two pairs of scalers so as to record counting rate and velocity separately for both directions of source motion. Figure 1 shows the counting rate (in arbitrary units) as a function of source velocity relative to the Fe 2 0 3 absorber for the stainless steel source. Absorption of the "unsplit...

826LETTERSTOTHEEDITOR to the question of the identity of neutrinos and antineutrinos. 2 We have accordingly re-evaluated the expected and extreme mean lives for comparison with the experimental results with the conclusion that the previous inference as to the inapplicability of the Majorana hypothesis (neutrino identical with antineutrino) stands. The quantitative argument follows: the available kinetic energy of the emitted neutrino, assuming no net neutrino emission in accordance with the Majorana hypothesis, is given by Johnson and Nier as 3.65db0.10 Mev. (We previously used the more favorable value 4.4±0.8 Mev). For this new energy figure a reasonable value for the mean life is 4X10 15 years, an extreme value is 1.9X10 18 years. 3 These lifetimes are to be compared with the experimental result of >4.4X10 18 years, a limit derived by considering the count rate associated with one standard deviation from a smoothed curve of count rate versus energy. 2 As pointed out by Tiomno, 4 it is possible to build a "mixed" theory in which double beta decay is unaccompanied by neutrino emission, and yet have the neutrino obey the Dirac equation. In this case an observably short lifetime for ft decay could have an ambiguous interpretation. Such a theory is restricted independently of the phenomenon of double beta decay by the negative experiment of Davis 5 in which an appreciable amount of such an admixture of neutrinos and antineutrinos from the decay of neutron-rich isotopes would have produced a positive result. W E have investigated the degree and sense of circular polarization of bremsstrahlung produced by I3~ rays. Near the high-energy end of the spectrum we find that the photons are almost completely circularly polarized, with their spin antiparallel to their direction of propagation.The question of parity conservation in weak interactions, raised by Lee and Yang, 1 has been partially answered by recent experiments which show that parity FIG. 1. Arrangement for analyzing degree and sense of circular polarization of bremsstrahlung from (3~ source.is not conserved in interactions involving neutrino emission. 2-4 The two-component neutrino theory 5-7 can account for these results in a natural manner. From this theory it follows that 0 rays are polarized longitudinally, and if time-reversal invariance is assumed the polarization is found to be ±v/c, where the plus sign is expected for positrons and the minus sign for negative electrons. 7-9 The existence of a polarization compatible with these ideas has recently been demonstrated for both electrons 10 and positrons. 11 It appeared to us worthwhile to investigate whether the longitudinal polarization of the ff rays will in turn give rise to a circular polarization of the bremsstrahlung which they produce. To search for such an effect, we used a source of Sr 90 +Y 90 in equilibrium. The decay scheme of this source is well known. 12 High-energy /3~ rays are emitted from the decay of Y 90 (maximum energy = 2.24 Mev, (v/c) mKX = 0.98; no y rays have been reported). The source...

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