A number of experiments made in a B-29 on the properties of cosmic rays are herein reported. These include the latitude effect of the following, performed along the 80th geographic west longitude from 64° geomagnetic north to the geomagnetic equator, all at a constant pressure altitude of 30,000 ft. (3.10 m of water equivalent): (1) Intensity at the vertical without and with lead absorber; (2) intensity at 45° West and 45° East both without and with lead absorber; (3) total ionization intensity; (4) extensive showers. Also measured at 48° North and at the geomagnetic equator were the following: (1) Zenith angle effect both without and with lead absorber; (2) intensity vs. air pressure without and with lead; (3) extensive showers vs. air pressure; (4) local showers. In addition to the above the variation in azimuth of the cosmicray intensity was measured with the various telescopes tipped at 22i°, 45°, and 67i° to the vertical at an elevation corresponding to 2.35 m of water equivalent at the geomagnetic equator. Two lead thicknesses were used, 10 and 20 cm, inserted between the counter trays. These experiments throw new light on the nature of the primary radiation and on the interaction of the primary particles with the matter through which they pass. ! z=o* Z«48* Z»67.5* -5 J -« J eo CM PB

T HE number of neutrons from deuteron bombardment of Li 8 has been measured for deuterons of energy between 250 and 2200 kev. These neutrons are thought to come from the two reactions: Li 6 +H 2 -*(*Be 8 )-*-Be 7 -fw +3.3 Mev, and Li 6 +H^(*Be 8 )^He 4 +He 3 +w-fl.7 Mev. Monoenergetic deuterons were obtained with the Rice Institute pressure Van de Graaff generator. Lithium enriched to 95 percent Li 6 was used as a target in the form of a thin film of IJ2SO4 374 micrograms per sq. cm thick, which is equivalent to 124 kev for a 1-Mev deuteron. 1 The neutrons emitted in the direction of the deuteron beam were detected by means of the argon recoils in a proportional counter filled with argon at atmospheric pressure. The counter was biased to count neutrons of energy greater than 1 Mev. To correct for the Li 7 impurity in the target, the yield of neutrons from a normal LJ2SO4 target of approximately the same thickness was measured under identical experimental conditions. Knowing the relative amounts of the two isotopes in each target, the contribution of each isotope alone can be determined. Plotted in Fig. 1 are the relative excitation curves for the two isotopes, corrected to indicate the yield of neutrons from targets of equal thickness of the pure isotopes. The units are arbitrary but are the same for both curves. The interval between successive points on the excitation curve is half the target thickness, and each point on the curve represents a count of at least 1280 on the neutron counter.The angular distribution of the neutrons from lithium has been determined at several deuteron energies by counting the proton recoils from a number of polyethylene foils inside an argon-filled proportional counter. The counter subtended a solid angle of 0.025TT at the target, and the neutrons were observed at 15-degree intervals between 0 and 150 degrees to the deuteron beam. The distribution of neutrons from Li 6 is essentially the same at 590, 1000, and 1700 kev, showing a maximum in the forward direction in the laboratory coordinates. The ratio of the counting rate at 0 degrees to that at 150 degrees is 7:4. The angular distribution of the Li 7 neutrons is practically spherical in laboratory coordinates at 605, 700, 820, and 1340 kev. At the 1020-kev resonance, the ratio of the counting rate at 0 and 150 degrees is approximately 2:1. This marked assymetry in the forward direction tends to exaggerate the effect of the 1020 resonance in observations made at 0 degrees.When allowance is made for the penetrability of the deuterons through the Coulomb barrier of the Li 6 nucleus, there appears to be a broad energy level in Be 8 excited by 5-deuterons of about § Mev energy, which corresponds to an excitation energy of 22.5 Mev in the Be 8 compound nucleus. The excitation curves have also been carried out for the two groups of protons from the competing reactions Li 6 +H 2 -^(*Be 8 )-^Li 7 -fH 1 +5.0 Mev and Li 6 +H 2 -*(*Be 8 )~>*Li 7 +H 1 -f 4.5 Mev, and for the alpha-particles from Li 6 +H 2 -K*Be 8 )-*He 4 +He 4 -f-22 Mev. In bo...

A continuation of experiments made in a B-29 airplane to investigate the properties of cosmic rays is herein reported. Part I describes results on the latitude effect at 30,000 ft measured with counter telescopes and with both shielded and unshielded ionization chambers, from 64° geomagnetic north to the magnetic equator. A considerably larger latitude effect for the shielded ionization chamber than with the unshielded one or with counter telescopes indicates a definite change in the character of the radiation as one goes toward the equator at this altitude. The "knee" of the latitude effect is investigated in detail by a number of similar flights. Part II describes measurements made on density and formation of extended air showers. The apparatus was of such a nature as to be sensitive to relatively sparse showers. The densities obtained can be fitted to an integral power law spectrum with a negative exponent of 1.50=fc0.05 for an altitude of 30,000 ft. Intensity-altitude curves are presented, showing that the development of smaller showers takes place nearer the top of the atmosphere than does the development of large showers. Derived zenith-angle dependencies at various altitudes are also given.

In order to calculate the relative positron activities the experimentally determined 4 ratio (JW/fo+VCKV/Sei+J"^^ was used. This gives a value of fiu + /^ai +ss 0.Q0l4:l from our observed value iW#6i=0.00775.The longest period of cyclotron bombardment which has been used for production of Cu w has been 4 hours. On the basis of the ratio of activities after 2J hours of bombardment time one finds that after 4 hours of bombardment time the relative positron activities /3 6 4 + /0 6 i + would be 0.00157. No positron source has been studied for a period lasting more than three half-lives of Cu 61 following the removal of the nickel target from the cyclotron. Using the data above one finds that even after three half-lives the sample which was bombarded for four hours would have a positron activity ratio /3 6 4 + /06i + =0.00733. Quite a bit less than one percent of the activity can thus be attributed to Cu 64 .This study verifies the fact that only negligible quantities of the Cu 64 positron activity existed in the samples which have been studied to determine the shape of the positron spectrum of Cu w .This work has been supported by the joint program of the ONR and AEC.i C. S. Cook and L. M. Langer. Phys. Rev. 74, 227 (1948). 2 G. E. Owen and C. S. Cook, Phys. Rev. 76, 1536 (1949. 3 The Auger electrons were assumed for this experiment to represent a ratio of intensities for the K-capture processes in the two isotopes under consideration. In reality a small amount of the intensity of the Auger line for Cu 61 would be caused by the internal conversion electrons. However, their intensity is much less than the iC-capture intensity and could not cause a detectable change in the experimentally observed value. [See Boehm, Blaser, Marmier, and Preiswerk, Phys. Rev. 77, 295 (1950) and Owen, Cook, and Owen (article to be submitted to Phys. Rev.).] * Bradt, Gugelot, Huber, Medicus, Preiswerk, and Scherrer, Helv.T HE change with geomagnetic latitude of the ionizing particles at 310 g/cm" 2 atmospheric pressure (30,000 ft.) that could penetrate various thicknesses of absorber was measured by Biehl, Neher, and Roesch 1 over a range of latitude of 64° geomagnetic north to the geomagnetic equator along longitude 80°W. These flights show that most of the latitude effect is over at 50° as one proceeds north and this was independent of the absorber used or of whether the total radiation at that altitude was measured or only that near the vertical. On the other hand Swann, 5 r 90 1 h h NO LEAD ABSORBER

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