The artificial radioactivity produced in targets of Cu, Ni, Ag, Cr and Mo by bombardment with four-Mev protons has been studied. In Cu, the (p, n) reaction gives rise to the radioelements Zn 63 (half-life 38.5 min., upper limit of positron spectrum 1.8 Mev) and Zn 65 . Two new radioactive isotopes of Cu are found in Ni bombarded with protons; they have tentatively been assigned as follows: Cu 58 , half-life 81 sec, and Cu 60 , half-life 7.9 minutes. Both emit positrons. Also produced in Ni are Cu 61 , both by the (p, n) and the (p, y) reaction (threshold < 1.8 Mev), and Cu 64 , by the (p, n) reaction (threshold apparently 2.1 Mev). Proton bombardment of Ag results in a radioactive Cd isotope which emits very soft negative electrons which are believed to be conversion electrons of a nuclear gammaray. The identification of the responsible Cd isotope and the mode of decay is discussed. The half-life of this radioelement is 6.7 hours; the threshold for the reaction is 2.4 Mev. 40-minute Mn 51 is formed by proton bombardment of Cr. This radioelement emits positrons. Three unassigned activities produced in Mo have half-lives of 45 min., 2.7 hours, and 36.5 hours; the last emits negative electrons.
pulse is less than five microseconds in duration. These pulses are received at Station B and appear as a broad line upon an oscilloscope which is kept in synchronism with the pulses by the commercial 60 cycle line connecting the two stations. Station B is also sending out 60 pulses per second. These produce a second broad line upon the oscilloscope at B. When these two lines are brought into coincidence by means of a phase changer the wave from B to A is acting precisely like a wave reflected from the ionosphere. The observer at A perceives two lines upon his oscilloscope, one due to his own pulse and the other due to a pulse which has traveled virtually from A to B and back again to A. The spot on his oscilloscope is being pulled across the screen at the rate of 1500 inches per second. He can therefore measure the time distance between the two lines with great accuracy. Twice the distance between the two stations divided by the time gives the required velocity.
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