By the use of a four electrode tube, in which high frequency voltages are applied in phase to the grids of the excitation and photo-electric systems, the life of the $2P$ state in hydrogen, excited by 10.2 volt electron impacts, was measured. Because of the small amount of hydrogen dissociated by the hot cathode it is improbable that absorption and re-radiation played any part. A discussion of other possible errors leads to the conclusion that the observed effects are due to the persistence of the radiation. The experimental results, which were obtained with tubes of different dimensions and for pressures from.075 to.25 mm, check well with those calculated on the assumption that starting at the instant of impact the radiation falls off exponentially. The exponential constant found was.83×${10}^8$ ${\sec }^{-1\mathrm{}}$. Unless the form of the curve is the result of a lag in the photo-electric effect, as seems improbable, the average duration of the radiation resulting from the 10.2 volt electron impact in hydrogen is $\tau =1.2\mathrm{}\times {10}^{-8\mathrm{}}$ sec. If the photo-electric lag is effective this is the maximum value of $\tau$. Preliminary measurements made for the 11.9 volt radiation, attributed to the hydrogen molecule, indicate an approximate value of $\tau =3.5\mathrm{}\times {10}^{-8\mathrm{}}$ sec.

Close

PrevNext

View figure in article