No abstract

The M/3ssbauer effect has been applied to the measurements of phase and amplitude relations in the vibrations of the guinea pig ear in vivo induced by sound in the normal hearing range. Measurements were made on the umbo and on the incudostapedial joint. The relative phase was near zero throughout the measured frequency range of 250 cps-9 kc/sec, and the lever-ratio was nearly constant at a value of about 2.0. INTRODUCTION ECHNIQUES of measuring the vibrations of the middle ear in response to sound stimulation have been summarized by Frei et al. (1966). The present article reports the first use of the M/Sssbauer method, proposed and described by one of the authors (Shtrikman, 1964). • This has certain advantages over previous techniques in sensitivity, in the possibility of measuring through small amounts of tissue and in the possibility of use in vivo, the measurements being relatively undisturbed by intermittent movement. In order both to test the technique and to obtain initial useful information on sound transmission in the middle ear, measurements have been made of the relative amplitudes and phases of the movements of the umbo and of the tympanic aspect of the end of the long process of the incus in anaesthetized guinea pigs, using sound levels near 80 dB ASA, over the frequency range 250 cps-9 kc/sec. The linearity of the response of the umbo was also checked at three frequencies. I. MOSSBAUER TECHNIQUE Since its discovery in 1957, the M/3ssbauer effect has been the subject of an enormous field of research (Frauenfelder, 1962). The effect relies upon the fact that gamma-ray emission from, or absorption by, a nucleus can, under certain conditions, take place with-• A preliminary report on this method (Hillman et al., 1964) inadvertently omitted the name of one of the authors (S.S.). 1232 Volume 41 Number 5 1967 out loss of energy to the recoiling nucleus. Under such circumstances, the emitted gamma ray carries away from the nucleus or delivers to nuclear excitation the full and exact energy of the nuclear transition. Since nuclei can exist only in certain well-defined energy states, a gamma ray can be emitted by a nucleus and absorbed by another identical nucleus--exciting it into the same energy state as the emitting nucleus had before decaying--only if the gamma ray carries and delivers the entire energy of that state. Actually, the energies of nuclear states are determined only to a finite accuracy or width, defined by the lifetime of that state and the indeterminacy principle. Thus, a gamma ray can be absorbed if its energy lies within the width of the relevant nuclear state. Because of the Doppler effect, the energy of a gamma ray can be changed by imparting a velocity to its source. With an appropriate choice of nuclear state, a velocity of as little as a fraction of a millimeter per second can shift the gamma ray energy "off resonance"--that is, outside the width of the state. It is therefore possible to measure such velocities by determining the degree of absorption of these gamma rays in the corres...

No abstract

No abstract

No abstract