Equipment and techniques for acoustic cavitation w o~k are desc ribed . . The tes t liquid and its eontainer form part of a se lf· sustaining programmable oscIllator. EmphasIs IS laId on the treatme nt of the liquid necessa ry to yield re producible res ults after artificial nucl ea tion ,. especially b y ne utrons , a-recoi ls, and fi ss ion. With ne utrons , for instance, th e ca vitatIOn rate rI ses rapI~ly WIth acoustIc (negativ e) press ure, and at fix ed pressure is proportional to ne utron flux . The ca vItat~on events are ra~dom, and no ap prec ia bl e indu c t.ion or decay tim es are obse rve d. Each cav itatIOn anses from the actIOn of a s in"l e ne ut.ron (or a -recoil , or fi ss ion). The ca vit.atio n " thres ho ld " (rou ghly negative press ure below whi c l cavital ion is rare) is hi ghl y variab le fro m liquid to liquid. Thres holds at about room temperature for liquids irradi a t.ed with 10 MeV ne utrons ranged from 1 to 2 bars for n-pentane, e ther, and fre on 113 to ove r 50 ba rs for wate r.Key Words: Acoustic cavitati on, alph a-p artic le -in duced ca vitat.ion, ca vitation, cav itation nucl e us, cavitation thres hold, fission-induced cav itation, ne utron-indu ced cav ita ti on, radiationindu ced cav itation, thres hold .

The speed of so und in distilled water wa,s m eas ured over the temperature ra nge 0° to 100° C with an acc uracy of 1 part in 30,000. The resu lts are given as a fifth-d egree polynomial a nd in tables . The water was contained in a cylindrical tank of fix ed leng t h, terminated at each end by a pla ne transducer, and the end-to-end time of flight of a pulse of so und was determined from a m easurement of t he pulse-repetition frequency required to set the success ive echoes into t im e coincidence.

An equation and tables for the speed of sound in water are reprinted from a recent paper published in The Journal of Research of the National Bureau of Standards.

We have set up and are using an apparatus for the measurement of total sound power output of a piezoelectric transducer radiating into water. This apparatus combines the better features of previously used methods which depend on radiation pressure. The input is modulated at a low frequency and the output power is intercepted by a target which experiences a force at the modulation frequency. The target is mounted on the armature of an electromagnetic receiver provided with an independent coil through which a current at the modulation frequency is adjusted in amplitude and phase, either manually or automatically by feedback, to arrest the motion of the armature. When the armature is stationary the force depends only on the current, and the apparatus can be calibrated using direct current and dead weights. It is thus absolute. In practice, the carrier frequency is swept over any part of the range 0.1-15 MHz while a recording of power output versus frequency is made. The results of comparisons made with those of other mehtods are encouraging. Examples of curves from normal and defective transducers are shown.

In response to increased interest in the use of calibrated sources of ultrasonic energy, we have developed a system comprising components grouped to facilitate the accurate transfer of calibration. Electronic circuitry supplied with and built into each ultrasonic transducer obviates both the use of not-readily-available radiofrequency equipment and the measurement of anything more exotic than dc voltage. Prototype transducers have shown good output at frequenices up to 78 MHz. Units now available to the public can be calibrated at output powers ranging from 5 mW to 500 mW at frequencies between 1 and 20 MHz.

A method for obtaining the signatures (waveforms) of certain acoustic emission events has been developed. The waveform is that at the source, free of contamination by ringing of the specimen, apparatus, and transducer. The technique is based on the comparison of two signals at the transducer, one from the event in question and one from an artificial event of known waveform. The apparatus is also adapted to the calibration of transducers in a certain sense. The configurations of source (real or simulated acoustic−emission event) and receiving transducer correspond to those of some special cases of Lamb’s problem. As a byproduct, the results may be of some interest to seismologists. Subject Classification: 40.42; 35.54, 35.80, 35.68; 40.50; 85.44.

A "sing-around" velocimeter of high stability and precision has been developed and tested. The instrument, which is of the fixed-path type, automatically measures and/or records the speed of sound in nondispersive liquids. Stabilities of about 50 ppm over a 24-hr period can be achieved.

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