20 -e- 



Comparison with experiment . 



Experiments mafle with small l jm. detonators have enaOlea the torejoing theoretical results 

 to oc testeO in various ways. 



(a) Shape of nulses. 



OetaiWa calculations of th? form of the external pr3ssure pulses nave been made, and on 

 the Basis of t^e results th£ 3ppo»rance of tne first two pulses has Deen sketched In Figure 3. In 

 tKese calculations, squation (2') »bs us;d in order to obtain tne form of tne pulses flown to a 

 pfessure amplitude of H /lOO, a separate estimation of the maximum rarefaction Deing made. 



Ftjure 1 shows a typical C.R.O. record of a detonator explosion. The receiver employed was 

 a 5(«a11 2i* quartz hydrophone calculated to have a principal resonance at aoout tOO kc/s. and aimed 

 to ^ave a flat response jt lower frequencies. The receiver was used in conjunction with an 

 amplifier having 'l hijh input impedance (lO - 20 megohms) and wide Band frequency response 

 (10 c/s to 100 Kc/s) . The deflections on the C.R.O. records are proportional to the voltage 

 variations across tne receiver ana therefore, for a perfect receiver, proportional to the pressure 

 variations n in the water. 



In a general way the appearance of the C.R.O, trace agrees with that calculated, as regards 

 the sharpness and Isolated character of the pulses. There is one difference, ho»ever; on the 

 C.R.O. record the initidi pressure rise is followed after a v^ry short time by a small sharp negative 

 pulse. This effect is more apparent in Figure 2 where more amplification has been used. Here It 

 appears that tne negative psal< is only associated with the first few explosions; it is absent from 

 later explosions wnere the pressure variations appear to accord ncre nearly with theory. This 

 effect may be due to the failure of the receiver to respond rtliaoly to the very high frequencies 

 which would be associated with the initial exolosions. 



(b) Amplitude of initial pressure pulse . 



Equation (25) enables tne peak pressure amplitude H at any external point to be calculated. 

 In Appendix I the following data are derived for the detonators 



p = 3700 atm. r = 0.62 cms. 

 '^o 



Substituting these in equation (25), absolute values are got for the pressure amplitudes: it is 

 calculated, for example, that the pressure at a .distance of 10 feet rises to 7.5 atmospheres. 

 Experimentally, a value of aOout 3 atmospheres is obtained at the same range. Accurate agreement is 

 here not to be expecteo, for tne calculated value is very materially dependent upon p and r , reliable 

 values for which are not available. 



fc ) The time intervrj! T between the first and second pulses . 



Equation (l2b) has been used in oroer to .jet a theoretical value for T. Taking, for example, 

 the case when a detonator is fired at a acptn of 15 feet below the surface of th'j sea, the total 

 pressure P at this depth is found to be 



P = 1.45 atm. = 1.45 10* dynes/cm^ 



In addition, the makers specify for tn-ir detonators 



0^ = 3 000° C = 32 73° K. 



m = 0.01:}6 corresponding to 300 ccs. of gas (Appendix l). 



y = 1.30. 



Usiny also the known values 



R = 8.3 10 ' ergs/gm. molecule. 

 / = 1.12. 



formula 



