No abstract

The complete sets of elastic constants of 4H and 6H silicon carbide single crystals were determined by Brillouin scattering. The elastic constants of 6H SiC are C11=501±4, C33=553±4, C44=163±4, C12=111±5, and C13=52±9 GPa; the corresponding ones of 4H SiC are the same within experimental uncertainties. The compressibility, 4.5×10−3 GPa, is about 3–5 times smaller than those reported for polycrystalline SiC materials.

Kinetic energy and neutron multiplicity a s a function of fragment inass were measured for the thermal neutron induced fission of 239Pu. By measuring the velocities and energies of t w o fission fragments simultaneously. both of the pre-neutron emission fragment mass nz* and the post-neutron inass In were obtained. 'l'he fragment mass dependent neutron multiplicity ii (m') was deduced by subtracting v z from n z '. T h e fragment mass dependent total kinetic energy TKE(?n*) was also obtained from this data. T h e fragment velocity w a s measured by time-offlight (TOF) method. for which the s t a r t signal w a s triggered by a very thin plastic scintillation film detector (TFD) and the stop signal w a s obtained by a silicon surface barrier detector (SSBD) which was also used for the measurement of the fragment kinetic energy. 'l'he present result of ~(i i z *) is in good agreement with that of Apalin rt a /. and that in the light fragment region of Fraser et u l. T h e obtained Tm(nz*) agrees well with the data of Wageinans ~t n l. . 4 calculation w a s carried out with the model proposed by Brosa rt n l. who assumed multichannel fission paths and a random neck rupture. It is seen that the calculated results of both fragment mass dependent kinetic energy and neutron multiplicity represent experimental data well.

The multiplicity and energy of the prompt neutrons emitted from the fission fragments for 239 Pu(nth, f) were measured as functions of the fragment mass and total kinetic energy. The results were compared with those for 233 U(nth, f) and with the predicted values by the multi-channel fission theory with the random neck rupture model.The measured and predicted values of the neutron multiplicity, (v)(m*), show the saw-tooth trend and agree with each other. The total neutron multiplicity decreases linearly with increasing total kinetic energy resulting in -d(TKE)/d(vt 0 t)=16.5±0.4MeV/neutron. The slope of the neutron multiplicity vs. the total kinetic energy, -d(v) / d(T KE), was plotted against the fragment mass. Its shape agrees with that for 233 U(nth, f).The average neutron emission energy, (rJ)(m*), follows a bell shape about the symmetric fission accompanying higher values for very asymmetric fissions and agrees with that for 233 U(nth, f). The total excitation energy (TXE)(m*) was determined by two manners: (1) neutron data and (2) Qmax-(TKE). Both results satisfactorily agree with each other as the case of 233 U(nth, f), and thereby the present derivation of (TKE) from the neutron data is confirned.

No abstract