- Email: [email protected]
122. Photofission of 238U and 232Th
V.
FISSION
121. T h e a n g u l a r d i s t r i b u t i o n of f i s s i o n f r a g m e n t s i n t h e p h o t o f i s s i o n of uranium. B . P . BANNIK, N. M. KULIKOVA,L. E. LAZAREVA and V. A. YAKOVLEV. Lebedev Physical Institute, Moscow, U.S.S.R.
k
Measurements of the angular distribution of photofission fragments from uranium have been made using the X-ray beam of the 30 MeV synchrotron. Nuclear plates 100p and 200p thick impregnated with a saturated solution of uranium acetate were placed along the X-ray beam at a distance of 1 m from the target. The irradiations were carried out at three synchrotron energies: 9.4 MeV, 12 MeV and 26.5 MeV. In the course of examining the plates only tracks of fission fragments with a dip angle of ~ 15° were selected. Since the point of separation of fragments was not fixed the angular distribution [Y(0) + Y(~ -- ~)] was determined. The observed angular distribution for-2ssu is anisofropic with a m a x i m u m at right angles to the X-ray beam. The a m o u n t of the anisotropy increases with decreasing photon energy. In the case of uranium the anisotropy is considerably less than for the photofission of thorium 1). The angular distribution obtained at 9.4 MeV has the form a + b sin 2 0 + c sin 9 ~ cos 9 O, which points to a considerable relative increase of quadrupole absorptions at energies less than 10 MeV. l) W i n h o l d , E.J., Demos, P.T. and H a l p e r n , L., Phys. Rev. 87(1953) 1139.
122. P h o t o f i s s i o n of 2SSu a n d 2S2Th. R. B. DUFFIELD and R. A. SCHMITT. University of Illinois, Urbana, Ill., U.S.A. Excitation functions for symmetric photofission (division into fragments of equal mass) and for asymmetric photofission (division into fragments of unequal mass) of ~ssu and 23~Th have been measured using the University of Illinois 22 MeV betatron. For 2Z2Th, the probability of symmetric photofission increases monotonically over betatron energies from 6.5 to 10 MeV. For 2ssU, the probability of symmetric fission increases from 5.5 MeV to a m a x i m u m at 6.0 MeV, decreases to a minimum at 8.0 MeV and then increases monotonically.
123. A n g u l a r d i s t r i b u t i o n of f i s s i o n f r a g m e n t s n e a r t h r e s h o l d . L. WILETS. University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico, U.S.A. The sideways-peaked angular distribution of fragments from neutron-induced fission of 282Th near threshold, measured by B r o l l e y and H e n k e l , is found to be consistent with the model of A. B o h r . I t is assumed t h a t the saddle-point states through which the fissioning nucleus passes include primarily only a few members of a particular rotational band. Indications are adduced t h a t this band has K = 3/2 and odd parity. --
1186
-
-
FISSION
121. T h e a n g u l a r d i s t r i b u t i o n of f i s s i o n f r a g m e n t s i n t h e p h o t o f i s s i o n of uranium. B . P . BANNIK, N. M. KULIKOVA,L. E. LAZAREVA and V. A. YAKOVLEV. Lebedev Physical Institute, Moscow, U.S.S.R.
k
Measurements of the angular distribution of photofission fragments from uranium have been made using the X-ray beam of the 30 MeV synchrotron. Nuclear plates 100p and 200p thick impregnated with a saturated solution of uranium acetate were placed along the X-ray beam at a distance of 1 m from the target. The irradiations were carried out at three synchrotron energies: 9.4 MeV, 12 MeV and 26.5 MeV. In the course of examining the plates only tracks of fission fragments with a dip angle of ~ 15° were selected. Since the point of separation of fragments was not fixed the angular distribution [Y(0) + Y(~ -- ~)] was determined. The observed angular distribution for-2ssu is anisofropic with a m a x i m u m at right angles to the X-ray beam. The a m o u n t of the anisotropy increases with decreasing photon energy. In the case of uranium the anisotropy is considerably less than for the photofission of thorium 1). The angular distribution obtained at 9.4 MeV has the form a + b sin 2 0 + c sin 9 ~ cos 9 O, which points to a considerable relative increase of quadrupole absorptions at energies less than 10 MeV. l) W i n h o l d , E.J., Demos, P.T. and H a l p e r n , L., Phys. Rev. 87(1953) 1139.
122. P h o t o f i s s i o n of 2SSu a n d 2S2Th. R. B. DUFFIELD and R. A. SCHMITT. University of Illinois, Urbana, Ill., U.S.A. Excitation functions for symmetric photofission (division into fragments of equal mass) and for asymmetric photofission (division into fragments of unequal mass) of ~ssu and 23~Th have been measured using the University of Illinois 22 MeV betatron. For 2Z2Th, the probability of symmetric photofission increases monotonically over betatron energies from 6.5 to 10 MeV. For 2ssU, the probability of symmetric fission increases from 5.5 MeV to a m a x i m u m at 6.0 MeV, decreases to a minimum at 8.0 MeV and then increases monotonically.
123. A n g u l a r d i s t r i b u t i o n of f i s s i o n f r a g m e n t s n e a r t h r e s h o l d . L. WILETS. University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico, U.S.A. The sideways-peaked angular distribution of fragments from neutron-induced fission of 282Th near threshold, measured by B r o l l e y and H e n k e l , is found to be consistent with the model of A. B o h r . I t is assumed t h a t the saddle-point states through which the fissioning nucleus passes include primarily only a few members of a particular rotational band. Indications are adduced t h a t this band has K = 3/2 and odd parity. --
1186
-
-