Y. Kitazoe

Classical many-body calculations for compressed density formation in high-energy heavy-ion collisions

A great interest has been pa id to the possibi l i ty of formation of high-densi ty nuclear mat te r in high-energy heavy-ion collisions (1). This formation is a major premise for appearance of exotic phenomena such as pion condensation (2) and densi ty isomers (3). Various theoret ical approaches have been proposed to describe high-energy heavy-ion collisions (1). Of these approaches, classical many-body calculations (4,5) are one of the most useful methods to examine whether nuclei are highly compressed. In this method, however, i t has been difficult to construct a stable nucleus because of the lack of Paul i principle. BODMER and PA~os (4) employed a two-body potent ia l with an a t t ract ive par t and a short-range repulsive par t , i.e.

An analytical treatment of time- and space-dependent asymptotic behaviour of slowing down neutron

Abstract Asymptotic aspects of space- and time-dependent slowing down of a pulsed neutron is analytically studied, based on the time-dependent diffusion equation. The calculations are mainly concerned with the flux distribution ψ(r, u, t) and the spatially dependent most probable slowing down time tmax(r, u). The analytic solution for ψ(r, u, t) indicates that its spatial dependence is determined only by the time-dependent neutron age τ(u, t), while tmax(r, u) is shown to be dominantly influenced by the stationary neutron age τs(u). Through these analyses, the interesting relations are obtained: (a) When t = t s ≡ «t a 0 {1 − ξ/(ξ + 4)(ξ + 2)} , τ(u, t), coincides with τs,(u), which implies that the spatial dependence of ψ(r, u, t) at that time is analogous to that of the stationary neutron distribution, where «ta0 is the first time moment. (b) The most probable slowing down time tmax(r, u) at r = √«r 2 a ) (standard notation) becomes equal to the most probable slowing down time tm of the spatially independent distribution ψ(u, t). The cross sections employed here are assumed to be constant, but different cross-sections for the source neutrons are allowed.

Excitation spectrum of « α-particle nuclear matter » and collective resonances

L a t e l y a g r e a t n u m b e r of e x p e r i m e n t s h a v e been ca r r ied ou t w i t h t he a im of s t u d y i n g t h e a -pa r t i c l e cor re la t ions . F o r l i gh t nuclei , t h e a -par t i c le mode l ha s been s h o w n to b e a successful m e t h o d for desc r ib ing t he b i n d i n g energies of e v e n e v e n nucle i a n d t he r o t a t i o n a l b a n d s exc i t ed in nuc lea r r eac t ions (1). Espec ia l ly g rea t i n t e r e s t in t h e mo lecu l a r aspec t s of t h e sys t em composed of a -par t i c les has been s t i m u l a t e d b y exper i m e n t a l i n f o r m a t i o n a f forded in h e a v y i o n reac t ions , a -nuc leus s c a t t e r i n g a n d so fo r th . Accord ing to t h i s mode l these are m a d e up of a -par t ic les w h i c h arc a r r a n g e d in space so as to g ive t h e closest poss ible pack ing . Most of t h e b i n d i n g ene rgy of each nuc l ide is due to t he b i n d i n g of i t s c o n s t i t u e n t a -par t ic les , t h e r e m a i n d e r be ing t h e ene rgy of t he b o n d s b e t w e e n t he a -par t ic les . I n t h e p r e s e n t no t e we exp lore t h e p rope r t i e s of a nuc leus as (( a -par t i c le nuc l ea r m a t t e r ,) r a t h e r t h a n t h e molecu la r aspects , in order to ge t some i n s igh t i n to t h e charact e r i s t i c b e h a v i o u r of t he nuc leus a t h i g h e x c i t a t i o n energy. I t is shown t h a t t he exci tat ion s p e c t r u m of t h e s y s t e m exh ib i t s a b e h a v i o u r s imi la r to t h a t of l i qu id h e l i u m (~-9) w h i c h swi tches g r a d u a l l y f rom p h o n o n s to s ing le -par t i c le t y p e pass ing t h r o u g h ro tons a n d also t h a t t h e cross-sec t ions in nuc lea r r eac t ions h a v e a r e sonance p e a k a r o u n d twice t he ene rgy of t h e e x t r e m u m p o i n t of t h e p h o n o n r o t o n d i spers ion curve . W e s t a r t w i t h a r ea sonab le a s s u m p t i o n t h a t t h e s y s t e m cons is t s of u-part ic les , wh ich is a va l i d one for l igh t nuc le i w i t h A = 4n. T he H a m i l t o n i a n of t h e s y s t e m of in te r -