Polarization of elastically scattered gamma-rays

~¢ p l ~ i t a t

~ microfilm without written permission frOm~he~i~biis[~:~r Y

i

i : P O L A R I Z A T I O N OF ELASTICALI~Y S C A T T E R E D

GAMMA-RAYS I. LOVAS

Ctnt~

Red'earth lnstitme /or Physics, Departmenl o] Neutron Ph!tsics , B.t,dapest Received 12 J u n e 1958

Disregarding resonance scattering, three different processes are responsible for the elastic scattering of gamma rays. These are the Thomson, the Rayleigh and the Delbriick scattering. Unfortunately, it ~.s not possible to determine accurately the angular distributions of the last two processes 1,~). Many experiments were performed to the elastic scattering but the results obtained were fairly ambiguous 3,4,5). The existence of the Delbriick .scattering is an unsolved problem. In the following we should like to suggest a possible w a y to obtain some definite information about the Delbriiek ~attefing. There is a difference between the angular dependence of the polarization of the t)elbriick scattering and that of the two other processes, Thus by' measuring the polarization of elastically scattered gamma rays it is very probable that a conclusive knowledge as to the existence of Delbrfick scattering may be obtained. The amplitudes of Thomson, Rayleigh and Delbrfick scattering are of the form 0,~,s) aT(~)e I • e 2, aR(O)e I • e~, and aD(0)e I • e2+b(0)(e I • n)(e~, n,) respectively, where 9 is the angle of scattering, ex and es unit vectors of polarization for the incident and for the scattered g a m m a rays, and n a unit vector in the direction of the change in m o m e n t u m . The differential cross section is therefore

da

d~oc!a(O)i"(e~" e2) -TLa (O~b(9)+a(~)b*(O)](e~" ea)(e~ n)(e~- n) + ib(~)?[(e~" n)(e~,- n)?, a(o) = aT(o) +a~(O)+aD(O). The coefficients aR(O), aD(~) and b(~9) are not yet exactly known; it is certain 9), however, that b (0) is a real function and appreciably smaller t:hai~ aR(~)'~ Therefore, the term ib(0)[%( ~ n)(e 2 n)] ~ can be negl c t d and olle may write : ~b(O) l~e Ea(O)j (e,-e~)(el"n)(e~,n), da ~ Q ~ (el" e2)2+ 155 :i

r

:i,~~,.

r

.

.

.

~ ~ : i ~,

/~0!~

,--

Reference~

~ ~ ~

,~i, ~ ~i~~ii:~i~ ~:% ~~ i~~!,~ ~ ~i~ ~ i ~ ~ ~ i~ ~/i~i~=ii'~ ~,i~ i:i i i~ii~-~,~,~ S~!~:~I~,~ ~ ~:~!i~:~:~-~ ~ ~~ ~ % ~,~% !ii~:~ ~ ........~ ~:~::~:~'~ ~°~ ~,i~!i~!~'¢ ~ ~,~I~I~L ~ i ~

L ~o . ~