ANGULAR DISTRIBUTIONS OF THE ALPHA PARTICLES EMITTED BY ORIENTED
241,243
Am NUCLEI
1
2
G.M.Gurevich , A.L.Erzinkyan , P.-D.Eversheim3, V.T.Filimonov4 , V.Golovko5, P.Herzog3,
I.Kraev5, A.A.Lukhanin6, A.A.Belyaev6, V.I.Noga6, V.P.Parfenova2, T.Phalet5, A.V.Rusakov1,
N.Severijns5, Yu.G.Toporov4, C.Tramm3, V.N.Vyachin7, D. Zakoucky8, E.Zotov4
1
Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia; 2 Institute of
Nuclear Physics, Moscow State University, Moscow, Russia; 3 Bonn University, Bonn, Germany;
4
Research Institute for Atomic Reactors, Dimitrovgrad, Russia; 5 Leuven University, Leuven,
Belgium; 6 Kharkov Institute of Physics and Technology, Kharkov, Ukraine; 7 All-Russian
Scientific Research Institute of Experimental Physics, Sarov, Russia;
8
Nuclear Research Institute, Rez, Czech Republik
Recently we measured angular anisotropy in the alpha decay of strongly deformed
Es and 255Fm nuclei [1] to investigate a relation between the angular anisotropy and nuclear
deformation. To study possible nuclear structure effects produced by the addition of two
neutrons in strongly deformed nuclei, measurements of the alpha particle angular distributions
has been performed for 241Am and 243Am using the low temperature (T = 10-100 mK) nuclear
orientation (LTNO) technique at the 3He – 4He dilution refrigerator of the Leuven University.
Spectroscopically thin sources for LTNO measurements were prepared by the ion
implantation of 241Am (isotopic purity 99,988 at. %) and 243Am (isotopic purity 99,997 at. %)
into foils of the pure iron at the electromagnetic isotope separator S-2 of the RFNC-VNIIEF
(Sarov) at the accelerating voltage about 40 kV which corresponds to the implantation depth 50100 A. Alpha particles were detected by seven silicon PIN-diode detectors mounted at different
angles with respect to the nuclear orientation axis inside the cold volume of the dilution
refrigerator (working temperature of detectors was around 10 K). The source temperature was
monitored by the 54Mn(Ni) nuclear orientation thermometer soldered to the cold finger of the
refrigerator together with the alpha source.
Temperature dependences of the alpha angular anisotropy were measured with good
statistical accuracy for one 241Am source and two 243Am sources of different activity. Rather
unexpectedly, we found qualitatively different behavior of the anisotropies for two isotopes. For
241
Am the observed angular distribution of the alpha particles corresponds to that expected for
axially symmetric prolate nucleus while for 243Am the observed angular distribution does not
show the axial symmetry.
The work was supported by INTAS (grant No. 00-00195) and by the Russian Foundation
of Basic Research (grant No. 03-02-16175).
253,254
[1] N.Severijns, A.A.Belyaev, A.L.Erzinkyan, P.-D.Eversheim, V.T.Filimonov, V.V.Golovko,
G.M.Gurevich, P.Herzog, I.S.Kraev, A.A.Lukhanin, V.I.Noga, V.P.Parfenova, T.Phalet,
A.V.Rusakov, Yu.G.Toporov, C.Tramm, V.N.Vyachin, D.Zakoucky, E.Zotov. Angular
distribution of  particles from oriented 253,254Es and 255Fm nuclei. Phys. Rev. C71 (2005)
044324.