Gamma Decay of the 3.90-MeV (2+) Level inCa40

Abstract

The lifetime and y-ray branching of the 3.90-MeV (2 ) state of Ca have been measured using the reactions Ca4 (p, p')Ca at a bombarding energy of 7.32 MeV and K39(p, y)Ca4 at the E& =1.344-MeV resonance. Consistent values for the lifetime were obtained from the Doppler shifts of the 3.90-MeV p rays in both reactions and from the 0' line shape in the K (p, y)Ca reaction. A value of v' =50 +5 fsec is adopted for the mean lifetime of the 3.90-MeV state. The 3.90 3.35-MeV branching ratio was measured by observing the 0.555-MeV cascade y rays in quadruple coincidence with the two annihilationp rays and the inelastic protons in the Ca (p, p')Ca reaction, or in triple coincidence with annihilation y rays in the K~-(p, y)Ca reaction. Results are in agreement and the adopted branch is (7.95 +0.8) &&10 By combining the lifetime and branching results, the 0.555-MeV E2 transition rate corresponds to s. B(5'2; 3.90 (2+) -3.35 (0+)) of 250 +35 et fm . This result is in excellent agreement with recent theoretical estimates of the transition strength. The mean lifetime of the 5.28-MeV (4 ) state of Ca was measured to be 310+60 fsec. The corresponding B(E2; 5.28 (4+) 3.90 (2+1)) of 535 +110 e fm4 is in reasonable agreement with expectations based on a strong-deformation rotational model of the states.

SuperdeformedΛhypernuclei with antisymmetrized molecular dynamics

“…Recently, many SD bands are investigated and identified in nuclei with A ∼ 40 [18][19][20]. For example, in 40 Ca, a SD band is confirmed by the observation of the K π = 0 + band built on the 0 + 3 state lying at 5.21 MeV, while its ground state is spherical due to the double closed-shell structure [19,21]. It is expected that in some Sc isotopes, the SD states will appear in the low-lying regions, which could be accessed by the 24 Mg + 24 Mg reaction fusion-evaporation experiment at the Grand Accélérateur National d'Ions Lourds (GANIL) [22].…”

Clustering and triaxial deformations ofCa40

“…Because of the strong population in the multinucleon transfer data and the strong E2 transitions [17], the 0 + (5.21 MeV), 2 + (5.63 MeV), and 4 + (6.54 MeV) states have been thought to belong to the superdeformed (SD) band with the dominant 8p-8h configuration. Recently, by using GAMMASPHERE array detectors, the level structure of the deformed bands in 40 Ca has been explored and many excited states up to high spin have been discovered.…”

Excitation of Rotational Bands inCa40Observed in the ReactionAr

“…This result may be an indication of band mixing as proposed by Gerace and Green. 13 If the sharp peak observed at 6.9 MeV excitation energy is really the 6 + member of the lowest K* = o + rotational band, one expects to find a strong E2 de-excitation y ray to the 4 + , 5.28-MeV leveL In fact, three states have been observed to decay strongly to the 4 + , 5.28-MeV level 9,14 : the states at 6.93, 7.4, and 7.68 MeV. States at 7.4 and (or) at 7.68 MeV are not seen in the reactions 36 Ar( 7 Li, £) 40 Ca 12 and 32 S( 12 C, a) 40 Ca, 10 whereas a level at 6.9 MeV is strongly excited in both cases.…”

“…Excitation of the ground state is strongly inhibited by the position of the kinematical window. Three rotational bands have been suggested in 40 Ca, two based onaF = 0 + state, one beginning with K* = 2\ 9 The lowest K* = 0 + band comprises the levels at 3.35 MeV (0 + ), 3.9 MeV (2 + ), and 5.28 MeV (4 + ). It is generally agreed that these levels are built up mainly by the promotion of four particles from the s-d shell to the f~p shell.…”