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SPINS OF SOME T = 1 STATES IN Al26
P. Horvat, P. Kump, M. Vakselj
To cite this version:
SPINS OF
SOME T
=
1
STATES IN AP6
P. HORVAT, P. KUMP and M. VAKSELJ Nuclear Institute « J. Stefan )), Ljubljana
Résumé. - Les états T = 1 dans 26A1 aux énergies 3,16 et 4,19 MeV ont été étudiés en mesurant les distributions et corrélations angulaires. Les attributions de spins et parités sont les suivantes :
2' pour le niveau à 3,16 MeV et 4+ pour le niveau à 4,19 MeV. Les transitions à partir de ces niveaux sont presque purement M 1.
Abstract.
-
The T = 1 states in A126 with the energies 3.16 MeV and 4.19 MeV have been stu- died by measuring the angular distributions and correlations. The following spin and parity assigne- ments have been found : J" = 2' for the 3.16 MeVlevel and J" = 4' for the4.19 MeVlevel. The transitions from these two levels are almost pure M 1.The present knowledge of spins and parities of excited states in ~ 1higher than 2 MeV is very poor ' ~ and does not give enough information for the theore- tical analysis. With this experiment an attempt bas been made to obtain the spins of 3.16 MeV and 4.19 MeV levels.
The detailed description of the experirnental set up has been given in the work of Horvat et al. Cl]. Now also the azimuthal angle can be varied, which enables us t o measure five geometries instead only two as was the case in [Il.
The proton resonances in the reaction Mg2'(p, y) Alz6 at 0.77 MeV and 1.38 MeV were chosen t o populate 3.16 MeV and 4.19 MeV states in From this resonances one obtains relatively simple spectra which contain a predominant transition to the one of the level of interest. The angular distributions and correlations were measured. The experirnental results were composed with theoretically predicted correlations which were calculated using the expres- sions given by Ferguson [2]. To the states populated by gamma rays, the parity assignments have been assumed and therefore should be considered as tenta- tive only.
The gamma cascade from 7.05 MeV through 3.16 MeV to 0.42 MeV levels has been studied mainly to determine the mixing ratio between M 1 and E 2 of the second transition, because the spin of 3.16 MeV level is known. The correlations were measured in the geometries assigned by Ferguson [2] as Al, A 2, C 1, C 2 and D.
Assurning that the transition from 7.05 MeV to 3.16 MeV level is predominantly E 1, the standard X 2 analysis of measured correlations first confirms the spin 2 for the 3.16 MeV level and gives the mixing ratio for the transition from 3.16 MeV to 0.42 MeV level 6 = E 2/M 1 =
+
0.10 f 0,07. To fit the measureddistributions of the second gamma rays no cos4 O term was required. Therefore, the analysis in terms of aniso- tropies is made and shows good agreement with the
x2
determination of 6.With the same assumptions that the first transition is E 1, we have started the studies of 4.19 MeV level. Observed distributions and correlations again did not require any cos4 O term to fit the experimental data. Therefore the analysis was made in terms of aniso- tropies. The measurements, yield a unique assignement of the spins and parities t o the 7.63 MeV and 4.19 MeV levels. The assignments are 1" = 3- and 4+ to the 7.63 MeV and 4.19 MeV states, respectively. From the present experiment it is also seen that the 7.63 MeV state is formed almost entirely through the channel spin 2. The comparison with experimental value for the anisotropies also shows that 3.77 MeV transition i s M 1 + E 2 w i t h 6 = E 2 / M 1 = - 0 . 1 3 k 0 . 1 0 . T h e present results are summarized in figure 1.
E
J"
7.63 MeV 7.05 MeV
FIG. 1. - The levels of A126 and transitions studied in the present work.
ÉTUDE DE RÉACTIONS NUCLÉAIRES AVEC U N SPECTROGRAPHE MAGNÉTIQUE C l -91
The low lying single particle states of odd mass nuclei in the neighbourhood of Alz6 are well described with an odd particle moving in a deformed potential[3]. If the residual neutron - proton forces in the nucleus are weak enough, the low lying single particle states of Alz6 should be well described with the odd neutron and odd proton moving independently in different Nilsson states. We have used this assumption to esti- mate the transition probabilities between the states in Alz6 to which we assigned energetically probable configurations. The transitions from both levels 3.16 MeV and 4.19 MeV are almost pure M 1, which
suggests that this two states are formed coupling two particles one in the Nilsson orbit (5) and the other in the orbit (7) or (11). To these configurations we ascribe the 1" = 2' for the 3.16 MeV level and
1" = 4' for the 4.19 MeV level. This two levels could be therefore ascribed to the simple confi- gurations with one particle in the lowest possible Nilsson state, and the second in the next two higher states. Further investigations should be devoted to the measurements of lifetime of these two transitions.
Bibliographie
[l] HORVAT (P.), KUMP (P.) and POVH (B.), Nucl. Phys.,
1963,45, 341.
[2] FERGUSON (A. J.), Angular Correlation Methods in Gamma-Ray Spectroscopy, North Holland Publ. Comp., Amsterdam, 1965.
[3] NILSSON (S. G.), Mat. Fys. Medd. Dan. Vid. Selsk., 1955,
29, No 16.
[4] ENDT (P. M.) and VAN DER LEUN (C.), NUCI. Phys.,
1962, 34, 1.
ÉTUDE
DE RÉACTIONS NUCLÉAIRES
AVEC UN SPECTROGRAPHE
M AGNÉTIQUE
Institut de Recherches Nucléaires, Strasbourg (France)
Résumé. - Des réactions nucléaires induites par des deutérons sur des cibles d'adénine ainsi que des réactions nucléaires induites par 3He sur des cibles de 12C, 13C et 14C ont été étudiées au
spectrographe magnétique à large bande, type Buechner.
Abstract. - Nuclear reactions induced by deuterons on adenine targets and nuclear reactions induced by He3 on C12, Cl3 and Cl4 targets have been studied with a Buechner-type magnetic
spectrograph.
Dans ce travail, nous nous sommes intéressés aux réactions suivantes : l 4 ~ ( d , p ) I 5 N et 13C(3He,p)15N,
14C(3He, p) 16N et 14C(3He, a) 13C, dans le but d'obtenir des informations relatives à l'existence et l'énergie des niveaux excités dans les noyaux de 15N, 16N et 13C. Certains groupes de protons et de particules a provenant des réactions de compétition sur 12C,
13C et 160 ont également été observés.
Le faisceau de deutérons ainsi que le faisceau de 3He étaient fournis par l'accélérateur Van de Graaff de 5,5 MeV du Centre de Recherches Nucléaires de Strasbourg-Cronenbourg et les particules lourdes étaient détectées à I'aide d'un spectrographe magné- tique à large bande, type Buechner.
1. Réactions 14N(d, p) 15N et 13C(3He, p) 15N.
-
Les premiers niveaux excités du noyau de 15N sont
bien connus quant à leur énergie d'excitation [l].
Par contre, les niveaux de
