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Submitted on 1 Jan 1971
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GAMMA TRANSITIONS IN 44Ti AND 48Cr FROM HEAVY ION INDUCED REACTIONS
R. Huber, W. Kutschera, C. Signorini, P. Blasi
To cite this version:
R. Huber, W. Kutschera, C. Signorini, P. Blasi. GAMMA TRANSITIONS IN 44Ti AND 48Cr FROM HEAVY ION INDUCED REACTIONS. Journal de Physique Colloques, 1971, 32 (C6), pp.C6-207- C6-208. �10.1051/jphyscol:1971644�. �jpa-00214862�
JOURNAL DE PHYSIQUE Colloque C6, supplLment au no 11-12, Tome 32, Novembre-De'cembre 1971, page C6-207
GAMMA TRANSITIONS IN 44Ti
AND 48Cr FROM HEAVY ION INDUCED REACTIONS
R. B. HUBER, W. KUTSCHERA and C . SIGNORINI (*) Physik-Department der Technischen Universitat, Miinchen, Germany
and P. BLASI
Istituto di Fisica dell'Universit8, Firenze, Italy
RBsum6. - Les temps de vie d'etats excites du 44Ti ont Bte determinks par la methode de la distance de recul, dans la reaction 32S(14N, pn)44Ti. On en a dtduit les temps de vie 7 m = 5,O f. 2,O et 1,0?b:: ps pour les niveaux respectivement B 1 083 keV (2 +) et 2 454 keV (4 +). Le premier Ctat excite du 48Cr a kt6 identifie 2 752 i 1 keV, grace ?une expMence de corncidence triple i
proton-neutron- y, dans la reaction 4oCa(loB, pn)48Cr.
Abstract. - Lifetimes of excited states in 44Ti have been determined with the recoil-distance method on the 32S(14N, pn)44Ti reaction. The mean lives Tm = 5.0 & 2.0 and 1.02;:; ps have been deduced for the levels at I 083 keV (2') and 2 454 keV (4+), respectively. The first excited state in 4SCr has been identified at 752 f 1 keV with a proton-neutron-y triple coincidence on the 4oCa(loB, pn)48Cr reaction.
1. Introduction. - Even-Even, N = Z nuclei above 40Ca(44~i, 4 8 ~ r , 52Fe), are of special interest in connec- tion with the quartet structure in f 712 nuclei. However, those nuclei are rather difficult to reach by ordinary reactions. Not much is known, therefore, about their level structure.
We have started a series of investigation on those nuclei by means of gamma spectroscopy via compound nuclear reactions caused by heavy-ion bombardment.
Some first results have been obtained for the lifetimes of the lower states in 44Ti and the position of the first excited state in 48Cr.
2. The 44Ti nucleus. - At El,, = 28 MeV, i. e.
around the Coulomb barrier the reaction 32S(14N, ~ n ) ~ ~ T i has been found stronger than the competing ones 32S(14N, 2 ~ n ) ~ ~ S c and 32S(14N, 2 ~ ) ~ ~ s ~ . Therefore, at this energy with a beam current of 10 nA, the measurements of the mean life of the first two excited states in 4 4 ~ i have been undertaken by means of the recoil-distance method.
The measuring set-up is very similar to that one used in ref. [I]. The target consisted in a layer of 0.6 mg/cm2 CdS deposited under vacuum onto 2 mg/cm2 Au foils ; the recoiling 4 4 ~ i nuclei were stopped in 4 mg/cm2 Au foil. Both target and stopper
(*) On leave of absence from : Istituto di Fisica dell'univer- sit8, Padova, Italy.
were stretched in order to have layers as uniform as possible.
Gamma ray spectra (Fig. 1) have been recorded at target to stopper distances ranging from 5 to 500 pm in steps > 5 pm with a 50 cm3 Ge(Li) detector placed at 00 to the beam-direction 5 cm from the target.
Both y-rays belonging to the 2+-0' and 4+-2' transitions [2] in 44Ti with Ey = 1 083 and 1 371 keV respectively could be analyzed.
The experimental results of the recoil-distance measurements for the 2' state are shown in figure 2.
If one substracts the long lived component (probably due to the feeding of the 2 + level from long living excited states) one gets 2 , = 5.0 f 2.0 ps for this state.
The deduction of the mean life of the 4' state was complicated by the fact that in the stopped peak, indicated in figure 1 a t E, = 1 371 keV, one has also the contribution from the y-rays of the first excited state in 24Mg, Ey = 1 368 keV, populated by the l2C(I4N, ~ n ) ' ~ M g reaction. Therefore, only the flight peak could be analyzed leading to z, = 1.0?::2 ps for the 4' state in 4 4 ~ i .
The transition strengths (in Weisskopf units) of the first 2' states in the even Titanium isotopes known (42 < A < 50) are reported in table I. It seems that the strength of the transition in 4 4 ~ i is about a factor 2 smaller than in 4 6 , 4 8 ~ i which may tentatively indicate that collective effects in that nucleus are becoming smaller.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971644
C6-208 R. B. HUBER, W. KUTSCHERA AND C. SIGNORINI
FIG. 1. - Spectra of y-rays from CdS target bombarded with 28 MeV 14N ions recorded at several distances (D) between target and stopper. The peak at 1 158 keV belongs to 44Ca (2+-0+ transition) populated by j?+ decay of 44Sc through
the 32S(14N7 2 p)44Sc reaction.
B(E 2)lB(E 2)
Ey(2+ + 0+) 7 s. P.
[keVl b s l (w. u.)
- -
42Ti 11
1 551 0.55 +
::;
') 19 + 744Ti 1 083 5.0 2.0 8
1 2 f 3 46Ti 889 6.5 f 0.3 (b) 22 f 1 48Ti 983 3.6 %- 0.5 (c) 23 & 3 50Ti 1 550 1.5 + 0.2 ( c ) 5 & 1
Lifetimes of the first 2+ states in 42Ti, 44Ti, 46Ti, 48Ti, s0Ti, (&) BROWN (B. A.) et al., Topical Conference on (( The Structure of 1 f 712 Nuclei 1) B.3.7.1971, Legnaro (Padova).
Italy.
(b) DEHNHARDT (W.), doctor thesis, Heidelberg, Ger- many (1970).
(c) Nucl. Data Sheets 1970, 3B, NO 5, 6.
3. The 48Cr nucleus. - Several reactions have been tried in order to populate excited states in 48Cr ; namely 40Ca(160, 2 ~ t ) ~ ~ C r , 4 0 C a ( 1 4 ~ , ~ t p n ) ~ ~ C r , 40Ca(12C, ~x)~'Cr and 40Ca(10B, ~ n ) ~ ~ C r . This last one has been the most successful with El,, = 25 MeV, i. e. around the Coulomb barrier.
In order to identify unambiguously the first excited state in 48Cr, previously reported [3] at 0.67 MeV, triple coincidences p-n-y have been performed. Back- scattered protons were detected with an annular Si-surface barrier detector at 180° at 7 mm from the target, neutrons with a liquid scintillator N E 213 (Elron pulse-shape-discrimination system) a t 900 and y-rays with a 50 cm3 Ge(Li) detector at 00. The target consisted of a 2 mm thick Ca metal. The results of the coincidences are presented in figure 3 ; from these and from the data obtained by the other reactions the gamma ray at E, = 752 + 1 keV has been assigned to the decay of the first excited (2') state in 48Cr.
4 4 ~ i
2+--0' (1.083Me~) p-n-y triple coincidence
-
c
$20 -
8
D 01 a2 a3 0.4 0.5
torge t-stopper distoncelrnrnl FIG. 3. - Results of p-n-y triple coincidence. The peaks at 88, 262 keV are coming from levels in 47V populated through FIG. 2. - Results of recoil-distance measurements for the first the 40CaPOB. > , 2 AvnV7V reaction. the veak at 752 keV has been
excited state in 44Ti. assigned to the first &cited state in 48Cr.
References
[I] KUTSCHERA (W.), DEHNHARDT (W.), KISTNER (0. C.), [2] SIMPSON (J. J.), DIXON (W. R.), and STOREY (R. S.) ; KUMP (P.), POVH (B.) and SANN (H. S.), to be Phys. Letters, 1969, 30B, 478.
published in Phys. Rev. [3] Nuclear Data Sheets, 1970, 4B, 3, 4.
