HAL Id: jpa-00214875
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Submitted on 1 Jan 1971
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A STUDY OF THE REACTION 16O + 16O → MASS 24 + 4He + 4He. A TEST OF THE
QUASIMOLECULAR MODEL
K. Purser, C. Gaarde, H. Gove, H. Kubo, R. Liebert
To cite this version:
K. Purser, C. Gaarde, H. Gove, H. Kubo, R. Liebert. A STUDY OF THE REACTION 16O + 16O
→MASS 24 + 4He + 4He. A TEST OF THE QUASIMOLECULAR MODEL. Journal de Physique Colloques, 1971, 32 (C6), pp.C6-253-C6-254. �10.1051/jphyscol:1971657�. �jpa-00214875�
JOURNAL DE PHYSIQUE Colloque C6, supplkment au no 11-12, Tome 32, Novembre-Dkcembre 1971, page C6-253
A STUDY OF THE REACTION 160
+
160 -, MASS 24+
4He+
4He.A TEST OF THE QUASIMOLECULAR MODEL
K. H. PURSER, C. C. GAARDE, H. E. GOVE, H. KUBO and R. B. LIEBERT Nuclear Structure Research Laboratory, University of Rochester, USA.
Rburnk. - ZRS co'incidences entre deux particules a Bmises dans la reaction 1 6 0 + '60 ont BtB mesurBes dans deux telescopes AE-E places a des angles + 0 et - 8 par rapport a la direction du faisceau, a une Bnergie incidente de 60 MeV. Les ~ofncidences ont kt6 mesurkes en fonction de 8. Aucune indication d'une augmentation de Pintensit6 n'a CtB observBe pour 8 = f 90° dans le centre de masse.
Abstract. - Coincident counts of the two alpha particles emitted in the reaction 1 6 0 + 1 6 0
were measured in two E-AB detectors located at angles + 0 and - 0 to the 60 MeV incident beam.
The coincidences were measured as a function of 8. No evidence for an increase in yield was found when the angles were i 900 in the center of mass.
A quasimolecular model has been proposed by Greiner [1] and his collaborators to explain heavy ion optical potentials. In this model during the impact of two heavy ions a significant increase in nuclear density occurs in the region of overlap so that it is expected that nuclear matter would be preferentially ejected in a direction a t right angles to the line joining the centers of the interacting nuclei. The observation of such an effect would be valuable as it would give a basis for understanding the optical potentials that are needed and would allow information to be obtained directly about the compressibility of nuclear matter.
The present experiment was designed to study the coincident alpha particles which are produced during an 160 + 160 collision at 60 MeV. Both SiO and A1,0, targets were employed. The emitted alpha particles were measured in coincidence E-BE detectors located a t equal angles on each side of the beam direction. If the model predictions are correct, it would be expected that there would be a maximum coincidence intensity when the sum of the two equal angles was 1800 in the center of mass.
In practice, the experiment must be done in the laboratory frame of reference so that it was necessary to take each individual coincident event, transform it to the center-of-mass system for the reaction, calculate the sum of the angles in the center of mass and then to construct a missing mass spectrum a t each set of angles.
The procedure for producing the missing mass spec- trum is outlined in figure 1 . Here the known momenta of the coincident alpha particles make it possible to calculate the momentum of the unobserved mass 24 system and hence its kinetic energy. The internal energy, which cannot be accounted for during this calculation, represents the (( missing mass )). Such a spectrum of missing mass is shown in figure 2 ; it can be
FIG. 1 . - Outline of missing mass calculations P a , , PaZ known in c. m.
pres = - (Pa, + Pa,)
seen clearly that a number of known states of 2 4 ~ g are strongly populated. Another example of a missing mass spectrum is shown in figure 3 and the various regions of the spectrum for which angular distributions have been plotted are indicated.
Transforming the coincidence intensity as function of angle of the various regions of the missing mass spectrum from the laboratory to the center-of-mass frame of reference was a somewhat laborious proce- dure requiring rather lengthy Monte Carlo computer calculations. The angular distributions in the center-of- mass system for various regions of the missing mass spectrum are shown in figures 4, 5, 6 and 7.
The angular distributions must be symmetric about 0, + 8, = 180°, and although the data could only be measured from 30° to 600 beyond 180°, it appears t o be symmetric about that angle. There is clearly no evi- dence whatsoever for any peaking at 1800.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971657
C6-254 K. H. PURSER, C. C. GAARDE, H. E. GOVE, H. KUBO A N D R. B. LIEBERT
FIG. 5. - Center-of-mass angular distributions for regions 4 ( x ) and 5 (0) of the missing mass spectrum.
Excitation in 241u19, MeV
FIG. 2. - Missing mass spectrum.
1
I2c + THRESHOLD- Center-of-mass angular distributions for regions 6 ( x ) and 7 (0) of the missing mass spectrum.
EXCITATION IN 2 4 ~ g , (MeV)
FIG. 3. - Missing mass spectrum showing the various regions for which angular distributions were plotted.
FIG. 4, - Center-of-mass angular distributions for regions FIG. 7. - Center-of-mass angular distributions for regions 1 ( x ) , 2 (0) and 3 (0) of the missing mass spectrum. 9 ( x ) , 10 (O), 11 (0) and 12 (A) of the missing mass spectrum.
3 - 1.5
1
0) t Z1.0- E t.
CK 2 C
d @
k a
0.5
I I , I
Reference -
"C +"c REGION
-
8 I t I
[I] GREINER (W.), (( Nuclear Reactions Induced by Heavy Ions u, 748; N o r t h Holland 1970.
100" 200° 250" 100" 150" 2 0 0 " 250"
150"
+ O2 (c.rn.1 8, + 82 (c.rn.1
