4
E. Bonnet
1.3 Results
To go further, we want to see behaviors of the different elements of the partitions.
To do so, we distinguish the
1,2,3 H isotopes, the
3,4 He isotopes and the heavier ones
gather in the A > 4 family. For each, we compute the mass fraction (X
(i) ) which is
the probability of one nucleon to belong to the (i) cluster. As we use the Z max as
sorting observable we have to remove from the X observable the nucleons belonging
to the biggest fragment for each partition. The (1.1) shows the explicit formula used
in the following: m i and A i are the multiplicity and the mass of the considered (i)
cluster, while A tot and A max are, respectively, the mass of the detected partition and
the mass of the biggest fragment. Evolution of multiplicities can be found in [7].
1.3.1 Z max Sorting
In Fig. 1.2, the mean evolution of the mass fraction with the Z max are shown for the
different clusters understudied. The free protons (
1 H ) behave differently compared
to the other clusters: starting from the evaporation regime, we observe a continuous
decrease in their contribution to the final partitions. For
2,3 H and
3 He clusters, we
observe a similar sequence already seen for the M Z ≥1 mean evolution in the Fig. 1.1
but with this representation: an increase in the evaporation and vaporization regime
which surrounded a plateau or even a decrease in the multifragmentation regime. For
4 He clusters, it is even more clear because the overall shapes are almost not affected
by the change in beam energies. On the contrary, for the lightest clusters, there is a
clear hierarchy with an increase of their contributions with the beam energy and on the
whole range of fragmentation degree. It has to be noted that
4 He contribution to the
final partitions is dominant whatever the regime. If we look at, now, simultaneously
to the evolution of
4 He and A > 4 contributions, we see that the increase of the
4 He
contribution surrounded the bell shape of A > 4 which sign the multifragmentation
window. During the passage between evaporation and multifragmentation, cluster
production is frozen until the exit to vaporization. One possible explanation of this
experimental fact is that the cost to build fragments and their associated surfaces make
the production of additional clusters impossible in terms of energy available in the
system. This is especially true for the lowest beam energies (32 and 40 MeV/nucleon)
where multifragmentation may occur at the threshold. Indeed, we see that, when
looking at the highest beam energies, the production of
1,2,3 H and
3 He is made
possible again due to additional energy deposited in the system. The main effect
of increasing the average deposited energy in the system is then an increase of the
final light species at the expense of the heavier ones. In this case, fragment partitions
are produced excited and go through secondary de-excitation and produce these
light clusters. Concerning the vaporization regime, we observe at the beam energy
E. Bonnet
1.3 Results
To go further, we want to see behaviors of the different elements of the partitions.
To do so, we distinguish the
1,2,3 H isotopes, the
3,4 He isotopes and the heavier ones
gather in the A > 4 family. For each, we compute the mass fraction (X
(i) ) which is
the probability of one nucleon to belong to the (i) cluster. As we use the Z max as
sorting observable we have to remove from the X observable the nucleons belonging
to the biggest fragment for each partition. The (1.1) shows the explicit formula used
in the following: m i and A i are the multiplicity and the mass of the considered (i)
cluster, while A tot and A max are, respectively, the mass of the detected partition and
the mass of the biggest fragment. Evolution of multiplicities can be found in [7].
1.3.1 Z max Sorting
In Fig. 1.2, the mean evolution of the mass fraction with the Z max are shown for the
different clusters understudied. The free protons (
1 H ) behave differently compared
to the other clusters: starting from the evaporation regime, we observe a continuous
decrease in their contribution to the final partitions. For
2,3 H and
3 He clusters, we
observe a similar sequence already seen for the M Z ≥1 mean evolution in the Fig. 1.1
but with this representation: an increase in the evaporation and vaporization regime
which surrounded a plateau or even a decrease in the multifragmentation regime. For
4 He clusters, it is even more clear because the overall shapes are almost not affected
by the change in beam energies. On the contrary, for the lightest clusters, there is a
clear hierarchy with an increase of their contributions with the beam energy and on the
whole range of fragmentation degree. It has to be noted that
4 He contribution to the
final partitions is dominant whatever the regime. If we look at, now, simultaneously
to the evolution of
4 He and A > 4 contributions, we see that the increase of the
4 He
contribution surrounded the bell shape of A > 4 which sign the multifragmentation
window. During the passage between evaporation and multifragmentation, cluster
production is frozen until the exit to vaporization. One possible explanation of this
experimental fact is that the cost to build fragments and their associated surfaces make
the production of additional clusters impossible in terms of energy available in the
system. This is especially true for the lowest beam energies (32 and 40 MeV/nucleon)
where multifragmentation may occur at the threshold. Indeed, we see that, when
looking at the highest beam energies, the production of
1,2,3 H and
3 He is made
possible again due to additional energy deposited in the system. The main effect
of increasing the average deposited energy in the system is then an increase of the
final light species at the expense of the heavier ones. In this case, fragment partitions
are produced excited and go through secondary de-excitation and produce these
light clusters. Concerning the vaporization regime, we observe at the beam energy