46
A. Sharma et al.
higher Fermi momentum in the IQMD model leads to unbound nucleons at the surface
(and hence their spurious emission). But at the same time, higher Fermi pressure leads
to stronger stability of density profile. Moreover, the interaction range in the IQMD
model is also system size-dependent to gain more stability of the density profile and
ultimately stable nuclei.
Next, we will investigate isospin effects via Coulomb forces, i.e., forces between
the projectile and target protons on the onset of mutifragmentation in asymmetric
reactions using IQMD model. The role of Coulomb forces on the onset of multifragmentation is important to understand because it was reported in [31] that there
occurs a deviation in the trajectory of the projectile when these forces are taken into
consideration. A careful survey of the literature shows that many studies have been
performed to probe isospin effects via coulomb interactions on various observables
[12, 31–33] at intermediate energy heavy-ion collisions. To check isospin effects via
Coulomb forces on the onset of multifragmentation in asymmetric reactions of
84
36 Kr +
197
79 Au, we calculated the charge distributions (3≤Z f ≤12) at different beam energies
using IQMD model and calculated results are displayed in Fig. 4.2. Note that results
shown in the figure are obtained in the presence of Coulomb forces using the soft
equation of state. From the figure, it is clear that charge distributions become steeper
with increasing incident energy and therefore reflects the violence of collisions. This
behavior of charge distributions with increasing beam energy is consistent with the
results reported in [34–36].
Next, to understand onset of multifragmentation, we fit charge distributions with
power law ∝ Z f
−τ for intermediate mass fragments (3≤Z f ≤12). Also, we have
extracted values of τ and these values are plotted as a function of incident energy in
Fig. 4.3. From the figure, we find that there is no minimum in the extracted values of
τ when plotted against incident energies. This pattern of τ values with beam energies
in the presence of Coulomb forces reflects the onset of multifragmentauon at beam
energies less than 35 MeV/nucleon.
To investigate this point, we have calculated the charge yields (3≤Z f ≤12) for the
asymmetric and highly charged system of
84
36 Kr +
197
79 Au in the absence of Coulomb
forces and results are shown in Fig. 4.4.
Again, the calculated charge distributions have been fitted with power law fits ∝
Z f
−τ and extracted values of parameter τ are plotted against incident energies in Fig.
4.5. From the figure, one can clearly see a sharp minimum for soft equation of state at
an incident energy of 55 MeV/nucleon. A remarkable effect of Coulomb forces is
observed when compared with the results shown in Fig. 4.4. To get more information,
we have also performed calculations for the asymmetric reactions of
40
18 Ar +
64
29 Cu
in the absence of Coulomb forces. For this asymmetric system, the extracted values
of τ show minimum at an incident energy of 17 MeV/nucleon. Thus, for a highly
charged asymmetric system of
84
36 Kr +
197
79 Au, minimum occurs at higher incident
energies when compared with the light charged asymmetric system of
40
18 Ar +
64
29 Cu.
This clearly shows the dependence of the onset of multifragmentation on the range
of Coulomb forces and reaction asymmetry.
A. Sharma et al.
higher Fermi momentum in the IQMD model leads to unbound nucleons at the surface
(and hence their spurious emission). But at the same time, higher Fermi pressure leads
to stronger stability of density profile. Moreover, the interaction range in the IQMD
model is also system size-dependent to gain more stability of the density profile and
ultimately stable nuclei.
Next, we will investigate isospin effects via Coulomb forces, i.e., forces between
the projectile and target protons on the onset of mutifragmentation in asymmetric
reactions using IQMD model. The role of Coulomb forces on the onset of multifragmentation is important to understand because it was reported in [31] that there
occurs a deviation in the trajectory of the projectile when these forces are taken into
consideration. A careful survey of the literature shows that many studies have been
performed to probe isospin effects via coulomb interactions on various observables
[12, 31–33] at intermediate energy heavy-ion collisions. To check isospin effects via
Coulomb forces on the onset of multifragmentation in asymmetric reactions of
84
36 Kr +
197
79 Au, we calculated the charge distributions (3≤Z f ≤12) at different beam energies
using IQMD model and calculated results are displayed in Fig. 4.2. Note that results
shown in the figure are obtained in the presence of Coulomb forces using the soft
equation of state. From the figure, it is clear that charge distributions become steeper
with increasing incident energy and therefore reflects the violence of collisions. This
behavior of charge distributions with increasing beam energy is consistent with the
results reported in [34–36].
Next, to understand onset of multifragmentation, we fit charge distributions with
power law ∝ Z f
−τ for intermediate mass fragments (3≤Z f ≤12). Also, we have
extracted values of τ and these values are plotted as a function of incident energy in
Fig. 4.3. From the figure, we find that there is no minimum in the extracted values of
τ when plotted against incident energies. This pattern of τ values with beam energies
in the presence of Coulomb forces reflects the onset of multifragmentauon at beam
energies less than 35 MeV/nucleon.
To investigate this point, we have calculated the charge yields (3≤Z f ≤12) for the
asymmetric and highly charged system of
84
36 Kr +
197
79 Au in the absence of Coulomb
forces and results are shown in Fig. 4.4.
Again, the calculated charge distributions have been fitted with power law fits ∝
Z f
−τ and extracted values of parameter τ are plotted against incident energies in Fig.
4.5. From the figure, one can clearly see a sharp minimum for soft equation of state at
an incident energy of 55 MeV/nucleon. A remarkable effect of Coulomb forces is
observed when compared with the results shown in Fig. 4.4. To get more information,
we have also performed calculations for the asymmetric reactions of
40
18 Ar +
64
29 Cu
in the absence of Coulomb forces. For this asymmetric system, the extracted values
of τ show minimum at an incident energy of 17 MeV/nucleon. Thus, for a highly
charged asymmetric system of
84
36 Kr +
197
79 Au, minimum occurs at higher incident
energies when compared with the light charged asymmetric system of
40
18 Ar +
64
29 Cu.
This clearly shows the dependence of the onset of multifragmentation on the range
of Coulomb forces and reaction asymmetry.