14
G. Chaudhuri et al.
We also have to state which nuclei are included in computing Q N 0 ,Z 0 (17). For
I, J , (the neutron and the proton number) we include a ridge along the line of stability.
The liquid drop formula above also gives neutron and proton drip lines and the results
shown here include all nuclei within the boundaries.
The long-range Coulomb interaction between different composites can be included
in an approximation called the Wigner–Seitz approximation. We incorporate this following the scheme set up in [3].
2.2.2 The Evaporation Code
The statistical multifragmentation model described above calculates the properties of
the collision averaged system that can be approximated by an equilibrium ensemble.
Ideally, one would like to measure the properties of excited primary fragments after
emission in order to extract information about the collisions and compare directly
with the equilibrium predictions of the model. However, the time scale of a nuclear
reaction(10
−20 s) is much shorter than the time scale for particle detection (10
−9 s).
Before reaching the detectors, most fragments decay to stable isotopes in their ground
states. Thus before any model simulations can be compared to experimental data, it
is indispensable to have a model that simulates sequential decays. A Monte Carlo
technique is employed to follow all decay chains until the resulting products are
unable to undergo further decay. For the purposes of the sequential decay calculations,
the excited primary fragments generated by the statistical model calculations are
taken as the compound nucleus input to the evaporation code. Hence, every primary
fragment is decayed as a separate event.
We consider the deexcitation of a primary fragment of mass A, charge Z , and
temperature T . The successive particle emission from the hot primary fragments
is assumed to be the basic deexcitation mechanism. For each event of the primary
breakup simulation, the entire chain of evaporation and secondary breakup events
is Monte Carlo simulated. The standard Weisskopf evaporation scheme is used to
take into account evaporation of nucleons, d, t,
3 He, and α. The decays of particle
stable excited states via gamma rays were also taken into account for the sequential
decay process and for the calculation of the final ground-state yields. We have also
considered fission as a deexcitation channel though for the nuclei of mass < 100
its role will be quite insignificant. The process of light particle emission from a
compound nucleus is governed by the emission width ν at which a particle of type
ν is emitted. The different equations for calculation of particle, gamma, and fission
widths are given in details in [23] and we will skip them here. Once the emission
widths are known, it is required to establish the emission algorithm which decides
whether a particle is being emitted from the compound nucleus. This is done [24]
by first calculating the ratio x = τ/τ tot , where τ tot = / / tot , tot =
ν ν and
ν = n, p, d, t,
3 He, α, γ or fission and then performing Monte Carlo sampling from
a uniformly distributed set of random numbers. In the case that a particle is emitted,
the type of the emitted particle is next decided by a Monte Carlo selection with the
G. Chaudhuri et al.
We also have to state which nuclei are included in computing Q N 0 ,Z 0 (17). For
I, J , (the neutron and the proton number) we include a ridge along the line of stability.
The liquid drop formula above also gives neutron and proton drip lines and the results
shown here include all nuclei within the boundaries.
The long-range Coulomb interaction between different composites can be included
in an approximation called the Wigner–Seitz approximation. We incorporate this following the scheme set up in [3].
2.2.2 The Evaporation Code
The statistical multifragmentation model described above calculates the properties of
the collision averaged system that can be approximated by an equilibrium ensemble.
Ideally, one would like to measure the properties of excited primary fragments after
emission in order to extract information about the collisions and compare directly
with the equilibrium predictions of the model. However, the time scale of a nuclear
reaction(10
−20 s) is much shorter than the time scale for particle detection (10
−9 s).
Before reaching the detectors, most fragments decay to stable isotopes in their ground
states. Thus before any model simulations can be compared to experimental data, it
is indispensable to have a model that simulates sequential decays. A Monte Carlo
technique is employed to follow all decay chains until the resulting products are
unable to undergo further decay. For the purposes of the sequential decay calculations,
the excited primary fragments generated by the statistical model calculations are
taken as the compound nucleus input to the evaporation code. Hence, every primary
fragment is decayed as a separate event.
We consider the deexcitation of a primary fragment of mass A, charge Z , and
temperature T . The successive particle emission from the hot primary fragments
is assumed to be the basic deexcitation mechanism. For each event of the primary
breakup simulation, the entire chain of evaporation and secondary breakup events
is Monte Carlo simulated. The standard Weisskopf evaporation scheme is used to
take into account evaporation of nucleons, d, t,
3 He, and α. The decays of particle
stable excited states via gamma rays were also taken into account for the sequential
decay process and for the calculation of the final ground-state yields. We have also
considered fission as a deexcitation channel though for the nuclei of mass < 100
its role will be quite insignificant. The process of light particle emission from a
compound nucleus is governed by the emission width ν at which a particle of type
ν is emitted. The different equations for calculation of particle, gamma, and fission
widths are given in details in [23] and we will skip them here. Once the emission
widths are known, it is required to establish the emission algorithm which decides
whether a particle is being emitted from the compound nucleus. This is done [24]
by first calculating the ratio x = τ/τ tot , where τ tot = / / tot , tot =
ν ν and
ν = n, p, d, t,
3 He, α, γ or fission and then performing Monte Carlo sampling from
a uniformly distributed set of random numbers. In the case that a particle is emitted,
the type of the emitted particle is next decided by a Monte Carlo selection with the