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Manuscript Title: TERS v2.0: An improved version of TERS
Authors: S. Nath
Program title: TERS v2.0
Catalogue identifier: AEBD_v2_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 180(2009)2392
Programming language: C.
Computer: The code has been developed and tested on a PC with Intel Pentium IV processor.
Operating system: Linux.
RAM: About 8 Mbytes
Keywords: Monte Carlo simulation, Recoil separator, Complete fusion reaction, Ion optics, Transmission efficiency.
PACS: 02.70.Uu, 29.30.h, 25.70.Jj, 41.85.p..
Classification: 17.7.

External routines: pgplot graphics subroutine library [1] should be installed in the system for generating residue trajectory plots. (Code included in the CPC distribution file).

Does the new version supersede the previous version?: Yes

Nature of problem:
Recoil separators are employed to select and identify nuclei of interest, produced in a nuclear reaction, rejecting unreacted beam and other undesired reaction products. It is important to know what fraction of the selected nuclei, leaving the target, reach the detection system. This information is crucial for determining absolute cross section of the studied reaction.

Solution method:
Interaction of projectiles with target nuclei is treated event by event, semimicro- scopically. Position and angle (with respect to beam direction), energy and charge state of the reaction products are calculated by Monte Carlo method. Trajectory of each nuclei inside the separator is then calculated by ion optical transfer matrix method. Ratio of the number of trajectories completing their journey up to the detection system to the total number of trajectories is a direct measure of absolute transmission efficiency of the separator.

Reasons for new version:
The method for calculating mean squared scattering angle (<v>2), used earlier[2], was found to be inadequate particularly for low energy heavy residues. Energy loss of beam in the target-backing foil and energy loss of residues in the charge-reset foil (wherever used) needed to be taken into account for better matching of simulated residue parameters with measurements.

Summary of revisions:
  1. A new method[3] for calculating multiple small angle Coulomb scattering of residues in the target has been adopted. The change is incorporated in function Weibull() in the program ters_pti2.c.
  2. Isotopically enriched targets are made on a thin backing foil (usually made of carbon) quite often. Energy loss of beam in the backing foil (assuming beam is made to pass through the backing foil first, which is the usual practice) need to be taken into account. This calls for minor changes in the input file ters_pti2.inp. Following is the modified list of input parameters in this file with explanation.
    Zp, Ap, Zt, At - Atomic no. and mass no. of projectile and target.
    Ep - Projectile energy [MeV ] in laboratory.
    BeamSpot, TarThick - Dia. [mm] of (circular) beam spot and target thickness [mg/cm2].
    Zback, Aback, BackThick - Atomic no. and mass no. of the backing material and thickness [mg/cm2] of the backing foil.
    Qvalue, ILPM - Q value [MeV ] for CN formation and inverse level density parameter.
    AlphaNo, ProtonNo, NeutronNo - Numbers of evaporated alphas, protons and neutrons.
    Salpha[c] - Alpha separation energies [MeV], to be left blank if no alpha evaporation.
    Sproton[c] - Proton separation energies [MeV], to be left blank if no proton evaporation.
    Sneutron[c] - Neutron separation energies [MeV], to be left blank if no neutron evaporation.
    NEVENT - Number of events i.e. residues to be considered by the program (maximum 5 × 105).
  3. A new function ThinFoil() has been introduced in the program ters_tra2.c. A thin foil can be inserted anywhere along the path of the residues by calling this function using the following syntax:

    Status = ThinFoil(argument list);
    if (Status == 0) continue;

    The function is particularly useful to place a residue charge-reset foil (usually made of carbon) after the target and is described in Table 1.

    Table 1
    Description of the function ThinFoil() used in the program ters_tra2.c. Function name is case sensitive.
    Name of the functionJob of the functionList of argumentsDescription of arguments
    ThinFoil()To calculate ion energy loss in a thin foilint arg1,
    int arg2,
    double arg3
    arg1 = atomic number of the foil material,
    arg2 = mass number of the foil material,
    arg3 = thickness of the foil [mg/cm2]
    The parameters in input line number 4 are new in this version. If the target is backed by a carbon foil of thickness 125 μg/cm2, the input line would look like "6 12 0.125". If the target is self-supporting, i.e. there is no backing, value of the last parameter (thickness) should be zero. However, the first two parameters must not be left blank or have 0 values. The input line would look like "6 12 0.0" in this case.
  4. There is a minor change in the input file ters_tra2.inp. Following is the modified list of input parameters in this file with explanation.
    Z0, A0 - Residue atomic number and mass number.
    E0, A00, q0 - Energy [MeV], mass no. and charge state of the reference particle.
    NEVENT - Number of events i.e. trajectories to be calculated.
  5. Program/input files which have been modified in this version are suffixed by "2" in their names (before the extension) e.g. ters_pti.c has been renamed as ters_pti2.c. The complete list of files included in the distributed code can be viewed in the readme file.

The present version of the code is applicable to complete fusion reactions only. Calculation of transmission efficiency has been illustrated with a specific recoil separator, viz. the Heavy Ion Reaction Analyzer (HIRA)[4,5], at IUAC. One has to make necessary changes in the code, while performing calculations for other recoil separators. Also, atomic number of the residual nucleus should not exceed 92, as the method used for calculating stopping power of ions [6] is valid for Z ≤ 92. The code can perform energy loss calculation only in elemental targets and foils (i.e. compounds or alloys are not supported). Further, number of events (NEVENT) in ters_tra2.inp should not exceed the same in ters_pti2.inp.

Running time:
From a few seconds to several minutes depending on the reaction, number of events and separator layout.

[1] http://www.astro.caltech.edu/ tjp/pgplot/.
[2] G.R. Lynch, O.I. Dahl, Nucl. Instr. Methods B 58 (1991) 6.
[3] L. Meyer, Phys. Status Solidi 44 (1971) 253.
[4] A.K. Sinha, N. Madhavan, J.J. Das, P. Sugathan, D.O. Kataria, A.P. Patro, G.K. Mehta, Nucl. Instr. and Methods A 339 (1994) 543.
[5] S. Nath, Nucl. Instr. Methods A 576 (2007) 403.
[6] J.F. Ziegler, J.P. Biersack, U. Littmark, The stopping and range of ions in solids, Vol. I (Pergamon Press, Oxford, 1984).