coulomb excitation data analysis codes; gosia 2007 - Physics and ...

11.3 Tutorial 1: Gosia basic flow sequenceThis tutorial requires the set of files contained in toyfit.tar which can be downloaded from the Gosia websitehttp://www.pas.rochester.edu/~cline/Gosia/index.html.This set of demonstration files (toyfit.tar) make a up a tutorial on the basic operations that are typicallyperformed to simulate and analyze experimental data. The toyfit.tar file contains a sample input, a simulateddata set and a set of sample output files, which can be compared to the results in this tutorial. On a Unix-likemachine, issue the following command to unpack the tar file in the desired working directory.tar —xvftoyfit.tarThe entire demo can be run using Gosia 2007 without any modification to the files. However, in order tolearntorunGosiaeffectively, it will be necessary to examine the files and compare sections of the input withthe corresponding entries in the Gosia manual. A brief overview of relevant sections of the code is given inthis tutorial, and the annotated inputs later in this chapter will also help to identify the various “options,”records and fields.11.3.1 SimulationThe planning of a Coulomb excitation experiment can be aided by simulating the expected yields based ona best guess of the level scheme, including as much previously measured data as possible. This examplecalculates the expected yields for Coulomb excitation of the fictitious nucleus to be investigated, 12055 Fi. Theassumed level scheme for 1207055 Fi is shown in figure 13. In the planned experiment, a beam of 35Br willbombard the 12055 Fi target. The example Gosia input simulate.inp produces simulated cross sections. Referto the relevant sections of chapter 5 in this manual for each Gosia “option” described below for more detaileddescriptions of each record and field. A brief flowchart of the entire simulation procedure is shown in figure14.The first Gosia “option” in simulate.inp is OP,FILE, which assigns a filename chosen by the user to eachauxiliary file to be used by Gosia. The files used will depend on the calculation options chosen. In this case,only the input file (simulate.inp), the output file (simulate.out) and a detector file (det.gdt) are assigned.If a needed file is not assigned a name, Gosia will look for or create a file named “fort.[n]”, where n is thefixed file number. It is acceptable to assign names to files that are not being read in a particular step. Thismeans that the user can define all necessary files for the entire process in an early stage, if desired.OP,TITL allows the user to reprint comments at the header of the output file.OP,GOSI (Gosia) is executed next. Alternatively, OP,COUL (Coulex) could have been used, butOP,GOSI is a more flexible version of OP,COUL that allows the user to fit matrix elements to data withfewer modifications to the input file. The first “sub-option” in OP,GOSI is LEVE, which gives the knownor predicted level scheme in any convenient order (except that level 1 must be the ground state). The firstthree excited states in the yrast sequence of the investigated nucleus are known (Figure 13). The 0 + to 6 +states are labeled in the example input simulate.inp as levels 1–4. Each level is defined on one line by thefollowing quantities: index (beginning with 1), parity (+/- 1), spin, energy (MeV). Note that comments arenot allowed on some lines of the input. Restrict comments to the lines which are commented in the examplefiles.Thesecondsub-optionofOP,GOSIisME, which defines the matrix elements, all E2 in this case. Theheader 2,0,0,0,0 indicates the beginning of E2 matrix elements, and all relevant E2 reduced matrix elementsare then listed with the initial and final indices in “odometer order.” The following quantities describe eachmatrix element: initial level, final level, matrix element, lower limit, upper limit. The lower and upper limitswill be used by Gosia in the fitting tutorial. Setting the lower and upper limits equal (1,1 in the presentinput) “fixes” the matrix element during a fit. The footer 0,0,0,0,0 terminates the ME input.The sub-option EXPT defines the “logical” experiments to be simulated, in this case only one. A“logical” experiment typically refers to detection of a scattered or recoiling particle over a particular solidangle. The first line of EXPT1,55,120tells Gosia that there is one experiment and that the investigated nucleus (for which Coulomb excitationcalculations are to be performed) has Z=55 and A=120. The following line156