Upload
dieter
View
44
Download
2
Tags:
Embed Size (px)
DESCRIPTION
GOSIA. As a S imulation T ool J.Iwanicki, H eavy I on L aboratory, UW. OUTLINE. O ur goal is to estimate gamma yieds What the yield is Point Y ield vs. Integrated Y ield What they are needed for What is needed to calculate it Definition of the nucleus considered - PowerPoint PPT Presentation
Citation preview
GOSIAAs a Simulation Tool
J.Iwanicki, Heavy Ion Laboratory, UW
OUTLINE
Our goal is to estimate gamma yieds
• What the yield is– Point Yield vs. Integrated Yield
• What they are needed for• What is needed to calculate it
– Definition of the nucleus considered– Definition of the experiment
YIELDGOSIA recognizes two types of yields:• Point yields calculated for:
– Excited levels layout– Collision partner– Matrix element values– CHOSEN particle energy and scattering
angle• Integrated yields calculated for:
– (... as above but ...)– A RANGE of scattering angles and energies
POINT YIELD
How GOSIA does it?• Assumes nucleus properties and collision partner;• starts with experimental conditions (angle,
energy) and matrix element set• solves differential equations to find level
populations;• calculates deexcitation using gamma detection
geometry, angular distributions, deorientation and internal conversion into acount.
POINT YIELD
Point yields:• are fast to be calculated...• ...so they are used at minimisation stage• OP,POIN – if one needs a quick look
• but are good for one energy and one (particle scattering) angle
INTEGRATED YIELD
Integrated yields• are something close to reality• but quite slow to calculate
Useful integration options:• axial symmetry option• circular detector option• PIN detector option (multiple particle detectors)
YIELD
• GOSIA calculates yields as differential cross sections, integrated over in-target particle energies and particle scattering angles– ‘differential’ in but integrated for particles
• The ‘GOSIA yield’ may be understood as a mean differential cross section multiplied by target thickness (in mg/cm2)
[Y]=mb/sr mg/cm2
88Kr simulation – level layout
88Kr simulation – level layout
One usually adds some „buffer” states on top of observed ones to avoid artificial population build-up it the highest observed state
4
3
2
1
5
6
megengeneration of matrix elements set
Apply transition selection rules to create a set of all possible matrix elements involved in excitation.
• This is easy but takes time and any error will corrupt the results of simulation!
• Tomek quickly wrote a simple code to do the job which uses data in GOSIA format.
megengeneration of matrix elements set
parity
level number
spin
level energy[MeV]
input termination
iwanicki@buka:~/Coulex/88Kr$ megen 1 Create setup for this multipolarity (y/n)n 2Create setup for this multipolarity (y/n)y Do you want them coupled ?n Please give limit value-1.5 1.5 3 Create setup for this multipolarity (y/n)n(…) 7 Create setup for this multipolarity (y/n)y Do you want them coupled ?n Please give limit value-1 1 8 Create setup for this multipolarity (y/n)n
megengeneration of matrix elements set
E2
M1
How to get matrix elementsfor simulation from?
• Check the literature for published values• Get all the available spectroscopic data
(lifetimes, E2/M1 mixing ratios, branching ratios)• Ask a theoretician
• Use OP,THEO to generate the rest from rotational model
• Do some fitting with spectroscopic data only
OP,THEOgeneration of a starting point
From the GOSIA manual:• OP, THEO generates only the matrix specified
in the ME input and writes them to the (...) file.• For in-band or equal-K interband transitions
only one (moment) marked Q1 is relevant. For non-equal K values generally two moments with the projections equal to the sum and difference of K’s are required (Q1 and Q2), unless one of the K’s is zero, when again only Q1 is needed.
• For the K-forbidden transitions a three parameter Mikhailov formula is used.
OP,THEO for 88KrOP,THEO20,41,2,3,42,25,621,10.3,0,01,20.05,0,00,07 1,20.05,0,00,00
number of bands (2)First band, K and number of statesband member indicesSecond band, K and number of statesMultipolarity E2Bands 1 and 1 (in-band)Moment Q1 of the rotational band
Multipolarity M1
4
3
2
1
5
6
band 1 band 2
end of band-band input
end of multipolarities loop
Minimisation with OP,MINI
• Some minimisation would be in order but minimisation itself is a bit complex subject...
• Let’s assume we have some best possible Matrix Elements set.
• Next step is the integration over particle energy and angle.
Integration with OP,INTG
Few hints:• READ THE MANUAL, it is not easy!• Integration over angles: assume axial
symmetry if possible (suboption of EXPT)• Theta and energy meshpoints have to be
given manually, do it right or GOSIA will go astray!
Integration with OP,INTG
• Yield integration over energies: stopping power used to replace thickness with energy for integration:
• One has to find projectile energy Emin at the end of the target to know the energy range for integration.
dE
dxdEYYdx
thickness E
E 0
min
max
1
YIELD COUNT RATE
• GOSIA is aware of gamma detectors set-up• Gamma yield depends on detector angle (angular
distribution)• However, angular distributions are flattened by
detection geometry (both for particle and gamma )
• Gamma detector geometry is calculated at the initial stage (geometry correction factors are calculated and stored for yield calculation)
YIELD COUNT RATE
• One may try to reproduce gamma detector set-up of the intended experiment
• or assume the symmetry of the detection array and calculate everything with a virtual gamma detector covering 2 of the full space (huge radius, small distance to target)
YIELD COUNT RATE• Taking into account the solid angle,
Avogadro number, barns etc, beam current, total efficiency...
y2c code
Aeffppscurrentyield ][106.7 6
Count Rate =
yield count rate
target
Having the yields calculated...
• Kasia is going to show the way to estimate experimental errors of matrix elements to be measured:
GOSIA
spectroscopicdata
generatedyields GOSIA
matrix elementerrors estimate
“Saturation” of the yield