Integrated yields
From GOSIA
for
Integrated yields
Jump to:
navigation
,
search
==The meaning of Gosia's YIELD output== Gosia calculates the complete excitation and decay process using OP,INTI (or OP,INTG) including all feeding, internal conversion branches and angular distributions. These calculations are referred to as ''integrations'' below. The p-<math>\gamma</math> angular distribution is integrated over the target thickness and the Ge solid angles, but the resulting "YIELD" is quoted in units of <math>mb (mg/cm^2) / sr</math>, where sr represents the solid angle subtended by the Ge. This leads to some common misunderstandings. The quoted yields represent the absolute cross sections for the chosen particle scattered into the solid angle of the particle detector and the <math>\gamma</math>-ray emitted into the solid angle of the Ge crystal or array, whichever is defined by the user. The reason for the confusion is usually the units of the YIELD output and two factors—the target thickness and the Ge solid angle—that often must be applied after the integration. After an integration, the cross section in mb is obtained by multiplying the yield by the Ge solid angle in <math>sr</math> and dividing by the target thickness in <math>mg/cm^2</math>. You can also calculate the absolute p-gamma counts expected using the equation following equation 6.44b in the manual: Detected p-gamma coincident events <math>N_i = 10^(-30) [Q / qe] [N_A / A] Y(I_i-->I_f) \epsilon_p \epsilon_\gamma \Delta \Omega_\gamma</math> If the absolute efficiency is known well, then it is possible to retrieve the actual counts measured in the photopeak by putting the efficiency into this equation. In the equation above the <math>epsilon_gamma</math> is the absolute efficiency as a fraction between 0 and 1 (not including angular effects already integrated in the "yield"). Let this be called the absolute photopeak efficiency. The <math>\Delta\Omega_gamma</math> term is the solid angle of the Ge detector. A typical absolute photopeak efficiency <math>\epsilon_\gamma<\math> is 10--15%. If the solid angle subtended by the crystal is ~0.1 sr, then for one crystal <math>\epsilon_\gamma \Delta\Omega_\gamma ~ 0.01<\math>. If the laboratory setup and the EM matrix are accurately represented in the Gosia input, then the absolute counts can be obtained: <pre> N <\pre> Refer to the page on the [particle_singles], which is a cross section given in the same output with the integrated yields. Maybe the answer to your last question is obvious now, but... I would not try to think of this as correcting for 4pi, since the gamma-ray angular distribution has to be calculated as a function of theta, phi for 4pi in order to make that correction. If you really want Gosia to tell you what the total yield would be for a 4pi array, you can change the *.gdt file entries after running OP,GDET. For Gammasphere the *.gdt file would look something like <pre> 1 25.0 5.000E-02 0. 0. 0.9951 0. 0. 0.9854 0. 0. 0.9711 0. 0. 0.9521 0. 0. 0.9379 0. 0. 0.9013 0. 0. 0.8699 0. 0. 0.8349 </pre> where the first two columns have been set to 0. to simulate a 4pi array--no angular attenuation. Then you would have in the YIELD column of the output the p-gamma events where the particle hit the detector as you defined it and the gamma ray is measured at all angles. In this case the epsilon_gamma would still be the absolute photopeak efficiency, but DeltaOmega_gamma would be 4*pi. See pages 48 and 117 in the newest manual version, if you want to do this. You should be able to figure out that the first two entries in the file above should be zero to represent a perfect 4pi array. I hope that is all clear. I can't ever figure out a brief way to explain things. Maybe after you figure this out, you can put it on the Wiki. Your questions come up often.
Return to
Integrated yields
.
Views
Page
Discussion
View source
History
Personal tools
Log in
Navigation
Main page
Community portal
Current events
Recent changes
Random page
Help
Search
Toolbox
What links here
Related changes
Special pages