Integrated yields
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Integrated yields
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==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. 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>. This leads to a common misunderstanding--that Gosia does almost everything. The reason for the confusion is in the units and two factors--the target thickness and the Ge solid angle--that must be applied after the integration. The "yield" from gosia is in mb(mg/cm^2)/sr, where sr represents the solid angle of the Ge. In the case of a raw detector, it should be the total solid angle of all crystals in the raw cluster. So, after an OP,INTG or OP,INTI calculation, the cross section in mb is obtained by multiplying the yield by the Ge solid angle in sr and dividing by the target thickness in mg/cm^2. You can also check the absolute p-gamma counts expected using equation after 6.44b in the most recent manual version: Detected p-gamma coincident events Ni = 10^(-30)[Q/qe][N_A/A] Y(I-->I_f) epsilon_p epsilon_gamma DeltaOmega_gamma If your absolute efficiency is known well, then you should be able to retrieve the actual counts in the peak, since you are putting the efficiency into the equation. In the equation above and your equation (1), the epsilon_gamma is the absolute efficiency as a fraction between 0 and 1 (not including angular effects already integrated in the "yield"). I think this is properly called the intrinsic efficiency, but I always worry that people understand the terms differently. I would call it the absolute photopeak efficiency, not efficiency per unit solid angle, because the solid angle is in the yield term and Delta_Omega. The DeltaOmega_gamma is the solid angle of the crystal or cluster. I would expect your efficiency epsilon_gamma to be 10--15%. If you have about 0.1 sr solid angle subtended by a crystal, then for one crystal epsilon_gamma * DeltaOmega_gamma ~ 0.01, and for a cluster of 4 ~0.04. So you can see if the numbers match what you fit in the energy spectrum. The answer to your first question, is the factor N_gamma_p only the sum below the photo-peak, is yes, as long as you are using the photopeak efficiency as I mentioned above. You definitely don't need any other corrections for the cascade in Gosia's "yield." About the "singles," they are the latter: the total number of particles hitting the detector. Gosia should reproduce this number using the "integrated rutherford cross section," which probably shouldn't be called "Rutherford," because it includes all the inelastic events. For the scattering kinematics, Gosia assumes that the Q-value is the energy of the first excited state--state #2 in LEVE. You can change this using the CONT option NCM, if you think that the probability of that state is <<1, for example. In that case, you might pick the ground state. If you put OP,STAR OP,EXIT in place of OP,YIEL, you can quickly see the probabilities of all states in the excitation. 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.
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