I have a question regarding an error output by Rachel when calculating simulated yields for the inverse kinematics Coulomb excitation of a 36Ar projectile on a 28Si target.

I have set up the calculation to integrate theta meshpoints (with endpoints defined by my particle detector's angular extent) between 10 and 30 degrees in the laboratory frame. From a kinematics spreadsheet calculator, I know that the maximum projectile scattering angle for this experiment at the “safe Coulex” energy is about 48.5 degrees in the laboratory frame (corresponding to a target recoil scattering angle of about 20 degrees). Thus, since in this inverse kinematics experiment the detector range spans the maximum scattering angle, I have input the target as the detected particle.

I've calculated the simulated yields for the logical experiments below (note that I've slowly decreased the minimum scattering angle to illustrate my soon-to-be-defined problem):

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# 1 2 3 4 5 6

theta_min 15.0 21.0 17.0 15.0 13.0 11.0

theta_max 42.0 30.0 30.0 30.0 30.0 30.0

phi_min 0.0 0.0 0.0 0.0 0.0 0.0

phi_max 360.0 360.0 360.0 360.0 360.0 360.0

un-inv. Z 14 14 14 14 14 14

un-inv. A 28 28 28 28 28 28

Ebeam 63.0 63.0 63.0 63.0 63.0 63.0

Safe energy 64 64 64 64 64 64

Tgt. thickness [mg/cm^2] 0.6 0.6 0.6 0.6 0.6 0.6

Detected t t t t t t

Inverse kin. True True True True True True

Kinematic solution -- -- -- -- -- --

Norm to expt # 1 2 3 4 5 6

Somm. param. 33.0 33.0 33.0 33.0 33.0 33.0

# of Ge detectors 1 1 1 1 1 1

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I noticed that even though all of the theta_min and theta_max ranges for scattered target nuclei span the kinematics solution corresponding to the maximum projectile scattering angle (except Experiment 2), I only get the following error for Experiment 6:

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Gosia reported an error:

ERROR- MAXIMUM SCATTERING ANGLE IS 48.00 DEGREES FOR EXPERIMENT 6

********* END OF EXECUTION **********

---------------------------Error----------------------------

You have exceeded the maximum beam scattering angle

(calculated inelastically) for this experiment. There are

two ways that you might fix this problem: (1) Define the

experiment(s) so that the target particle is detected in the

case of inverse kinematics, or (2) Set the state for

calculation of the scattering kinematics to the ground state

using the Gosia Controls button, option k.

Done.

Fri Sep 30 13:11:01 PDT 2011 ...

Processing cannot continue properly due to the error above.

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I get this error for the same experiment (11deg<theta_lab<30deg) even if I shuffle their order, so it's not tied to the last experiment listed.

If I understand correctly, I have properly defined the experiments such that “the target particle is detected in the case of inverse kinematics” and therefore I shouldn't get this error? Or perhaps I am making a silly mistake. Either way, a hint would be helpful so I know whether I can put faith in my calculations or not.

Many thanks and cheers,

Phil