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RADIATION FROM MUONS AT RHIC
Brookhaven National Laboratory
Upton, New York 11973
Possible effects on both personnel and the environment from radiation resulting
from beam loss at RHIC have been previously evaluated"2',3 and found to be well below
DOE guideliness. The only radiation source which was not considered in these
evaluations are muons which can, in principle, penetrate considerable distances in
accelerator shielding materials. In the proposed ISABELLE accelerator for example,
calculations showed that a 0.1% beam loss in certain locations would result in radiation
levels at the site boundary which approached or exceeded the 5 mRem/year limit.4)
However, the muon shielding surrounding the RHIC tunnel was designed for
ISABELLE which would have had an annual accelerated energy greater than 10 times
that of RHIC and a significantly greater maximum energy per nucleon (400 GeV
contrasted with RHIC protons at 250 GeV). A priori we therefore anticipate a negligible
problem from muons in RHIC. The calculations presented here validate this expectation.
Method And Geometry Of Calculation
Muon dose was calculated using a version of the hadronic cascade Monte Carlo
program CASIM(5'6) modified to calculate energy deposition from muons resulting from
three sources: (1) pion decay, (2) kaon decay, and (3) direct production. The energy loss
mechanism of muons in matter is discussed elsewhere.7 Measurements of muon flux
exterior to the earth shielding at FNAL have been made and found to agree with CASIM
predictions to better than a factor of 2.(8)
The earth shielding around the RHIC tunnel, including muon "lobes" which reach
their maximum radial extension at the center of each arc, is shown in Fig. 1. CASIM
calculates energy deposition from muons in finite bins. Figure 2 shows the
approximation made of the RHIC tunnel and the radial bins used in the calculation made
here. The bin sizes are 2.5 m (radial) by 0.5 m (vertical) by -8.5 m (beam direction). The
number of bins in the radial direction varies from 10 at the entrance to the "regular
lattice" to 35 at the midpoint of the arc. As shown in Fig. 2, the tunnel radius is taken as
2.5 m, the "expanded" tunnel section being ignored. Further approximations adopted in
describing the magnet lattice are described in Appendix A.
Three locations have been considered as sources of beam interactions: (a) the
crossing point, (b) a point on the vacuum pipe 20.5 meters upstream of the entrance to
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J., Stevens A. & Foelsche, H. Radiation From Muons At RHIC, report, October 5, 1988; United States. (digital.library.unt.edu/ark:/67531/metadc872116/m1/2/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.