RHIC Experiment Shielding Working Group Status Report

Minutes and presentations are kept at :

http://www.c-ad.bnl.gov/kinyip/Radiation/RHIC_Shielding.html

Kin Yip

May 14, 2003

p

0.01 FS

5 additional ft of concrete

5 additional ft of concrete

0.2 FF p

1.2FB

5 ft concrete

p

FS

FB

FF

cylindrical tunnel

Fluxes &

shielding

p @ 100 GeV

Sources of the background: PHENIX, STAR and BRAHMS all have evidence to believe that their backgrounds are due to beam scraping at the magnet triplets (Q2 or Q3), rather than beam gas. 

PHENIX has not had background problem until the beams are steered into collision. 

For BRAHMS, changing the  * from 2 to 3 during the d+Au run decreased their backgound by a factor of 10 to 20. 

PHOBOS also did not have background problem when the * was set to 3 and their background seems to be strongly correlated to the beam gas pressure increase.

PHENIX and PHOBOS (at least) have seen backgrounds considerably more on the outside of the ring during the deuteron-gold runs.

Simulation aspects:

Tool: MCNPX (newest version 2.5.c)

Sources: protons (100 GeV) scraping the inner radii of Q2/Q3 magnets

Only turned on protons/neutrons at the moment

Major problem (!): MCNPX does NOT have magnetic field.

Plan to learn/use MARS for a more complete/realistic simulation but this probably will take some time …

Gap 3Gap 4

Shield at DX

beam direction

vertical

Shield at D0

beam direction

vertical

Cross-sectional view

platform

The rest of the blocks are shields.

100 cm

Ver

tica

l

(cm

)

Horizontal (cm)

Mesh Tallies in MCNPX (2.5.c) without shielding

beam direction

vertical

One split into halfGap 4

Gap 3

Cross-sectional viewshields closer to the beampipe

65 cm

Platform

What we have done/learnt …

Flux (Gap 3) ~ 0.5-0.6 Flux (Gap 4)

Energy cuts change the absolute fluxes/energy deposition but doesn’t change the ratios

different physics models tried

Source at Q2 ~ source at Q3

For the same length of concrete (5ft), shielding effect :

closer to beampipe > DX > D0 > Q2

Source from Q3

Flux

(cm-2)

Energy Deposition (MeV/g)

Flux

(cm-2)

Energy Deposition (MeV/g)

No shield F E F' E'

DX 0.24 F 0.21 E 0.23 F' 0.21 E'

D0 0.47 F 0.50 E 0.49 F' 0.52 E'

Split 0.18 F 0.15 E 0.17 F' 0.16 E'

Gap 4 (closer to magnets) Gap 3

Conclusion ?

Without magnetic field, we probably can’t really predict for sure how good our shielding will be

Nevertheless, we have some idea where it may be better to put the shielding (eg. closer to the beampipe)

We may go to have a close inspection in the tunnel to see where we could put any kind of shielding at all as close to the beampiple as possible