Chapter 5. Stray Magnetic Fields
36
Installation Planning Guide
01-999021-00 A0100
“TLVs [Threshold Limit Values] refer to static magnetic flux densities to which it is
believed that nearly all workers may be repeatedly exposed day after day without adverse
health effects. These values should be used as guides in the control of exposure to static
magnetic fields and should not be regarded as a fine line between safe and dangerous levels.
“Routine occupational exposures should not exceed 60 milliteslas (mT)—equivalent to 600
gauss—whole body or 600 mT (6000 gauss) to the extremities on a daily [8 hour], time-
weighted average basis. A flux density of 2 teslas (20,000 gauss) is recommended as a
ceiling value.”
5.2 Stray Field Plots
show stray field plots for 200, 300, and 400 systems,
respectively. The axial (vertical) and radial (horizontal) distances shown are measured in
meters from the magnet centerline (CL). The values are typical but may vary between
individual magnets. Gauss levels should be checked after a particular magnet has been
installed.
The magnet system stray field values in
were provided by Oxford technical
documentation.
Table 18. Stray Field Data for Oxford Magnets
Magnet Type
Radial Distance (cm)
Axial Distance (cm)
(MHz/mm)
0.6 kG
6 kG
20 kG
0.6 kG
6 kG
20 kG
Base to
CL (cm)
Magnet Outside
to CL (cm)
400/54 and long-
hold magnets
39
a
a
59
b
b
33.2
36.2
300/54 and long-
hold magnets
a
a
a
38
b
b
23.9
24.7
200/54 and long-
hold magnets
a
a
a
33
b
b
23.9
24.7
a. Where no radial position is given, the point is within the cryostat body.
b. The axial point is in the cryostat bore. Compare with magnet center line (CL) distance.
Table 19. Stray Field Data for NMR Magnet Systems
Magnet Systems
Axial Distance (m) from Magnet
Center Line
Radial Distance (m) from Magnet
Center Line
MHz/mm
Tesla
5-gauss
10-gauss
25-gauss
5-gauss
10-gauss
25-gauss
200/54
4.69
1.75
1.45
1.05
1.50
1.20
0.90
300/54
7.04
2.20
1.75
1.26
1.70
1.30
0.97
400/54
9.39
2.80
2.24
1.65
2.20
1.76
1.29