Radiation Protection In Veterinary Medicine - Recommended Safety Procedures For Installation And Use Of Veterinary X-ray Equipment - Safety Code 28

Appendix II (Continued)- Shielding Guides for Veterinary X-Ray Facilities

To determine the shielding necessary for a veterinary X-ray facility, certain preliminary information is essential. In many instances the thickness of lead or concrete required to reduce radiation levels to the maximum permissible level can be determined directly from Tables 1 and 2 of this Appendix. In other cases, contact the appropriate agency to enquire about shielding requirements and calculations. In both instances answers to the following questions are required.

1. What is the distance between the nearest point of the area to be shielded and the usual operational position of the X-ray tube?
2. Is the area to be designated as a controlled or uncontrolled area? (The area occupied by radiation workers is subject to the limit of mSv per year, whereas areas occupied by non-radiation workers are subject to the limit of 1 mSv per year.)
3. Will the intervening shield between the X-ray tube and the occupied area act as a primary or as a secondary protective barrier, i.e. will the barrier be required to attenuate the direct X-ray beam or stray radiation only?
4. What will be the anticipated maximum workload of the X-ray unit? (The workload indicates the operational time of an X-ray machine expressed in terms of milliampere-seconds per week.)
5. What will be the nominal and average X-ray tube voltages?

Table 1. Primary Protective Barrier Requirements for 17.5 µGy (2 mR) per Week (Ucontrolled Area)

The tabulated values give the minimum amount of lead or concrete shielding required to reduce the exposure in uncontrolled areas to 17.5 µGy (2 mR) in one week. These thicknesses of shielding are for a single source of radiation. If more than one source irradiates the location of interest, the contribution from each source must be taken into account in determining the amount of shielding required. Planned and existing structural materials should be fully considered when calculating a barrier requirement.

The thicknesses of lead and concrete required have been rounded off to the next highest 0.05 mm and 0.5 cm respectively.

Note: lead sheet is commercially available only in discrete thicknesses given in Table 3.

Table 1. A. Lead

X-ray tube voltage kVp	Effective workload mA-sec/week	mm of lead required at a source distance of
		1m	2m	3m	4m	5m	8m
70	500	0.75	0.50	0.40	0.30	0.25	0.20
	250	0.65	0.40	0.30	0.25	0.20	0.15
	100	0.50	0.30	0.20	0.15	0.15	0.10
	50	0.40	0.20	0.15	0.10	0.10	0.05
	25	0.30	0.15	0.10	0.10	0.10
	10	0.20	0.10	0.10	0.05
	5	0.15	0.10	0.05
100	500	1.90	1.35	1.05	0.85	0.75	0.45
	250	1.60	1.10	0.85	0.65	0.55	0.30
	100	1.30	0.80	0.55	0.40	0.30	0.20
	50	1.05	0.60	0.40	0.30	0.20	0.10
	25	0.80	0.40	0.25	0.20	0.15	0.05
	10	0.55	0.25	0.15	0.10	0.05
	5	0.35	0.15	0.10	0.05
125	500	2.30	1.70	1.40	1.20	1.05	0.70
	250	2.00	1.45	1.15	0.95	0.80	0.50
	100	1.60	1.10	0.85	0.65	0.50	0.30
	50	1.35	0.85	0.60	.045	0.35	0.20
	25	1.10	0.65	0.40	0.30	0.20	0.10
	10	0.80	0.40	0.20	0.15	0.10
	5	0.60	0.25	0.15	0.10	0.05
150	500	2.60	2.00	1.70	1.45	1.30	0.95
	250	2.30	1.75	1.40	1.20	1.05	0.75
	100	1.90	1.35	1.10	0.90	0.75	0.45
	50	1.65	1.10	0.85	0.65	0.55	0.30
	25	1.35	0.90	0.60	0.45	0.35	0.15
	10	1.05	0.60	0.35	0.25	0.15	0.05
	5	0.80	0.40	0.20	0.15	0.10

Table 1. B. Concrete

X-ray tube voltage kVp	Effective workload mA-sec/week	cm of concrete required at a source distance of
		1m	2m	3m	4m	5m	8m
70	500	8.5	6.5	5.0	4.5	3.5	2.5
	250	7.5	5.5	4.0	3.5	3.0	1.5
	100	6.0	4.0	3.0	2.0	1.5	1.0
	50	5.0	3.0	2.0	1.5	1.0	0.5
	25	4.0	2.0	1.5	1.0	0.5
	10	3.0	1.0	0.5	0.5
	5	2.0	1.0	0.5
100	500	15.0	11.5	10.0	9.0	7.5	5.5
	250	13.0	10.0	8.0	7.0	6.0	4.0
	100	11.0	8.0	6.0	5.0	4.0	2.0
	50	9.5	6.5	4.5	3.5	2.5	1.0
	25	8.0	5.0	3.5	2.0	1.5	1.0
	10	6.0	3.0	1.5	1.0	0.5
	5	4.5	2.0	1.0	0.5
125	500	19.0	15.0	12.5	11.0	10.0	7.5
	250	17.0	13.0	11.0	9.0	8.0	5.5
	100	14.5	10.5	8.5	7.0	5.5	3.5
	50	12.5	8.5	6.5	5.0	4.0	2.0
	25	10.5	7.0	5.0	3.5	2.5	1.0
	10	8.0	4.5	3.0	1.5	1.0
	5	6.5	3.0	1.5	0.5	0.5
150	500	23.0	18.5	16.0	14.0	12.5	9.5
	250	20.5	16.0	13.5	12.0	10.5	7.5
	100	18.0	13.0	11.0	9.0	7.5	4.5
	50	15.5	11.0	8.5	7.0	5.5	2.5
	25	13.0	9.0	6.5	4.5	3.0	1.5
	10	10.5	6.5	3.5	2.5	1.5	0.5
	5	8.5	4.0	2.0	1.0	0.5