Section 39.55 - Tritium neutron generator target sources(a) Use of a tritium neutron generator target source, containing quantities not exceeding 1,110 GBg [30 curies] and in a well with a surface casing to protect fresh water aquifers, is subject to the requirements of this part except §§ 39.15 , 39.41 , and 39.77 .(b) Use of a tritium neutron generator target source, containing quantities exceeding 1,110 GBg [30 curies] or in a well without a surface casing to protect fresh water aquifers, is subject to the requirements of this part except § 39.41 . 68 FR 75390 , Dec. 31, 2003