lest.ing underground and therefore has not curbed the qualiEaEive inProvement of nuclear reapons. In 1974, the soviet Unton and the united SEates reached agreenent on a Thresbolit Test Ban Treaty Ehat reatricBs underground explosions at nuclear test sites to an exPlosive yieLtl belos 150 kilotons. In 19?6r the Peaceful NuclearA/40/553 Eng lish Page 43 Explosions Treaty placed a sinilar restriction on explosions at locations otherthan test siles. while neither of bhese Ereaties has yet been ratified, thesighatories have indj.cated their intentions of abiding by their terns. 157. Proposars for a conprehensive test ban have been discussed in a varieEy ofnultilateral and bilateral foruns for nore than two decades, with considerableprqtresa but, so far, no final result, Among the facEors a! issue, according tocerEain states, have been the guestion of verification. conpliance with a tocal banand tbe argumeht that sone testing is necessary to naintain confidence in thereliabil-ity of existing nuclear stockpires. oehers considered Ehat such argunentsuere only attenpts Eo avoid the formulation and conclusion of a comprehensive testban t.reaty' since they considered that no such technical obstacles exist, 158. Even uith t.he exigtence of a comprehengive nuclear-tesE ban, nuclear weaponsnight 6t.iII be built. but the confidence in untested weapon5 tould necessarily below. The sane eould gradually apply Co tbe reliability of stockpiles of oldertested types of rdeapons, At tbe sane Eine. a prohibltion on future tests wouldretard the nuclear prograt tes of Ebe existing nuclear States by effecbivelylittiting qualitative inprovenents resulCing from new designs for rrarheads. AcomPrehenslve teaE ban uight thus herp restraln both horizonlal and vert.icalproliferation of nuclear $eapons.
**Analysis**
The text discusses the issue of nuclear weapons testing and the implications of a comprehensive test ban treaty. It highlights the challenges in achieving such a treaty, including the verification of compliance and the argument that some testing is necessary to maintain confidence in the reliability of existing nuclear stockpiles. The text also mentions the potential impact of a comprehensive test ban on the development of new nuclear weapons. Given the focus on nuclear weapons and their testing, it seems likely that the text is related to the field of science and technology.

**Category**
Science and technology