Nov05-final.qxd 25/11/2005 12:40 PM Page 339 ARTICLE DE FOND ( EARLY DEVELOPMENT OF ... SNO ... ) EARLY DEVELOPMENT OF THE UNDERGROUND SNO LABORATORY IN CANADA by G.T. Ewan and W.F. Davidson Fundamental physics measurements can be made by many Inco VP, Wint Newman, our host, had set up a meeting with different techniques. In particle physics they usually involve the Sudbury Regional Council, i.e. all the local mayors, so expensive high-energy particle accelerators. In the late sev- that we could let them know about our proposed project enties interest grew in non-accelerator particle physics first hand, and through them, reach the local public. This which makes use of very low back- proved to be a seminal meeting. The mayors also learned ground laboratories built deep that we had been looking in Timmins underground. Some experiments had for an underground site, but realizing already been started deep under- Fundamental physics meas- the benefits that could accrue to ground - studies of high energy cos- urements can be made by Sudbury, unanimously approved that mic rays, solar neutrino measure- we should come to Creighton. ments, and searches for rare process- many different techniques. es such as proton decay and This was the first time we met EE-decay. In 1982, Los Alamos In the late seventies interest Tom Davies, the regional council National Laboratory hosted a work- grew in non-accelerator par- chairman, who became an enthusias- shop on Science Underground, tic supporter of the project as he was which reviewed experiments being ticle physics which makes very keen to diversify the interests of done underground and examined use of very low background the Sudbury region. To increase the possibility of building a National awareness and understanding of the Underground Science Facility laboratories built deep project we also met Doug Hallman (NUSF) in the USA [1]. In late underground. and other faculty at Laurentian 1982 Norman Ramsay (Harvard University, and David Pearson, the University) and in early 1983 director of the new science center, Ken Lande (University of Science North. Fig. 1 shows the Pennsylvania) gave colloquia at NRC, Ottawa and discussed authors of this article at the 7000 ft. level in 1983. the future trends in particle physics. Following these visits a small group led by George Ewan (Queen's University), In August 1983 NSERC asked that we present our prelimi- Walter Davidson (NRC) and Pierre Depommier (Université nary proposal to an expert review panel for consideration de Montréal) started to explore the possibility of developing alongside groups with fully developed proposals involving a deep underground laboratory in Canada for fundamental major collaboration in the OPAL experiment at the LEP col- physics research. A study of possible sites and a considera- lider at CERN and at the HERA experiment at the DESY lab- tion of potential experiments led to a proposal for a proton oratory in Hamburg. Our goal was to obtain funding in decay experiment in Inco's Creighton mine in Lively, near order to continue our feasibility study and develop a Sudbury. Other sites were considered but this was selected detailed proposal. The panel recommended that the two out- as the best available and Inco management was very cooper- of-country proposals be funded, and decided to turn down ative. In collaboration with Ken Lande, a preliminary pro- our request. We were disappointed at this rejection as posal was made to develop an experiment to search for Canada could have been a major player earlier in the fast nucleon decay using a liquid scintillator detector system. developing area of non-accelerator particle physics. We con- The project involved the construction of a large modular, tinued to explore the possibilities of non-accelerator experi- extremely pure liquid scintillation detector with a special ments in fundamental physics and the role that Canada high transparency mineral-oil-based scintillator. This was to could play if a world-class laboratory were built deep be located at the 4800 ft. level in Creighton mine. underground in a site such as that in the Creighton mine. We made several presentations to the scientific community We visited Sudbury with Ken Lande in early May 1983 to and found great interest in the possibilities. In 1984 explore the potential of Creighton Mine and to discuss with Ted Litherland reviewed the field at the CAP annual con- Inco management the possibility of doing an experiment in gress in Sherbrooke. Although not directly involved he was their mine. They already had a small research activity grow- enthusiastic about the type of physics that could be done. ing plants underground in association with Laurentian At that time there was already one experiment in Canada University. We had set up the visit with Inco beforehand in an underground laboratory: a small group led by and Inco staff was generous with their time. They took us down to the 6600 ft. level, the 7000 ft. level (to inspect the George T. Ewan <[email protected]>, Depart- crusher station), and the 4800 ft. level where they suggested ment of Physics, Queen's University, Kingston, Ontario; a site that might be suitable for the proton-decay experiment and Walter F. Davidson, National Research Council of and would not interfere with the operation of the mine. The Canada, Ottawa, Ontario LA PHYSIQUE AU CANADA novembre / décembre 2005 339 Nov05-final.qxd 25/11/2005 12:40 PM Page 340 FEATURE ARTICLE ( EARLY DEVELOPMENT OF ... SNO ... ) John Simpson, University of Guelph, pointed out that a very large heavy and including Barry Robertson, water (D20) detector (several kilo- Queen's University, was searching tonnes) would be excellent for for evidence of EE-decay in 76Ge in detecting solar neutrinos [3]. This an experiment located in a salt mine paper suggested the detection of near Windsor, Ontario. This required electron neutrinos by the Charged very low radioactive backgrounds Current (CC) reaction on deuterium and this group's expertise in deter- (Qe + d p + p + e-). Heavy water mining extremely low levels of had been used by other Irvine scien- radioactive contamination in materi- tists in experiments at LAMPF and als and in evaluating environmental Savannah River, but never in a very backgrounds was of great value in large detector. In a later paper, Chen the selection of materials used in the pointed out that all types of neutri- construction of the SNO detector and nos could also be observed by the in estimating background counting Neutral Current (NC) reaction [4]. rates in the proposed site. Detection of the neutral current reac- tion (Qx + d n + p + Qx) involved In January 1984 we presented our the measurement of the neutrons in ideas on a Canadian underground the SNO detector. Extremely low laboratory at an International backgrounds were essential for these Conference at Park City, Utah [2]. The experiments. Heavy water had pre- presentation created great interest in viously been suggested for neutrino the possibilities of the proposed site, detection [5], but availability and cost particularly since little progress was were a deterrent: a heavy water being made at that time in the USA detector had been used by to attract funding for a large under- T.L. Jenkins (Case Western Reserve ground facility [1]. As a result of the University) but it was too small and Park City conference, many scientists could only put an upper limit on the contacted us and several went to solar neutrino flux. Chen produced a Sudbury and were impressed with prototype design similar to that in the possibilities. In March 1984, Fig. 1 The authors at the 7000 ft. level in the the light water (H2O) detector being under the leadership of Al Mann, Creighton mine, May 1983. used at Kamioka, designed originally University of Pennsylvania, a small for proton decay experiments and group deeply involved in the U.S. proposal visited Ottawa later used for solar neutrino measurements. This design and Sudbury. A presentation in Ottawa summarized the required several kilotonnes of heavy water and he talked to great potential of science underground. In Sudbury our visi- Cliff Hargrove, with whom he had previously collaborated tors were impressed with the potential of the proposed site at LAMPF (Los Alamos), to explore the possibility of using in Creighton mine. Inco's positive attitude and their enthusi- heavy water on loan from Canada's reserve for its CANDU astic readiness to host an experiment were extremely help- reactor program. Preliminary discussions with Geoff Hanna ful in convincing potential collaborators of the viability of and Ara Mooradian of AECL indicated that, under appro- an underground science laboratory in Canada. As a result of priate conditions, it might be possible to borrow 1000 tonnes the increased interest we were invited to collaborate in of heavy water (value ~ $300M), provided it was returned preparing proposals for several experiments both in Canada in the same condition as when supplied, and for a limited and abroad. One of the visiting scientists was Herb Chen time until it was required for installation in a new nuclear (University of California at Irvine), whose group was work- power reactor. The availability of such a large quantity of ing on a 7 kilotonne liquid argon time projection chamber heavy water was unique to Canada. As a result, we had a for use in solar neutrino studies and proton decay experi- meeting at the NRC in Ottawa in September 1984, at which ments. Later, as discussed below, he would suggest the it was decided that, since there was a possibility of obtain- heavy water solar neutrino detector, which led to the forma- ing heavy water on loan, we would proceed with a feasibili- tion of the SNO collaboration.