Strategic Research at Los Alamos Rajan Gupta and David E. Watkins os Alamos National Laboratory from a broad base of scientific expert- The fullest utilization by the Army of is a scientific institution whose ise and develop effective responses in a the civilian resources of the nation Lprimary mission is to be a timely fashion. cannot be procured by prescribing the steward of the nation’s nuclear deter- Unlike many research environ- military characteristics and require- rent. In a broader context, the ments, ours must balance the freedom ments of certain types of equipment. Laboratory’s mission is to preserve to explore new ideas with a strong Scientists and industrialists are more the security and safety of the United communal commitment to meeting likely to make new and unsuspected States against present and future national security challenges and to contributions to the development of threats. To anticipate future threats making sacrifices when necessary. the Army if detailed directions are and develop the necessary ideas and This balance requires the presence of held to a minimum . .” This kind of technologies to detect, foil, and miti- scientific leaders who can inspire oth- thinking is reflected again in the gate possible attacks, we must be ers to contribute innovative ideas and Atomic Energy Act of 1954: “The working at the cutting edge of who can lead the integration of those commission is directed to exercise its research in many branches of engi- ideas into practical solutions. Not only powers in such manner as to insure the neering and science, and we must must we divide our efforts between continued conduct of research and simultaneously integrate a wide range basic research and applied research development and training activities in of research advances from academia and development activities, but we the fields specified . .” and industry. must also recognize and seek out syn- Currently, within the Department The long-term success of any scien- ergistic research opportunities in of Energy (DOE) structure, the tific organization is tied to its ability to which progress in one field yields Laboratory-Directed Research and recruit and retain exceptional people greater understanding in another. Development (LDRD) program pro- and to foster collaboration and mean- Finally, there must be a deep recogni- vides resources for discretionary ingful relationships with the finest tion that the evolution of ideas is research. Although this particular for- institutions worldwide. In addition, at rarely predictable and that the Lab mal structure is young compared with Los Alamos and other mission-oriented must position itself to encourage the the 60-year history of the Lab, the ori- laboratories, an environment must be creation and exploitation of new ideas gins of the program go back to the maintained in which the creativity of to meet future challenges. beginning of the weapons program. the staff is readily tapped in order to After World War II, key decision Indeed, some have argued that the ini- implement those missions. Sustaining makers recognized the value of pro- tial work on spherical implosion rep- that kind of environment is a formidable viding scientific organizations with the resents the first LDRD-like effort at task. It has been made more complicated flexibility necessary to pursue innova- Los Alamos. In late April 1943, Seth because emerging threats—global ter- tive ideas. While serving as Army Neddermeyer proposed that a three- rorism, nuclear proliferation, poverty, chief of staff, General Eisenhower dimensional implosion would be a disease, diminishing fossil-fuel and wrote, “Scientists and industrialists potentially more effective means of water resources, stressed ecosystems— must be given the greatest possible assembling a supercritical mass than require that the Laboratory respond freedom to carry out their research. the one-dimensional “gun assembly,” 200 Los Alamos Science Number 28 2003 Strategic Research at Los Alamos which was the baseline design con- cept. Neddermeyer’s concept was ini- tially considered unnecessary and Resolving the Solar Neutrino Problem outside the mainstream of work. Andrew Hime Although the spontaneous rate of plutonium-239 fission is twice that of Since the seminal discovery of the neutrino by Los Alamos researchers Clyde uranium-235, the difference did not Cowan and Fred Reines in the late 1950s, there has been a continuous effort appear to warrant a different design. by Laboratory scientists to study neutrinos and their interactions. Central to Nevertheless, Oppenheimer decided that study is the question of whether the different neutrino flavors—electron, to fund the work on spherical implo- muon, and tau—have mass, a question that has been answered decisively sion to keep the option open. It was with recent data from the Sudbury Neutrino Observatory (SNO). not until the data came in on the reactor-produced plutonium, which SNO was built to resolve the long-standing solar neutrino problem, wherein contained enough plutonium-240 to the measured flux of solar neutrinos reaching Earth is significantly lower than significantly increase the spontaneous predicted. But all previous experiments had been sensitive to only electron neutrinos. Whereas those are the only fission rate, that the work on spherical neutrinos that can be created by the (a) implosion carried out by nuclear fusion reactions powering the Neddermeyer and Kistiakowsky was Sun, the other flavors can be “produced” recognized as essential. Today, the if neutrinos have mass. Through the flexibility afforded through the LDRD process of flavor mixing, massive elec- program continues to provide the tron neutrinos from the Sun can “trans- nation with science and technology form” into muon and tau neutrinos as critical to our defense and security. they travel to Earth. This process would The synergy between the nuclear explain why the measured solar electron weapons program and basic science is neutrino flux is lower than predicted by exemplified by the work of Nobel the standard solar model. Laureate Fred Reines. During the war, A multinational decade-long effort, SNO Reines worked on many different was designed to detect all neutrino aspects of nuclear weapons design. (b) 8 flavors. Los Alamos was involved in SNO SNO ) φ φ After the war, he became an expert on ES CC all aspects of the project, including –1 7 s nuclear weapons effects and played a detector construction, commissioning, –2 6 cm lead role in nuclear weapons testing. simulation, and calibration, as well as 6 5 SNO SSM (10 φ Toward 1948, Reines wanted to return data analysis and scientific manage- 4 φ τ NC NC ment. The primary detector contains ν , to basic science. Carson Mark, his µ 3 division director actively encouraged 1000 tonnes of ultrapure heavy water ν 2 this transition and gave Reines the in a large “bottle,” shown in (a). The 1 freedom to “sit and think.” This he did deuterium in the water can interact Flux of with high-energy electron neutrinos 0 for almost a year, during which time 031 2564 through charged-current (CC) weak Flux of ν (106 cm–2 s –1) he decided to search for the elusive e ν → – interactions and with all neutrino fla- CC: e + d p + p + e – 1.44 MeV neutrino, a neutral particle with little ν → ν vors through neutral-current (NC) NC: x + d p + n + x – 2.22 MeV ν – → ν – or no mass, whose existence was pos- weak interactions. All neutrino fla- ES: x + e x + e tulated on the basis of the fundamen- vors also undergo elastic scattering tal principle of energy conservation. If (ES) with electrons, but the reaction is sensitive mostly to electron neutrinos. theory was correct, this particle By enabling a direct comparison of the CC, NC, and ES reaction rates, SNO should be produced in copious quanti- could determine if the neutrinos from the Sun are a mix of electron, muon, ties during a nuclear explosion. and tau neutrinos. As seen in (b), the best fit to the data (dotted circles are Under the nurturing eye of Carson confidence limits) indicates that two-thirds of the electron neutrinos born in Φ SSM Mark, Fred pulled together his vast the Sun transform into muon and/or tau neutrinos. ( NC is the NC flux pre- dicted by the standard solar model.) Together with data from other experi- experience with detection of different ments, these results demonstrate that flavor mixing almost certainly resolves forms of radiation, his abilities to do the solar neutrino problem and that neutrinos have mass. Moreover, the total big science, and the technical capabil- flux of neutrinos measured at SNO agrees with predictions and our basic ities of Los Alamos to build a detector knowledge of how the Sun shines. Continued on page 204 Number 28 2003 Los Alamos Science 201 Strategic Research at Los Alamos A New Source of Ultracold Neutrons Chen-Yu Liu, Steve K. Lamoreaux, Thomas J. Bowles, and Christopher Morris A neutron will normally diffuse right through materials We have recently conducted experiments to under- such as steel or lead, but if the neutron’s energy is stand and characterize the performance of solid deu- exceedingly low, it will instead be reflected by those terium as a so-called superthermal UCN source. As (or other) materials. We can now produce neutrons with seen in graphic (a), a pulse of high-energy protons kinetic energies less than about 300 nano–electron from the Los Alamos Neutron Science Center is volts. When placed in a “bottle” directed to a tungsten target that of the right material, these ultra- (a) sits inside a liquid nitrogen dewar. cold neutrons (UCNs) become B Valves A High-energy spallation neutrons trapped, enabling us to collect exit the target, lose most of their them and to make a high-density To experiment energy in a layer of polyethylene, UCN source.