Question: Who was the director of the lab that designed bombs for the project that used mass spectrometers to separate isotopes of uranium?

Context paragraphs:
Molecular laser isotope separation: Molecular laser isotope separation (MLIS) is a method of isotope separation, where specially tuned lasers are used to separate isotopes of uranium using selective ionization of hyperfine transitions of uranium hexafluoride molecules.  It is similar to AVLIS.  Its main advantage over AVLIS is low energy consumption and use of uranium hexafluoride instead of vaporized uranium.

Mass-independent fractionation: Mass-independent isotope fractionation or Non-mass-dependent fractionation (NMD), refers to any chemical or physical process that acts to separate isotopes, where the amount of separation does not scale in proportion with the difference in the masses of the isotopes.  Most isotopic fractionations (including typical kinetic fractionations and equilibrium fractionations) are caused by the effects of the mass of an isotope on atomic or molecular velocities, diffusivities or bond strengths.  Mass-independent fractionation processes are less common, occurring mainly in photochemical and spin-forbidden reactions.  Observation of mass-independently fractionated materials can therefore be used to trace these types of reactions in nature and in laboratory experiments.

Selected ion monitoring: Selected ion monitoring (SIM) is a mass spectrometry scanning mode in which only a limited mass-to-charge ratio range is transmitted/detected by the instrument, as opposed to the full spectrum range.  This mode of operation typically results in significantly increased sensitivity.  Due to their inherent nature, this technique is most effective—and therefore most common—on quadrupole mass spectrometers and Fourier transform ion cyclotron resonance mass spectrometers.

Elementar: Elementar is a German multinational manufacturer of elemental analyzers and isotope ratio mass spectrometers for the analysis of non-metallic elements like carbon, nitrogen, sulphur, hydrogen, oxygen or chlorine.  The company emerged from Heraeus, a multinational German engineering company that produced analytical instrumentation.  Elemental analyzers and isotope ratio mass spectrometers are used in the fields of analytical and environmental chemistry to measure the elemental and isotopic composition of diverse materials like chemicals, pharmaceuticals, fuels, food, water, plants, soil or waste.

History of mass spectrometry: The history of mass spectrometry has its roots in physical and chemical studies regarding the nature of matter.  The study of gas discharges in the mid 19th century led to the discovery of anode and cathode rays, which turned out to be positive ions and electrons. Improved capabilities in the separation of these positive ions enabled the discovery of stable isotopes of the elements.  The first such discovery was with the element neon, which was shown by mass spectrometry to have at least two stable isotopes: Ne (neon with 10 protons and 10 neutrons) and Ne (neon with 10 protons and 12 neutrons).  Mass spectrometers were used in the Manhattan Project for the separation of isotopes of uranium necessary to create the atomic bomb.

Bradbury–Nielsen shutter: A Bradbury–Nielsen shutter (or Bradbury–Nielsen gate) is a type of electrical ion gate, which was first proposed in an article by Norris Bradbury and Russel A. Nielsen, where they used it as an electron filter.  Today they are used in the field of mass spectrometry where they are used in both TOF mass spectrometers and in ion mobility spectrometers

Manhattan Project: The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons.  It was led by the United States with the support of the United Kingdom and Canada.  From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers.  Nuclear physicist Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs.  The Army component of the project was designated the Manhattan District; "Manhattan" gradually superseded the official codename, Development of Substitute Materials, for the entire project.  Along the way, the project absorbed its earlier British counterpart, Tube Alloys.  The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US $2 billion (about $ in 2016 dollars).  Over 90% of the cost was for building factories and to produce fissile material, with less than 10% for development and production of the weapons.  Research and production took place at more than 30 sites across the United States, the United Kingdom, and Canada.

Wilhelm Walcher: Wilhelm Walcher (7 July 1910 in Kaufbeuren – 9 November 2005 in Marburg) was a German experimental physicist.  During World War II, he worked on the German nuclear energy project, also known as the Uranium Club; he worked on mass spectrometers for isotope separation.  After the war, he was director of the Institute of Physics at the University of Marburg.  He was a president of the German Physical Society and a vice president of the German Research Foundation.  He helped found the Society for Heavy Ion Research and the German Electron Synchrotron DESY.  He was also one of the 18 signatories of the Göttingen Manifest.

Time-resolved mass spectrometry: Time-resolved mass spectrometry (TRMS) is a strategy in analytical chemistry that uses mass spectrometry platform to collect data with temporal resolution.  Implementation of TRMS builds on the ability of mass spectrometers to process ions within sub-second duty cycles.  It often requires the use of customized experimental setups.  However, they can normally incorporate commercial mass spectrometers.  As a concept in analytical chemistry TRMS encompasses instrumental developments (e.g. interfaces, ion sources, mass analyzers), methodological developments, and applications.

Sibyl M. Rock: Sibyl Martha Rock (August 1, 1909 – November 17, 1981) was a pioneer in mass spectrometry and computing.  Rock was a key person in Consolidated Engineering Corporation's (CEC) mass spectrometry team at a time when mass spectrometers were first being commercialized for use by researchers and scientists.  Rock was instrumental in developing mathematical techniques for analyzing the results from mass spectrometers, in developing an analog computer with Clifford Berry for analysis of equations, and in sustaining an ongoing dialog between engineers and customers involved in development of both the mass spectrometer and an early digital computer, CEC's Datatron.

Supporting paragraphs: History of mass spectrometry Manhattan Project
Answer: Robert Oppenheimer