Question: What element was used during the Manhattan Project's second line process?
About the article "Manhattan Project", section "Plutonium".

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Current plans for the Second Avenue Subway provide for the Q to be extended northward from 57th Street via the BMT 63rd Street Line, which is currently used only during service disruptions.
The Q would stop at Lexington Avenue – 63rd Street at the currently-hidden northern side of the platforms to provide a cross-platform interchange to the IND 63rd Street Line (currently served by the train).
East of Lexington Avenue, it would curve northward to merge with the Second Avenue Line at about 64th Street.
The first phase of construction, due to be completed by December 2016, will extend Q service north to Second Avenue at 96th Street.
At the conclusion of the project's second phase, the Q's new northern terminal will be 125th Street, providing residents of Spanish Harlem and the Upper East Side with direct subway service via Second Avenue and Broadway to western Midtown, Lower Manhattan, and Brooklyn.  
Also tentatively called "radium F", polonium was discovered by Marie and Pierre Curie in 1898, and was named after Marie Curie's native land of Poland ()Poland at the time was under Russian, German, and Austro-Hungarian partition, and did not exist as an independent country.
It was Curie's hope that naming the element after her native land would publicize its lack of independence.
Polonium may be the first element named to highlight a political controversy.
This element was the first one discovered by the Curies while they were investigating the cause of pitchblende radioactivity.
Pitchblende, after removal of the radioactive elements uranium and thorium, was more radioactive than the uranium and thorium combined.
This spurred the Curies to search for additional radioactive elements.
They first separated out polonium from pitchblende in July 1898, and five months later, also isolated radium.
In the United States, polonium was produced as part of the Manhattan Project's Dayton Project during World War II.
It was a critical part of the implosion-type nuclear weapon design used in the Fat Man bomb on Nagasaki in 1945.
Polonium and beryllium were the key ingredients of the 'urchin' detonator at the center of the bomb's spherical plutonium pit.
The urchin ignited the nuclear chain reaction at the moment of prompt-criticality to ensure the bomb did not fizzle.
Much of the basic physics of polonium was classified until after the war.
The fact that it was used as an initiator was classified until the 1960s.
The Atomic Energy Commission and the Manhattan Project funded human experiments using polonium on 5 people at the University of Rochester between 1943 and 1947.
The people were administered between of polonium to study its excretion. 
The 216th Army Air Forces Base Unit (AAF BU) (Special) provided base services at Wendover Army Airfield, where the 509th Composite Group was stationed during World War II.
As such, it became involved in the Manhattan Project's program of testing bombs and aircraft under the codename Project W-47. 
Extending between Sunnyside, Queens, and Grand Central, the project will route the LIRR from its Main Line through new track connections in Sunnyside Yard and through the lower level of the existing 63rd Street Tunnel under the East River.
In Manhattan, a new tunnel will begin at the western end of the 63rd Street Tunnel at Second Avenue, curving south under Park Avenue and entering a new LIRR terminal beneath Grand Central.
Current plans call for 24-trains-per-hour service to Grand Central during peak morning hours, with an estimated 162,000 passenger trips to and from Grand Central on an average weekday.
Connections to AirTrain JFK at Jamaica Station in Jamaica, Queens, will facilitate travel to John F. Kennedy International Airport from the East Side of Manhattan.
However, the tunnels of the East Side Access can only be used by M3, M7, and M9 railcars due to a height restriction created when the 63rd Street Tunnel was first built.
C3 railcars and EMD DE30AC and DM30AC locomotives will not be able to use the tunnels.
A new LIRR train station in Sunnyside at Queens Boulevard and Skillman Avenue along the Northeast Corridor (which the LIRR uses to get into Pennsylvania Station) will provide one-stop access for area residents to Midtown Manhattan.
The station may spur economic development and growth in Long Island City.
The project's estimated cost has increased from $3 billion in 1998 to $6.3 billion in 2006, $8.4 billion in 2012, and $10.8 billion in 2014.
Though construction work is ongoing, the completion date for the project has been continually pushed back by the MTA.
Once planned to be operational by 2013, the MTA has pushed back the completion date several times, most recently to September 2023, although the terminal can open as soon as 2019.
With the seven-year delay in the completion date and the 180% cost increase to $8.4 billion, the U.S.
DoT Inspector General wants an audit done on the project.
The project is likely to increase passenger loads on the already overcrowded IRT Lexington Avenue Line, the sole East Side subway line, and on surface bus routes on the East Side.
The project has, therefore, focused attention on the long-delayed Second Avenue Subway along the far East Side of Manhattan, which is again under construction and is expected to relieve north/south commuting pressure.
At the same time, the project will reduce the load on morning, northbound rush-hour E train service between Pennsylvania Station and Midtown East. 
SHoP Architects led the design process in the creation of the East River Esplanade, consulting community members during the planning years between 2002 and 2006.
A year-long study was undertaken in 2004, allowing designers to derive ways that would "enhance waterfront access".
Other groups critical to the project's planning phase include the New York City Department of Transportation, the Department of Parks and Recreation, the Economic Development Corporation, the Department of City Planning and other agencies and groups.
$137 million was secured with the Lower Manhattan Development Corporation, and work began on a "pilot section" in 2009 between John Street and Wall Street.
According to the Department of City Planning, the overall plan is listed as: The esplanade itself: The new esplanade will consist of a recreation zone along the water’s edge with seating and plantings, pavilions under the FDR Drive to support outdoor activities, and a bikeway along South Street that ties into the Manhattan Greenway.
Consistent paving, seating, railings, and lighting will be used throughout.
Pavilions and “get-downs”: New, proposed pavilions will help reconnect the city to the river’s edge, creating concentrated areas for recreation where appropriate.
At Peck Slip and Rutgers Slip, the new esplanade design will mark historic locations by carving steps into the bulkhead line—creating means to “get down” to the water.
Archipelago: In order to provide a continuous greenway between Battery Park and the new East River Waterfront, the path between the Battery Maritime Building and Old Slip will be extended over the existing shoreline, creating a walkway out over the water with a of the city.
Pier 15: The proposed pier will lift its primary recreation area to a second tier, offering new and intimate views of the tall, historic ships that could be docked in this location.
Pier 35: This large pier will be opened to the public with a second tier that will function like an amphitheater facing west and southwest towards the city, the waterfront, Governor’s Island, and Brooklyn.
Sustainability: In keeping with the City’s PlaNYC initiatives, the East River Waterfront project will seek LEED certification for its pavilions and park uses.
Plans aim to reduce energy demand and consumption, conserve natural resources, improve air quality, and catch and reuse rainwater water.
The FDR Drive viaduct will be clad, and South Street will be narrowed for much of its length to make room for additional sidewalk space.
The glass pavilions will be located underneath the viaduct, and the bike lanes would be moved to the side of the pavilion, underneath the FDR Drive.
The piers would be reconstructed to encourage marine growth, by having reef balls to attract fish populations.
Access to the Esplanade from the neighboring areas would be undertaken with the redevelopment of "slips" - wedge-shaped road shapes which previously allowed ships to berth.
Some of these slips have been used as parking facilities, while others are the southern termini for critical north-south thoroughfares.
Reconstructions of the existing slips in the Financial District, the Lower East Side and Chinatown will feature bikeways and landscaped medians.
Five of these slip projects are at varying stages of construction.
From east to west, they areMontgomery Slip,Rutgers Slip,Pike/Allen Slip,Peck Slip, and Burling Slip.
The project is being undertaken in 3 phases, with first phase completed (including Pier 15).
Second phase construction started in summer 2011 (from Old Slip to the Battery Maritime Building).
Construction on the third phase (Pike Slip to Pier 35, Montgomery Slip) began in fall 2011.
This phase will last until 2014 and will cover the rehabilitation underneath the FDR Drive from Maiden Lane to Pier 35.