In early 1988, the British neuropsychiatrist Dr. Peter Fenwick, an expert on near-death experiences, appeared in the BBC documentary “Glimpses of Death” to comment on the near-death visions of people who had briefly died, or nearly died, and then come back to life. After it aired, thousands of people wrote him letters describing similar stories. Dr. Fenwick sent them a lengthy questionnaire to categorize their accounts. He presented his findings in “The Truth in the Light: An Investigation of Over 300 Near-Death Experiences,” the book that he wrote with his wife, Elizabeth Fenwick, published in 1995.

After Dr. Fenwick died on Nov. 22 at age 89, his obituary brought a wave of comments from readers about their own near-death experiences. A selection, condensed and edited, is below.

“I once knew a teacher who told me about his experience with his mother when she died. A few seconds before she left this world, she suddenly said very clearly: ‘It is so beautiful!’ And then she passed away. I’m not a religious person and I have no idea if there’s a life after this present one. But that story has stayed with me ever since I heard it in 1991.” — Michel Forest, Montreal, Quebec

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“In 1981, I was working in an offshore oil rig when a 1,000-pound metal pipe fell on my thigh, snapped my femur and severed my femoral artery. I was bleeding to death. After a quick medevac flight to the emergency room, I lost so much blood that my blood pressure dropped and my heart stopped. I flatlined.

At that moment, I found myself hovering above myself on the hospital table. No pain. I could see my disfigured leg and felt sorry for my body. Then a beautiful bright light came through a dark tunnel. It was stunning and as ‘real’ as any memory I have. But then I realized I had to go back and instantly awoke in massive pain. I had never heard about near-death experiences and was afraid to tell this story due to ridicule. But it happened. It was as ‘real’ as life is. I don’t fear death now. It’s just another level of consciousness.” — Jeff Sears, Norwalk, Conn.

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“Dec. 3, 2003, I had a sudden, severe pancreatitis attack. The pain was extreme. With my wife and daughter out for the weekend, I had to drive myself to the emergency room five minutes away. I passed out as I entered the emergency area. Lying on the gurney, I saw ‘the light’ at the ceiling and knew I was either dead or near death. The feeling was extraordinarily blissful; I knew that it would be a loving transition to a new world. I had to decide — stay or go. I was not done playing with my children, so I stayed. I looked up and there was my 16-year-old daughter.” — Elliot Hoffman, San Francisco

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“I had a near-death experience when I was in the hospital with peritonitis in my late 20s, about 50 years ago. I was surrounded by the most seductive feeling of peace and calm I’ve ever experienced — light and airy. I saw my grandfather (who looked very young), who said to me, ‘What are you doing here?’ I said, ‘You know, Grandpa.’ He said, ‘You’re not supposed to be here now.’ I remember making tight fists to keep me in my body because I was floating upward. Since that day, I have had no fear of dying.” — Emily Danies, Tucson, Ariz.

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“I am now 78. When I was 22, I had a near-death experience. I went into anaphylactic shock from a severe allergic reaction to penicillin. I didn’t go through a tunnel, see a light or any dead relatives. Instead, I had an out-of-body experience. I was floating above my body in the emergency room, watching the physicians and staff trying to save me. It was the most peaceful I have ever felt. When I recounted the experience to my physician, who had been present, he expressed disbelief until I told him how many were working on me, where he was standing, what they said and what they did to save me.” — Marion Novack, Bronx, N.Y.

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“I am not a religious person. I do have a background in science. And I believe in what Dr. Fenwick uncovered. In 1991, I held my grandfather as he passed away from kidney failure. He was totally cogent as we said our goodbyes. I felt his weak body go totally limp, but then, seconds later, he sat straight up; his face got calm, and his eyes were bright as he stared straight ahead, focused on seemingly nothing. Then he uttered the word “Mamma!” He said it in his original Italian language, something I had not heard him use in decades. He passed with a smile on his face.” — Marianne Pontillo, Philadelphia

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“I lost my wife in 1989 during an asthma attack in an ambulance on the way to the emergency department. I watched her slip away within a minute or two. They were unable to revive her. A few months earlier, she had woken up early one morning from a startling dream. She told me that she had been in a dark tunnel heading toward a bright, white light, when her deceased father appeared. He said to her, “Go back, Susan; it is not your time yet.” As she was being lifted onto the ambulance, her last words to me were that she wasn’t ‘going to make it.’ I have lived with her words since that night.” — Marvin Wilkenfeld, Newton, Mass.

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“I remember thinking: ‘This is it. I’m dying.’ I distinctly remember hoping my younger brother would get my pixies, a couple of little ceramic decorations that he had always wanted but I’d never let him even touch. Then, I had a sudden thought that I had a choice to make: If I died then, I’d go straight to heaven, but if I chose to live, there were no guarantees. I remember deciding, strongly, that I wanted to live. When I hit the ground, my skull fractured.” — Judith Hanson Hume, Dallas

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Rebecca Halleck and Amisha Padnani contributed research.

President-elect Donald J. Trump has picked Brandon Williams, a former Navy officer and one-term congressman, to become the keeper of the nation’s arsenal of thousands of nuclear bombs and warheads.

Mr. Trump’s selection is a shift from a tradition in which the people who served as administrator of the National Nuclear Security Administration typically had deep technical roots or experience in the nation’s atomic complex. What’s unknown publicly is the extent of Mr. Williams’ experience in the knotty intricacies of how the weapons work and how they are kept reliable for decades without ever being ignited.

Terry C. Wallace Jr., a former director of the Los Alamos weapons laboratory in New Mexico, expressed surprise at Mr. Trump’s pick.

Dr. Wallace said he had “never met him or had a meeting” with Mr. Williams and characterized him as having “very limited experience” with the N.N.S.A.’s missions, based on his own decades of work in and around the nation’s atomic complex.

Hans M. Kristensen, the director of the Nuclear Information Project at the Federation of American Scientists, said Mr. Williams “will be facing an incredibly complex, technical job.”

Mr. Williams did not return calls for comment on his selection by Mr. Trump or his credentials.

The credentials and credibility of whoever becomes N.N.S.A.’s new leader may face close scrutiny because advisers to Mr. Trump have suggested that the incoming administration may propose a restart to the nation’s explosive testing of nuclear arms. That step, daunting both technically and politically, would end U.S. adherence to a global test ban that sought to end decades of costly and destabilizing arms races.

From 2023 to early this year, Mr. Williams, a Republican, represented New York’s 22nd Congressional District, an upstate area that includes the cities of Syracuse and Utica. He was defeated by a Democrat in the November election.

Mr. Williams joined the U.S. Navy in 1991 and served as an officer on the U.S.S. Georgia, a nuclear submarine, before leaving the service as a lieutenant in 1996.

In his congressional biography, Mr. Williams said he made a successful transition during his Navy career into nuclear engineer training, calling it “a very steep learning curve” that he met “against significant odds.” The program is widely considered one of the U.S. military’s most demanding.

Mr. Trump announced his choice of Mr. Williams as the nation’s nuclear weapons czar in social media posts on Thursday morning, calling him “a successful businessman and Veteran of the U.S. Navy, where he served as a Nuclear Submarine Officer, and Strategic Missile Officer.”

According to his congressional biography, Mr. Williams founded “a software company that now helps large industrial manufacturers modernize their production plants, secure their critical infrastructure from cyberattacks, and paves the way for reduced emissions through advances in artificial intelligence.”

Chris Wright, Mr. Trump’s nominee for secretary of energy, the cabinet-level post that oversees the N.N.S.A., called Mr. Williams “a smart, passionate guy” who wants to “defend our country and make things better,” according to an interview on Wednesday with the website Exchange Monitor.

A lengthy 2022 profile of Mr. Williams described him as a multimillionaire who starts each morning by reading a section of the Bible. After high school, it said, Mr. Williams went to Baylor University, a private Christian school in Waco, Texas, and then transferred to Pepperdine University in Malibu, Calif.

His congressional biography says he earned a bachelors from Pepperdine in liberal arts, and later an MBA from the Wharton School, a contrast with the advanced degrees in physics or engineering that typically dot the résumés of weaponeers who end up in senior positions of the nation’s atomic complex.

The outgoing administrator of the National Nuclear Security Administration, Jill Hruby, offers a striking contrast with Mr. Williams in terms of technical background and nuclear experience. Before her 2021 nomination to the post, she had a 34-year career at Sandia National Laboratories, retiring in 2017 as director. By training, she is a mechanical engineer.

Sandia is one of the nation’s three nuclear weapons labs, with its main branch located in Albuquerque. It is responsible for the nonnuclear parts of the nation’s arsenal of atomic bombs and warheads.

Other N.N.S.A. administrators have had backgrounds in national security, nuclear operations, the military or scientific fields related to nuclear technology. The first was an Air Force general and a former deputy director of the C.I.A.

The overall responsibilities of the N.N.S.A. include designing, making and maintaining the safety, security and reliability of the nation’s nuclear arms; providing nuclear plants to the Navy; and promoting global atomic safety and nonproliferation. In Nevada, the agency runs a sprawling base larger than the state of Rhode Island, where the United States in the latter years of the Cold War tested its weapons in underground explosions.

Dr. Wallace, the former Los Alamos director, said he had tracked Mr. Trump’s search for an agency leader and found that “any candidate will be making a pitch for resumption.” He added, “That more or less disqualifies any recent director of any nuclear weapons lab.”

Many experts see a restart as unnecessary given the depth and breadth of the nation’s nonexplosive testing program, which the N.N.S.A. runs at an annual cost of roughly $10 billion. Experts argue that the program’s decades of analyses have led to deeper understanding of nuclear arms and greater confidence in weapon reliability than during the explosive era.

Dr. Wallace said Mr. Trump was aided in his hunt for a nuclear czar by Robert C. O’Brien, his national security adviser from 2019 to 2021. Last year in Foreign Affairs magazine, Mr. O’Brien, a lawyer, argued that Washington “must test new nuclear weapons for reliability and safety in the real world.” He added that the freshly tested arsenal would be a deterrent to China and Russia.

Republicans have long criticized the test ban and urged a testing restart. President Bill Clinton, a Democrat, signed the accord in 1996. In 1999, however, he suffered a crushing defeat when the Senate refused to ratify the test ban treaty.

In spite of the treaty’s defeat, successive administrations have informally abided the terms of the test ban. That position began to come under fire during Mr. Trump’s first administration.

In 2018, the Defense Department declared that “the United States must remain ready to resume nuclear testing.” John R. Bolton, Mr. Trump’s national security adviser from 2018 to 2019, reportedly argued for a restart but made little headway.

In 2020, when Mr. O’Brien was the national security adviser, the Trump administration reportedly discussed whether to conduct nuclear test explosions in a meeting with national security agencies.

Opponents of a restart see the nonnuclear tests as more than sufficient to ensure arsenal reliability. “We have more confidence today than when we stopped explosive testing,” Victor H. Reis, the program’s architect, said in an interview.

Siegfried S. Hecker, a former Los Alamos director, argued that a restart would probably start a chain reaction of testing among the world’s atomic powers and perhaps among the so-called threshold states. Like Iran, they’re considered close to being able to build a bomb.

Dr. Hecker noted that during the Cold War, China conducted 45 test explosions, France 210, Russia 715 and the United States 1,030. He said that Beijing, which in recent years has rebuilt its base for nuclear tests, had a major incentive to design and explosively test a new generation of nuclear arms. He argued that the arms could make its expanding missile force more lethal.

“China,” Dr. Hecker added, “has much more to gain from resumed testing than we do.”