Most people around the world cannot bring themselves to think about nuclear war or the spreading of nuclear arms or the chances of nuclear terror because the death and destruction would be so awful that the human mind refuses to grasp it.

Yet the prospects are that a nuclear device in an oil tanker or cargo ship sailing into a large port or on a medium-sized truck driven into an athletic stadium or city hall or in a suitcase left in a downtown bus depot could be detonated in the near future.

Jonathan Medalia, a specialist on nuclear issues, has estimated that a small bomb could kill half a million people and cause $1 trillion worth of damage.

Even so, only 45 percent of Americans surveyed by the Pew Research Center found the spread of nuclear weapons to be among the world's greatest dangers. In a report last week, Pew also found that only 21 percent of the French, 29 percent of the Chinese, 31 percent of the Russians and 32 percent of the British — all citizens of nuclear powers — were worried.

Exceptions were Japan and Israel. The Japanese, with 68 percent anxious, are still dealing with the nuclear allergy from the 1945 atomic bombings and the current nuclear threat from North Korea and possibly China and Russia. The Israelis, with 66 percent concerned, are confronted with the possibility of a nuclear attack from Iran.

Curiously, only 29 percent of the South Koreans queried said they were troubled by a nuclear threat from North Korea. Many of them have argued that their North Korean cousins will never attack them. Besides, Seoul has recently gotten a renewed pledge that the nuclear umbrella of the U.S. still shelters South Korea.

All of this helps to explain why the nuclear summit called by President Obama in Washington last week seemed to drop like a pebble into a pond. "The leaders of 47 nations came together to advance a common approach and commitment to nuclear security at the highest levels," the State Department said. A more skeptical view came from the Economist magazine, which called it an "eye-catching piece of nuclear theatrics."

The summit did little about the most immediate nuclear threats, the arsenals being assembled by Iran and North Korea.

North Korea's current diplomatic ploy is to insist on negotiating a peace treaty with the U.S., the Korean war of 1950-53 having ended in a truce. Pyongyang, through its official Korean Central News Agency, said last week: "There is no other alternative than to conclude a peace treaty if the vicious cycle of distrust between the DPRK and the U.S. is to be removed and the denuclearization process is to be pushed forward."

The U.S., under Republican and Democratic administrations, has asserted that North Korea must first give up its nuclear ambitions in an irreversi-ble and verifiable manner.

Meantime, the Obama administration, in its nuclear posture released this month, said that proliferating states, for which read North Korea, must understand that "any use of nuclear weapons will be met with a response that would be effective and overwhelming."