Why Marie Curie’s coffin lined with lead and still remains radioactive even after 100 years

Marie Curie is renowned for her revolutionary research in radioactivity, for which she was awarded the title 'Mother of Modern Physics' and two Nobel Prizes. Her revolutionary discoveries of the radioactive elements polonium and radium transformed science and opened the door to further breakthroughs. But her tireless experimentation with these materials came at a personal price. The extended duration of radiation exposure had a lasting effect on her health, eventually leading to her death. Despite the risks, Curie's findings in science, especially in medicine and cancer treatment, have had a lasting, significant impact on the world.
Marie Curie being the only woman to receive two Nobel Prizes in two different fields. Her career began in 1896 when French scientist Henri Becquerel found that uranium salts emit beams which were eerily similar to X-rays in their ability to penetrate the body.
Then Curie started research on the phenomenon in her Ph.D. dissertation. She was also assisted by her husband Pierre Curie, when she and he obtained two new radioactive elements, polonium and radium, in 1898. Their study of the elements contributed so significantly to the discovery of radioactivity that they received half of the Nobel Prize in Physics in 1903. The other half was given to Henri Becquerel for the original discovery.

On 4 July 1934, Marie Curie died from a rare lethal blood disease because of the exposure to the radioactive elements. The disease called Aplastic anemia is the disease in which the bone marrow fails to generate sufficient amounts of blood cells which ultimately lead to infection, fatigue and other life-threatening complications. While at work, the long exposure to radiation and mostly handling the radioactive substances like radium was dangerous. And in 1934 Marie Curie died with a ‘radioactive body’ and was buried in the lead coffin.
Until 1995, Curie wasn't that popular when they found out that they were going to have radiation hazards on their side, the French government hired the services of the agency for radiation protection so that none of their employees was exposed to the hazard during the exhumation.

The black box that held Curie’s coffin was discovered that was not made of wood but actually 2.5 millimetres thick black lead. Even Curie's body itself was so well preserved and only remnants of alpha and beta radiation existed. All this means that in her advanced age Curie had been taking precautions to limit exposure to radiation, and it saved her body even after she died as per Journal of British Society for the History of Radiology. None of her other belongings, however, has been so nicely preserved as the papers. Many of Curie's clothing, furniture, and books, especially lab instruments, remain very radioactive after more than 100 years.
Objects like her laboratory notebooks are stored in lead-lined boxes at the Bibliothèque Nationale in Paris. Anyone wishing to use the materials has to sign liability releases and take personal protective equipment because the radium-226 is very poisonous and still presents a radiation risk. Because it has a half-life of 1,600 years, radium-226 will continue to be hazardous for centuries to come, a testament to Marie Curie's work and the price she paid pursuing her seminal discoveries.

In 1911 after the sudden tragedy that was the death of her husband, Pierre Curie, in 1906, Marie Curie received the Nobel Prize in Chemistry for purification research on radium. She worked all day in the following years on the chemical makeup of radioactivity material and if it can be used in curing disease like cancer. Her research and work led to the modern-day treatments using radiation like cancer.
Because of her long exposure to radiation and radioactive substances somehow irreparably damaged her health.
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