The shroud of Turin is to be shown on television for the first time in 40 years on Easter Saturday as a new claim that the four-metre-long linen cloth dates from ancient times proves its enduring ability to fascinate and perplex.

As what the Vatican described as his parting gift to the Roman Catholic church before he resigned, Benedict XVI signed off on a special 90-minute broadcast of the shroud that will take place from Turin Cathedral and be introduced in a brief preamble by his successor, Pope Francis.

"It will be a message of intense spiritual scope, charged with positivity, which will help hope never to be lost," said the archbishop of Turin, Cesare Nosiglia.

Timed to mark the 40th anniversary of the shroud's last appearance on TV – ordered by Pope Paul VI in 1973 – the unusual programme on Italian state broadcaster Rai comes as the new pope, the former cardinal Jorge Bergoglio, prepares for his first Easter as head of the world's 1.2 billion Roman Catholics.

It also comes amid new claims that the piece of fabric, which many Catholics believe Jesus was buried in, does indeed date from around his lifetime. Previous tests apparently confirmed the shroud to be a clever medieval forgery.

Giulio Fanti, associate professor of mechanical and thermal measurement at Padua University, claims tests had shown that the cloth, which bears the image of a man's face and body, dates from between 280BC and 220AD.

Fanti claims that the carbon-14 dating used in a landmark study in 1988 was "not statistically reliable". That study claimed that the shroud actually dated from the Middle Ages. But the mystery of the cloth has lingered ever since.

The Vatican does not have a position on its authenticity. When he was still cardinal Joseph Ratzinger, the previous pope wrote that the shroud was "a truly mysterious image, which no human artistry was capable of producing".

Fanti's results are detailed in a new book, Il Mistero della Sindone (The Mystery of the Shroud), written by him and journalist Saverio Gaeta.

Although it is rarely displayed, Catholics and historians keen for a closer look at the shroud will be able to study it at their leisure with the help of a new app launched on Friday. Users of smartphones and tablets will be able to download the multilingual application for free and examine detailed images of the shroud courtesy of high-definition technology.

On Thursday the Catholic church's first Latin American leader celebrates the Holy Thursday mass in a youth detention centre on the outskirts of Rome, where he will wash the feet of a dozen prisoners, two of them women.

On Friday he will lead a Good Friday procession from the Colosseum marking the stations of the cross and on Easter Sunday he will celebrate mass in St Peter's square and give the traditional Urbi et Orbi – "to the city [of Rome] and to the world"– blessing. Tens of thousands of pilgrims are expected to attend.

• This article was corrected on 31 March 2013 to make it clear that the photograph is a negative of the image and therefore enhances the appearance of a face.