TOKYO - Worries over radiation are so rampant in Japan after last year's nuclear meltdowns that the world's first cellphones with built-in radiation monitors are going on sale.

Softbank Corp., the carrier for the hit iPhone and iPad in Japan, says the Pantone 5 mobile device, which shows the microsieverts-per-hour number on a display at a push of a button, will go on sale in July. Pricing was not announced.

The tsunami last March in northeastern Japan set off meltdowns and explosions at Fukushima Dai-ichi nuclear plant.

Areas near the plant are a no-go zone. But "hot spots" have popped up in many places, including Tokyo. Many Japanese are worried, especially families with children.

Softbank President Masayoshi Son publicly opposes nuclear power after the disaster, and is an aggressive proponent of solar and other renewable energy.

He said he was responding to concerns sent into the company, including requests on Twitter.

The device by Japanese electronics maker Sharp Corp. works like a dosimeter. It measures the radiation in one's surroundings, such as on the ground or in the air, in two minutes. It does not measure radiation in food or water.

People in parts of Fukushima are still being exposed to radiation higher than the 1 millisievert a year set as safe by Japan before the disaster.

Studies have found that cancer risks rise at an annual exposure of 100 millsieverts or above but aren't statistically detectable at lower levels. Below 100, experts can't say for sure whether it's safe, just that a link to cancer can't be proven.

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  • Members of the media, wearing protective suits and masks, visit the Unit 3 and Unit 4 reactor buildings of tsunami-crippled Fukushima Dai-ichi nuclear power station of Tokyo Electric Power Co., during a press tour escorted by TEPCO officials, in Okuma, Fukushima prefecture, northeastern Japan, Tuesday, Feb. 28, 2012. (AP Photo/Kimimasa Mayama, Pool)

  • A radiation monitor indicates 131.00 mSv per hour near Unit 3 and 4 reactor buildings at Tokyo Electric Power Co.,'s tsunami-crippled Fukushima Dai-ichi nuclear power station in Okuma, Fukushima prefecture, northeastern Japan, Tuesday, Feb. 28, 2012. (AP)

  • A journalist checks radiation level with her dosimeter near stricken Fukushima Dai-ichi nuclear power plant of Tokyo Electric Power Co., during a press tour led by TEPCO officials, in Okuma town, Fukushima prefecture, northeastern Japan Tuesday, Feb. 28, 2012. (AP)

  • Damage of tsunami-crippled Fukushima Dai-ichi nuclear power station building is seen through a bus window during a press tour led by officials of Tokyo Electric Power Co., in Okuma, Fukushima prefecture, northeastern Japan, Tuesday, Feb. 28, 2012. (AP Photo/Kimimasa Mayama, Pool)

  • A journalist visits stricken Fukushima Dai-ichi nuclear power plant of Tokyo Electric Power Co., during a press tour led by TEPCO officials, in Okuma town, Fukushima prefecture, northeastern Japan Tuesday, Feb. 28, 2012. (AP)

  • Stricken Fukushima Dai-ichi nuclear power plant buildings of Tokyo Electric Power Co., are seen in Okuma town, Fukushima prefecture, northeastern Japan Tuesday, Feb. 28, 2012. (AP)

  • Trucks are overturned before the Unit 4 reactor building of stricken Fukushima Dai-ichi nuclear power plant of Tokyo Electric Power Co., in Okuma town, Fukushima prefecture, northeastern Japan Tuesday, Feb. 28, 2012. (AP)

  • Tokyo Electric Power Co workers stand near stricken Fukushima Dai-ichi nuclear power plant buildings during a press tour in Okuma town, Fukushima prefecture, northern Japan, in Okuma town, Fukushima prefecture, northeastern Japan Tuesday, Feb. 28, 2012. (AP)

  • Damaged Unit 3, left, and Unit 4, right, reactor buildings are seen at Tokyo Electric Power Co.,'s tsunami-crippled Fukushima Dai-ichi nuclear power station in Okuma, Fukushima prefecture, northeastern Japan, Tuesday, Feb. 28, 2012. (AP Photo/Kimimasa Mayama, Pool)

  • Takeshi Takahashi, center, head of Tokyo Electric Power Co.,'s Fukushima Dai-ichi nuclear power plant, speaks to journalists at the emergency operation center of the crippled nuclear power plant in Okuma town, Fukushima prefecture, northeastern Japan Tuesday, Feb. 28, 2012. (AP)

  • A worker takes a rest at the emergency operation center of the stricken Fukushima Dai-ichi nuclear power plant of Tokyo Electric Power Co., in Okuma town, Fukushima prefecture, northeastern Japan Tuesday, Feb. 28, 2012. (AP)

  • Debris is seen scattered near the Unit 6 reactor building of stricken Fukushima Dai-ichi nuclear power plant of Tokyo Electric Power Co., in Okuma town, Fukushima prefecture, northeastern Japan Tuesday, Feb. 28, 2012. (AP)