How do I charge the Proto Statue to get a Crown Vault portal?

How do I charge the Proto Statue to get a Crown Vault portal? - Boy Wearing Crown Statue

I'm confused about how the charging of the Proto Statue works. Nuclear Throne Wikia says the portal charges by absorbing rads, but I'm killing enemies near the statue and the rads won't move towards it. How do I make it absorb rads and give me a Crown Vault portal?

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How do I charge the Proto Statue to get a Crown Vault portal? - Woman Wearing Crown Holding Frog Figurine

How do I charge the Proto Statue to get a Crown Vault portal? - Ancient sculpture of holy warrior in park

Nuclear Throne (Normal, Crown Vault, Y.V Mansion) Portal Background screen

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