Harriet Brooks: First Glimpse of Radioactive Recoil (1904)

Recoilwyn is a respectful pixel portrait of Harriet Brooks, after William Notman & Son’s 1898 photograph, with two motes of light flying apart before her: a light fast one and a heavy slow one.

The Physics

Harriet Brooks (1876–1933) was Ernest Rutherford’s first graduate student at McGill. She helped show that radium’s “emanation” was a new radioactive gas (radon), early evidence that one element can turn into another. Her 1904 Nature letter, “A Volatile Product from Radium”, reported active deposit turning up on the walls of the vessel, an early observation of what was later explained as alpha recoil: when a nucleus emits an alpha particle, the daughter nucleus is kicked the other way.

p_α = −p_R ⇒ E_R = (m_α / m_R) E_α

• p_α, p_R: momenta of the alpha particle and the recoiling daughter nucleus (kg m s⁻¹)
• E_α, E_R: their kinetic energies (non-relativistic) (J or MeV)
• m_α, m_R: their masses (kg or u)

For radium-226 (E_α ≈ 4.78 MeV) the radon-222 daughter recoils with about 4.78 × 4.0/222 ≈ 86 keV, enough to fly free of a surface and lodge in the walls. Sources: H. Brooks, Nature 70, 270 (1904), doi:10.1038/070270b0; Dictionary of Canadian Biography, “Brooks, Harriet”; Russ & Makower, Proc. R. Soc. A 82, 205 (1909), doi:10.1098/rspa.1909.0028.

Honest caveat: Brooks observed the effect; the recoil explanation came later (Hahn, and Russ & Makower, 1909). The discovery of radon is shared with Rutherford, Owens and Dorn.

In character

Something leapt from the radium and landed where it should not have been. I wrote down exactly what I saw. The explanation could catch up later.

On the hoodie

Front: two arrows from one dot, a long thin one and a short thick one. Front label: “HARRIET BROOKS · FIRST OBSERVED 1904”. Back: a pixel portrait of Harriet Brooks with “CROWNED IN HER OWN LIGHT” and “HARRIET BROOKS - 1904”. Gildan 18500 Heavy Blend hoodie, Black, S to 5XL.

Part of the Unsung Hands set with Sponara, Ayrtha. Browse all physics hoodies, more particle & nuclear physics designs, or the Deep Cuts.