RPR-29

Specific gamma-ray constant Γ

Ḣ = Γ A / r². Point-source air-kerma rate for a sealed gamma emitter.

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ExternalSpecific gamma constant

Governing equation

\dot H=\Gamma A/r^{2}

$r \in \left[0.1, 20\right]$

where

\Gamma: Specific gamma constant (µSv m²/MBq/h)
A: Activity (GBq)
r: Distance (m)
\dot H: Air-kerma rate (µSv/h)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

\dot H=\Gamma A/r^{2}

$r \in \left[0.1, 20\right]$

$r = 0.1$ $\dot H = 81600$

Along the curve

②

Domain of the variable — blue

r_{\min} = 0.1,\quad r_{\max} = 20

$r \in \left[0.1, 20\right]$

$r = 0.1$ $r = 0.1$

Along the curve

③

Response curve — green

\dot H=\Gamma A/r^{2}

$r \in \left[0.1, 20\right]$

$r = 0.1$ $\dot H = 81600$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}\dot H}{\mathrm{d}r}

$r \in \left[0.1, 20\right]$

$r = 0.225$ $\dot H^{\prime} = -2.99\times 10^{5}$

Along the curve

Lecture brief

Historical brief

Inverse-square, half-value layer, ICRP weighting and ALARA are the protection craft since the 1920s commissions. The lab computes transmission, equivalent dose and a shielding snapshot. This sheet (RPR-29 — Specific gamma-ray constant Γ) is the form associated with Specific gamma constant. Working symbols: $\Gamma$ , $A$ , $r$ $\rightarrow$ $\dot H$ . Γ_Cs-137 ≈ 0.0816 µSv m² MBq⁻¹ h⁻¹; Γ_Co-60 ≈ 0.351; Γ_Ir-192 ≈ 0.125. Air attenuation is ignored here.

Purpose

Purpose: compute

\dot H

from

\Gamma

A

r

in Radiation protection via

\dot H=\Gamma A/r^{2}

Ḣ = Γ A / r². Point-source air-kerma rate for a sealed gamma emitter. Use it when a real radiation protection question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

\Gamma = 0.082\,\mathrm{\mu Sv m^{2}/MBq/h}

A = 10.000\,\mathrm{GBq}

r = 1.000\,\mathrm{m}

, the governing relation

\dot H=\Gamma A/r^{2}

yields

\dot H = 816.00\,\mathrm{\mu Sv/h}

. A sealed source, expanding spheres, a survey meter. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Specific gamma constant \Gamma0.0816 µSv m²/MBq/hActivity A10 GBqDistance r1 m

Outputs

Air-kerma rate \dot H816.00 µSv/h

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Narration of this film

A sealed source, expanding spheres, a survey meter.

Γ_Cs-137 ≈ 0.0816 µSv m² MBq⁻¹ h⁻¹; Γ_Co-60 ≈ 0.351; Γ_Ir-192 ≈ 0.125. Air attenuation is ignored here.

Reading speed

Watch on YouTube