Chimney Top Calculators

F-18 dose rate & shielding calculator

Dose rate from a Fluorine-18 point source at any distance, with shielding — or solve for activity, distance or shield thickness. Γ = 0.57 R·m²/(Ci·h), half-life 109.8 minutes.

Calculator

Calculated — choose the unit for the result.

Calculated — choose the unit for the result.

When solving for shield thickness this is the target dose rate behind the shield.

Calculated — choose the unit for the result.

Results

Dose rate
570 mR/h
Exposure rate
570 mR/h
Air-kerma rate
4.996 mGy/h
Dose-equivalent rate (≈, 1 R ≈ 1 rem)
5.7 mSv/h · 570 mrem/h
Activity
1 Ci · 37 GBq
Distance
1 m · 3.281 ft
Γ used
0.57 R·m²/(Ci·h)
  • F-18: Two 511 keV annihilation photons per positron (96.7 % β+).

About Fluorine-18

PET imaging (FDG).

Principal photons: 511 keV annihilation (193.5 %). Specific gamma-ray constant used here: 0.57 R·m²/(Ci·h) (5.7 R·cm²/(mCi·h)). Two 511 keV annihilation photons per positron (96.7 % β+).

Unshielded exposure rate by distance

Activity0.3 m1 m2 m5 m10 m
1 mCi (37 MBq)6.33 mR/h0.57 mR/h0.143 mR/h0.0228 mR/h0.0057 mR/h
1 GBq (27 mCi)171 mR/h15.4 mR/h3.85 mR/h0.616 mR/h0.154 mR/h
1 Ci (37 GBq)6,330 mR/h570 mR/h143 mR/h22.8 mR/h5.7 mR/h

Multiply mR/h by 10 for an approximate µSv/h figure (1 R ≈ 10 mSv for photons).

The formula

Ẋ [R/h] = 0.57 × A [Ci] × T / d² [m²]

T is the shield transmission (1 with no shield). See the main calculator page for the full derivation and assumptions.

Worked example

A 10 mCi F-18 source at 2 m: Ẋ = 0.57 × 0.010 / 2² = 1.42 mR/h. Halving the distance to 1 m quadruples it to 5.7 mR/h.

Frequently asked questions

What is the dose rate at 1 meter from 1 Ci of F-18?
About 570 mR/h (0.57 R/h) for an unshielded point source, using Γ = 0.57 R·m²/(Ci·h). That is roughly 5.7 mSv/h with the 1 R ≈ 10 mSv photon convention.
What is the gamma constant of F-18 in SI units?
About 0.154 µSv/h at 1 m per MBq (approximate dose-equivalent rate), or 5.7 R·cm²/(mCi·h).
What is the half-life of F-18?
109.8 minutes (ENSDF evaluated value via NuDat 3). Use the decay calculator to correct a source's activity to today's date before computing a dose rate.
Is there shielding data for F-18?
The broad-beam table used by this site (NCRP Report 49) does not list F-18. Choose "Custom HVL" in the calculator and enter a half-value layer from a reference appropriate to its photon energies.

Sources

  1. Unger, L. M. & Trubey, D. K. (1982). Specific Gamma-Ray Dose Constants for Nuclides Important to Dosimetry and Radiological Assessment. ORNL/RSIC-45/R1, Oak Ridge National Laboratory. www.osti.gov
  2. U.S. Department of Health, Education, and Welfare (1970). Radiological Health Handbook, revised edition. Public Health Service, Bureau of Radiological Health.
  3. National Nuclear Data Center, Brookhaven National Laboratory. NuDat 3 (ENSDF evaluated half-lives and photon emission data). www.nndc.bnl.gov
  4. ICRU Report 85 (2011). Fundamental Quantities and Units for Ionizing Radiation. (Mean energy per ion pair in dry air, W/e = 33.97 J/C.)