---
title: "Compton Coincidence Energy Analyzer Interactive Lab | Sandbox Physics"
description: "Two pulses. One energy account. Use an active scattering target to retain recoil and photon pulse heights with their time difference. Move the coincidence window, subtract time sidebands, and infer the incoming energy from the retained pairs."
canonical_url: "https://sandboxphysics.com/labs/compton-coincidence-energy/"
language: "en"
page_type: "lab"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/labs/compton-coincidence-energy/"
last_modified: "2026-10-18"
---

ACTIVE SCATTERER / COINCIDENCE

# Compton Coincidence Energy Analyzer

Use an active scattering target to retain recoil and photon pulse heights with their time difference. Move the coincidence window, subtract time sidebands, and infer the incoming energy from the retained pairs.

> Interactive simulation: open this page in a web browser to change the parameters and run the model.

Ideal full containment of recoil energy and scattered-photon energy, calibrated independent Gaussian channels. True-pair timing is Gaussian; accidental pulse heights are independent of a flat time distribution. No real source rate, trigger efficiency, binding, escape or detector continuum. Sideband subtraction is conditional on these assumptions.

Incoming photons travel rightward. The detector faces the target at the selected angle. Paths and sizes are schematic; energy data appear below.

CALIBRATED PULSE HEIGHTS / RETAINED EVENTS

## Keep both energies and their time difference.

Collimated photon Active recoil target Two energy channels + timing

Every candidate pair retains two calibrated pulse heights and a delay. The analysis window can move after acquisition. The simulated candidate mixture does not model source activity or trigger rates.

Ready. Predict, then acquire.

RAW DETECTOR RECORDS

### A shared event leaves complementary energies.

$E_\gamma/\mathrm{keV},\quad K_e/\mathrm{keV}$

Inside time gate Outside time gate Inferred energy sum

Color uses the time gate only. The analyzer never receives a true-pair label. Recoil energy is deposited inside the active target, not at a separate electron collector.

ALL CANDIDATE DELAYS / DISJOINT SIDEBANDS

### Select a prompt window. Measure the background.

$\Delta t/\mathrm{ns},\quad N_{\rm bin}$

REBINNED FROM THE SAME RAW PAIRS

### The energy sum after sideband subtraction.

$(E_\gamma+K_e)/\mathrm{keV},\quad N_P-\alpha N_B$

Teal: prompt counts. Gold: width-scaled sideband counts. Purple: their difference with approximate counting errors. Negative bins are preserved. Source energy never enters this histogram.

INFERENCE / RECORDS ONLY

### What the retained observations support

Retained events

$\text{—}$

Sideband-corrected incoming energy

$\text{—}$

Approximate standard error

$\text{—}$

Net prompt excess

$\text{—}$

Sideband correction assumes time-independent accidental energy distributions. A weak net prompt excess withholds the energy estimate. Gaussian true-pair tails can leak into sidebands at extreme timing spread; this is not an automatic background classifier.

IN-MEMORY COMPARISON

Save a run to compare or restore its settings and raw events.

[Measure the angular spectrum](https://sandboxphysics.com/labs/compton-angular-spectrometer/) [Read the historical evidence](https://sandboxphysics.com/stories/quantum-evidence/compton-scattering-energy-momentum/) [ORTEC apparatus reference](https://www.ortec-online.com/-/media/ametekortec/third%20edition%20experiments/10-compton-scattering.pdf?la=en) [Compton 1923 paper](https://journals.aps.org/pr/abstract/10.1103/PhysRev.21.483)

Physics tutorial

## Compton Coincidence Energy Analyzer

**Background** Use an active scattering target to retain recoil and photon pulse heights with their time difference. Move the coincidence window, subtract time sidebands, and infer the incoming energy from the retained pairs.

**Why it matters** A constant is inferred through a calibrated response and retained observations.

Start with the essentials

- **Focus question**: Two pulses. One energy account.
- **One-sentence intuition**: Keep source assumptions separate from estimates made from records.

### Core mathematical model

#### Two deposited energies

$$
E_0=E_\gamma+K_e
$$

The target contains the recoil electron; the distant detector contains the scattered photon. Both measured pulse heights carry independent resolution noise.

#### Use time to subtract accidentals

$$
\begin{aligned}N_{\rm net}&=N_P-\alpha N_B\\[2pt]\alpha&=\frac{2w}{2(160-80)\,\mathrm{ns}}\end{aligned}
$$

Prompt means absolute delay within the selected half-width. Two sidebands run from eighty to one hundred sixty nanoseconds in absolute delay. A flat time background is required.

#### An estimate from weighted records

$$
\widehat E_0=\frac{\sum_{i\in P}(E_{\gamma i}+K_{ei})-\alpha\sum_{i\in B}(E_{\gamma i}+K_{ei})}{N_P-\alpha N_B}
$$

No latent labels or source energies enter. Negative subtracted bins remain visible. Weak net excess withholds the energy estimate; the displayed standard error is approximate, not a confidence interval.

### Common difficulties

#### A simulation supplies its law

**Typical misconception** Recovering a source parameter independently confirms the law.

**Better mental model** These synthetic records test a measurement and inference workflow. They are not historical observations, a parameter confidence interval, or external scientific certification.

### Run the experiment

1. 01

   #### Acquire the candidate stream

   Keep photon energy, target energy and delay for every candidate pair.

   **What to observe:** Prompt points cluster along a constant energy sum. Gray points are outside the time gate, not known background labels.

2. 02

   #### Move the window after acquisition

   Change the analysis half-width without reacquiring.

   **What to observe:** All raw pairs remain. Both timing counts and the subtracted energy-sum histogram are recomputed from the same stream.

3. 03

   #### Remove true pairs

   Select no correlated pairs and acquire a new stream.

   **What to observe:** A gate can select accidental pairs too. Sidebands and weak-information diagnostics prevent a fabricated conservation estimate.

Physical conclusion

Ideal full containment of recoil energy and scattered-photon energy, calibrated independent Gaussian channels. True-pair timing is Gaussian; accidental pulse heights are independent of a flat time distribution. No real source rate, trigger efficiency, binding, escape or detector continuum. Sideband subtraction is conditional on these assumptions.

Quantum & fields · Starter path

## Start from a single measurement

Predict outcomes and collect counts, building from one qubit to wave packets, bound states and two-photon interference.

[Start here → **Quantum State & Born Measurement** Predict a probability, turn the analyzer, then compare it with the frequency of acquired shots. Observe · 15 min](https://sandboxphysics.com/labs/qubit-state/)

1. [1 Quantum State & Born Measurement](https://sandboxphysics.com/labs/qubit-state/)
2. [2 Stern–Gerlach Sequence](https://sandboxphysics.com/labs/stern-gerlach-sequence/)
3. [3 Wave Packet & Uncertainty](https://sandboxphysics.com/labs/wave-packet-uncertainty/)
4. [4 Quantum Harmonic Oscillator](https://sandboxphysics.com/labs/quantum-harmonic-oscillator/)
5. [5 Which Path & Quantum Eraser](https://sandboxphysics.com/labs/quantum-eraser/)
6. [6 Hong–Ou–Mandel Two-Photon Interference](https://sandboxphysics.com/labs/hong-ou-mandel/)

[View the full path →](https://sandboxphysics.com/topics/quantum/#starter-path)