1. J. MOLLOY and J. SIEBER, “Classification of

microheterogeneity in solid samples using mu XRF,” Anal.

Bioanal. Chem., 392, 995 (2008).

2. J. MOLLOY and J. SIEBER, “Assessing microscale

heterogeneity of batches of reference materials using

microbeam XRF,” X-ray Spectrom., 40, 306 (2011).

NUCLEAR FORENSIC REFERENCE MATERIALS: SRMS 4600 & 4601

SURROGATE POST-DETONATION URBAN DEBRIS

J. L. Mann, M.A. Tyra, J.L. Molloy, R. Paul (NIST)

J. Buscaglia, J. Leggitt (FBI)

K. Pfeuffer, B. Fallon, J. Dettman (ORISE – FBI)

D. Haws, S. Castro (now AFTAC), T.D. Kelly (now AFTAC), D. Turner, J.W. McClory, (AFIT)

S. Jerome (NPL) 

Contact Jacqueline Mann 

NIST, 100 Bureau Drive, Stop 8462, 

Gaithersburg, MD 20899, USA 

phone: 301-975-4472, email: jmann@nist.gov

Goal: Deliver the first post-detonation nuclear forensic Standard Reference Materials (SRMs) to enable laboratories 

to establish the traceability, accuracy, and precision of nuclear forensic measurements and provide the ability to 

benchmark measurement methods essential to meeting the requirements of legal scrutiny. 

Problem

Post-nuclear weapon detonation urban debris characterization is

complicated by the high concentrations of elements like Ca, Fe, Al,

and Si and other materials that would be entrained into a nuclear

fireball from the local environment. This characterization can

potentially identify the fuel type, weapon design, production

process, and date. The resulting nuclear forensics characterization

data collected must be anchored by validated measurement

methods and be accurate and precise as conclusions drawn from

this data will be coupled with law enforcement and intelligence

information to identify who is responsible for the attack.

SRMs

Standard Reference Materials:

 Establish accuracy and precision and the traceability of nuclear

forensic measurements

 allow benchmarking of investigative analytical methods meeting

the requirements of legal scrutiny

NIST, as a part of its mission as the US National Metrology

Institute (NMI) to deliver standards and foster homeland

security, has launched the first certification campaign of

measurement traceable post nuclear detonation SRMs. NIST, in

cooperation with partner labs (AFIT (DoD), FBI (DOJ), and NPL)

and with support from the FBI, has developed two Surrogate

Post-Detonation Urban Debris (SPUD) Standard Reference

Materials (SRMs) – SRM 4600 and 4601.

Project status - Homogeneity Characterization

A priority for any reference material producer is to supply a material that is suitably homogeneous, with suitability being driven by

the instrumental methods being performed by the measurement community or customer. Delivery of a homogeneous reference

material is required to achieve comparability between measurement communities. Two approaches are being used to assess the

homogeneity of the minor and trace elements in the SPUD materials: microbeam X-ray fluorescence (μXRF) spectrometry and

neutron activation analysis. Preliminary data results are below.

SRM 4600 (Unat) SRM 4601 (U235)

Element τ (between 

bottle STD)

s (within

Bottle STD)

P-value τ (between 

bottle STD)

s (within Bottle 

STD)

P-value

As 0.075 0.177 0.42 0.346 0.224 0.0167

Co 0.303 0.478 0.41 0.313 0.315 0.078

Cr 12.65 10.91 0.062 6.549 5.959 0.122

Fe 0.158 0.189 0.10 0.148 0.070 0.003

Mo 1.89 2.76 0.42 -- -- --

Ta 0.158 0.322 0.41 0.127 0.176 0.109

Th 0.224 0.360 0.42 0.083 0.319 0.415

W 0.089 0.476 0.42 0.109 0.410 0.419

U 0.314 0.741 0.42 1.379 1.222 0.075

U238 -- -- -- 1.094 1.017 0.095

U235 -- -- -- 0.300 0.227 0.030

-10 0 10 20 30

-5

0

5

10

15

20

25

Scores on PC 1 (67.16%)

Scores on PC 2 (28.79%)

 Ca

 Cr Fe

 Ni

 Zr

 U

-5 0 5

-6

-4

-2

0

2

4

6

Scores on PC 1 (45.13%)

Scores on PC 2 (26.67%)

 Na Mg

 Al Si

 P K

 Ca

 Ti

 V

 Cr Mn

 Fe

 Co

 Ni

 Cu

 Sr

 Zr

 Nb

 Mo

 U

Figure 2: PCA results after averaging 250 spectra

from SRM 4600. All elements fall within the red

confidence ellipse indicating no measureable

nugget effects at a sample size of 1 mg.

SRM 

4600

SRM 

4601

Element mg/g mg/g

Aluminium 51800 55690

Arsenic 20.3 18.7

Calcium 142000 144900

Chromium 575 500

Cobalt 45.7 46.24

Copper 240.8 262.7

Iron 195500 188400

Magnesium 3350 3160

Manganese 1812 1874

Molybdenum 263 261

Nickel 360 611

Niobium 77 78.5

Phosphorus 331 349

Potassium 2610 2718

Silicon 168800 172800

Sodium 749 734

Strontium 295 308.3

Tantalum 40.3 43.3

Thorium 16.38 16.16

Tin 29.4 28.13

Titanium 1205 1248

Tungsten 34 19.6

Uranium 62.61 81.072

Vanadium 130.8 141.3

Zinc 14 12.2

Zirconium 53.5 56.8

What is It?

SRMs 4600 and 4601 simulate the

expected debris mixture from the

detonation of an Improvised Nuclear

Device (IND) in an urban environment.

They are capable of producing fresh fission

products and neutron activation products.

 The elemental composition (Table to

right) of the vitrified debris materials is a

composite of minerals and metals

characteristic of the building materials

(e.g., concrete and steel) that would be

exposed to a nuclear detonation and

whose resulting activation products

would be found in rubble samples

collected for forensics evidence.

 Post-detonation samples would also

contain short-lived fission products, thus

the debris materials have been doped

with Uranium (U). To create the nuclear

fission products, samples of the SPUD

materials can be placed in a wellcharacterized nuclear reactor and

exposed to a set neutron flux and

energy, causing the encased U atoms to

split and yield short-lived fission

products.

How it Works as SRM?

Because a known amount of U and other

elements is added to the SPUD materials it

is feasible to determine the concentration

of the resulting fission and activation

products. The subsequent irradiated SPUD

glass would be chemically similar to

samples that would be generated in an

actual detonation, and thus can serve as a

standardized reference material for nuclear

forensic post detonation measurements.

Figure 1: PCA results for one sample of SRM 4600. The

red ellipse denotes three standard deviations from the

center of the PCA model built on the XRF ‘stability run’

data obtained for this sample. The PCA model suggests

that four elements (Cr, Fe, Ni and U) lie outside the

ellipse and exhibit detectable “nugget effects” or

sample heterogeneity.

Bottle-specific average

Measured data

Neutron Activation

Irradiation Conditions

 Sample size ~ 250 mg

 Irradiated for 1 h in NIST 20 MW 

Neutron Beam Split-Core Reactor 

(NBSR)

 Neutron fluence rate of 

approximately (3 x 10

13 n-2

·s

-1

), 

thermal energies

 Irradiated at two day intervals

Random Effects Model

μXRF + PCA Analysis

Samples that have between

bottle standard deviations

> the within bottle

standard deviations and

small p-values may be

heterogeneous (e.g. Cr).

Samples where 

the red circles are 

more scattered 

(in the vertical 

direction) than 

the typical 

distance between 

pairs of blue dots 

may be 

heterogeneous.

Homogeneous Suspect

Heterogeneous

Takeaways

 Elements measured by INAA are less heterogeneous in SRM 4600 then in SRM 4601 (for 250 mg sample).

 Only Cr seems to be heterogeneous for SRM 4600 for 250 mg sample.

 As, Fe, and U are suspect for SRM 4601; Co is suspicious at 250 mg.

 Preliminary mXRF + PCA analysis of SRM 4600 suggests that Cr, Fe, Ni, and U maybe heterogeneous at 50 mg sample size.

 Data suggest that Cr is heterogeneous for SRM 4600 at any sample size and that for smaller sample sizes (< 250 mg) Fe,

Ni and U may also be heterogeneous.

 HOWEVER, thus far only one sample has been run through PCA analysis so the suggestion that only 1 mg is required for

all the elements to be homogeneous should be taken lightly.

The PCA evaluation requires:

 A ‘stability run’ (repeated μXRF measurements at one location on

the sample) - any variance observed is related to instrument and

measurement sources.

 A ‘random run’ (microXRF measurements are taken randomly

within a defined region of interest) - any observed variability is

due to instrument and measurement sources and sample

heterogeneity.

The ‘stability run’ represents an essentially homogenous

sample and can be used as a homogeneity standard to build

the PCA model. The PCA model is then built upon

comparison of the ‘stability run’ to the ‘random run’ to

characterize variance due to sample heterogeneity as detailed

in Molloy and Sieber [1, 2]. Using a combination of PCA and

microXRF an estimated minimum sample mass can be

derived for the entire sample where sample heterogeneity is

not considered to be a large contributor to the measurement

uncertainty.